Abstract
Port Stephens, on the central New South Wales coast, provides ideal oceanographic and benthic conditions for the settlement and growth of larvae of tropical species delivered from the north by the East Australian Current. The popularity of the bay for recreational and scientific diving has facilitated extensive documentation of the biota over several decades, confirming its high biodiversity. Of the 313 species of heterobranch sea slugs recorded from Port Stephens to date, 30 are not known to occur further south. Our observations increase the number of taxa with a southern distribution limit at Port Stephens by 12 species and add to a growing list of marine taxa that are progressively extending their southern range, potentially as a result of climate change.
Highlights
Heterobranch sea slugs are predominantly tropical marine animals that, on the eastern Australian coast, exhibit a latitudinal gradient with rapid attenuation of species diversity from more than 1,000 species in the northern Great Barrier Reef (GBR) to approximately 500 in central New South Wales (NSW) (Rudman & Willan, 1998)
The current moves offshore and generates eddies that deliver an intermittent supply of these tropical larvae to the central and southern NSW coast (Burn, 2006)
Comprehensive data on the occurrence of a range of marine organisms tend to be confined to locations near major population centres due primarily to the proximity of research facilities (Smith 2005, 2008a, b; Burn, 2006)
Summary
Heterobranch sea slugs (hereafter sea slugs) are predominantly tropical marine animals that, on the eastern Australian coast, exhibit a latitudinal gradient with rapid attenuation of species diversity from more than 1,000 species in the northern Great Barrier Reef (GBR) to approximately 500 in central New South Wales (NSW) (Rudman & Willan, 1998). Comprehensive data on the occurrence of a range of marine organisms tend to be confined to locations near major population centres due primarily to the proximity of research facilities (Smith 2005, 2008a, b; Burn, 2006) For this reason, species lists for the central NSW coast, especially adjacent to Sydney, are comprehensive, Nimbs et al Marine Biodiversity Records (2016) 9:27. Coastal lagoons and estuaries provide sheltered locations for successful settlement and growth of more tropically adapted marine organisms (Willan et al, 1979) and accessible, safe diving conditions. These factors, combined with the increasing popularity of diving-based citizen science activities in the region These factors, combined with the increasing popularity of diving-based citizen science activities in the region (e.g. Smith & Edgar, 2014 and the current Sea Slug Census program) increase the likelihood that additional species will occur in the region, and that they have a reasonable probability of being found
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