Undergraduate’s Perspective: Coral Review

Stemming from my last post (see here), I briefly mentioned coral transplantation and the species I am studying. However, I failed to recognize that a year ago all of the terms, ideas, and experiments were a bunch of individual puzzle pieces that I struggled to put together to get the complete picture. I went to The Bahamas with limited knowledge on the nearshore ecosystems that I was going to be working in all summer (guess who learned quite quickly on the job?). As I was re-reading my first blog post, I had the notion that if an undergraduate assistant didn’t know the work she was getting herself into, then there is a possibility that whomever is reading these posts is just like me. Thus, I thought I might provide some background information on corals that will make my puzzle of an experiment much easier to follow.




Fun fact of the day: Coral are animals. More specifically, they are a colony of individual jellyfish-like organisms that produce a calcium exoskeleton that creates the structure of reefs. Many people think corals are plants because of their dependency on light, but inside their calcified skeleton they house algae known as zooxanthellae. It is the zooxanthellae that needs sunlight, and in turn to having a place to safely reside, provides nutrients to the coral. Without adequate light, the algae cannot provide enough nutrients for the coral to secrete its outer calcium skeleton to build reefs. Land runoff, containing loose sediment and nutrients, restrict light by clouding the water. The zooxanthellae will expel themselves from the coral in response, leaving the skeleton white or “bleached”. Further, the small individual polyps cannot collect enough food for the colony to survive and ultimately, the coral colony dies. Therefore, corals grow best in clear, high flow water free from runoff, excess nutrients, or algal blooms.


There are two main types of corals: soft corals and hard corals. The hard corals are the most important for reef building as they have hard calcium skeletons and unique growth patterns that create refuge for reef dwelling organisms (e.g., fish, invertebrates). The species I will be studying is Elkhorn coral (Acropora palmata). This species is listed as critically endangered by the IUCN Red List as their population has declined over 80% throughout the Caribbean in the past 30 years1. Acroporids, the main reef builders in the Caribbean, are particularly sensitive to sedimentation due to their lack of effectiveness in trapping and removing it from their surface2. They are also incredibly susceptible to large, fleshy macroalgae that tends to overgrow and outcompete corals when nutrient runoff is high. An example of their vulnerability to macroalgae was distinctly shown in the early 1980s when a sea urchin, named Diadema antillarum, experienced 97% mortality. This species is ecologically significant due to its consumption of macroalgae. Consequently, when the Diadema vanished, the macroalgae was able to flourish, inhibiting coral growth throughout the Caribbean.



As one can hopefully see from this brief run through, the efforts of coral transplantation are crucial for regenerating the lost reefs (in depth information on coral restoration can be read here). My next post will specifically be covering my project and experience with the setup.

1. Aronson, R., Bruckner, A., Moore, J., Precht, B. & E. Weil. 2008.Acropora palmata. The IUCN Red List of Threatened Species 2008.

2. Rogers, Cs. “Responses of Coral Reefs and Reef Organisms to Sedimentation.” Marine Ecology Progress Series Mar. Ecol. Prog. Ser. 62 (1990): 191-94.

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