REPRODUCTION IN THE DIADEMATOID SEA-URCHIN CENTROSTEPHANUS-RODGERSII IN CONTRASTING HABITATS ALONG THE COAST OF NEW-SOUTH-WALES, AUSTRALIA

Reproduction in the sea urchin Centrostephanus rodgersii was examined in two types of habitats (''barrens'', i.e. habitats characterised by the high crustose coralline algal cover typical of urchin-barren groun ds, and by the absence of macroalgae; and ''fringe''. i.e. habitats ch aracterised by a high macroalgal biomass and few C. rodgersii) at four locations in New South Wales. The four locations: the Solitary Island s, Sydney, Ulladulla and Eden, span the distribution of C, rodgersii f rom the subtropics at its northern limit to temperate waters near its southern limit. Histology and estimates of gonad retrieval rate (GRR) from January 1994 to October 1995 indicated that reproduction was sync hronous at all locations. An increase in the tempo of gametogenesis in May and onset of spawning in June at all locations is consistent with entrainment in response to exogenous factors. Over the range studied, C. rodgersii experienced relatively similar daylength cycles and cont rasting sea-temperature cycles. Short days and lunar conditions coinci ding with the solstice appear likely proximate cues for the onset of s pawning. The major difference in reproduction among locations was in t he duration of spawning. In the southern parts of its range breeding o ccurred over a 5 to 6 mo period, whereas at the Solitary Islands it la sted similar or equal to 1 mo. At most locations the GRRs were signifi cantly higher in the fringe habitat than in the barrens habitat. The l ower reproductive output of urchins in the barrens habitat was attribu ted to the feed-poor conditions typical of this habitat. The developin g fishery for C. rodgersii is likely to be most effective from March t o early May. Urchins from barrens areas may not provide sufficient yie ld to warrant harvesting.