Factors influencing the deterioration of the carapace surface during the moult cycle of Carcinus maenas (Linnaeus, 1758)

During its life cycle Carcinus maenas (Decapoda, Portunidae) goes through several phases of the moulting process (ecdysis) which allow it to grow despite having a rigid, non-living outer surface. As an individual approaches ecdysis, the exoskeletal calcium is solubilized (decalcification) from the shell and transferred through the integumentary epithelium to the blood, where much of it is transported to cells, tissues and organs of temporary storage where it is later mobilized for deposition into the new exoskeleton. We hypothesised that the decalcification process caused deterioration of the features and structures (e.g. tubercles and setae) characterizing the crab carapace, but that this can be reversed by moulting. We also tested whether wear and tear caused by abiotic and biotic influences between moults might also cause surface deterioration. Any such deterioration would be detrimental to C. maenas. For example, compromise of the function of these structures could influence the settlement rate of epibionts on the crab surface as well as interfering with sensory and regulatory physiology. In this study, animals characterized as intermoult, premoult and postmoult crabs, were selected and their carapace surfaces analysed to evaluate the relationship between deterioration and moulting stage. Data showed that the outer surfaces of Carcinus maenas were subject to deterioration of their fine microtopographies throughout their life, probably influencing epibiotic settlement. Furthermore, the moulting process, already recognized as crucial for growth and removal of fouling epibionts, also proved to be necessary for the periodic restoration of surface microtopography. These findings, besides providing new insights into details of the crab life cycle, indicate a likely antifouling property for carapace microtopography in C. maenas.