AbstractsBiology & Animal Science

Nudibranchs are a diverse group of gastropod molluscs that are distributed around the world found inhabiting coral reef ecosystems. Baseline data on nudibranchs is lacking in the mid west region of Western Australia. Four sub-regions across the Midwest; Geraldton and the three groups at the Abrolhos Islands, the Easter Group, the Wallabi Group and the Pelsaert Group were the focus of nudibranch diversity surveys. Collection of quantitative information to establish a biogeographical baseline for the nudibranchs of this region was one of the main aims of this study. In total 89 dives were made over the duration of this study, with an average dive time of 30 minutes. A total of 296 individual nudibranchs were observed. The most abundant family found was Chromodorididae and Chromodoris westraliensis was the dominant species. Equal numbers of nudibranchs were found at shallow and deep sites, with depth found to not have a significant difference on nudibranch abundance or species abundance. Sub-region was suggested to be the predominant influence in nudibranch abundance and species richness. The probable cause for this is the influence from the Leeuwin Current and its effects on the habitat composition. The Leeuwin Current is believed to strongly influence recruitment of planktonic larvae along the Western Australian coast. Suggesting that larval recruitment of all marine species including nudibranchs, nudibranch prey items and benthic flora nudibranchs inhabit is influenced by the Leeuwin Current. Investigations into key nudibranch prey items and their seasonal occurrence may help in predicting abundance of sub-annual nudibranch species in an area. Benthic habitat differences and nudibranch prey items could be distributed at different rate over each sub-region due to local hydrology effects from the Leeuwin Current. Geraldton was found to be clearly different to the three Abrolhos Island groups, with sub-region being a determining factor for abundance and species abundance. Greater sampling effort into destructive day-time and night-time sampling is also predicted to increase the number of species and abundance of nudibranchs found in the Midwest region.