Warmer temperatures reduce rates of gametogenesis in temperate mussels, Mytilus galloprovincialis

Temperature is known to have a substantial effect on the rate of reproductive maturation in many marine organisms, yet the effect of a range of temperatures on the rate of gametogenesis in Mytilus galloprovincialis has not been thoroughly investigated. Temperature influences natural reproduction and population dynamics in bivalves, and is often used in hatcheries to regulate broodstock conditioning. In this study mussels were held at, 7 °C, 10 °C, 13 °C, 16 °C, and 19 °C, which includes temperatures within the natural range. Feeding ration was 10% of the dry weight of the mussels, and samples were collected regularly throughout the nine week conditioning period. Gametogenesis occurred at varying rates according to conditioning temperature. Glycogen concentration decreased in all temperatures at the same rate. At 7 °C larger oocytes were significantly more frequent and space in the mantle tissue was greater than at 16 °C. A greater proportion of vitellogenic oocytes were produced in mussels at 10 °C and 13 °C compared to other temperatures. Glycogen storage tissue, as a percentage of the mantle tissue, was greatest at 19 °C, and lowest at 7 °C and 10 °C. Fecundity and D-veliger larvae production were not influenced by temperature. These results suggest that the effect of temperature on the rate of gametogenesis is strongly influenced by energy balance. At low temperatures gametogenesis is more rapid, while at high temperatures gametogenesis is slowed by the increased demands of metabolism and potentially decreased assimilation efficiency, limiting surplus energy for reproduction. This information can be applied within a hatchery setting to optimise broodstock conditioning.