Associations of microalgae and meiofauna in floating detritus at a mangrove island, Twin Cays, Belize

Abstract

Associations of benthic microalgae and meiofauna affected by temperature, salinity and dissolved oxygen concentrations were examined in floating detritus in a shallow mangrove embayment in a 6 day time-series investigation. 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, dinoflagellates were present in highest proportion (50–90%), followed by diatoms (5–15%), cyanobacteria (3–25%) and dinoflagellate cysts (1–7%). Microalgal densities correlated significantly with dissolved oxygen concentrations ( r 2 = 0.763, P < 0.01) and with depth + time + dissolved oxygen concentrations ( r 2 = 0.902, P < 0.01). The vertical distributions of microalgal taxa in detritus were different with depth and time. In floating detritus, nematodes, ciliates, copepods and crustacean larvae were the most numerous. In bottom detritus, dominant meiofauna were: nematodes (1.8 × 10 3 to 3.2 × 10 3 organisms 1 −1, ciliates (5.3 × 10 2 to 1.1 × 10 3 organisms 1 −1), crustacean larvae (2.7 × 10 2 to 2.4 × 10 2 organisms 1 −1 and copepods (0 to 1.1 × 10 2 organisms 1 −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 depth ( 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 dinoflagellates in the aggregates.