Patterns of shelter use and their effects on the relative survival of subadult California spiny lobster (Panulirus interruptus)

Spiny lobsters use refuge habitat and gregarious behaviour to reduce predation risk, particularly in their vulnerable juvenile and subadult stages. We characterised patterns of sheltering behaviour in the California spiny lobster (Panulirus interruptus (Randall)) on southern California rocky reefs and used manipulative experiments to examine how these behaviours affect the survival of subadult lobsters and shelter selection. Lobsters generally were gregarious and subadults were commonly found inhabiting shelters with adult lobsters. Tethering experiments with subadults indicated that communal denning increases the odds of survival only when adult lobsters are part of aggregations. This corresponded to results from a shelter choice experiment in the laboratory, where the presence of predators caused subadults to shelter more often with adult conspecifics rather than other subadults. Despite the gregarious nature of P. interruptus, solitary subadults were common at all sites. Although field experiments clearly indicated that solitary lobsters increased their odds of survival by inhabiting shelters scaled to body size, evidence that lobsters exhibit shelter scaling on natural reefs was mixed. Our results indicate that subadult P. interruptus exhibit similar behavioural strategies as other spiny lobsters to reduce predation risk, and they provide a more comprehensive examination of P. interruptus behaviour than previously available.