ABSTRACT

The reproductive cycle of the sea urchin Centrostephanus rodgersii was investigated in two populations in the Sydney region, New South Wales, Australia. Animals were collected at monthly intervals from February 1992 through January 1993. The reproductive cycle was determined by histological examination of oogenesis and spermatogenesis, monthly measurements of gonad index (GI), and the induction of spawning by KCl injection. C. rodgersii was found to have an annual reproductive cycle that was highly synchronous, with spawning coinciding with the lowest temperatures and shortest day-lengths of the year. From February to June, gamete growth and proliferation were accompanied by a decline in the presence of nutritive tissue in the gonads. The urchins became mature in the period June to September with a peak in spawning in July and August, as indicated by a sharp drop in GI, and the presence of spent and partly-spawned animals in the following months. Almost immediately following spawning, the nutritive phagocyte layer increased and the GI returned to near pre-spawning levels. The “spent” phase was therefore rarely found in C. rodgersii. GI measurements did not show any conclusive trends through time, with the exception of a significant decrease following the spawning of urchins from one site. Specimens spawned from May to October in response to KCl injection, and maximum spawning was recorded in July.