Mortality of Pentactulae During Intraovarian Brooding in the Apodid Sea Cucumber Leptosynapta clarki.

Abstract

Estimates of mortality during development in brooders have been restricted by the lack of a reliable method for determining the number of embryos at the start of brooding. The calcareous ring of the pentactulae of Leptosynapta clarki can be used to determine initial embryo number because the ring is present for about 93% of the brooding period, is retained within the ovary, and is not resorbed after embryo death. Pentactulae mortality was found to be variable in female Leptosynapta clarki, with up to 100% mortality (= total brood loss) in some females. Estimates of instantaneous mortality in L. clarki ranged from 0 to -0.0114 d-1 and were of similar magnitude to those for other brooding marine invertebrates. The resorption of dead pentactulae in the ovary may provide additional material to the ovarian fluid for the nutrition of living pentactulae. The retention of hard embryonic structures (e.g., calcareous parts, shells) in other brooding marine invertebrates may allow further estimates of mortality during brooding, and provide an insight into the importance of embryo mortality in the evolution of marine invertebrate life histories.