June 6, 2011
A major component of our work during the Global Reef Expedition focuses on understanding factors and processes that enhance the resilience of coral reefs. We evaluate a number of ecological, physical and chemical parameters at each reef we visit, which allows us to compare and rank reefs within a single location and across large spatial scales to come up with a coral reef health index. We combine data on coral population structure, recruitment, health and disease, algal community assemblages, degree of herbivory, fish community structure and biomass, and other parameters we collect during our rapid assessments to determine how resilient a reef is. We will then develop recommendations on actions that can be taken to either protect that resilience or enhance it in stressed locations.
This approach is being taken by other researchers as well, but the parameters that are measured vary and the strategy to compare the resilience of reefs also varies. What is your baseline for a healthy or resilient reef? Is the best location in a particular country or region the highest ranked site and all others are ranked against this standard? Is a reef that is considered in near-pristine state (which is difficult to find nowadays) the standard and all others are compared against this standard? Is a reef that has changed significantly due to a widespread decline of one of the most important reef building corals (star corals), from which recovery to their former glory would require 100s of years (like many Caribbean reefs) still considered resilient if much of the structure is still present, assemblages of other species are intact, and there are high levels of recruitment, herbivory and other processes we consider essential for a properly functioning reef? What is the reef resilient to?
Most resilience assessments today are targeting one parameter in particular: coral reef bleaching. Reef-building corals and other organisms have symbiotic relationships with single-celled photosynthetic algae (dinoflagellates), known as zooxanthellae (other similar symbionts occur in sponges and other organisms). These organisms are vital to the health and proper functioning of a coral, providing food, removing metabolic waste products, aiding in calcification and a host of other functions. Bleaching is a phenomenon where the coral animal (polyp) becomes stressed and the zooxanthellae are expelled, or the zooxanthellae lose their photosynthetic pigments, and the coral becomes pale, or in extreme cases stark white, as if someone poured chlorine bleach on the coral.
Various stages of bleaching in a mountainous star coral (Montastraea faveolata)
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