Population dynamics of threatened elkhorn coral in the northern Florida Keysr USA

摘要

Caribbean elkhorn coral Acropora palmata (Lamarck, 1816) was once so widespread and abundant that geologists use its fossils to measure sea levels from the Pleistocene through the Holocene. Now it exists at a small fraction of its former abundance and is listed, along with a congener, as 'threatened' under the US Endangered Species Act. We conducted annual demographic surveys on the northern Florida Keys (USA) population from 2004 to 2010. Percent cover of the benthos, number of colonies, and dominance by large individuals declined throughout the study period. We created population matrix models for each annual interval of the study, which included a severe hurricane year (2005-2006). Hurricane recurrence was simulated stochastically along with multiple outplanting scenarios. Population depletion is predicted given a return time for severe hurricanes of 20 yr or less. Elasticity analysis showed that the largest individuals have the greatest contribution to the rate of change in population size. Active management through out-planting can provide a positive population trajectory over the short term, especially if colonies are reared for several years before transplanting. However, the former abundance of this species suggests that background life history traits, specifically rates of growth versus shrinkage measured herein, are fundamentally different from what they must have been in the past. Ultimately, recovery of this species will depend on enacting local short-term management solutions while improving regional and global environmental conditions.