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

Matt Nimbs,Stephen Smith

doi:10.3390/d10030099

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.

Highlights

By far the majority of Indo-Pacific sea slug species are tropical [1] with diversity declining away from the equator
The highest diversity occurs in the tropical western Pacific, and in particular in the area known as the Coral Triangle
On the Australian east coast, diversity attenuates from the northern Great Barrier Reef (GBR), Queensland (QLD), where approximately 1000 species have been recorded [3], to the southern tip of the mainland with 400 species recorded from Victoria and Bass Strait [4]

Summary

Introduction

By far the majority of Indo-Pacific sea slug species are tropical [1] with diversity declining away from the equator. The highest diversity occurs in the tropical western Pacific, and in particular in the area known as the Coral Triangle (bounded by Indonesia, the Philippines, and the Solomon Islands). Records are extremely patchy both spatially and temporally, with many regions receiving very little recent attention (e.g., eastern Indonesia) [2]. On the Australian east coast, diversity attenuates from the northern Great Barrier Reef (GBR), Queensland (QLD), where approximately 1000 species have been recorded [3], to the southern tip of the mainland with 400 species recorded from Victoria and Bass Strait [4]. The oceanographic conditions on the central eastern Australian coast, which extends from the southern GBR in southern QLD to northern NSW, are heavily influenced by the East Australian The subtropical region of New South Wales (NSW) supports both tropical and temperate taxa representing a biogeographic ecotone, as well as several endemic taxa restricted to this overlap zone [5].

Methods

Results

Conclusion