Caveat observator: the many faces of pre-spawning atresia in marine bivalve reproductive cycles

Of the hundreds of publications on bivalve reproductive cycles, only a handful reports the presence of pre-spawning oocyte autolysis, or atresia. This is at variance with the author's practical experience, in which prespawning oocyte atresia has been found in every bivalve reproductive cycle investigated. Failure to identify prespawning atresia will lead to over-estimations of fecundity, reproductive effort, and anticipated larval density and recruitment. On the intuition that the phenomenon is underreported due to unfamiliarity with the histological characteristics of atresia, it is presented here within the context of the study of bivalve reproductive cycles, the reported incidence of pre-spawning atresia, and the histological profiles of this phenomenon in several commercially important bivalve families. Despite superficial variability, the assembled data allow the presentation of underlying common characteristics. It is postulated that pre-spawning oocyte atresia is a widespread, yet seldom-identified phenomenon in marine bivalves, which probably affects previous and current data on fecundity and reproductive effort, both in wild and cultured populations. The information presented here is intended to both increase awareness of this process, and lead to more realistic interpretations of bivalve reproductive cycles, fecundity, and reproductive effort.