MT

Main content

Chapter Introduction

Endangered green sea turtle and diver over a coral reef.

Khoroshunova Olga/ Shutterstock.com

Change font size

help

Main content

Core Case StudyThe Jellyfish Invasion

Learning Objectives

· LO 11.1Describe a jellyfish bloom and the problems it can cause.

· LO 11.2Explain why some marine scientists are concerned about the rapid growth of jellyfish populations.

Jellyfish, which are not fish, were the first invertebrate animals in the earth’s oceans. They dominated the oceans around 500 million years ago in the Cambrian period, long before fish evolved.

A jellyfish (see Figure 8.2) is mostly made of water and has no brain, blood, head, heart, bones, or protective shell. The bell-shaped bodies of jellyfish are filled with a jelly-like substance. A network of nerves at the base of their dangling tentacles can detect warmth, food, odors, and vibration.

Jellyfish move by drifting on water currents and by squirting pulsating jets of water from their bodies. They use tentacles dangling from their bodies to sting or stun prey, to draw food into their mouth on the underside of their body, and to defend themselves against predators such as other jellyfish, tuna, sharks, swordfish, and sea turtles.

Jellyfish eat almost anything that floats their way. Most are carnivorous and typically feed on zooplankton, fish eggs, small fish, shrimp, and other jellyfish. They are caught for food in 15 countries, and are considered a delicacy in countries such as China and Japan.

Jellyfish sizes vary widely. Some are as small as a mosquito. The largest jellyfish is the lion’s mane (Figure 11.1). It has a body up to 2.4 meters (8 feet) wide, has tentacles as long as 30 meters (100 feet), and can weigh as much as 150 kilograms (350 pounds).

Figure 11.1

The lion’s mane is the largest jellyfish species.

wizdata/Fotolia LLC

The sting of a jellyfish can cause itching or a burning sensation that lasts for several days. Most stings occur when people accidentally brush up against a jellyfish. However, a sting from the Portuguese man-of-war, the Australian box jelly, or the tiny Irukandji jellyfish can kill a human within minutes if untreated. Each year, the stings of lethal jellyfish kill around 40 people on average.

Jellyfish are often found in large swarms, or blooms, of thousands, even millions of individuals. In recent years, the number of these blooms has been rising. Often, they are as big as 5 to 6 city blocks in diameter.

Jellyfish blooms cause beach closings, disrupt commercial fishing operations by clogging or tearing nets, wipe out coastal fish farms, and shut down ship engines. They can also close down coal-burning and nuclear power plants by blocking their cooling water intakes.

According to Chinese oceanographer Wei Hao and other marine scientists, the startling growth of jellyfish populations threatens to upset marine food webs and ecosystem services and turn some of the world’s most productive ocean areas into jellyfish empires. Once jellyfish take over a marine ecosystem, past evidence indicates that they might dominate it for millions of years. Later in this chapter, we discuss why jellyfish populations have been increasing at an alarming rate.

In this chapter, we examine the effects of human activities on aquatic biodiversity. We also explore ways to prevent or lessen these effects in order to help sustain aquatic life.

Change font size

help

Main content

11.1Threats to Aquatic Biodiversity

· LO 11.1AList three general patterns that scientists have observed related to marine biodiversity.

· LO 11.1BList six reasons why we should care about sustaining aquatic biodiversity.

· LO 11.1CState the extent of the threat to coral reefs according to World Resources Institute (WRI) estimates.

· LO 11.1DDescribe five major threats to coral reefs and the threats to mangrove forests, sea grass beds, and ocean bottom habitats.

· LO 11.1EExplain how ocean acidification threatens marine biodiversity.

· LO 11.1FExplain how threats represented by the acronym HIPPCO can threaten aquatic biodiversity, using at least two examples for each threat.

Change font size

help

Main content

11.1aAquatic Biodiversity

We live on a water planet with 71% of its surface covered by salty ocean water to an average depth of 3.7 kilometers (2.3 miles). Yet, we have explored less than 5% of the earth’s interconnected oceans and have limited knowledge about marine biodiversity. We also have limited knowledge about freshwater biodiversity.

Scientists have observed three general patterns related to marine biodiversity. First, the greatest marine biodiversity occurs around coral reefs, in estuaries, and on the deep-ocean floor. Second, biodiversity is greater near the coasts than in the open sea because of the larger variety of producers and habitats in coastal areas. Third, biodiversity is generally greater in the bottom region of the ocean than in the surface region because of the larger variety of habitats and food sources on the ocean bottom.

The deepest part of ocean, where sunlight does not penetrate (see Figure 8.5), is the planet’s least explored environment but this is changing. More than 2,400 scientists from 80 countries are working on a 10-year project to catalog the species in the deep ocean zone. They have used remotely operated deep-sea vehicles to identify more than 17,000 species living in this zone and are adding a few thousand new species every year.

Change font size

help

Main content

11.1bWhy Should We Care About Aquatic Biodiversity?

Why should we care about sustaining life in the oceans? What difference will it make if coral reefs, sharks, or whales disappear? There are a number of economic, health-related, and ecological reasons:

· Worldwide, about 300 million jobs in fishing and tourism depend on the oceans.

· About 42% of the world’s people get 15–20% of their animal protein and essential nutrition from seafood.

· Oceans generate 50-70% of the oxygen we breathe, mostly from the phytoplankton floating on or near the ocean surface.

These economic and ecosystem services are provided by the diversity of species living and interacting in the oceans. This explains why learning about and sustaining marine biodiversity should be one of our top priorities. As oceanographer and National Geographic Explorer Sylvia Earle reminds us: “With every drop of water you drink, with every breath you take, you are connected to the sea, no matter where on Earth you live.” Freshwater systems, which occupy only 1% of the earth’s surface, also provide important economic and ecological services (see Figure 8.14).

Change font size

help

Main content

11.1cHuman Activities Threaten Aquatic Biodiversity

A serious threat to marine biodiversity is the loss and degradation of aquatic habitat. Human activities have destroyed or degraded much of the world’s coastal wetlands, coral reefs (see Chapter 8 Core Case Study), mangroves, seagrass beds, and the ocean floor. They also have disrupted many freshwater ecosystems such as rivers and lakes.

Ecologist Douglas J. McCauley and a team of other scientists reviewed data about the state of the oceans from hundreds of sources and concluded that “the oceans are facing a major extinction event.” They also said that “the impacts are accelerating but they’re not so bad we can’t reverse them.”

As with terrestrial biodiversity, the greatest threats to aquatic biodiversity and ecosystem services can be remembered with the aid of the acronym HIPPCO, with H standing for habitat loss and degradation.

Shallow, warm-water coral reefs that are centers of aquatic biological diversity (Figure 11.2) are disappearing. They occupy only 0.1% of the world’s oceans, but are home for about 25% of world’s marine fish species. They also provide jobs and about $375 billion a year in economic and ecosystem services, according to National Atmospheric and Oceanic Administration (NOAA) Coral Reef Watch. For example, Australia’s Great Barrier Reef—the world’s largest coral reef system—provides about 70,000 jobs and millions of dollars a year in tourism revenue.

Figure 11.2

Coral reefs are endangered centers of marine biodiversity.

Vlad61/ Shutterstock.com

Since the 1920s, about half of the world’s shallow, warm-water coral reefs (90% in the Indian Ocean and Caribbean) have been destroyed (Figure 11.3) or degraded, according to the Global Coral Reef Monitoring Network. Threats include coastal development, overfishing, pollution, warmer ocean water, and ocean acidification.

Figure 11.3

Dead coral reef.

Richard Whitcombe/ Shutterstock.com

A World Resources Institute (WRI) study estimated that 75% of the world’s remaining shallow warm-water coral reefs are at risk of being destroyed by a combination of warmer ocean water, overfishing, pollution, and ocean acidification (Science Focus 11.1). Today, shallow coral reefs, on average, are exposed to the warmest and most acidic ocean waters of the past 400,000 years—a double threat from the excess carbon dioxide that we have been adding to the atmosphere, mostly from burning fossil fuels.

Science Focus 11.1

Ocean Acidification: The Other  Problem

The burning of large amounts of carbon-containing fossil fuels, especially since 1950, has added carbon dioxide  to the atmosphere faster than it can be removed by the carbon cycle (see Figure 3.20). According to extensive research, this increase in the atmospheric concentration of  has played an important role in the observed increase in the lower atmosphere’s average temperature and in changing the earth’s climate, especially since 1980. Extenstive research and climate models indicate that continuing to increase  levels in the atmosphere will very likely play an important role in the disruption of the earth’s climate during this century, as discussed in Chapter 19.

Ocean acidification, a rise in the acidity of the oceans, is another serious environmental problem related to increased  emissions. The oceans have helped reduce atmospheric warming and climate change by absorbing about 25% of the excess  that human activities have added to the atmosphere.

However, when this absorbed  combines with ocean water, it forms carbonic acid , a weak acid also found in carbonated drinks. This increases the level of hydrogen ions  in the water and makes the water less basic (with a lower pH; see Figure 2.6). This also decreases the level of carbonate ions  in the water because these ions react with hydrogen ions  to form bicarbonate ions .

The problem is that many aquatic species—including phytoplankton, corals, sea snails, crabs, and oysters—use carbonate ions to produce calcium carbonate , the main component of their shells and bones. In less basic waters, carbonate ion concentrations drop (Figure 11.A) and shell-building species and coral reefs grow more slowly. When the hydrogen ion concentration of seawater gets high enough, the calcium carbonate in the shells and bones of these organisms begins to dissolve.

