HOLOCENE DECLINE OF ACROPORA PALMATA: DEATH BY NATURE OR HOMO STUPIDUS?

Since the 1970s, a major decline in coral cover due to a host of anthropogenic stresses has dramatically reduced the accretionary potential of the world’s reefs. White Band Disease (WBD) in particular has played a major role in the decimation of Acropora palmata, a major shallow-water reef builder in the Caribbean. Gaps in the record of this species ca. 6,000 and 3,000 years ago suggest that factors other than human influence may have come into play. Twenty samples of dead A. palmata were collected from standing dead colonies on the present reef surface (killed by WBD) and from an excavation into the reef interior (deposited by normal processes). Samples were impregnated and made into large-format thin sections. The abundance of post mortem epibionts were determined by point counting along twenty equally spaced transects around the perimeter.

Cluster analysis revealed different signatures in the two sampled populations. Biont on colonies killed by WBD (“standing dead”) were dominated by thick (> 300 microns) coralline algal crusts, vermetid gastropods and the foram Gypsina spp. In contrast, samples from the reef interior were covered by Carpenteria spp. and lesser amounts of corallines. The latter signature reflects encrustation within cryptic spaces in the reef while those on the ”standing dead” colonies were dominated by photic bionts. These distinct post-mortem signatures reflect the different pathways of the two assemblages and may be useful in relating apparent gaps in the A. palmata record to a recent decline of the species.