Abstract
Cycles of oogenesis were studied in populations of Strongylocentrotus purpuratus by disaggregation of ovaries and measurement of the number of vitellogenic and mature oocytes. Average egg yields upon spawning were recorded. As reported by many previous authors, fecundity of intertidal S. purpuratus females is seasonal. Two peaks of fertility are observed per year in subtidal animals from a southern California location, and for some months of each year virtually none of these animals contain vitellogenic or mature oocytes. In contrast, a fraction of animals living at 50–70‐foot depths in a kelp bed display vitellogenic and mature oocytes at all seasons of the year. Different individuals in these deep‐water sea urchin populations are in different stages of the process of oogenesis at any one time, and their fecundity is not entrained with the seasons. Annual yield of eggs of average females in deep‐water and intertidal populations is about the same. Groups of mature females derived from both deep‐water and subtidal populations and held in our large scale laboratory S. purpuratus maintenance system (SpMS) resemble the deep‐water populations. Reproductive cycles in these females are in different phases even within the same tank and remain so for at least several years. Initially synchronous populations eventually drift apart in phase when held in the SpMS in the absence of seasonal environmental stimuli. We show that in SpMS females the fertility of each group can be predicted from oocyte count data, and that it can to a large extent be controlled by the frequency of induced spawning.