ASSOCIATIONS OF MICROALGAE AND MEIOFAUNA IN FLOATING DETRITUS AT A MANGROVE ISLAND, TWIN-CAYS, BELIZE

Associations of benthic microalgae and meiofauna affected by temperatu re, salinity and dissolved oxygen concentrations were examined in floa ting detritus in a shallow mangrove embayment in a 6 day time-series i nvestigation. Floating detritus exhibits a diurnal movement: it rises to the surface via oxygen bubbles generated by attached microalgae at sunrise and sinks down at sunset. In floating mangrove detritus, dinof lagellates were present in highest proportion (50-90%), followed by di atoms (5-15%), cyanobacteria (3-25%) and dinoflagellate cysts (1-7%). Microalgal densities correlated significantly with dissolved oxygen co ncentrations (r(2) = 0.763, P < 0.01) and with depth + time + dissolve d oxygen concentrations (r(2) = 0.902, P < 0.01). The vertical distrib utions of microalgal taxa in detritus were different with depth and ti me. In floating detritus, nematodes, ciliates, copepods and crustacean larvae were the most numerous. In bottom detritus, dominant meiofauna were: nematodes (1.8 X 10(3) to 3.2 X 10(3) organisms l(-1)), ciliate s (5.3 X 10(2) to 1.1 X 10(3) organisms l(-1)), crustacean larvae (2.7 X 10(2) to 2.4 X 10(2) organisms l(-1)) and copepods (0 to 1.1 X 10(2 ) organisms l(-1)); however, in midwater these heterotrophic organisms were the lowest, and they were intermediate in surface detritus. The distribution of heterotrophic taxa was significantly different with de pth (r(2) = 0.577, P < 0.001), but it did not vary significantly with day or time. Ciliates and nematodes were the major consumers of dinofl agellates in the aggregates.