The reproductive biology of the dendrochirote sea cucumber Cucumaria frondosa (Echinodermata: Holothuriodea) using new quantitative methods

Abstract

Summary Previous studies on the reproductive cycle of echinoderms have used the gonadal index and descriptions of histological preparations of the gonad to determine reproductive state. The size frequency distributions of oocytes are also commonly used to delineate the various phases of the reproductive cycle. These methods, however, do not provide accurate descriptions of the reproductive cycle of the sea cucumber Cucumaria frondosa because they do not show a clear single spawning event. In this study, several more quantitative methods were applied and they all point to a single spawning event in the spring. Methods that provided good indications of reproductive condition included a combination of gonad volume fraction and gonad dry weight, measurements of cross-sectional tubule area and tubule wall area. In males, the percentage of tubule area occupied by the haemal fluid and the spermatids/spermatozoa provided good indications of spawning. The increase in haemal fluid immediately after spawning indicates that the haemal system may be involved in delivery or storage of nutrients. Although sea cucumbers exhibit a definite seasonal feeding rhythm, the process of gametogenesis continues even in the non-feeding periods. This indicates the ability of C. frondosa to store nutrients for extended periods.