Ostrea edulis populations are in decline worldwide throughout a wide geographical range from Norway over Morocco to the Black Sea, with current stock level estimates below those made during the 1800s (Anon, 2007). O. edulis population from the Solent is one of these declining populations with several collapses during the last century.
The reasons of the last decline in the Solent oysterpopulation from 2006 are still unknown. This species has constituted an important fishery in the Solent with commercial explotation since 1800’s. Due to some life characteristics of this species oyster beds are very vulnerable to commercial exploitation and overfishing (Laing et al., 2005; Orton, 1927c). However, other hypotheses point to trends in increasing sea temperatures, habitat degradation, chemical and physical pollution.
Recent studies have analysed the current situation on reproductive parameters of O. edulis population finding a significant reduction in the number of brooding female-phase oysters (Eagling, 2012), reduction on fecundity of brooding oysters and skewed sex ratio towards male-phase oyster (Eagling, 2012; Kamphausen, 2011). Athough a number of speculations for this behaviour have been made, the factors causing this change in sex phase in O. edulis remain unknown.
Hormones controlling the development of secondary sexual organs in molluscs are poorly understood and more research on this topic is need to clarify the cause of male bias and most recent O. edulis