BENTHIC FORAMINIFERAL FACIES OF A CARIBBEAN, MID-HOLOCENE CORAL REEF, ISLA COLON, BOCAS DEL TORO, PANAMA

Land-use changes along Caribbean coastlines have caused declines in marine communities. We are using environmental indicator species to compare modern marine coastal habitats of Bocas del Toro, Panama (BDT), to their previously “pristine,” state to suggest causes for observed changes. The portion presented here is a study of the distribution and community structure of benthic foraminifera from habitats associated with the mid-Holocene reef. Benthic foraminifera are useful for paleoenvironmental reconstructions because the modern ecology of many species found as Quaternary fossils is known. Samples were collected on Isla Colon from ~3ha of an excavated Acropora cervicornis-dominated reef ~6 ka. Bulk sediment samples were taken ~7m below mean sea level and classified into biofacies based on field observations of macrofossils, primarily corals and mollusks. Species’ relative abundance, richness and evenness are used to measure diversity, and foraminiferal wall types are used to associate species with salinity levels. The distribution of benthic foraminiferal species >63 µm in these samples will distinguish tropical habitats and build a baseline for future comparisons with their modern equivalents in BDT.

Initial findings for foraminiferal assemblages from three biofacies: in situ A. cervicornis-dominated reef, lagoonal mud, and seagrass show distinct differences in diversity and test wall types. The reef sample has a near-50/50 split of hyaline and porcellaneous wall types, agreeing with typical coral reef assemblages; the small test size, relatively low diversity and mostly thin-walled tests conform more to a low-energy, back-reef setting than a high-energy fore-reef or mid-reef. The mud sample is dominated by hyaline types, ~91%, particularly Ammonia and Elphidium, which are common indicators of nearshore, normal marine to slightly brackish lagoons. The seagrass sample has the greatest diversity, ~63% hyaline types; although hyaline species may be common in seagrass habitats, the sample lacks typical seagrass indicator species such as Archais and Sorites. Further research on benthic foraminifera from this reef will identify reefal, seagrass and mangrove assemblages that will be compared to those of nearby modern habitats to determine changes in coastal water quality over the past 6,000 years.