Zooplankton was sampled in a mangrove forest, a mangrove drainage creek, the main stream of a mangrove dominated estuary, a seagrass flat at the entrance to the mangrove estuary and at an offshore (10 km) station in northeastern Australia approximately every 6 weeks between April 1985 and February 1986. Copepods, in particular Parvocalanus crassirostris, Paracalanus spp., several species of Oithona and Euterpina acutifrons were numerically dominant. Community structure often differed amongst mangrove habitats but mangrove habitats clustered separately from seagrass and bay habitats in classification analyses due to the abundance of meroplankton taxa, particularly invertebrate eggs and brachyuran zoea, in mangrove habitats. Total densities of zooplankton in mangrove and seagrass habitats were always higher than in the offshore bay habitat. Mangrove and seagrass habitats exhibited marked seasonality in densities of most taxa. Generally, seasonality in most taxa did not correlate with water temperature, salinity, mangrove litter fall or fish predation, although fish may have a significant influence on brachyuran zoea. There were often significant tidal variations in densities in mangrove creeks; low-tide densities were usually lower than high-tide values. Comparisons of the density of major prey taxa of fish in seagrass and mangrove habitats gave only partial support to the hypothesis that mangroves are more important nursery sites for zooplankton feeding juvenile fish because they are areas of greater food abundance; during the summer recruitment period of juvenile fish, brachyuran zoea, a major prey of fish, were an order of magnitude more abundant in mangrove habitats.
This research was undertaken to investigate zooplankton dynamics in mangrove and other nearshore habitats and to test the hypothesis that between habitat differences in the densities of juvenile zooplankton feeding fishes reflect differences in the standing stock or taxonomic composition of zooplankton in these habitats.
The mangrove forest site was sampled using a specially designed floating pump system (EZY-ZOOP). A boat-towed net (50cm diameter mouth, 105um mesh and fitted with a General Oceanic flow meter) was used to sample daytime zooplankton in the mangrove creek, mangrove mainstream, seagrass and bay habitats. Sampling was carried out using 5 minute oblique tows.
