Assessment of turtle grass (Thalassia testudinum ex Banks Konig) community structure in a UNESCO Biosphere Reserve

Tropical turtle grass beds (Thalassia testudinum) were investigated in an UNESCO Biosphere Reserve in St. Johns Island, United States Virgin Islands. Four coastal bays were studied to assess floral characteristics, benthic invertebrate density and secondary production. These bays varied with respect to oceanic exposure and anthropogenic stresses. Results indicate that Coral Bay Harbor, the most anthropogenetically impacted site, had the highest T. testudinum biomass, but the lowest floral diversity. Its faunal community was dominated by small polychaetes with significantly lower secondary production. The most protected site (Hurricane Hole) maintained the highest floral and faunal species richness, faunal density, faunal diversity, and secondary production. The other two bays, Great Lameshur and Little Lameshur, demonstrated intermediate plant biomass and species richness, faunal density and secondary production. Each of these bays, however, had high oceanic exposure due to their orientation which also demonstrated a sediment size shift to larger particles compared to the other sites. One unique finding was a significant increase in the shoot:root ratio in Little Lameshur where green turtle (Chelonia mydas) grazing was frequently observed, suggesting a potential top-down structuring force in this bay.