The cause and consequence of ontogenetic changes in social aggregation in New Zealand spiny lobsters

Abstract

Ontogenetic changes in the behavior, spatial distribution, or habitat use of a species are presumably adaptations to ecological forces that dlffer in their effect on various life stages. The New Zealand rock lobster Jasus edwardsii is one of several species of spiny lobster that exhibits dramatic ontogenetic shifts in sociality and spatia.1 distribution, and we tested whether such changes are adaptive. We first surveyed several natural populations of J. edwardsii to document size-speclfic differences in aggregation. To determine i f chemical cues discharged by conspecifics promote aggregation of certain ontogenetic stages, we tested the responsiveness of lobsters of 3 ontogenetic stages (early benth~c juvenile, juvenile, and subadult) to the chemical cues produced by conspecifics of different sizes. Finally, we tethered lobsters of different ontogenetic stages alone and in groups to test the effect of lobster size and aggregation on mortality. Our results offer compelling evidence that pre-reproductive J. edwardsii undergo an ontogenetic change in sociality that alters their spatial distribution and sunrival. Our field surveys show that J. edwardsii are solitary as early benthic juveniles and become social and aggregate as they grow larger. We then demonstrate, using laboratory experiments, that there is a sizespecific increase in the response of pre-reproductive J. edwardsii to the chemical cues of larger conspecifics which facilitates these ontogenet~c changes in aggregation. Finally, our tethering results confirm that this change in social condition is selectively advantageous: aggregation does not increase the survival of small lobsters, but larger lobsters survive better in groups. Thus, in this study we demonstrate the linkage between ontogenetic changes in the spatial distribution of a species, the behavioral process that creates the pattern, and the selective advantage conferred by these developmental changes.

Podding of juvenile king crabs Lithodes santolla (Molina, 1782) (Crustacea) in association with holdfasts of Macrocystis pyrifera (Linnaeus) C. Agardh, 1980

“…The authors indicated that pods could vary in form and structure depending on the species, time of year, and area where the pods formed, as well as the characteristics of the individuals that form them (maturity stage, intermoult stage). A protective function has also been suggested for juvenile aggregations of spiny lobsters (Eggleston et al, 1990;Smith & Herrnkind, 1992;Butler et al, 1999).…”

Habitat-based intraguild predation by Caribbean reef octopus Octopus briareus on juvenile Caribbean spiny lobster Panulirus argus

“…In contrast, there is no evidence that spiny lobsters use olfactory cues to detect and avoid piscine predators (Schratwieser 1999), nor would flight or multiple den entrances seem a particularly valuable strategy for evading fastswimming fish predators. Instead, group defense by spiny lobster is a well-documented and effective means of reducing piscine predation (Mintz et al 1994, Eggleston et al 1997, Butler et al 1999 , and our results demonstrate that it is also effective against octopuses. Alternatively, multiple lobsters fleeing an octopus predator in a confined space may have lessened predation due to a confusion effect on the octopus (Neill & Cullen 1974).…”

“…Aggregation with conspecifics increases the survival of lobsters subject to predation (Smith & Herrnkind 1992, Mintz et al 1994, Butler et al 1999, Dolan & Butler 2006; therefore, we also investigated whether the presence of octopuses on a site effected the local pattern of lobster aggregation in artificial shelters. First, we calculated a standardized Morisita's index of dispersion (I δ ) for each site to determine if the lobsters present were evenly distributed (I δ < 0), randomly distributed (I δ = 0), or clumped (I δ > 0).…”

“…Tethering has proven to be a reliable method for discerning differences in relative mortality of lobster among sites (Mills et al 2008) without the bias of treatment × artifact interactions (Barshaw et al 2003). The presence or absence of lobsters and any injuries they sustained were recorded after 24 and 48 h. Lobsters rarely escape from properly constructed tethers (Butler et al 1999); if lobsters were absent, we considered them to have been killed by a piscine predator if the tether was cut or if only a tiny fragment of the lobster's carapace remained. Lobsters killed by octopus were conspicuous and identified by the presence of an empty, dismembered exoskeleton (Lavalli & Spanier 2001).…”

Spatiotemporal bioeconomic performance of artificial shelters in a small-scale, rights-based managed Caribbean spiny lobster (<em>Panulirus argus</em>) fishery

“…The hypothesized functional benefits of den sharing include the dilution effect or group defence against predators (Eggleston and Lipcius 1992, Mintz et al 1994, Butler et al 1999), the guide effect, which reduces predation risk during the search for shelter (Childress and Herrnkind 2001), and cohabitation of smaller more vulnerable juveniles with larger conspecifics that have greater defensive abilities (Sosa-Cordero et al 1998, Briones-Fourzán et al 2007.…”