Gut Instincts: Feeding behaviour of the rock lobster, Jasus edwardsii

Abstract

Predator-prey interactions play a critical role in structuring community dynamics, such as lobster predation, which has been shown to affect both soft sediment and rocky reef community structure. In recent years there have been major concerns regarding the over-exploitation of rock lobster stocks. The significant decline and sustained low lobster abundance have led to many populations becoming functionally extinct, resulting in large regime shifts in rocky reef habitats. Despite the ecological importance of lobsters, conservation efforts in northeastern New Zealand are hindered by a lack of understanding concerning their nearshore feeding biology and sensory drivers. Therefore, this thesis aimed to assess the feeding behaviours and movements of the rock lobster, Jasus edwardsii, including the sensory mechanisms driving food selection. Cafeteria experiments showed that large male lobsters exhibited a strong preference for soft-sediment bivalves over rocky-reef prey. Although urchins had the highest profitability, urchins were the least preferred when lobsters were presented with prey choice. Detection and selection of buried soft-sediment prey were primarily driven through chemoreception. The antennules, in particular, appeared to play a disproportionate role in prey detection. Furthermore, lobsters play a key role in controlling urchin populations, whose intensive grazing can turn lush kelp forests into barren habitats. Predation pressure of male lobsters fluctuated throughout the year and was predominantly dictated by the moult stage and a preference for urchins with a high gonad index. This seasonal variability and selective predation may have implications in using lobsters as a mitigation tool to reduce the expansion of urchin barren habitats. Lastly, foraging-associated movements validate the historically observed offshore migrations being food driven and suggest that lobster home ranges extend well beyond rocky reef margins. Unexpectedly, visually-impaired lobsters showed increased movement, and the associated energy expenditure may have cascading effects on foraging efficiency, shelter selection and predator avoidance. Collectively, this thesis’s findings have significant implications for fisheries and conservation management regarding marine protection design. In particular, ensuring that soft-sediment feeding habitats are better understood and protected remains critical for this valuable yet vulnerable predator.