Figure 11.A

Calcium carbonate levels in ocean waters, calculated from historical data (left), and projected for 2100 (right). Colors shifting from blue to red indicate where waters are becoming less basic. In the late 1800s, when  began to accumulate rapidly in the atmosphere, tropical corals were not yet affected by ocean acidification. However, carbonate levels have dropped substantially near the Poles, and by 2100, they may be too low even in the tropics for most coral reefs to survive. (Sources: Andrew G. Dickson, Scripps Institution of Oceanography, U.C. San Diego, and Sarah Cooley, Woods Hole Oceanographic Institution. Used by permission from National Geographic.)

Maps: Ted Sickley; NGM Maps/National Geographic Image Collection

According to a study by more than 540 of the world’s experts on ocean acidification, the average acidity of ocean water has risen 30% (actually a 30% decrease in average basicity) since 1800. It has risen 15% since the 1990s, with the largest increase occurring in deep cold waters near the poles, especially in the Arctic Sea, and along the West Coast of the United States, and is projected to keep acidifying throughout this century. According to the study, the oceans are acidifying “faster than at any time during the last 300 million years.” The report warned that this would reduce the ability of the oceans to help slow the rate of climate change by absorbing  from the atmosphere.

We can slow the rise of acidity levels in ocean waters by protecting and restoring mangrove forests, sea grasses, and coastal wetlands. These aquatic systems take up and store some of the atmospheric  that is at the heart of this problem.

Marine biologists project that if we fail to act rapidly to reduce this serious threat, ocean food webs will shift dramatically. As corals and other calcifying organisms die off green algae and jellyfish (Core Case Study), which thrive in acidic and warm waters, will dominate many ocean food webs.

Critical Thinking

1. How might widespread losses of some forms of marine aquatic life due to ocean acidification affect life on land? How might it affect your life? (Hint: Think food webs.)

Warmer ocean waters can cause shallow tropical corals to expel their colorful algae and leave behind white coral—a process called  coral bleaching  (see Figure 8.1). It can weaken and sometimes kill corals. For example, 93% of the corals in Australia’s Great Barrier Reef have experienced coral bleaching. Ocean acidification (see Science Focus 11.1) also threatens to weaken or dissolve coral. According to marine biologist Malin L. Pinsky, “If you cranked up the aquarium heater and dumped some acid in the water, your fish would not be very happy. In effect, that’s what we are doing to the oceans.”

Connections

Sunscreens and Coral Reefs

Certain ingredients in many sunscreens have been shown to promote the growth of a harmful virus within the algae that live in coral reefs. When people dive down to see the reefs, these chemicals can wash off. This can kill the algae and promote coral bleaching.

The loss of coral reefs is not just an ecological disaster. It affects the half a billion people that depend on coral reefs for food, especially protein. Projected future losses of coral reefs could worsen hunger in parts of the world.

If given enough time, many species of corals can adapt to changes in environmental conditions such as warmer and perhaps more acidic water. However, corals are threatened with rapidly rising water temperatures, acidity, and sea levels during this century, which will not give them enough time for adaptation.

According to fossil and other evidence, coral reefs were devastated in each of the earth’s five mass extinctions that took place over the last half-billion years (see Figure 4.19). Evidence indicates that in each mass extinction, high levels of dissolved  and prolonged ocean warming and acidification played a role in dissolving the calcium carbonate that coral polyps use to build the reefs. With each mass extinction, the corals disappeared and did not come back for 4 million to 10 million years. If we have triggered a sixth mass extinction as some scientists say, many of the coral species that are currently centers of marine biodiversity are likely to disappear again for millions of years.

Learning from Nature

United Nations Environment Programme (UNEP) scientists reported that a fifth of the world’s ecologically and economically important mangrove forests (see Figure 8.8) have been lost since 1980. They continue to be destroyed for firewood, coastal construction, and shrimp farming. Another study revealed that 58% of the world’s coastal sea-grass beds (see Figure 8.9) have been degraded or destroyed, mostly by dredging and coastal development.

58%

Percentage of the world’s coastal sea-grass beds that have been degraded or destroyed

Sea-bottom habitats are being degraded and destroyed by impacts from dredging operations and trawler fishing boats. Like giant submerged bulldozers, thousands of trawler fishing boats drag huge nets weighted down with chains and steel plates over the ocean floor to harvest a few species of bottom fish and shellfish (Figure 11.4). This destroys large areas of deep, cold-water coral reefs and other ocean-bottom habitats. Marine scientist Elliot Norse calls bottom trawling “probably the largest human-caused disturbance to the biosphere.” An increase in seabed mining also threatens biologically diverse ocean-bottom habitats.

Figure 11.4

Natural Capital Degradation: An area of ocean bottom before (left) and after a trawler net scraped it like a gigantic bulldozer (right).

Critical Thinking:

1. What land activities are comparable to this?

Courtesy of Peter J. Auster/National Undersea Research Center

Habitat disruption is also a problem in freshwater aquatic zones. The main causes are the building of dams and excessive withdrawal of river water for irrigation and urban water supplies. These activities destroy aquatic habitats, decrease water flows, and disrupt freshwater biodiversity. Globally, the extinction rate for freshwater species is five times the rate for terrestrial species, according to the latest IUCN Red List.

Change font size

help

Main content

11.1dHarmful Invasive Species

Another problem that threatens aquatic biodiversity is the deliberate or accidental introduction of hundreds of harmful invasive species into coastal waters, wetlands, and lakes throughout the world. According to the U.S. Fish and Wildlife Service, harmful invasive species are responsible for about two-thirds of all fish extinctions in the United States since 1900 and have caused huge economic losses.

Many of the more than 1,450 different aquatic invader species in the United States arrived in the ballast water stored in tanks in large cargo ships to keep them stable. The ships take in ballast water from one harbor, along with whatever microorganisms and tiny fish species it contains, and dump it into another—an environmentally and economically harmful effect of globalized trade. Even when ballast water is flushed from an oceangoing ship’s tank before it enters a harbor—which is now required in many ports—the ship can still bring invaders that are stuck to its hull.

One invasive species that worries scientists and the fishing industry on the east coast of North America is a species of lionfish, (Figure 11.5). Scientists believe it escaped from outdoor aquariums in Miami, Florida, that were damaged by Hurricane Andrew in 1992.

Figure 11.5

The common lionfish has invaded the eastern coastal waters of North America, where it has few, if any, predators.

Cigdem Sean Cooper/ Shutterstock.com

In addition to threatening native species, invasive species can disrupt and degrade whole ecosystems and their ecosystem services. This is the focus of study for a growing number of researchers (Science Focus 11.2).

Science Focus 11.2

How Invasive Carp Have Muddied Some Waters

Lake Wingra lies within the city of Madison, Wisconsin, surrounded mostly by a forest preserve. The lake contains a number of invasive plant and fish species, including purple loosestrife (see Figure 9.9) and common carp. The carp were introduced in the late 1800s, and since then have made up as much as half of the fish biomass in the lake. They devour algae called chara, which would normally cover the lake bottom and stabilize its sediments. Consequently, fish movements and winds stir these sediments, which accounts for much of the water’s excessive turbidity, or cloudiness.

Knowing this, Dr. Richard Lathrup, a limnologist (lake scientist) who worked with Wisconsin’s Department of Natural Resources, speculated that if the carp were removed, the bottom sediments would settle and become stabilized, allowing the water to clear. Clearer water would in turn allow native plants to receive more sunlight and become reestablished on the lake bottom, replacing purple loosestrife and other invasive plants that now dominate its shallow shoreline waters.

Lathrop and his colleagues installed a thick, heavy vinyl curtain around a 1-hectare (2.5-acre), square-shaped perimeter that extended out from the shore. This barrier hung from buoys on the surface to the bottom of the lake, isolating the volume of water within it. The researchers then removed all of the carp from this study area observed results. Within 1 month, the waters within the barrier were noticeably clearer, and within a year, the difference in clarity was dramatic (Figure 11.B), and native plants once again grew in the shallow shoreline waters.

Figure 11.B

Lake Wingra in Madison, Wisconsin (USA) became clouded with sediment partly because of the introduction of invasive species such as the common carp. Removal of carp in the experimental area shown here resulted in a dramatic improvement in the clarity of the water.

© Mike Kakuska

Lathrop notes that removing and keeping carp out of Lake Wingra would be a daunting task, perhaps impossible, but his controlled scientific experiment clearly shows the effects that an invasive species can have on an aquatic ecosystem. In addition, it reminds us that preventing the introduction of invasive species in the first place is the best and least expensive way to avoid such effects.

Critical Thinking

1. What are two other results of this controlled experiment that you might expect? (Hint: Think food webs.)

Change font size

help

Main content

11.1ePopulation Growth and Pollution

According to United Nations Environment Programme (UNEP), about 80% of the world’s people live along or near seacoasts, mostly in large coastal cities. This coastal population growth—the first P in HIPPCO—has added to the already intense pressure on the world’s coastal zones. The UNEP estimates that about 80% of all ocean pollution comes from land-based coastal activities.

