The Demise of Acropora Palmata in Caribbean Reefs: Past, Present and Future

The dramatic acceleration of coral-reef decline over the past two decades is largely a response to global phenomena that have broadened the temporal and spatial scales of deterioration beyond the point where biological studies alone can adequately address the relationship between environmental stress and reef response. The genus Acropora has emerged as the poster child for decline in the Caribbean. Bleaching and White Band Disease have decimated the population regionally, changing the fundamental dynamics of shallow-water community structure. However, Holocene cores reveal two intervals (ca. 5800-5300 and 3000-2300 CalBP) during which Acropora palmata was significantly less abundant. Possible relevance to the recent decline of this species can be assessed only if we can identify a preservable "fingerprint" left by the recent mortality that can be used to evaluate the similarity of past declines within the same species.

A preliminary examination of 30 A. palmata samples from Buck Island (USVI) reveals a statistically significant difference between the epibiont signature on standing dead A. palmata colonies (mostly thick and conformable coralline algae and vermetid gastropods) versus storm-deposited branches that form the substrate on which they sit (primarily Carpenteria utricularis and Biarrititzina carpenteriaetermis). This difference reflects more exposed versus cryptic post-mortem micro-environments, respectively, following the two scenarios of coral mortality. Studies are planned to increase the sample size and the number of sites. In addition, a detailed census of massive corals is underway to characterize regional changes in community structure deeper along the forereef.

It is unlikely that today's reefs will ever see environmental conditions akin to the early twentieth century. This argues for strategies that will be successful in a world that will be different than the one in which Holocene reefs developed. A look back in time may provide the best means for understanding reef change in response to future conditions.