Reproductive cycle, sex change, and mortality during brooding of a viviparous sea cucumber Leptosynapta clarki

Reproduction in the viviparous apodid sea cucumber Leptosynapta clarki was studied on the west coast of Vancouver Island, Canada. The reproductive cycle of Leptosynapta clarki is annual with gonad growth during the summer months. Male sea cucumbers spawn during November and December and internally fertilize the oocytes within the ovary. Embryonic development is rapid so that within two weeks fertilized eggs reach the pentactula stage. Pentactulae have an open mouth and anus and actively move in the ovarian tubules feeding on droplets and fluid derived from the resorption of unfertilized eggs. Changes in the ovarian wall during the reproductive cycle were examined using histology and TEM.;Mortality of pentactulae during brooding was measured by counting calcareous rings of dead pentactulae. Pentactulae mortality in Leptosynapta clarki can be extremely high (up to 100%), and questions the assumption that the lowest mortality will be found in viviparous species.;Juvenile Leptosynapta clarki are released from the ovary at a length of 1-2 mm in the early spring (April-May). Laboratory growth experiments and regular field sampling show growth to a mean length of 21.1 mm by the reproductive season in the following November. These Year 1 individuals are all reproductively active as males. In their second year, some individuals continue to reproduce as males, while others undergo protandric sex change to reproduce as females. Analysis of the relationship between size and sex revealed a "critical" size for sex change at a body weight of 200-400 mg with a 1:1 sex ratio above 500 mg total weight. Transitional gonads were observed with previtellogenic oocytes and mature spermatozoa suggesting that the "decision" to change sex is made before reproducing in the current reproductive season.;Leptosynapta clarki shows the three commonly associated traits of small adult size, brooding and hermaphroditism. A test of the allometric hypothesis on the association of small size and brooding found no evidence for scaling constraints on brood size. Sequential hermaphroditism in L. clarki may be a method to reduce inbreeding in a low mobility species.