80%

Percent of ocean pollution that comes from land-based coastal activities

Today, more than 400 oxygen-depleted zones (“dead zones”) have formed in coastal areas around the world, and the number is increasing. They form when high levels of plant nutrients from fertilizers and soil erosion flow from the land into rivers that empty into coastal waters. These inputs support large algal blooms. When these algae die, they sink to the bottom, where bacteria begin to decompose them. Because the decomposition requires oxygen, levels of this dissolved gas in the water become depleted. Marine organisms either suffocate due to lack of dissolved oxygen or leave the area if they can. It is another example of how human activities can lead to changes in ocean chemistry and biodiversity.

Mercury and other toxic pollutants from industrial and urban areas can harm people and some forms of aquatic life. Some of the highly toxic mercury in ocean waters comes from natural sources. However, toxic mercury released into the atmosphere by coal-burning plants can move over the ocean, be taken up by ocean producers, and magnified to high levels in ocean food webs. Because of this input from natural and human sources, top predator fish such as sharks, tilefish, swordfish, king mackerel, and white tuna can contain high levels of toxic mercury.

Partially decomposed particles of plastic items dumped from ships and garbage barges, and left as litter on beaches, kill up to 1 million seabirds and 100,000 mammals annually (Figure 11.6). These animals mistake the plastic particles for plankton or small fish. Certain compounds in these plastics can be concentrated in some types of seafood that people eat. By the middle of this century, the world’s oceans may contain more plastic wastes than fish by weight.

Figure 11.6

This Hawaiian monk seal was slowly starving to death before a discarded piece of plastic was removed from its snout.

Doris Alcorn/U.S. National Maritime Fisheries

Change font size

help

Main content

11.1fClimate Change

Climate change also threatens aquatic biodiversity and ecosystem services. Greenhouse gas emissions and heat, mostly from the burning of fossil fuels, have played an important role in warming the atmosphere and changing the earth’s climate. For decades, the earth’s oceans have absorbed about 90% of this excess heat. If they had not, the earth’s atmosphere would be much warmer and the climate would be changing much more rapidly. As energy expert John Abraham puts it: “The ocean is doing us a favor by grabbing about 90% of our heat output. But it is not going to do it forever.”

As a result, the ocean has been getting warmer. The surface warms the most, but vertical currents (see Figure 7.11) transfer some of this heat to deep water. This ocean heating affects marine food webs and makes some marine habitats unlivable for some species by exceeding the range of temperatures they can tolerate (see Figure 5.15). Unless they can migrate to cooler water, they can face extinction. Measurements indicate that the rate at which the ocean absorbs heat is slowing. Eventually some of this heat will flow back into the atmosphere and accelerate atmospheric warming and climate change.

Ocean warming has caused some marine species to migrate from the equator toward the poles to cooler waters. This can threaten some of these species because their new habitats can be less hospitable, having lower dissolved oxygen levels. A warmer ocean could also boost populations of some species such as the coral-eating thorn-of-crown starfish that poses a threat to Australia’s Great Barrier Reef.

The ocean has also removed and dissolved about 27% of the excess  that human activities have added to the atmosphere, which has helped slow atmospheric warming and climate change. However, as ocean water warms, it holds less . Thus, rising ocean temperatures could release huge amounts of  into the atmosphere and trigger rapid climate change.

A big threat from a warmer atmosphere and ocean is a rising sea level due to thermal expansion as ocean water warms and the partial melting of land-based ice in glaciers and ice sheets as atmospheric temperatures rise. In 2014, the Intergovernmental Panel on Climate Change (IPCC) estimated that the average global sea level is likely to rise by 40–60 centimeters (1.3–2 feet) by the end of this century—about 10 times the rise that occurred in the 20th century. Recent research projects a rise of 0.2–2.0 meters (8 inches–6 feet) by 2100. A rise in sea level of 0.9 meter (3 feet) would destroy shallow coral reefs, swamp some low-lying islands, drown many coastal wetlands, and put parts of many coastal areas and cities underwater. In addition, some Pacific island nations could lose more than half of their protective coastal mangrove forests by 2100, according to a UNEP study.

Connections

Protecting Mangroves and Dealing with Climate Change

Protecting mangrove forests and restoring them in areas where they have been destroyed are important ways to reduce the impacts of rising sea levels and storm surges, because mangrove forests can slow storm-driven waves. These ecosystem services will become more important if tropical storms continue to intensify because of climate change. Protecting and restoring these natural coastal barriers is much cheaper and more effective than building concrete sea walls or moving threatened coastal towns and cities inland.

Warmer and more acidic ocean water is also stressing phytoplankton, the foundation of marine food webs (see Figure 3.16). These tiny life forms produce at least half of the earth’s oxygen and absorb much of the  emitted by human activities. A team of scientists led by marine ecologist Boris Worm found that global phytoplankton populations have declined by 40% since the 1950s, probably because of warmer and more acidic ocean waters.

Change font size

help

Main content

11.1gOverfishing

Another threat to aquatic biodiversity is overfishing. Fish and fish products provide 20% of the world’s animal protein for billions of people. A  fishery  is a concentration of a wild aquatic species suitable for commercial harvesting in a given ocean area or inland body of water.

Five countries—China, Spain, Taiwan, Japan, and South Korea—account for 85% of the fish caught in the world’s oceans. China’s deep-sea fishing fleet, assisted by nearly $22 billion a year in subsidies from the Chinese government, is by far the world’s top contributor to overfishing.

Today, more than 4 million fishing boats hunt for and harvest fish from the world’s oceans. Industrial fleets use a variety of methods to find and harvest fish and shellfish. They include global satellite positioning equipment, sonar fish-finding devices, huge nets, long fishing lines, spotter planes and drones, and refrigerated factory ships that can process and freeze their enormous catches. These highly efficient fleets supply the growing demand for seafood, but critics say that they are overfishing many species (Figure 11.7), reducing marine biodiversity, and degrading important marine ecosystem services. Figure 11.8 shows the major methods used for the commercial harvesting of various marine fishes and shellfish.

Figure 11.7

The threatened Atlantic bluefin tuna is being overfished because of its high market value.

zaferkizilkaya/ Shutterstock.com

For example, trawlers have destroyed vast areas of ocean-bottom habitat (Figure 11.4). In addition, their nets often capture endangered sea turtles (Figure 11.9), causing them to drown.

Figure 11.9

This endangered green sea turtle died after being caught in a fishing net.

Mark Foley/State Archives of Florida, Florida Memory

Another fishing method, purse-seine fishing (Figure 11.8), is used to catch surface-dwelling species such as tuna, mackerel, anchovies, and herring, which tend to feed in schools near the surface or in shallow waters. After a spotter plane locates a school, the fishing vessel encloses it with a large purse-seine net. Some of these nets have killed large numbers of dolphins that swim on the surface above schools of tuna.

Some fishing vessels also use long-lining, which involves putting out lines up to 100 kilometers (60 miles) long, hung with thousands of baited hooks to catch swordfish, tuna, sharks, and ocean-bottom species such as halibut and cod. Long lines also hook and kill large numbers of sea turtles, dolphins, and seabirds each year.

With drift-net fishing, fish are caught by drifting nets that can hang as deep as 15 meters (50 feet) below the surface and extend to 64 kilometers (40 miles) long. These nets trap and kill large quantities of unwanted fish, called  bycatch , along with marine mammals and sea turtles. Nearly one-third of the world’s annual fish catch by weight consists of bycatch species that are mostly thrown overboard dead or dying. This adds to the depletion of these species and puts stress on some of the species that feed on them.

A fishprint is the area of ocean needed to sustain the fish consumption of an average person, a nation, or the world based on the weight of fish they consume annually. It helps scientists and government officials distinguish between sustainable and unsustainable levels of fishing and evaluate the effects of fishing policies.

The world’s highly efficient fishing fleets help supply the growing demand for seafood but critics say they are overfishing many species, reducing marine biodiversity, and degrading important marine ecosystem services. According to the Woods Hole Oceanographic Institute, 57% of the world’s commercial fisheries have been fully exploited and another 30% have been overfished.

87%

Percentage of the world’s commercial fisheries that have been harvested at full capacity (57%) or overfished (30%)

In most cases, overfishing leads to commercial extinction, which occurs when it is no longer profitable to continue harvesting the affected species. Overfishing can temporarily deplete a species, as long as depleted areas and fisheries are allowed to recover. However, as industrialized fishing fleets take more and more of the world’s available fish and shellfish, recovery times for severely depleted populations are increasing and can be two decades or more.

Overfishing has led to the collapse of some of the world’s major fisheries such as the Atlantic cod fishery off the coast of Newfoundland, Canada (Figure 11.10). According to research by a team of marine scientists, the fishery has not recovered since it collapsed decades ago because the Gulf of Maine has warmed, which decreased reproduction and increased mortality among the once-abundant Atlantic cod. This put at least 35,000 fishers and fish processors out of work in more than 500 coastal communities.

Figure 11.10

Natural Capital Degradation: Collapse of Newfoundland’s Atlantic cod fishery.

Data Analysis:

1. By roughly what percentage did the catch of Atlantic cod drop between the peak catch in 1960 and 1970? (Compiled by the authors using data from Millennium Ecosystem Assessment.)

One result of the increasingly efficient global hunt for fish is that larger individuals of commercially valuable wild species—including cod, marlin, swordfish, and tuna—are becoming scarce. This is not surprising because, for example, a single bluefin tuna can sell for $180,000 in Japan. Another effect of overfishing is that when larger predatory species dwindle, rapidly reproducing invasive species such as jellyfish (Core Case Study) can take over and disrupt ocean food webs. Some depleted fisheries might not recover.

