Seasonal variation in epiphytic foraminiferal biotas from Thalassia seagrass habitats, Twin Cays, Belize

Abstract

The epiphytic foraminifera1 biotas living on the seagrass T/zzalassia testzrrlimun were surveyed at four sites in the Twin Cays, Belize (Boston Bay, Sponge Haven, the Main Channel near the dock, and 'Cuda Cut) during June 2001 and February 2002 in order to investigate seasonal variation in diversity, distribution, and abundance. Twelve blades were surveyed from each site and all live epiphytic foraminiferans were identified to species (S=41) and counted (N=15,455). The sites surveyed showed distinct seasonal differences in mean density of individuals per unit blade area (~ lcm" , species richness (S), and evenness (E), between June 2001 (the warmer, wet season) and February 2002 (the cooler, dry season). The mean density of individuals per unit blade area was higher at all sites in June 2001, compared with February 2002. Although mean species richness per blade did not show a significant seasonal signal, the total species richness recorded at each site was higher during June 2001, relative to February 2002, for all sites except Boston Bay. Likewise, values of evenness were higher in June 2001, relative to February 2002, except for the Boston Bay site. Both abiotic and biotic factors are considered to influence the seasonal differences in the population densities and species composition of the epiphytic foraminiferans living on T. testudirzunz in the vicinity of the Twin Cays mangrove island. It is suggested that seasonal differences at this locality may result from an influx of nutrients from the adjacent mangrove fringe during the wet season, an incursion of open-water species into the mangrove habitats during the dry season, and the thermal tolerances of individual species. The high dominance of the encrusting, milioline species Rhizorzubecula sp. observed at all sites in the Main Channel in June 2001, and again at the Dock site in February 2002, highlights the potential utility of this species as a bioindicator of increased nutrients in mangrove habitats.