The reproductive biology of the sea cucumber Holothuria atra Jaeger, 1833 (Echinodermata: Holothuroidea) in Laucala Bay, Fiji, with notes on its population structure and symbiotic associations

The reproductive periodicity of the sea cucumber Holothuria atra Jaeger 1833 in Laucala Bay, Fiji was determined at two sites, Makeluva and Sandbank Reefs, through measurement of gonad index, sperm activity, oocyte diameter, and gonad tubule diameter over a 14 month period. Population structure and distribution patterns were compared between the two sites. Associates of H. atra were enumerated and factors affecting their abundance discussed. Holothuria atra is dioecious. It is an asynchronous spawner in Fiji with a main breeding period in summer (September to December). Gonad indices and mean maximum gonad tubule diameter trends showed that the breeding season of H. atra is confined to a few months in summer. Sperm activity, gonad staging and oocyte size frequency trends, however, showed that the breeding season was prolonged, with ripe oocytes present all year around. The increase in gonad mass was periodic, but the ripeness of gonads was prolonged. Reproductive seasonality is probably influenced by temperature. Reproductive effort was greater in female H. atra from Makeluva Reef than females from Sandbank Reef. However, there was no significant difference in reproductive effort between males at both sites. Size at first sexual maturity was about 80 g gutted weight or 19 cm total length. H. atra is fissiparous at the sites studied but fission rates were very low. Holothuria atra is the most abundant holothurian on Laucala Bay reefs with a unimodal size structure. There was a noticeable absence of females early in the study and no juveniles (