The decline in commercially valuable large species, has led the fishing industry to turn to other species such as sharks, which are now being overfished (see the Case Study that follows). In addition, as large species are overfished, the fishing industry has been working its way down to lower trophic levels of marine food webs by shifting to smaller marine species known as forage fish, such as anchovies, herring, sardines, and shrimp-like krill. Much of this catch is converted to fishmeal and fish oil, and fed to farmed fish. Scientists warn that this reduces the food supply for larger fish species and makes it harder for them to rebound from overfishing. The result is further disruption of marine ecosystems and their ecosystem services.

Case Study

Why Should We Protect Sharks?

Sharks have roamed the world’s oceans for at least 400 million years. Certain shark species are keystone species in their ecosystems. These sharks, feeding at or near the top of their food webs, remove many injured and sick animals. Without this ecosystem service, the oceans would be clogged with dead and dying fish and marine mammals. Shark activity also influences the distribution and feeding habits of other species, which helps maintain balance in marine ecosystems.

The world’s more than 1,000 known species of sharks vary widely in size. They range from the 15-centimeter (6-inch) long dwarf dog shark to the whale shark (Figure 11.11, left), which can grow to the length of a city bus and weigh as much as two full-grown African elephants.

Figure 11.11

The threatened whale shark (left), which feeds on plankton, is the ocean’s largest fish and is quite friendly to humans. The great hammerhead shark (right) is endangered.

Left: Rich Carey/ Shutterstock.comRight: frantisekhojdysz/ Shutterstock.com

Many people, influenced by movies, popular novels, and media coverage of shark attacks, think of sharks as vicious monsters. In reality, the three largest species—the whale shark (Figure 11.11, left), basking shark, and megamouth shark—are gentle giants. These sharks swim through the water with their mouths open, filtering out and swallowing huge quantities of zooplankton and small fish.

Media reports on shark attacks greatly exaggerate the dangers to humans from sharks. Every year, members of a few species, including the great white, bull, tiger, and hammerhead sharks (Figure 11.11, right), injure 60 to 80 people and typically kill 5 to 10 people worldwide and 1 person in the United States. Sometimes these sharks are thought to mistake swimmers and people on surfboards or paddle boards for their usual prey of sea lions and other marine mammals. According to shark attack files at the Florida Museum of History, you are much more likely to be killed by a falling coconut, than by a shark. In 2017, many more people in the world were killed taking selfies (97) than by shark attacks (4).

Each year human activities kill more than 200 million sharks. As many as 73 million sharks die each year after being caught for their valuable fins, a practice called shark finning. After capture, their fins are cut off. Then the sharks are thrown into the water and in the worst cases, they bleed to death or drown because they can no longer swim. Sharks are also killed for their livers, meat, hides, and jaws, and because we fear or hate them. Each year, an estimated 100 million sharks die when fishing lines and nets trap them.

Harvested shark fins are widely used in Asia as an ingredient in expensive soup ($100 or more a bowl) and as an alleged pharmaceutical cure-all. The large dorsal fin of a whale shark (Figure 11.11, left) can be worth up to $10,000 in Hong Kong or Taiwan and is often hung outside Asian restaurants to advertise shark fin soup. According to the wildlife conservation group WildAid, there is no reliable evidence that shark fins provide flavor or have any nutritional or medicinal value. The group also warns that consuming shark fins and shark meat can be harmful to human health because they often contain high levels of mercury and other toxins.

According to an IUCN study, 25% of the world’s open-ocean shark species are threatened with extinction, primarily from overfishing. Because some sharks are keystone species, their extinction can threaten the ecosystems and the ecosystem services they provide. Sharks are especially vulnerable to population declines because they grow slowly, mature late, and have only a few offspring per generation. Today, sharks are among the earth’s most vulnerable and least protected animals.

With research support from the National Geographic Society, the late Samuel H. Gruber, biologist, devoted his life to studying lemon sharks in the Florida Keys and the Bahamas. One of his goals was to help us understand and reduce the slaughter of these sharks, which he called “fantastic and amazing creatures.” Protecting sharks is one way for us to live more sustainably by increasing our beneficial environmental impacts.

Overfishing can also make affected species more vulnerable to the stresses of ocean warming and ocean acidification. Marine mammals such as whales have also been threatened by overfishing (see the second Case Study that follows), as have endangered sea turtles (see third Case Study that follows).

Case Study

Protecting Whales: A Success Story . . . So Far

Overharvesting threatens some marine mammals with extinction. The most prominent examples are whales, or cetaceans, that range in size from the 0.9-meter (3-foot) porpoise to the giant 15- to 30-meter (50- to 100-foot) highly endangered blue whale. Cetaceans are divided into two major groups: toothed whales and baleen whales (Figure 11.12).

Figure 11.12

Cetaceans are classified as either toothed whales or baleen whales.

Toothed whales, such as the porpoise, sperm whale, and killer whale (orca), bite and chew their food and feed mostly on squid, octopus, and other marine animals. Baleen whales, such as the blue, gray, humpback, minke, and fin, are filter feeders. Attached to their upper jaws are plates made of baleen, or whalebone, which they use to filter plankton, especially tiny shrimp-like krill (Figure 3.16), from the seawater.

Whales are easy to kill because of their large size and because of their need to come to the surface to breathe. Whale hunters became efficient at hunting and killing whales using radar, spotters in airplanes, fast ships, and harpoon guns. Whale harvesting, mostly in international waters, has followed the classic pattern of a tragedy of the commons (see Chapter 1, Degrading Commonly Shared Renewable Resources: The Tragedy of the Commons). In the 20th century, whalers from 46 countries, led by Norway, Japan, the U.S.S.R., and the United Kingdom killed about 3 million whales. Between 1925 and 1975, this overharvesting drove 8 of the 11 major species to commercial extinction and the blue whale close to biological extinction.

The endangered blue whale is the earth’s largest animal. Its heart is the size of a small car, its tongue weighs as much as an adult elephant, and some of its blood vessels are big enough for you to swim through. It is also one of the fastest-swimming animals in the sea.

In 1946, the International Whaling Commission (IWC) was established to regulate the whaling industry by setting annual quotas to prevent overharvesting. However, IWC quotas often were based on insufficient data or were ignored by whaling countries. Without enforcement powers, the IWC was not able to stop the decline of most commercially hunted whale species.

In 1970, the United States stopped all commercial whaling and banned all imports of whale products. Under pressure from conservationists and governments of many nonwhaling nations, the IWC imposed a moratorium on commercial whaling starting in 1986. It worked. The estimated number of whales killed commercially worldwide dropped from a peak of nearly 40,000 in 1958 to about 1,500 in 2016. The population of the endangered blue whale has increased from about 1,000 in the mid-1920s to 15,000 today, with 2,000 of them living in California coastal waters.

Most whaling today is done by Japan, Norway, and Iceland. Since the 1986 ban on commercial whaling, these nations and some tropical island nations have pressured the IWC to lift the ban and reverse the international ban on buying and selling whale products. They contend that the ban on whaling is emotionally motivated and interferes with their cultural diet traditions, which they say are no different from the western cultural tradition of killing cows for beef. Many conservationists dispute this claim and contend that whales are intelligent and highly social mammals that should be protected for ethical and ecological reasons.

Whaling proponents also point out that populations of minke, humpback, and several other whale species have rebounded enough since the moratorium on whaling to be removed from the ban. Others question IWC estimates of the allegedly recovered whale species, noting the inaccuracy of such estimates in the past.

Among the most threatened of all marine species are sea turtles (see chapter-opening photo) that have been roaming the oceans for more than 110 million years—about 550 times longer than the latest human species has been around. Today six of the seven species of sea turtles (Figure 11.13) are in danger of becoming extinct, mostly because human activities taking place during the last 100 years have reduced the world’s number of sea turtles by about 95%.

Figure 11.13

There are seven species of sea turtles, six of them threatened with extinction. All but the flatback are found in U.S. waters and are listed as endangered.

Sea turtles spend most of their lives traveling the world’s oceans, but adult females normally return to the beaches where they were born to lay their eggs. They come ashore at night and use their back flippers to dig nests on sand beaches and coastal dunes. Each female lays a clutch of around 100 to 110 eggs, buries them, and returns to the ocean. After the baby turtles hatch, they dig their way out of the nest, often at night, to scamper toward the water. During this dangerous trip, birds and other predators eat many of them. Only about one of every thousand sea turtle hatchlings survives to adulthood.

Sea turtles are threatened by trawler fishing (Figure 11.4), which destroys many of the coral gardens that have served as their feeding grounds. The turtles are also hunted for their skin and their eggs are taken for food. They often drown after becoming entangled in fishing nets (Figure 11.9) and lines, as well as in lobster and crab traps.

Beachgoers and motor vehicles sometimes crush their nests. Artificial lights can disorient newly hatched baby turtles, which try to find their way to the ocean by moving toward moonlight reflected from the ocean’s surface. Going in the wrong direction increases their chances of ending up as food for predators.

Pollution of ocean water is another threat. Sea turtles can mistake discarded plastic bags for jellyfish and choke to death trying to eat them. In addition, the threat of rising sea levels from climate change during this century will flood many sea turtle nesting habitats and change ocean currents, which could disrupt their migration routes.

Several sea turtle species eat jellyfish (Core Case Study) and help control their populations. Continuing population declines of these endangered sea turtles could promote the takeover of parts of the sea by rapidly expanding populations of jellyfish (Science Focus 11.3).

