ABSTRACT
Although there are numerous estimates of larval mortality in planktonic species, there are only a few studies that focus on mortality during brooding. A unique system for measuring embryonic mortality was found in the intraovarian brooding sea cucumber Leptosynapta clarki. After fertilization in November, the pentactulae hatch in 1–2 weeks and remain in the ovarian tubules for 5–6 months before release from the mother in April/May. During brooding some pentactulae die and the body tissues are resorbed. The calcareous ring, however, remains visible for some time. Accurate counts can thus be made of the numbers of living and dead pentactulae and the mortality rate determined based on the number of pentactulae at the start of brooding. These results suggest that mortality in a viviparous species can be extremely high (up to 100%). In addition, there were no clear relationships between features of the mother (size, number of brooded pentactulae) and the percent mortality. While more information needs to be collected in other brooding echinoderms, the present research questions our long-held assumption that the lowest mortality is found in species with internal brooding. Partial support for this research was provided by an NSERC Grant to F-S. Chia.
