Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the continental shelf off central Chile

Abstract

Newly settled individuals and juveniles of several benthic decapod crustaceans spend their first months or years in nursery habitats different from those of the adult population. It was unknown if this was the case for the squat lobster Pleuroncodes monodon, an exploited crustacean which inhabits the continental shelf off central Chile, and of which 2 adult populations exist, the larger Achira (35' 10' S to 36' 15' S) and the smaller Biobio (36' 35' S to 36' 50' S). We report here the presence of a large nursery area of the species, connecting both adult populations; the habitat is dominated by extensive sulphide microbial communities which fluorish at very low oxygen concentrations. We inferred the existence of northerly and southerly migration routes from the nursery ground to the adult populations, with juvenile year classes migrating as they advance through age classes. The juvenile population was composed of 2 year classes: 0 yr old (newly settled mdividuals) and 1 yr old juveniles; thus juveniles seemed to spend their first year of life in the nursery area. Total abundance was estimated as 3290 x lo6 individuals (asymmetric 95 % confidence interval: 2153 to 7039 x lo6), although the above figure is a lower bound because the sampling did not cover the whole nursery area. We hypothesize that the Biobio adult population is not self-sustaining, but depends on a surplus production of juveniles from the Achira population.