Beyond Capricornia: Tropical Sea Slugs (Gastropoda, Heterobranchia) Extend Their Distributions into the Tasman Sea

Abstract

There is increasing evidence of poleward migration of a broad range of taxa under the influence of a warming ocean. However, patchy research effort, the lack of pre-existing baseline data, and taxonomic uncertainty for some taxa means that unambiguous interpretation of observations is often difficult. Here, we propose that heterobranch sea slugs provide a useful target group for monitoring shifts in distribution. As many sea slugs are highly colourful, popular with underwater photographers and rock-pool ramblers, and found in accessible habitats, they provide an ideal target for citizen scientist programs, such as the Sea Slug Census. This maximises our ability to rapidly gain usable diversity and distributional data. Here, we review records of recent range extensions by tropical species into the subtropical and temperate waters of eastern Australia and document, for the first time in Australian waters, observations of three tropical species of sea slug as well as range extensions for a further six to various locations in the Tasman Sea.

First Survey of Heterobranch Sea Slugs (Mollusca, Gastropoda) from the Island Sangihe, North Sulawesi, Indonesia

“…Because marine Heterobranchs are also very attractive to tourists, additional data are and will be available through citizen science due to documentation in websites or personal information and provision of images on personal bases. This was shown lately by Nimbs et al [16] and Nimbs and Smith [17] where long-term documentation of scientists and recreational divers led to the identification of new tropical species introduced in Port Stephens, on the central New South Wales coast of Australia, and Tasman Sea. In order to monitor potential damage to the environment around Sangihe, irrespective of its original cause, we have started with a first survey in 2016, focusing on marine Heterobranchia.…”

Biodiversity citizen science: Outcomes for the participating citizens

“…Deguines et al., 2012; Pellisier et al., 2019; Richardson et al., 2018), sea slugs (e.g. Nimbs & Smith, 2018) and plants (e.g. Brodschneider et al., 2019).…”

Sea Slugs—“Rare in Space and Time”—But Not Always

“…Long-term data are necessary to assess patterns of rarity and to determine if this is due to: temporal variability linked to normal seasonal fluctuations [26]; persistent presence but numerical rarity; or vagrancy. Climate-change-driven poleward range extensions of several species of sea slug [27][28][29] is also resulting in designation of rarity for species occurring at novel locations [30], or as single observations [28]. Although some species may be spatially or numerically rare, there are others that are very common within specific locations [8,31] and to which the blanket term "rare in space and time" does not apply.…”