Proposal

BIOL 384

05/04/2018

The effects of pH on the prevalence of plankton off the Cabrillo Beach Coast

Abstract

The objective of this study is to determine the prevalence of plankton in the three different areas at Cabrillo Beach and see if there is a correlation with the concentration of pH in each area. We also want to determine if the three areas are statistically different from one another regarding pH. We hypothesized that the prevalence of plankton, within the three different areas off the coast of Cabrillo Beach will differ in concentrations of pH and abundance of plankton, such that an area with a higher pH is correlated with a higher number of plankton present. A pH probe was used to obtain pH values for the three sampling areas of the beach. 60 μm nets were used to captured plankton within these areas to determine their abundance. The results showed that there is no significant difference between the three areas (A, B, C) regarding their respective pH values (p= 0.0507). The results of this study also showed a general trend were a higher pH value (more basic) was correlated with a higher number of plankton within a specific area. The opposite was also evident, were a lower pH value (more acidic) was correlated with a lower number of plankton observed. Overall, these results can potentially contribute to further understand the effects of global climate change on the marine environment.

Introduction

Global climate change has shown to have extreme consequences for all ecosystems on Earth, especially for marine ecosystems. Specifically, climate change has had various implications on the habitats of several species leading to them having to adapt or migrate to different areas that have more favorable conditions for them to thrive on (Levinton, 2018). Global climate change is the result of an increase in CO2 production due to burning fossil fuels, which also results in increasing the temperature of the earth (Levinton, 2018). Atmospheric greenhouse gases trap some of the heat energy that would otherwise go into space, causing the Earth to warm up. The consequential increase in global temperature can result in a surge of physical and chemical changes in the marine environment (Harley et al., 2006).

According to researchers, the continuation of atmospheric CO2 uptake is expected to decrease the pH of ocean water. This also means that the saturation of aragonite, calcite, and other minerals for calcifying organisms changes along with pH (Harley et al., 2006). Decreasing calcification rates in response to increased CO2 has been observed in species such as pteropod mollusks and zooplankters (Harley et al. 2006). The chemical changes that have occurred due to global warming are still unclear and that is why it is essential to further study the changes in pH and how they may affect organisms such as plankton.

Few studies have focused how the pH of seawater affects the growth rate of phytoplankton and the ecology of marine phytoplankton. Phytoplankton are photosynthetic planktonic protists and are composed of single celled organisms. Zooplankton are non- photosynthetic and have skeletal structures made out of chitin, cellulose and calcium. Studies have shown that some species have maximum growth near equilibrium pH and others have a range of pH, where growth rate is not affected by changes in pH (Hinga, 2002). Researchers believe that the pH of seawater may limit the rate of primary production, growth, and total

abundance of phytoplankton (Hinga, 2002). Other studies on phytoplankton and zooplankton show that the biomass and number of taxa tends to be less in acidic areas of water, with a pH around 4.0 (Holopainen, 1992). pH levels have shown to increase during the summer and spring while CO2 decreases because of phytoplankton production. They also determined that alkalinity did not affect the concentrations of CO2. Overall primary productivity has shown to increase during spring and summer, along with a decrease in pH levels with high CO2 concentrations (Shi et al., 2017).

So far, it is not very well known if geographical barriers play a role in lowering pH levels and this needs to be further studied. The main objective of this experiment is to determine the prevalence of plankton in the three different areas at Cabrillo Beach and see if there is a correlation with the concentration of pH in each area. We also want to determine if the three areas being observed are statistically different from one another regarding pH. It is important because these organisms are vital for other marine organisms to thrive and the effects of climate change may alter their function and composition. Based on what we know so far, we hypothesize that the prevalence of plankton within the different areas off the coast of Cabrillo Beach will be different with differences in pH in the given area, with a decrease in pH, more acidic sea water, will be correlated to a decrease in plankton. We also expect to see a difference in pH from the three different areas at Cabrillo Beach, such that the three areas will be statistically different from one another.

