Aggregating behaviour of the spider crab maja squinado in shallow waters

Abstract

A year's monitoring of a population of Maja squinado in Galicia, NW Spain, revealed the seasonal formation of pods. From September to November 1994, we analysed samples from five pods located in two areas near the coast, Mexilloeira and O Carreiro, as well as specimens living in isolation in the same area. These pods were made up mainly of juveniles, except for the aggregation detected in September in O Carreiro, where 72% of the animals were adults. The sex ratio was around 1:1 in juveniles, with a predominance of females in the adult population. No differences were found in the proportion of juveniles vs. adults, sex ratio, size range, or intermoult stage between animals in pods and isolated specimens. The arrangement of the animals in the pod as well as the large number of specimens in the premoult or postmoult stage would suggest that these pods serve as a form of protection.