COMPARING COMMUNITY SIGNALS USING ABUNDANCE AND BIOVOLUME MEASURES ON MODERN AND FOSSIL REEFS, SAN SALVADOR, BAHAMAS

The current biodiversity crisis is often represented by the rapid deterioration of coral reefs worldwide, and paleontologists have successfully argued that fossil reefs provide a useful baseline upon which conservation strategies can be based. The modern reefs on San Salvador, Bahamas are directly comparable to the exceptional Pleistocene fossil reefs exposed on the island. Although previous studies have examined the similarity of modern and fossil reefs, in-depth comparisons of different sampling techniques used to retrieve ecological patterns have been lacking. This study compares the differences in community data derived by biovolume versus abundance counts at different spatial scales.

Two fossil and four modern reefs were surveyed on the eastern side of San Salvador. Multiple parallel transects (> 10 m long and > 1 m apart) were measured on each reef. Abundance data include all benthic organisms encountered along the transect. Biovolume was estimated using the Linear Point Intercept method at a centimeter scale. Comparisons of abundance and biovolume were made within transects, between transects, between sites, and between modern and fossil reefs. Pearson’s correlation was used to compare species occurrences (measured by abundance or biovolume), and r-values > 0.256 were significant (> 100 degrees of freedom, p < 0.01). Biovolume (b) and abundance (a) data were positively correlated albeit weakly in some instances (within transects a:b, r = 0.39 – 0.76; between transect a:b, r = 0.38 – 0.75). At each site, transects were positively correlated (a:a, r = 0.58 – 0.85; b:b, r = 0.51 – 0.86).

When comparing community composition between sites, the fossil reefs were not significantly correlated. Modern sites were not significantly correlated either, likely due to differences in depth and algal cover. Modern and fossil sites were not significantly correlated even when un-calcified species (low preservation potential) were excluded, likely reflecting the change in coral communities following the regional die-offs of Acropora in the 1980s. These results suggest that it is important to compare both abundance and biovolume, as each can reveal different ecological signals within community data. The results of this project have implications for both paleontology and conservation biology.