In U.S. waters, the National Marine Fisheries Service requires the use of turtle excluder devices on commercial fishing nets that allow captured sea turtles to escape (Figure 11.14). Since 1990, fishing regulations have reduced accidental sea turtle deaths in U.S. waters by 90%.

Figure 11.14

This endangered loggerhead turtle is escaping a fishing net equipped with a turtle excluder device.

© NOAA

Science Focus 11.3

Why Are Jellyfish Populations Increasing?

Jellyfish look fragile but have a number of survival traits. They can reproduce rapidly, survive without food for long periods by shrinking and waiting until conditions improve, eating many different things, and feeding in murky waters. They can also survive in low-oxygen, warm, and acidic waters.

Scientists have identified several possible causes for the increased number and size of jellyfish swarms in many areas of the world’s oceans (Core Case Study). One likely factor is the decline in populations of their natural predators such as tuna, sharks, swordfish, and endangered sea turtles, mostly due to overfishing. Overfishing also increases food sources for jellyfish because it reduces populations of fish such anchovies and sardines that eat much of the same food as jellyfish. As humans overfish commercially valuable fish species, jellyfish can take over, eat fish eggs and small fish, and hinder or prevent the recovery of overfished species.

Human activities play a key role in ocean warming and ocean acidification, which are favorable for jellyfish. Another environmental change caused by human activities is the overfertilization of coastal waters by huge inputs of the plant nutrients nitrogen and phosphorus. They come from the runoff of fertilizers from large areas of land into rivers that flow into coastal waters. The excess plant nutrients create massive blooms of algae and other plankton, which die, sink, and are decomposed.

This process, called cultural eutrophication, depletes dissolved oxygen in ocean bottom waters and kills or drives away marine organisms that require oxygen. Jellyfish populations can erupt in these so-called “dead zones” such as the massive one that forms each year in the Gulf of Mexico. At least 400 other dead zones, where almost nothing but jellyfish survives, form in various parts of the world.

Jellyfish have also benefited from the rapid increase in global trade involving ships carrying goods throughout the world. Some species of jellyfish can survive in the ballast water of ships, and polyps of various jellyfish species can attach to ship hulls and end up inhabiting new areas of the ocean throughout the world.

More research is needed, but the rise of jellyfish in the world’s ocean waters is probably the result of a mixture of these factors. Think about it. We are doing things that favor jellyfish: depleting populations of their major predators, depleting populations of fish species that compete with them for food, warming and making the oceans more acidic, creating numerous large oxygen-depleted zones, and using ships to spread them throughout the world.

Critical Thinking

1. What are two ways in which exploding jellyfish populations might affect your life or the lives of any children and grandchildren you might eventually have?

Industrialized fishing requires huge amounts of energy to propel the ships, fuel spotter planes, and freeze the catches. The species that require the largest energy input are, in order, shrimp, lobster, Pacific albacore tuna, scallops, and skipjack tuna.

Learning from Nature

Sharks easily glide through the water because tiny grooves in their skin form continuous channels for water flow. Scientists are studying this to design ship hulls that will save energy and money by moving through the water with less resistance.

Learning from Nature

The huge humpback whale can turn quickly in tight circles to trap its prey, and scientists have found that bumps on the front of its fins, called tubercles, help it to do so. Engineers are now applying this knowledge to designing blades for wind turbines, hydroelectric turbines, and irrigation pumps, all of which work more efficiently with tubercle technology.

Change font size

help

Main content

11.2Protecting and Sustaining Marine Biodiversity

· LO 11.2ADescribe four factors that make protection of marine biodiversity difficult.

· LO 11.2BExplain how marine protected areas (MPAs) can help protect marine biodiversity and list two limitations of many MPAs.

· LO 11.2CExplain how no-take marine reserves can benefit fish populations.

help

Main content

11.2aProtecting Marine Species with Laws and Treaties

Protecting marine biodiversity is difficult for several reasons:

· The human ecological footprint and the fishprint are expanding so rapidly that it is difficult to monitor their impacts.

· Much of the damage to the oceans and other bodies of water is not visible to most people.

· Many people incorrectly view the seas as an inexhaustible resource that can absorb an almost infinite amount of waste and pollution and still produce all the seafood and other products we want.

· Most of the world’s ocean area lies outside the legal jurisdiction of any country. Thus, much of it is an open-access resource, subject to overexploitation. This is a classic example of the tragedy of the commons (see Chapter 1).

Nevertheless, there are several ways to protect and sustain marine biodiversity, thereby increasing our beneficial environmental impact. One involves passing and enforcing laws. For example, we can protect endangered and threatened aquatic species, as discussed in Chapter 9, and we can restore and sustain degraded streams, wetlands, and other aquatic systems.

National and international laws and treaties that help protect marine species include the 1975 Convention on International Trade in Endangered Species (CITES), the 1979 Global Treaty on Migratory Species, the U.S. Marine Mammal Protection Act of 1972, the U.S. Endangered Species Act of 1973 (ESA; see Chapter 9), the U.S. Whale Conservation and Protection Act of 1976, and the 1995 International Convention on Biological Diversity. The ESA and several international agreements have been used to identify and protect endangered and threatened marine species, including whales, seals, sea lions, and sea turtles. However, it is hard to get all nations to comply with some of these agreements. Even when agreements and regulations are enforced, the resulting fines and punishments for violators are often inadequate.

Change font size

help

Main content

11.2bEstablishing Marine Sanctuaries

By international law, a country’s offshore fishing zone extends to 370 kilometers (200 nautical miles) from its shores. Foreign fishing vessels can take certain quotas of fish within such zones, called exclusive economic zones, but only with a government’s permission. Ocean areas beyond the legal jurisdiction of any country are known as the high seas, and laws and treaties pertaining to them are difficult to monitor and enforce.

For example, poachers catch an estimated one of every five fish sold in stores and served in restaurants. This illegal catch is difficult to monitor and control. However, in 2015 a new satellite tracking system, funded by the Pew Charitable Trusts, was launched to help crack down on this illegal activity.

The United Nations Law of the Sea treaty went into effect in 1984 and by 2018, had been signed by 168 countries but not by the United States. Under this treaty, the world’s coastal nations have jurisdiction over 42% of the ocean surface and about 90% of the world’s fish stocks. Instead of using this treaty to protect their fishing grounds, many governments have promoted overfishing by subsidizing fishing fleets and failing to establish and enforce stricter regulation of fish catches in their coastal waters.

We can establish protected marine sanctuaries. Since 1986, the IUCN has helped several nations to establish a global system of marine protected areas (MPAs)—areas of ocean partially protected from human activities. According to the U.S. National Ocean Service, more than 5,800 MPAs cover about 2.8% of the world’s ocean surface and their numbers are growing.

However, most MPAs allow dredging, trawler fishing (Figure 11.4), and other ecologically harmful resource extraction activities. In addition, many of them are too small to be effective in protecting larger species. However, since 2007, the U.S. state of California has been establishing the nation’s most extensive network of MPAs covering 16% of the state’s coastal water in which fishing is banned or strictly limited. Costa Rica (see Chapter 10 Core Case Study) expanded one of its MPAs to help protect a number of marine species, including the critically endangered leatherback sea turtle and the endangered scalloped hammerhead shark (Figure 11.11, right). The United States has more than 1,700 MPAs, which receive varying degrees of protection.

Change font size

help

Main content

11.2cEstablishing Marine Reserves

Many scientists and policymakers call for protecting and sustaining entire marine ecosystems and their ecosystem services within a global network of fully protected no-take marine reserves, some of which already exist. These areas are declared off-limits to commercial fishing, dredging, mining, and waste disposal in order to enable their ecosystems to recover and flourish.

When patrolled and protected, marine reserves work and they work quickly. Studies show that in fully protected marine reserves, on average, commercially valuable fish populations double, average fish size grows by almost a third, fish reproduction triples, and species diversity increases by almost one-fourth. These improvements can happen within 2 to 4 years after strict protection begins. Reserves also benefit nearby fisheries because fish move into and out of the reserves. Currents also carry fish larvae produced inside reserves to adjacent fishing grounds, thus bolstering fish populations there. In addition, marine reserves increase the ability of protected marine ecosystems to respond to the growing stresses of ocean warming and ocean acidification.

Many marine scientists propose setting aside 10–30% of the world’s oceans as fully protected marine reserves—an important way to increase our beneficial environmental impact. Sylvia Earle, one of the world’s leading marine scientists, is spearheading this effort (Individuals Matter 11.1).

Individuals Matter 11.1

Sylvia Earle—Advocate for the Oceans

Tyrone Turner/National Geographic Image Collection

Sylvia Earle is one of the world’s most respected oceanographers and is a National Geographic Society Explorer. She has taken a leading role in helping us to understand and protect the world’s oceans. Time magazine named her the first Hero for the Planet and the U.S. Library of Congress calls her “a living legend.”

Earle has led more than 100 ocean research expeditions and has spent more than 7,000 hours underwater, either diving or descending in research submarines to study ocean life. She has focused her research on the ecology and conservation of marine ecosystems, with an emphasis on developing deep-sea exploration technology.

She is the author of more than 175 publications and has been a participant in numerous radio and television productions. During her long career, Earle has also served as the Chief Scientist of the U.S. National Oceanic and Atmospheric Administration (NOAA). She also founded three companies that develop submarines and other devices for deep-sea exploration and research. She has received more than 100 major international and national honors, including a place in the National Women’s Hall of Fame.

