Epibenthos of mangrove waterways and open embayments in tropical northeastern Queensland, Australia

The macro-epibenthos of tidal mangrove creeks in Missionary Bay and in the Murray River estuary in tropical northeastern Queensland was sampled on a seasonal basis. Missionary Bay has an extensive (50 km2) mangrove forest dissected by several tidal creeks, only one of which (Bowen Creek) has significant freshwater input. In contrast, the nearby Murray River catchment receives a rainfall of >2000 mm/y and estuarine salinity ranged from 3.2-31.0 parts per thousand at the sampling sites used in the study.

The inshore (mangrove habitats)-offshore (embayment) patterns in total faunal taxonomic richness (means ranging from 0 to 32·5 taxa per trawl) and density (range of means, < 1·55 individuals/m2) were generally complex, with patterns across the gradient changing seasonally. Patterns in total biomass (range of means 0-740mg/m2) were clearer, with highest biomasses recorded in May (post-wetseason) and lowest in February (mid-wet season), with no significant cross habitat gradient in biomass. Densities and biomasses were lower than those recorded in other studies, probably owing to the physically harsh conditions available to epibenthos and to the low quality of mangrove detritus as a food source. The significant difference in the structure of epibenthic communities in mangrove and embayment habitats in the dry season months (August and October) was likely due to the longer residence time of water in mangrove waterways at that time of the year. Greater tidal amplitudes and increased tidal current velocities in February transported mangrove detritus and many faunal taxa into embayments. Variation in the quantities of exported mangrove detritus in nettings explained significant proportions of the variance in total (and component taxa) epibenthic standing stocks in mangrove and embayment habitats. Several factors may be important in causing the positive response of different groups within the epibenthos to mangrove detritus. For penaeid shrimps it seems likely that clumps of exported mangrove detritus provide refuges from predatory fish in both mangrove and embayment habitats.