Carapace colour, inter-moult duration and the behavioural and physiological ecology of the shore crab Carcinus maenas

Adult male Carcinus maenas occur on the shore with carapace colours ranging from green to deep red. In the past, this was believed to be indicative of moult state; green crabs having recently moulted and red ones being in late inter-moult. A series of different studies carried out in recent years has shown that this is not the full story. Green males have been shown to be more tolerant of salinity fluctuations and aerial exposure than red males. Conversely, red males compete more successfully for mates and food. It is hypothesized that some crabs remain in inter-moult longer than others, developing stronger and thicker carapaces and chelae, and are thus more likely to win mating conflicts. This advantage is gained at the cost of reduced tolerance to the conditions of intertidal life. The change in colouration is believed to be due to photo-denaturation of pigments in the carapace over a long inter-moult. This paper is a synthesis of studies which have led to these conclusions, and their importance is discussed in relation to the behavioural and physiological ecology of other intertidal Crustacea.