Earle is currently leading a campaign called Mission Blue to finance research and to ignite public support for a global network of marine protected areas, which she calls “hope spots.” Her goal is to help save and restore the oceans, which she calls “the blue heart of the planet.” She says, “There is still time, but not a lot, to turn things around. . . . This mostly blue planet has kept us alive. It’s time for us to return the favor.”

Marine scientists also call for establishing protected corridors to connect the global network of marine reserves, especially those in coastal waters. This would help species move to different habitats in response to the effects of ocean warming, acidification, and many forms of ocean pollution.

Critical Thinking

1. Do you support setting aside at least 30% of the world’s oceans as fully protected no-take marine reserves? Why or why not? How would this affect your life?

Change font size

help

Main content

11.2dRestoring Marine Biodiversity and Preventing Aquatic Ecosystem Degradation

A dramatic example of marine system restoration is Japan’s attempt to restore its largest coral reef—90% of it dead—by seeding it with new corals. Divers drill holes into the dead reefs and insert ceramic discs holding sprigs of fledgling coral. Figure 11.15 shows how protection has helped to restore coral reefs near Kanton Island, an atoll located in the South Pacific.

Figure 11.15

Recovery of a coral reef in a protected area near Kanton Island in the South Pacific.

Brian J. Skerry/National Geographic Image Collection

Many scientists support efforts to restore aquatic systems, but they warn that these projects could fail if the problems that caused their degradation are not addressed. They call for more emphasis on preventing aquatic ecosystem degradation, which is far less expensive and more effective than restoration efforts.

Australia manages its huge Great Barrier Reef Marine Park in this way, and more than 100 integrated coastal management programs are being developed throughout the world. Another example of such management in the United States is the Chesapeake Bay Program (see Chapter 8, Case Study).

Change font size

help

Main content

11.3Managing and Sustaining Marine Fisheries

· LO 11.3AExplain why many fishery and environmental scientists argue for using the precautionary principle for managing fisheries and large marine ecosystems.

· LO 11.3BDescribe a co-management approach to managing local fisheries.

· LO 11.3CExplain how government subsidies can encourage overfishing.

· LO 11.3DDescribe four ways in which consumers can support sustainable production of seafood.

Change font size

help

Main content

11.3aEstimating and Monitoring Fishery Populations

The first step in protecting and sustaining the world’s marine fisheries is to make the best possible estimates of their fish and shellfish populations. The traditional approach has used a maximum sustained yield (MSY) model to project the maximum number of individuals that can be harvested annually from fish or shellfish stocks without causing a population drop. However, the MSY concept has not worked very well because of the difficulty in estimating the populations and growth rates of fish and shellfish stocks. In addition, harvesting a particular species at its estimated maximum sustainable level can affect the populations of other marine species.

In recent years, some fishery biologists and managers have begun using the optimum sustained yield (OSY) concept, which attempts to take into account interactions among species. Similarly, another approach is multispecies management of a number of interacting species, which takes into account their competitive and predator–prey interactions. An even more ambitious approach is to develop complex computer models for managing multispecies fisheries in large marine systems. However, it is a political challenge to get groups of nations to cooperate in planning and managing such large systems.

There are uncertainties built into using any of these approaches because the biology of marine species and their interactions is poorly understood, and because of limited data on changing ocean conditions. As a result, many fishery and environmental scientists are increasingly interested in using the precautionary principle for managing fisheries and large marine systems. This means sharply reducing fish harvests and closing some overfished areas until they recover and until we have more information about what levels of fishing they can sustain.

Change font size

help

Main content

11.3bRegulating Fish Harvests

An obvious step to take in protecting marine biodiversity—and therefore fisheries—is to regulate fishing. Traditionally, many coastal fishing communities have developed allotment and enforcement systems for controlling fish catches in which each fisher gets a share of the total allowable catch. Such catch-share systems have sustained fisheries and jobs in many communities for hundreds and sometimes thousands of years.

However, the influx of large state-of-the-art fishing boats and international fishing fleets has weakened the ability of many coastal communities to regulate and sustain local fisheries. Community management systems have often been replaced by co-management, in which coastal communities and the government work together to manage fisheries.

With this approach, a central government typically sets quotas for various species and divides the quotas among communities. The government may also limit fishing seasons and regulate the types of fishing gear that can be used to harvest a particular species. Each community then allocates and enforces its quota among its members based on its own rules. When it works, community-based co-management illustrates that we can prevent overfishing and the tragedy of the commons.

Change font size

help

Main content

11.3cGovernment Subsidies Can Encourage Overfishing

Governments around the world give more than $35 billion per year in subsidies to fishers to help them keep their businesses running, according to fishery experts U. R. Sumaila and Daniel Pauly. In 2018, UN scientists estimated that harmful fishing subsidies—those that encourage overfishing and expansion of the fishing industry—amount to more than $20 billion per year. The result is too many boats chasing too few fish. Some argue that such subsidies are not a wise investment because they promote overfishing of targeted fish stocks. In 2018, the World Bank reported that poor fisheries management squanders roughly $80 billion per year in lost economic potential.

Critical Thinking

1. Do you think that government fishing subsidies that promote unsustainable fishing should be eliminated or drastically reduced? Explain. Would your answer be different if your livelihood depended on commercial fishing?

Change font size

help

Main content

11.3dChoosing Sustainably Produced Seafood

An important component of sustaining aquatic biodiversity and ecosystem services is pressure from consumers who demand sustainably produced seafood. Consumers can choose to purchase only sustainably harvested seafood or sustainably farmed seafood. One way to help consumers make such choices is to label sustainably caught and raised fresh and frozen fish and shellfish. The London-based Marine Stewardship Council (MSC) was created in 1999 to support sustainable fishing and to certify sustainably produced seafood. Another approach is to certify and label products of sustainable aquaculture, or fish-farming operations.

Consumers of seafood raised by aquaculture can help sustain aquatic biodiversity by consuming plant-eating species of fish, such as tilapia, catfish, and carp. Carnivorous species, such as salmon and shrimp, raised through aquaculture are often fed fishmeal made from wild-caught fish and some of these species are being overfished.

Individuals can also help reduce the waste of seafood. A study published in Global Environmental Change found that American consumers discard about 0.6 billion kilograms (1.3 billion pounds) of seafood annually. This, combined with waste that occurs in producing seafood, amounts to nearly half of all edible seafood going to waste each year in the United States. Figure 11.16 summarizes actions that individuals, organizations, and governments can take to help sustain global fisheries, marine biodiversity, and marine ecosystem services.

Figure 11.16

Ways to manage fisheries more sustainably and protect marine biodiversity.

Critical Thinking:

1. Which four of these solutions do you think are the best ones? Why?

Change font size

help

Main content

11.4Protecting and Sustaining Wetlands

· LO 11.4AList six ecosystem services provided by coastal and inland wetlands.

· LO 11.4BExplain how more than half of U.S. wetlands have been lost due to human activities.

· LO 11.4CExplain why at least half of the attempts to create new wetlands through mitigation banking have failed, according to the National Academy of Sciences.

· LO 11.4DSummarize the story of the degradation of, and attempts to restore, the Florida Everglades.

Change font size

help

Main content

11.4aCoastal and Inland Wetlands Are Disappearing

Coastal wetlands and marshes (Figure 8.7) and inland wetlands—often called swamps, bogs, or fens—support aquatic biodiversity and provide vital economic and ecosystem services. Their ecosystem services include feeding downstream waters and reducing flooding by acting as “nature’s sponges” by absorbing and slowing the movement of storm water. Wetlands also reduce storm damage by absorbing waves (coastal wetlands), recharge groundwater supplies, and reduce water pollution by filtering and cleaning flowing water. They also, reduce erosion, and provide fish and wildlife habitat. They are often called “nurseries of life” because they are home for a variety of species and provide foods such as rice, shrimps, oysters, and crabs. Some inland wetlands are the handiwork of beavers, which build dams to create their own pond habitats (See Science Focus 11.4).

Science Focus 11.4

The Ecological Importance of Beavers

Beavers are nature’s engineers. These large rodents use their powerful jaws and strong teeth to cut down trees (Figure 11.C, left), from which they use the limbs and branches to build dams and to create their own pond habitats (Figure 11.C, right). Within the ponds, they then build hollow mounds, called lodges, where they live and raise their young.

Figure 11.C

Beavers cut down trees (left), which they use to build dams (right) in order to creates ponds or wetlands where they live.

Procy/ Shutterstock.com; O Brasil que poucos conhecem/ Shutterstock.com

help

Main content

11.4bPreserving and Restoring Wetlands

Some laws protect wetlands. In the United States, zoning laws have been used to steer development away from wetlands. The U.S. government requires a federal permit to fill in wetlands occupying more than 1.2 hectares (3.0 acres) or to deposit dredged material in wetlands. According to the U.S. Fish and Wildlife Service, this law has helped to cut the average annual wetland loss by 80% since 1969.

However, there are continuing attempts by land developers to weaken such wetlands protection. Only about 6% of the country’s remaining inland wetlands is federally protected, and state and local wetland protection is inconsistent and generally weak because of intense pressure from coastal developers and landowners.

94%

Percentage of U.S. inland wetlands that are not protected by federal law against development and degradation

The stated goal of current U.S. federal policy is zero net loss in the functioning and value of coastal and inland wetlands. A policy known as mitigation banking allows destruction of existing wetlands as long as an equal or greater area of the same type of wetland is created, enhanced, or restored. However, a study by the National Academy of Sciences found that at least half of the attempts to create new wetlands failed to replace lost ones. Furthermore, most of the created wetlands did not provide the ecosystem services of natural wetlands, even decades after completion. The study also found that wetland creation and restorations often fail to meet the standards set for them and are not adequately monitored.

