Long-term interannual cycles of the gametogenic ecology of the Antarctic brittle star Ophionotus victoriae

Abstract

Spermatogenesis, oogenesis and fecundity are described and the gonad index calculated for 10 individuals from each month using histological and image analysis techniques for the Antarctic brittle star Ophionotus victoriae (Bell 1902). Individuals were collected between September 1997 and December 2000 from a shallow water population (15 to 20 m) on the west of the Antarctic Peninsula. Both male and female gonad index varied seasonally, where proportions of large oocytes and mature sperm decreased markedly between November and December of each year, indicating the spawning period. Although the annual timing of reproduction was consistent among years, O. victoriae displayed considerable inter-annual variation in reproductive effort. This variability was notable in the gonad and gut index of both males and females and in female fecundity, which showed no discernible change in some years, but varied more than an order of magnitude in others. We identify 3 main aspects to the reproductive ecology of 0. victoriae: (1) spawning was synchronous and annually consistent; (2) long periods were required for gamete development, with oocytes requiring similar to18 to 24 mo to mature; (3) there was clear inter-annual variability in reproductive effort and nutritional condition, which could be associated with the extent of the preceding organic sedimentation event. Subsidiary effects may also have been felt from the seasonal ice profile and temperature signal. A combination of all or some of these patterns may be an adaptation to the distinct seasonality and low level resource supply characteristic of the Antarctic and the long-term cycles intrinsic in polar environmental variables.