Conspecific cues affect stage-specific molting frequency, survival, and claw morphology of early juvenile stages of the shore crab Carcinus maenas

Benthic conspecific cues are used by competent larvae of many marine invertebrates to locate and settle on suitable habitat. However, aggregations of conspecifics can generate strong intraspecific competition and inter-cohort cannibalism. We investigated the effects of adult conspecific cues on general fitness parameters of juvenile Carcinus maenas (stages J1–J5), and used geometric morphometrics to investigate patterns of allometric growth indicative of life-history strategies and resource use potential. Cues induced faster metamorphosis and slightly shortened intermolt time in J2 individuals, at the expense of acute mortality in J1 crabs. These effects are cumulative but compensatory processes nullify differences by the end of the experiment. Allometric carapace change toward the adult standard remained unchanged, but conspecific cues induced first a change in size (J1) and then in shape (J5) of claws. In both control and cued juveniles, heterochely was incipient but apparent in J5 crabs. Independently of body side, conspecific cues triggered a very marked increase of the propodus posterior margin, presumably enhancing general strength. Therefore, early benthic stages may grow slightly faster to a size refuge, and develop stronger claws providing competitive advantage for the use of high-value food items when population density-dependent processes are more probable.