Creating and restoring wetlands has become a profitable business. Private investment bankers make money by buying wetland areas and restoring or upgrading them or creating new wetland. This creates wetlands banks or credits that the bankers sell to developers. This approach is a small step toward full-cost pricing because it puts a monetary value on the biodiversity and ecosystem services of wetlands that are sold by the bankers.

It is difficult to restore, enhance, or create wetlands (see the Case Study that follows). Thus, most U.S. wetland banking systems require replacing each area of destroyed wetland with twice the area of restored, enhanced, or created wetland (Figure 11.17) as a built-in ecological insurance policy.

Case Study

Can We Restore the Florida Everglades?

South Florida’s Everglades was once a 100-kilometer-wide (62-mile-wide), knee-deep sheet of water flowing slowly south from Lake Okeechobee to Florida Bay (Figure 11.18, red dashed lines). As this shallow body of water—known as the “River of Grass”—trickled south, it created a vast network of wetlands with a variety of wildlife habitats.

Figure 11.18

Florida’s Everglades is the site of the world’s largest ecological restoration project—an attempt to undo and redo an engineering project that has been destroying this vast wetland and threatening water supplies for south Florida’s rapidly growing population.

To help preserve the wilderness in the lower end of the Everglades system, in 1947 the U.S. government established Everglades National Park. However, this protection effort did not work—as conservationists had predicted—because of a massive water distribution and land development project to the north. Between 1962 and 1971, the U.S. Army Corps of Engineers transformed the wandering 166-kilometer-long (103-mile-long) Kissimmee River into a mostly straight 84-kilometer (52-mile) canal flowing into Lake Okeechobee (Figure 11.18, black dashed line). The canal provided flood control by speeding the flow of water, but it drained large wetlands north of Lake Okeechobee, which farmers then converted to grazing land.

This and other projects have provided south Florida’s rapidly growing population with a reliable water supply and flood protection. However, much of the original Everglades has been drained, paved over, polluted by agricultural runoff, and invaded by a number of plant and animal species. The Everglades is now less than half its original size and much of it has dried out, leaving large areas vulnerable to summer wildfires.

The Everglades National Park is known for its astonishing biodiversity, and each year more than a million people visit the park. However, its biodiversity has been decreasing, mostly because of habitat loss, pollution, and invasive species. About 90% of the wading birds in Everglades National Park have vanished and populations of many remaining wading bird species have dropped sharply. In addition, populations of vertebrates, from deer to turtles, are down 75–95%.

By the 1970s, state and federal officials recognized that this huge plumbing project was reducing populations of native plants and wildlife—a major source of tourism revenues for Florida. It was also cutting the water supply for the 7 million residents of south Florida. In 1990, Florida’s state government and the U.S. government agreed on a plan for the world’s largest ecological restoration project, known as the Comprehensive Everglades Restoration Plan. The U.S. Army Corps of Engineers is supposed to carry out this joint federal and state plan to partially restore the Everglades.

The project has several ambitious goals, including restoration of the curving flow of more than half of the Kissimmee River; removal of 400 kilometers (248 miles) of canals and levees that block natural water flows south of Lake Okeechobee; conversion of large areas of farmland to marshes; the creation of 18 large reservoirs and underground water storage areas to store water for the lower Everglades and for south Florida’s population; building of a canal–reservoir system for catching the water now flowing out to sea and pumping it back into the Everglades; and raising a major highway that has dammed parts of the Florida Bay for nearly 100 years.

Jose Antonio Perez/ Shutterstock.com

help

Main content

11.5Protecting and Sustaining Freshwater Lakes, Rivers, and Fisheries

· LO 11.5AList six threats to freshwater ecosystems.

· LO 11.5BExplain how four prominent invasive species now threaten the Great Lakes ecosystem.

· LO 11.5CList four ecosystem services provided by rivers and streams and four threats to those services.

· LO 11.5DExplain why protecting a stream or lake from pollution requires protecting its watershed.

· LO 11.5EList the three major requirements of sustainable management of freshwater fisheries.

Change font size

help

Main content

11.5aFreshwater Ecosystems Are in Jeopardy

The ecosystem and economic services provided by many of the world’s freshwater lakes, rivers, and fisheries are severely threatened by human activities. According to studies by U.S., Canadian, and Mexican scientists, at least 40% of the freshwater fish species in North America are vulnerable, threatened, or endangered.

Many of the world’s freshwater wetlands have been destroyed. Aquatic species have been crowded out of at least half of the world’s freshwater habitat areas and more than 60% of the world’s longest rivers have been dammed or otherwise engineered. Invasive species, pollution, and climate change threaten the ecosystems of many lakes, rivers, and wetlands. Many freshwater fish stocks are overharvested and during this century, increasing human population pressure and climate change will intensify these threats.

Sustaining and restoring the biodiversity and ecosystem services provided by freshwater lakes and rivers is a complex and challenging task, as shown by the following Case Study.

Case Study

Can the Great Lakes Survive Repeated Invasions by Alien Species?

Invasions by nonnative species are a major threat to the biodiversity and ecological functioning of many lakes, as illustrated by what has happened to the five Great Lakes, located on the border between the United States and Canada.

Collectively, the Great Lakes are the world’s largest body of freshwater. Since the 1920s, these lakes have been invaded by at least 180 nonnative species and the number keeps rising. Many of the alien invaders arrive on the hulls of, or in bilge-water discharges of, oceangoing ships that have been entering the Great Lakes through the St. Lawrence Seaway since 1959.

One of the biggest threats, the sea lamprey, reached the westernmost Great Lakes as early as 1920. This parasite attaches itself to almost any kind of fish and kills the victim by sucking out its blood (Figure 5.8). Over the years, it has depleted populations of many important sport fish species such as lake trout. The United States and Canada keep the lamprey population down by applying a chemical that kills lamprey larvae where they spawn in streams that feed the lakes. These and other control measures cost more than $20 million annually.

In 1986, larvae of the zebra mussel (Figure 9.9) arrived in ballast water discharged from a European ship near Detroit, Michigan. This thumbnail-sized mollusk reproduces rapidly. It has displaced other mussel species and thus depleted the food supply for some other Great Lakes aquatic species. The mussels have also clogged irrigation pipes, shut down water intake pipes for power plants and city water supplies, fouled beaches, and jammed ships’ rudders. They have grown in thick masses on many boat hulls, piers, and other exposed aquatic surfaces (Figure 11.19). The mussel has also spread to freshwater communities in parts of southern Canada and, as of 2018, 32 U.S. states. Damages and attempts to control this mussel cost the two countries well over $1 billion a year—an average of more than $114,000 per hour.

Figure 11.19

These zebra mussels are attached to a water current meter in Lake Michigan.

© NOAA

Sometimes, native species can help control a harmful invasive species. For example, populations of zebra mussels are declining in some parts of the Great Lakes because a native sponge growing on their shells is preventing them from opening up their shells to breathe. However, it is not clear whether the sponges will effectively control the invasive mussels and what harmful ecological effects the sponges might have.

In 1989, a larger and potentially more destructive species, the quagga mussel, invaded the Great Lakes, probably discharged in the ballast water of a Russian freighter. It can survive at greater depths and tolerate more extreme temperatures than the zebra mussel can. By 2018, scientists reported that quagga mussels had almost completely carpeted the bottom of Lake Michigan and that the mussel had reached all five Great Lakes. This has reduced the food supply for many fish and other species, thus leading to a major disruption of the lakes’ food webs. There is concern that quagga mussels may spread by river transport and eventually colonize eastern U.S. ecosystems such as the Chesapeake Bay (see Chapter 8, Case Study) and waterways in parts of Florida.

The Asian carp (Figure 11.20) is the most recent threat to the Great Lakes system. In the 1970s, catfish farmers in the southern United States imported two species of Asian carp to help remove suspended matter and algae from their aquaculture farm ponds. Heavy flooding during the 1990s caused many of these ponds to overflow, which allowed some of the carp to enter the Mississippi River. After working their way up the Mississippi River system, these invaders are now close to entering Lake Michigan, if they have not already done so. Joel Brammeier, president of the Alliance for the Great Lakes, warned that “if Asian carp get into Lake Michigan, there is no stopping them.”

Figure 11.20

Asian carp may be the next major invasive species to threaten the Great Lakes.

© Michigan Sea Grant College Program

These fish can quickly grow as long as 1.2 meters (4 feet) and weigh up to 50 kilograms (110 pounds). They can eat as much as 20% of their own body weight in plankton every day, which can disrupt lake food webs. When startled they jump clear of the water, and several boaters have been hit and injured by jumping carp. These fish have no natural predators in the rivers they have invaded or in the Great Lakes.

Federal, state, and local agencies are developing plans to prevent the Asian carp from reaching and spreading throughout the Great Lakes, which would threaten the lakes’ $7 billion-a-year fishing industry. Proposed measures include electric barriers to limit access through rivers flowing into the Great Lakes and laws to prevent the transporting of fish across state borders. In addition, some chemical companies are developing carp-specific poisons. In 2017, an Asian carp was found and removed within a few miles of the lake beyond an electronic barrier designed to block its entry into the lake. However, as of 2018, there was no evidence of a population of the carp established in the lake.

