Seasonal and oceanographic variation in larval flatfish assemblages off the southeast Australian Coast

Distribution patterns of larval flatfish assemblages at 3 oceanographic monitoring stations off southeastern Australia (North Stradbroke Island [NSI], about 27°30′S; Port Hacking [PH], about 34°6′S; and Maria Island [MAI], about 42°30′S) are described from monthly ichthyoplankton samples collected between 2014 and 2021. A total of 4873 flatfish larvae were collected from 6 families: Bothidae (Arnoglossus spp., intermediate flounder [Asterorhombus intermedius], Crossorhombus spp., Engyprosopon spp., Grammatobothus spp., and crested flounder [Lophonectes gallus]), Cynoglossidae, Paralichthyidae (Pseudorhombus spp.), Pleuronectidae, Samaridae, and Soleidae. Abundances of different taxa varied seasonally, and the assemblage composition varied between season and years, but with no overall change in abundances over the study period. Markedly different larval flatfish assemblages were caught at the 3 stations, corresponding to the latitudinal variation in water mass characteristics (temperature, salinity, and chlorophyll). The number of larval flatfish taxa decreased with increasing latitude and were highest at the sub-tropical NSI and lowest at the temperate MAI. Most bothid larvae were caught at NSI and PH except crested flounder, which was only caught at PH and MAI. Cynoglossid, Pseudorhombus spp., samarid, and soleid larvae were only caught at NSI and PH, while pleuronectid larvae were only caught at MAI. These distinct larval assemblages provide a useful benchmark to monitor the progress of the strengthening East Australian Current in a known hotspot of climate change.