Materials and Methods

Samples that were used for this project were collected at Cabrillo Beach California. Materials that were used for this experiment include, nets, a pH meter, and a microscope. To examine the prevalence of plankton found in a given area, 60 μm nets were used in order to obtain samples of seawater. Samples were obtained for three different areas that were indicated in Fig 1. Because we will be collecting data on three different dates, we will have a total of nine samples that will be examined for the duration of the project. The section, within each area, where the samples were collected were kept the same throughout the project. When utilizing the net, the number of strokes was also kept constant, 15 strokes/sample. Each sample was then transferred into their designated glass bottles, each labeled A, B, C for the respective area. A pH meter was also used to record the pH of the three areas (A, B, C) and three readings were recorded per area on each day that data was collected. The probe was placed in the water near the shallow part of the ocean, facilitating the recording of readings. The area of water where the probe was placed within each sample site was also kept consistent.

A microscope was then used to see the abundance of any zooplankton and phytoplankton present in each of our samples. To do this, a subsample from our sample in the glass bottle was examined under the microscope. Once we counted the number of zooplankton and phytoplankton for each sample we obtained the average of the totals and created a correlation graph, looking at pH over the average of plankton found within each area. This type of graph was constructed, using Excel to see the correlation between pH and the number of zooplankton and phytoplankton. We then used an ANOVA test to determine if the pH values recorded for the three areas over a specific period are statistically different from one another. A Bar graph (histogram) was also created to illustrate this.

Results

pH

The first ANOVA analysis established if there was a difference in pH in one area (A, B or C) over time. In area A the pH values for the three sampling dates were not significantly different from each other (p= 0.0692). However, in areas B and C the pH values recorded throughout the investigation indicated that the values were significantly different within each area (p= 1.1137E-08 and p= 2.349E-05) (Table 1). The average pH values recorded for each area also changed over time (Figure 1). The next ANOVA analysis was utilized to determine if there is a significant difference between all three areas (A, B and C). The results showed that there is no significant difference between the three groups regarding their respective pH values (Table 1).

Plankton Abundance

Regarding the number of plankton, the results showed that all the three areas were significantly different from one another based on the number of plankton that were accounted for in the seawater samples (Table 1). For area A the number of plankton was significantly different (p= 0.0190) based on the data collected over the four-week period. The number of plankton in areas B & C were not significantly different over the four-week period (p= 0.2897, p=0.3852).

Correlation

During the weeks of sampling, the results showed that there was a correlation between the number of phytoplankton and zooplankton and pH where an area with a lower pH is correlated with a lower number of zooplankton and/or phytoplankton (Figure 2). From our data, area A had the lowest pH (pH= 7.74) and the lowest number of phytoplankton and zooplankton accounted for (n=0.833, Figure 2). In contrast, area C, had the highest pH (pH= 8.29) and had the highest number of phytoplankton and zooplankton in that area (Figure 2).

Table 1. ANOVA Analysis for pH and number of plankton observed for each area. Three reading were recorded each data collection day and then averaged.

Figure 1. Changes in pH over the four-week period of data collection from March 2nd, 2018 – March 30th, 2018.

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pH

pH Values over four week period

Area A Area B Area C

ANOVA Analyses

pH Number of Plankton

Area A p= 0.0692 p= 0.0190

Area B p= 1.1137E-08 p= 0.2897

Area C p= 2.349E-05 p= 0.3852

Area A, B & C p= 0.0507 p= 0.3262

Figure 2. Correlation graph pH vs. number of Plankton observed. Average number of phytoplankton and zooplankton observed correlated with the pH in areas A, B &C (R2 = 0.9348).