Change font size

help

Main content

11.5bManaging River Basins

Rivers and streams provide important ecosystem services (Figure 11.21), but overfishing, pollution, dams, and water withdrawal for irrigation are disrupting these services. Currently, these ecosystem services are given little or no monetary value when the costs and benefits of dam and reservoir projects are assessed. According to environmental economists, attaching even crudely estimated monetary values to these ecosystem services—an application of the full-cost pricing principle of sustainability—would help to sustain them.

Figure 11.21

Rivers and streams provide some important ecosystem services.

Critical Thinking:

1. Which two of these services do you think are the most important? Why?

An example of such disruption and loss of freshwater biodiversity is what happened in the Columbia River, which runs through parts of southwestern Canada and the northwestern United States. The river and all of its tributaries have more than 400 dams. Of those, 14 are on the main stem of the Columbia River and are used to provide hydroelectric power.

The Columbia River dams have benefited many people, but have also sharply reduced populations of wild salmon. These migratory fish hatch in the upper reaches of the streams and rivers that form the headwaters of the Columbia River. They migrate to the ocean where they spend most of their adult lives, and then swim upstream to return to the place where they were hatched to spawn and die. Dams interrupt their life cycle by interfering with the migration of young fish downstream, and blocking the return of mature fish attempting to swim upstream to their spawning grounds.

help

Main content

11.5bManaging River Basins

Rivers and streams provide important ecosystem services (Figure 11.21), but overfishing, pollution, dams, and water withdrawal for irrigation are disrupting these services. Currently, these ecosystem services are given little or no monetary value when the costs and benefits of dam and reservoir projects are assessed. According to environmental economists, attaching even crudely estimated monetary values to these ecosystem services—an application of the full-cost pricing principle of sustainability—would help to sustain them.

Figure 11.21

Rivers and streams provide some important ecosystem services.

Critical Thinking:

1. Which two of these services do you think are the most important? Why?

An example of such disruption and loss of freshwater biodiversity is what happened in the Columbia River, which runs through parts of southwestern Canada and the northwestern United States. The river and all of its tributaries have more than 400 dams. Of those, 14 are on the main stem of the Columbia River and are used to provide hydroelectric power.

The Columbia River dams have benefited many people, but have also sharply reduced populations of wild salmon. These migratory fish hatch in the upper reaches of the streams and rivers that form the headwaters of the Columbia River. They migrate to the ocean where they spend most of their adult lives, and then swim upstream to return to the place where they were hatched to spawn and die. Dams interrupt their life cycle by interfering with the migration of young fish downstream, and blocking the return of mature fish attempting to swim upstream to their spawning grounds.

Since the dams were built, the Columbia River’s wild Pacific salmon population has dropped by an estimated 90 to 94% and nine of the Pacific Northwest salmon species are listed as endangered or threatened. As of 2018, the U.S. federal government and northwest electric utilities have spent nearly $7 billion in efforts to save the salmon, with little success.

Change font size

help

Main content

11.5dProtecting Freshwater Fisheries

Sustainable management of freshwater fisheries involves supporting populations of commercial and sport fish species, preventing such species from being overfished, and reducing or eliminating populations of harmful invasive species. The traditional approach to managing freshwater fish species is to regulate the time and length of fishing seasons and the number and size of fish that can be taken.

Other techniques include building reservoirs and ponds, stocking them with fish, and protecting and creating fish spawning sites. In addition, some fishery managers try to protect fish habitats from sediment buildup and other forms of pollution. They also work to prevent or reduce large human inputs of plant nutrients that spur the excessive growth of aquatic plants.

Some fishery managers seek to control predators, parasites, and diseases by improving habitats, breeding genetically resistant fish varieties, and using antibiotics and disinfectants. Hatcheries can be used to restock ponds, lakes, and streams with prized species such as trout, and entire river basins can be managed to protect valued species such as salmon.

Change font size

help

Main content

11.6Priorities for Sustaining Aquatic Biodiversity

· LO 11.6ASummarize the six priorities of the ecosystem approach to sustaining aquatic biodiversity and ecosystem services.

· LO 11.6BExplain how individuals can support the ecosystem approach to sustaining biodiversity and ecosystem services.

Change font size

help

Main content

11.6aEcosystem Approach to Sustaining Aquatic Biodiversity and Ecosystem Services

Edward O. Wilson (see Individuals Matter 4.1) and other biodiversity experts have proposed the following priorities for an ecosystem approach to sustaining aquatic biodiversity and ecosystem services:

· Map and inventory the world’s aquatic biodiversity.

· Identify and preserve the world’s aquatic biodiversity hotspots and areas where deteriorating ecosystem services threaten people and many forms of aquatic life.

· Create large and fully protected marine reserves to allow damaged marine ecosystems to recover and fish stocks to be replenished.

· Protect and restore the world’s lakes and river systems, which are among the world’s most threatened ecosystems, but emphasize pollution prevention because ecological restorations are expensive and have a high failure rate.

· Initiate worldwide ecological restoration projects in systems such as coral reefs and inland and coastal wetlands.

· Find ways to raise the incomes of people who live on or near protected waters so that they can become partners in the protection and sustainable use of aquatic ecosystems.

There is growing evidence that the current harmful effects of human activities on aquatic biodiversity and ecosystem services could be reversed over the next two decades. Doing this will require implementing an ecosystem approach to sustaining both terrestrial and aquatic ecosystems. According to Edward O. Wilson, such a conservation strategy would cost about $30 billion per year—an amount that could be provided by a tax of 4 cents per cup of coffee consumed in the world each year.

A key part of this strategy will be for individuals to “vote with their wallets” by trying to buy only products and services that have no or low harmful impacts on terrestrial and aquatic biodiversity. For example, we can eat more sustainable seafood. California’s highly respected Monterey Bay Aquarium (Figure 9.21) publishes and regularly updates a sustainable seafood guide called Seafood Watch that can be viewed at its website or with a free mobile phone app.

According to Sylvia Earle (Individuals Matter 11.1), failure to act now “means that in 50 years there may be no coral reefs and no commercial fishing, because the fish will simply be gone. . . . Imagine what that means to our life-support system.”

Big Ideas

· The world’s aquatic systems provide important economic and ecosystem services, and scientific investigation of these poorly understood ecosystems could lead to immense ecological and economic benefits.

· Aquatic ecosystems and fisheries are being severely degraded by human activities that lead to aquatic habitat disruption and loss of biodiversity.

· We can sustain aquatic biodiversity by establishing protected sanctuaries, managing coastal development, reducing water pollution, and preventing overfishing.

Change font size

help

Main content

Tying It All TogetherInvading Jellyfish and Aquatic Sustainability

Olga Khoroshunova/ Dreamstime.com

This chapter began with a look at populations of a number of jellyfish species that are exploding, disrupting marine food webs, and taking over parts of the ocean ( Core Case Study ). Throughout the chapter, we examined how loss of aquatic habitats, invasive species, population pressures, climate change, ocean acidification, and overexploitation are harming many marine and freshwater aquatic species. We looked at how many of the world’s fisheries are being depleted. We discussed why jellyfish populations are exploding and why this is a serious threat.

We also explored possible solutions to these problems, including the jellyfish invasions. We know that when areas of the oceans are left undisturbed, marine ecosystems tend to recover their natural functions, and fish populations can rebound quickly. In addition, the best approach to sustaining freshwater biodiversity is to use an ecosystem approach.

We can achieve greater success in sustaining aquatic biodiversity by applying the three scientific principles of sustainability. This means reducing inputs of sediments and excess nutrients, which cloud water, lessen the input of solar energy, and upset aquatic food webs and the natural cycling of nutrients in aquatic systems. It also means valuing aquatic biodiversity and putting a high priority on preserving the biodiversity and ecosystem services of aquatic systems. Applying the full-cost pricing, win-win, and ethical principles of sustainability can help us to achieve these goals.

Change font size

help

Main content

Chapter Review

help

Main content

Chapter Review

Doing Environmental Science

1. Pick a coastal area, river, stream, lake, or wetland near where you live and research and write a brief account of its history. Then survey and take notes on its present condition. Has its condition improved or deteriorated during the last 10 years? What governmental or private efforts are being used to protect this aquatic system? Write a report summarizing your findings. Based on your report along with your ecological knowledge of this system, write up some recommendations to policymakers for protecting it. Try presenting your recommendations to one or more local policymakers.

Change font size

help

Main content

Chapter Review

Ecological Footprint Analysis

A fishprint provides a measure of a country’s fish harvest in terms of area. The unit of area used in fishprint analysis is the global hectare (gha), a unit weighted to reflect the relative ecological productivity of the area fished. When compared with the fishing area’s sustainable biocapacity (its ability to provide a stable supply of fish year after year, expressed in terms of yield per area), its fishprint indicates whether the country’s annual fishing harvest is sustainable. The fishprint and biocapacity are calculated using the following formulas:

The following graph shows the earth’s total fishprint and biocapacity. Study it and answer the questions that follow.

1. Based on the graph,

1. What was the status of the global fisheries with respect to sustainability in 2000?

2. In what year did the global fishprint begin to exceed the biological capacity of the world’s oceans?

3. By how much did the global fishprint exceed the biological capacity of the world’s oceans in 2000?

2. Assume a country harvests 18 million metric tons of fish annually from an ocean area with an average productivity of 1.3 metric tons per hectare and a weighting factor of 2.68. What is the annual fishprint of that country?

Change font size

help