ELSEVIER Journal of Experimental Marine Biology and Ecology, 197 (1996) 159-175 JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY Associations of microalgae and meiofauna in floating detritus at a mangrove island, Twin Cays, Belize Maria A. Faust*, Rose A. Gulledge Department of Botany, National Museum of Natural History, Smithsonian Institution, 4201 Silver Hill Road, Suitland, MD 20746, USA Received 1 November 1994; revised 28 June 1995; accepted 5 September 1995 zyxwvutsrqponmlkjihg 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 (5-1.5%), cyanobacteria (3-25%) and dinoflagellate cysts ( l-7%). Microalgal densities correlated significantly with dissolved oxygen concentrations (r’ = 0.763, P < 0.01) and with depth + time + dissolved oxygen concentrations (r’ = 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 X IO’ to 3.2 X IO’ organisms I-‘), ciliates (5.3 X IO* to I.1 X IO3 organismsl-‘), crustacean larvae (2.7 X 10’ to 2.4X 10’ organisms I ‘) and copepods (0 to I .I X IO* organisms I I); 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’ = 0.577, P < zyxwvutsrqponmlkjih 0.001 ), but it did not vary significantly with day or time. Ciliates and nematodes were the major consumers of dinoflagellates in the aggregates. Keywords: Ciliates; Cyanobacteria; Detritus; Diatoms; Dinoflagellates; Mangrove; Meiofauna; Nematodes 1. Introduction Shallow subtropical waters serve as habitats to assemblages of microalgae and *Corresponding author. Fax: (I) (301) 238-3667. 0022.0981/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0022-098 I (95)00159-X