Reproduction in Mytilus edulis L. (Mollusca: Bivalvia) in Carlingford Lough, Northern Ireland

Abstract

The reproductive cycles of several Mytilus populations in Carlingford Lough were investigated between November 1968 and May 1971. The annual cycle varied slightly from population to population though spawning began simultaneously at all stations in the spring months when sea temperature was rising rapidly between 7.5° and 12°C. A secondary phase of gametogenesis during the summer months was confirmed by oocyte counts and the onset of the secondary spawning period occurred from 4-8 weeks after the initial spring emission. Although no significant differences were recorded in oocyte size in the different populations immediately before spawning oocyte densities were greatest at the seaward stations. Similarly, low shore populations had higher oocyte densities than those higher in the littoral zone where feeding time is severely curtailed. Size did not seem to influence gametogenesis nor did the severely polluted conditions prevailing in Belfast Lough. Seasonal changes in glycogen and lipid content of the mantle were studied in relation to the annual reproductive cycle. Primary settlement of early plantigrades on algae occurred principally in summer and winter. Secondary settlement on artificial substrates coincided with the disappearance of early plantigrades from the algae.