Reproductive activities in the sesarmid crab Sesarma intermedia in the coastal and estuarine habitats of Hakata,Japan

Aspects of activity pattern, mating, breeding behaviour and reproductive organs were studied in Sesarma intermedia (de Hann) along the Tatara river estuary, Hakata Bay, western Japan. Activity started from early May after a six-month hibernation period. The daily activity pattern was bimodal with one peak after sunset and another before sunrise. Mating started after emerging from hibernation and was ended by July. Practically no mating was seen in August and thereafter, by which time most of the females were carrying eggs. Larger males mated more frequently with any sized adult female. Copulation seemed to take place both in the burrow and on the surface of natural shelter. Females began to carry eggs from mid June on the estuarine habitat, whereas on the coastal habitat ovigerous females could be seen from mid-May. Multiple ovipositions of eggs were realized. Females were able to oviposit three times without any repeated mating. It took about 30 d to incubate one egg mass and less than one week to spawn again. The release of larvae was not sporadic but rather took place within a limited time interval. Sunset seemed to have a great influence on larvae release along the seashore. Energy allocation for reproductive purposes seemed to start before crabs awoke from the hibernation period. Towards the end of the breeding period there was a drastic decline in ovarian development with a remarkable gain in hepatopancreas, a reservoir for energy.