Comparison of Caribbean Coral Reef Communities before and after Plio-Pleistocene Faunal Turnover: Analyses of Two Dominican Republic Reef Sequences

The extent to which origination and selective extinction influenced the structure and dynamics of Caribbean coral reef communities is evaluated by comparing the diversity and distributional patterns of coral species in two Dominican Republic reef sequences prior to and following late Cenozoic Caribbean faunal turnover. The two sequences consist of the late Miocene Arroyo Bellaco reef of the Cibao Valley, northern Dominican Republic, and the late Pleistocene 125-ka reef terrace of the southern Dominican Republic. Samples were collected along 20-meter transects (10 Miocene, 10 Pleistocene); species identifications were made using standard sets of characters and morphometrics. In particular, species of Montastraea annularis-like corals were distinguished within each sequence using a 2-dimensional landmark technique involving average linkage cluster analysis, discriminant analyses, and non-parametric tests. Four Miocene and four Pleistocene species were recognized. Subsequent community analysis was two-fold: (1) whole coral community, and 2) distribution of the Montastraea "annularis" complex. For the whole coral community, occurrence matrices of transect samples, assembled separately for Miocene (35 species) and Pleistocene (20 species) reef sequences, were analyzed using average linkage cluster analysis, multidimensional scaling, similarity percentages, one-way analysis of similarity, and non-parametric tests for independent samples (Mann-Whitney U, Kruskal-Wallis H). Three assemblages were recognized within each sequence, which correspond with back-reef, reef-crest, and reef-front facies defined independently on the basis of sedimentological criteria. Comparisons between the two sequences suggest that widespread species (ecological generalists) are more common within the Pleistocene sequence than within the Miocene sequence. Fifteen of thirty-five (43%) Miocene species occur in single reef facies compared to five of twenty (25%) Pleistocene species. Of the five species found within both reef sequences, four occur in all three of the identified Miocene reef facies; one was found in two of these three facies. For the distribution of the Montastraea "annularis" complex, samples of M. annularis-like corals were examined to determine if distributional patterns of species within the complex were similar before and after faunal turnover. The four M. annularis-like corals identified within each reef sequence had markedly different distributional patterns. During the late Miocene, cohabitation within reef facies was low. Following faunal turnover, cohabitation within facies increased. This result further suggests that niche partitioning may have been reduced on post-turnover reefs. The results support the hypothesis of selective extinction of ecologically restricted species during Plio-Pleistocene turnover. Despite the prolonged and continuous nature of faunal turnover, reef community change involved more than species replacement-the underlying structure of reef communities and their biological interactions were fundamentally altered.