ABSTRACT
Discrete breeding seasons of echinoderms could be an adaptation to seasonal variation in abundance of plankton suitable as larval food. To test this hypothesis, gametogenesis in the seasonally spawning asteroid Pisaster ochraceus was shifted six months out of phase using photoperiod, so that experimental animals were spawned in September, approximately six months out of phase with field animals. Resulting larvae were reared in the field in nitex-covered cages, where they fed exclusively on available plankton in oceanographic conditions that contrasted with the upwelling conditions when larvae are normally present. Larval size and survival, time to metamorphosis, and initial post-metamorphic juvenile size in this experiment were all indistinguishable from those in an experiment using conspecific larvae reared in the field near the normal time of spawning. These results suggest that within-year variation in plankton food availability does not select for seasonal breeding in this species, a finding consistent with data from other echinoderms. We suspect that factors influencing early juvenile survival may be selecting for reproductive seasonality.
