Seasonal reproductive patterns of the sea urchin Strongylocentrotus purpuratus (Stimpson) at three contrasting habitats in San Diego, CA
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Monthly samples of gonads from 20 adult sea urchins, Strongylocentrotus purpuratus, were collected over a period of one year from three contrasting coastal habitats at San Diego, CA. The habitats included (1) a rocky intertidal zone, and two subtidal areas at: (2) 8 m and (3) 18 m depths within a forest of the giant kelp Macrocystis pyrifera. These sites differ in temperature and the amount of drift kelp available as food for urchins. The gonads were preserved and prepared for light microscopical analysis using standard histological techniques. Sections of gonadal tissue were examined to determine (1) the sex ratio, and (2) the reproductive stage of each adult ovary over the one year period. Results showed that San Diego populations of S. purpurattis follow a reproductive pattern generally similar to those of other western North American coastal populations of the same species. There was a markedly female-skewed sex ratio for the intertidal and 8m subtidal sites. The intertidal females appeared to be approximately one month ahead of the subtidal ones in timing of reproductive events, and to spend a larger percentage of the year in the recovery phase. It is likely that an environmental factor such as photoperiod synchronizes the timing of events between populations while more variable factors such as temperature and food availability cue the onset of gametogenesis and cause slight between-site variations in the timing of reproduction.