Growth, reproduction, and life span inSacculina carciniThompson (Cirripedia: Rhizocephala) in the Isefjord, Denmark

Abstract

A study of major events in the life cycle of Sacculina carcini parasitizing shore crabs, Carcinus maenas (L.), was undertaken at a northern boreal locality (c. 56° N). During 1979 –82, 28 388 crabs were collected fairly regularly from May to September, supplemented with smaller samples from October to April. Infestation ranged between 1.85 and 2.90 %, female crabs being less often infected than males. The internal phase of the life cycle is calculated to last at least 33 –34 months. Observations in the field and on 200 sacculinized crabs kept under surveillance in cages in the sea showed that the externae normally break through the host’s abdomen in June –July. Growth of the externae does not occur until c. 1 July and only if cells from pelagic male cyprids are transferred to the externa’s receptacles. At 15 –18° C the externae grow to maturity and a width of 14 –17.5 mm in 17 –24 days. The main breading season extends from mid –July to September/October during which up to 6 batches each containing 1 –3 × 10⁵ eggs are produced at a minimum interval of 12 days. The production of Sacculina larvae peaks in August –September when the 0-group of crabs is most abundant. From November to April breeding stops almost completely but the externae which survive the winter enter a second, shorter breeding period in May or June in which male cyprids, indispensible for the growth of the small externae, are produced. Most externae die and drop off the host before they are a year old; old ones survive better on female than on male crabs.