Discussion

The objective of this study was to investigate the prevalence of plankton in the three different areas at Cabrillo Beach and determine the correlation between this and the concentration of pH in a given area. With the presence of possible geographical barriers and different compositions of the three areas, we hypothesized that the prevalence of plankton within the three different areas off the coast of Cabrillo Beach will be different due to differences in pH. We expect to see a lower pH in the area with less plankton and a higher pH in the area with the most plankton accounted for. At the three testing areas at Cabrillo Beach, we found that the pH values for these areas were not significantly different from each other. The number of plankton found at the three sampling sites were also not significantly different from one another.

Overall our results indicate that there is a correlation between the pH value and number of plankton found in one of the three areas analyzed in this study. The bay area at Cabrillo Beach (Area A), had the lowest pH and also had the lowest number of plankton accounted for. In contrast, Area C which encompass the tide pools at Cabrillo Beach had the highest pH value and the highest number of plankton found within that area and was consistent with our hypothesis. This trend is further supported by previous studies where, the biomass and number of phytoplankton and zooplankton were low in acidic areas of water (Holopainen, 1992). They found that the pH of the acidic pond was between 4.0-4.5 and the main pond had a pH of 6.1-6.6 during the same period of time. Their results showed that the biomass and number of taxa was greater in the main pond than the acidic pond (Holopainen, 1992). This could further support our

R² = 0.9348

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pH vs. Number of Plankton Observed

hypothesis that the less acidic the seawater is, the more number of organisms are found within that area that cannot survive under those conditions.

Based on the statistical analysis, the differences between the three areas, in regard to pH, the mean values for the three different sampling days were not statistically different indicating that the means are considered to be equal. The same was seen for the number of plankton found in the three areas, where there is no significant difference among the groups indicating that the mean for each group is the same. It can further be inferred that the seawater between each area is actually mixing to a certain extent, contradicting our hypothesis, despite the presence of geographical barriers and the different compositions of each area studied.

For the second day of sampling, we had no access to a pH probe and therefore had to resort to using pH strips, which could have made our results inaccurate for that day. An estimation on the pH value was made based on the color of the strip, using the color guide provided. For example, as a result, it was quite difficult to make an estimation between a pH reading of 8.00-8.99 which could have skewed the data. Because of this inconsistency, our end results in the statistical analyses could have been inconsistent to a certain extent. Our results also showed that there was an increase in the pH over the span of four weeks. This could possibly indicate that various temperature changes could have played a role in the change of pH and possibly on the abundance of plankton. For future studies on this matter, temperature may be a variable to possibly to look into.

To further investigate the effects of pH on the abundance of plankton in these areas, analysis on salinity and CO2 levels can also be done to measure how these variables affect the composition of sea water and as a result affect specific marine organisms. In a study conducted by Shi, Li, et al., 2017, low levels of CO2 increased the pH and as a result increased in phytoplankton. Their results showed that pH levels increased during the summer and spring while CO2 decreased because of phytoplankton production (Shi, Li, et al., 2017). In conducting some of these future studies, we may be able to have a greater understanding on the effects of global climate change (temperature, pH and CO2 levels) to the marine environment. In turn having more information on this matter may be useful for conservation efforts for some species who are on the verge of extinction.

References

Harley, C. D., Randall Hughes, A. , Hultgren, K. M., Miner, B. G., Sorte, C. J., Thornber, C. S., Rodriguez, L. F., Tomanek, L. and Williams, S. L. (2006). The impacts of climate change in coastal marine systems. Ecology Letters, 9: 228-241.

Hinga, KR. (2002). Effects of pH on coastal marine phytoplankton. Marine Ecology- progress Series. 238. 281-300.

Holopainen, I. (1991). The effects of low pH on planktonic communities. Case history of a small forest pond in eastern Finland. Annales Zoologici Fennici, 28(2), 95-103.

Levinton S. Jeffrey. Marine Biology Function, Biodiversity, Ecology., 2018.

Shi X, Li S, Wei L, Qin B, Brookes JD. (2017). CO2 alters community composition of freshwater phytoplankton: A microcosm experiment. Science of The Total Environment. Volumes 607–608.2017 Pages 69-77.