Agonistic behaviour and reproductive biology of squat lobsters

Squat lobsters are ubiquitous in many benthic habitats yet very little is known about their behavioural ecology. This chapter synthesises reports of agonistic and reproductive interactions of squat lobsters in order to understand the evolution of behavioural and reproductive traits. Squat lobsters often occur in dense aggregations where individuals frequently interact, but these interactions rarely escalate to higher levels of aggression. Ritualised behaviours may reduce the possibility of agonistic interactions and, if escalation occurs, autotomy can help to lower the risk of cannibalism. Reproduction in most studied species is highly seasonal, and larvae are usually released during periods of high primary production. Depending on environmental conditions, females may produce more than one brood during a reproductive season. Female squat lobsters mate during the intermoult phase and can incubate several consecutive broods without moulting in between. The main moulting period is usually after the reproductive season and starts slightly earlier in males than in females. Sexual dimorphism in body size and chela strength is suggestive of strong sexual selection: in shallow-water species males are usually larger and stronger than females, indicating that they compete for access to reproductive females. Present knowledge suggests the existence of two principal mating strategies: ‘pure search’, where males roam in search for receptive females, mating interactions are brief and the couple separates quickly after sperm transfer; and ‘search and defend’ where males guard reproductive females for extended periods before, and occasionally after, copulation. Each species usually adopts one mating strategy but initial observations suggest ontogenetic changes in male mating strategies for some species. A solid understanding of mating system evolution in squat lobsters requires better knowledge of the mating behaviours in different species and under different environmental scenarios (e.g. population densities). This information is considered particularly essential to achieve sustainable management of the populations of exploited species.