In our brave new world, animals that have naturally high abundances, and are not subject to hunting, fishing, loss of habitat, habitat fragmentation, or loss of prey species, are dying off en masse. They are sessile, clonal, marine organisms that can be described as a cross between a block of concrete and a plant. They are corals. The US Government is currently reviewing the population status of 82 species of coral for listing under the Endangered Species Act (ESA). The primary culprit is climate change which is predicted to cause the dissolution of reefs by mid to end of century. Can population dynamics help us manage these long lived (or formerly long-lived) creatures? We examined the short-term population dynamics of the endangered Caribbean elkhorn coral, Acropora palmata, in four locations – Florida, Jamaica, Curaçao, and Puerto Rico – using size-based matrix models. The models are parameterized based on data from annual field visits to permanently tagged A. palmata colonies, and include demographic and environmental stochasticity.
Results/Conclusions
Though A. palmata population growth rates are positive in some locations, rates from one size-class to the next are probably too slow to ensure recovery in a 50-100 year time frame. The model helps reveal that large colonies are particularly important as the primary sexual and asexual reproducers in the population, but sadly the predicted stable size distribution is dominated by small individuals. The eighty-two corals proposed for listing vary broadly in their natural history. However, they are all clonal, sessile organisms, separated from their environment by an epithelial layer merely one cell thick. A. palmata makes an instructive test case, not as a canary - unusually sensitive to its environment; but rather, because it has weedy characteristics and relatively good data, and yet recovery is far from certain. The ESA, in its current incarnation, is implemented species by species. Even if an ecosystem based approach is used, and even if, as in the case of A. palmata, we have decent information about population dynamics, we will have to rely on significant local protection efforts as well as global climate change reversal if we want to ensure long-term persistence of corals.
