Preservation of community structure in modern reef coral life and death assemblages of the Florida Keys: Implications for the Quaternary fossil record of coral reefs

摘要

The reef fossil record is the exclusive database from which analyses of the response of coral communities to environmental change over geological time scales may be gauged. However, few studies have attempted to ascertain whether the reef fossil record is a reasonably accurate representation of a once living coral community. To address this issue, we first assume that an assemblage of dead corals accumulating in close proximity to a living coral reef(including the dead portions of living colonies) provides a reasonable proxy for the material that potentially becomes fossilized We then perform a systematic comparison of the taxonomic composition and diversity present in coral life assemblages and death assemblages accumulating in reef tract and patch reef environments adjacent to Key Large, Florida. The death assemblage is distinct from the life assemblage, but matches exactly the zonation of live corals between reef tract and patch reef environments. The difference in taxonomic composition between life and death assemblages is the result of a striking growth form bias in the depth assemblage: massive coral colony forms predominate in the life assemblages in both environments, whereas branching colony forms predominate in the death assemblages. Calculations of species richness and the Shannon-Wiener index of diversity produced conflicting results. At one reef tract site, the death assemblage was more diverse than the life assemblage. Unlike the Indo-Pacific, the subset of the life assemblage retained as recognizable corals in the death assemblage is not less diverse. We attribute this difference to a more diverse "starting pool" of live corals in the Indo-Pacific. Fidelity indices were similar to those calculated for life and death assemblages occurring in the Indo-Pacific, but very different than those compiled for molluscan shelly assemblages. If the death assemblages we examined represent a reasonable proxy for a potential fossil assemblage, analyses of relative changes in coral reef community structure during Quaternary time should provide reliable base line data for assessing the response of modern Caribbean reefs to global change.