Southern range extensions of the tropical Australian heterobranch sea slug fauna may be symptomatic of climate change, particularly in south-eastern Australia, a recognized climate change hot-spot. In the Solitary Islands Marine Park, northern New South Wales, the presence of biogeographic mixing means that the southern coastal distribution limit of several tropical marine species and the northern limit of some temperate species overlap. During a year-long series of monthly surveys of sea slug communities on intertidal rocky shores, we observed four species beyond their previously recorded range – Colpodaspis thompsoni, Elysia pusilla, Phidiana bourailli and Herviella claror. The southern migration of species is an anticipated response to warming seas and we note an apparent extension of the southern limit for these taxa.
