DISTRIBUTION AND RHYTHMIC LOCOMOTOR PATTERNS OF ESTUARINE AND OPEN-SHORE POPULATIONS OF CARCINUS-MAENAS

Populations of Carcinus maenas (Crustacea: Decapoda) from an estuary and from the open shore were compared for salinity tolerance and rhythmic locomotor activity. Estuarine crabs were shown to be predominantly green; red and orange individuals were rare within the estuary in contrast to the open shore. Red crabs were less able to tolerate prolonged exposure to low salinity than green crabs. Spontaneous circatidal rhythms of locomotor activity were similar in red and green forms, but red crabs from the open shore reacted earlier, and were more active upon salinity reduction, than green crabs from the estuary which also showed rapid habituation to episodes of salinity change.