Composition of the metazooplankton community and structure across the continental shelf off tropical NW Australia

This talk focuses on the distribution pattern and grazing impact of different functional metazooplankton groups in a tropical marine ecosystem. We studied the metazooplankton distribution across the continental shelf from eutrophic mangrove areas to the oligotrophic deep blue ocean off NW Australia. Chlorophyll a concentrations were reduced by factor 10 along the transect including a shift towards small sized primary producers. The metazooplankton biomass followed the same pattern. Even though low in abundance, copepods were most frequent followed by larvaceans, doliolids other thaliacea and chaetognaths. Small size classes <200 μm dominated the zooplankton and e.g. 80 % of the larvacean community belonged to the micro-size fraction. We show that gelatinous zooplankton is of key importance for the carbon cycling in this tropical area. Larvaceans exceeded the copepod grazing impact on the primary producers especially in oligotrophic areas. The metazooplankton community structure and production reflect biotic and abiotic conditions of the system. We show that small size classes, especially larvaceans, have a higher contribution to secondary production and carbon cycling in tropical oligotrophic areas than previously thought