Research paper

Richard Acosta

Senior Seminar, Section U03

Detailed Outline

Title: Temperature variability and coral bleaching

I. Introduction

A. Increase in ocean temperatures is the major cause of coral bleaching. (Hoegh-Guldberg Ove 1999)

B. Coral reefs are in danger because of the hot temperatures that they are experiencing which are now higher than they have ever been before. (Abdo 2012)

C. Hypothesis 1: High frequency temperature variability reduces the risk of coral bleaching of lowering the effectiveness of symbionts.

D. Hypothesis 2: Putting corals through temperature fluctuations on a daily basis will reduce coral bleaching.

II. High water temperatures cause coral bleaching by decreasing the effectiveness of symbionts.

A. High temperatures cause coral bleaching.

1. Bleaching is due to elevated temperature (Brown, B. 1997)

2. Warming seasons decrease coral development (Glynn and D'Croz 1990)

B. At high temperatures, symbiont photosynthesis rate decreases and oxidant production increases.

1. Oxidant production

a. photo-oxidative stress causes bleaching (Nielsen et al. 2018)

2. Photoprotection (Jones and Hoegh‐Guldberg 2001)

C. Acquiring a heat-resistant strain of symbiont can make bleaching adaptive.

1. Some corals have adapted to higher temperatures

a. Hosting specifically adapted Symbiodinium (Rowan 2020)

2. Changes in their Symbiodinium might allow corals to better tolerate warm temperatures (Oliver 2011)

III. Temperature variability reduces the risk of coral bleaching by reducing their thermal stress.

A. Fluctuating temperatures cause corals to acclimate to higher temperatures.

1. Thermally fluctuating environments increase coral thermal tolerance

a. Low mortality rate (Oliver, T.A. and Palumbi, S.R. 2011)

2. Corals from reef pools with wide temperature fluctuations resist stress better than corals from less extreme pools (Donner 2005)

B. Fluctuating temperatures also allow the symbiont to acclimate to higher temperatures.

1. This demonstrates that while highly fluctuating temperatures enhance coral resilience to thermal stress

a. Dipsastraea sp. showed resistance (Herrera et al. 2020)

2. Symbiont acclimatization (Coles 2003)

C. Temperature variability in warm seasons reduces thermal stress of corals and causes them to withstand coral bleaching events. (Sully et al. 2019)

IV. Adaptations of corals and symbionts to high temperatures.

A. Some species of corals are showing signs of adaptation to warmer temperatures

1. Thermal adaptation of corals and their endosymbionts

a. Symbiosis of corals become more resistant (Donner et al. 2005)

2. Adaptation by symbiont shuffling (Jury et al. 2019)

B. Corals that contain the symbiont Symbiodinium clade D are more tolerant than any other corals that contain a different symbiont.

1. Clade D Symbiodinium are more tolerant to coral endosymbionts

a. Symbiodinium D outcompete other symbionts (Smith et al. 2017)

2. Coral adaptation

a. Corals can adapt to ocean warming (Schoepf et al. 2019)

b. Genetic Adaptation (Kubicek et al. 2019)

C. Corals are adapting to ocean acidification to avoid coral bleaching (Lesser 1997)

V. Solutions

A. Slowing global warming is a needed global solution.

B. Better monitoring of regional and local conditions can help predict bleaching events and this could avoid greater damage to coral reefs around the world.

C. Locally, corals can be exposed to more temperature variations.

D. Heat-adapted coral and symbiont strains can be introduced.

Literature cited

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