Acoustic tracking of a large predatory marine gastropod, Charonia tritonis, on the Great Barrier Reef

Abstract

Crown-of-thorns starfish Acanthaster planci (COTS) outbreaks are a major cause of coral cover loss on the Great Barrier Reef (GBR), with manual culling having only localised success. The endangered giant triton snail Charonia tritonis is a natural predator of COTS, although aquarium and field observations indicate the intensity of direct predation may be inadequate to significantly mediate outbreaks. However, their mere presence can elicit a chemically induced sensory behavioural response which may suppress COTS populations when in non-outbreak status. While there is increasing knowledge of the sensory biology of both species, little is known regarding giant triton snail numbers on the GBR or about how they move and occupy space, making it difficult to determine their true zone of influence and thus their capacity to disrupt COTS behaviour. We used passive acoustic telemetry to establish short-term activity space and movement patterns of giant triton snails on the GBR. Individuals were tracked for up to 41 d, were observed to travel 234.24 m d-1, with a mean total cumulative distance travelled at night (1923.19 m) nearly double that observed during the day (1014.84 m). These distances encompass those reported for COTS (10.3 m d-1) and align with COTS nocturnal behaviour. Space utilisation distributions (UDs) revealed a mean (±SD) home range of 1179.40 ± 659.40 m2 (95% UD) and a core area of 195.68 ± 141.31 m2 (50% UD). Revealing the short-term movement patterns of this natural COTS predator within a reef environment advances knowledge of its spatial ecology and will provide information for its future conservation and for COTS management efforts.