Survival and behaviour of juvenile red rock lobster, Jasus edwardsii, on rocky reefs with varying predation pressure and habitat complexity

Abstract

The role of large predatory fish in coastal communities is generally unknown because of overfishing. In order to understand the direct and indirect impacts of these increased population sizes on coastal food chains, the effect of areas with more fish predators on the survival and behaviour of potential prey was assessed. Juvenile lobsters, Jasus edwardsii (10–20 mm carapace length), were tethered on rocky reefs inside and outside marine reserves in northeastern New Zealand to assess survival under differing predator densities. Since rocky reef habitats in northeastern New Zealand include zones of kelp forest and barren reef, a two-way factorial design was used to determine the effects of predators, habitat, and the interaction of these two factors on juvenile lobster survival. Overall, the results indicated that neither varying large fish density nor varying kelp density had direct impacts on the survival rate of juvenile lobsters. Laboratory manipulations demonstrated behavioural changes by juvenile lobsters such that when a large predatory fish was present, juvenile lobsters spent significantly less time moving, even when separated from the predator by a porous barrier. Thus areas with more fish predators may increase juvenile lobster survival but potentially at the cost of reduced feeding opportunities.