Physiological ecology of mussel larvae

Abstract

Mussels produce large numbers of planktotrophic larvae that spend several weeks in the surface waters. This planktonic stage in the species' life-history is a critical phase concerned with feeding, growth and development, dispersal and the selection of a suitable site for the sedentary adult life. The process of development, from the small 70 μm egg through to the pediveliger larva (ca. 300 μm shell length) which settles and undergoes metamorphosis, is outlined. A maximum growth rate of ca. 12 μm day −1 in shell length results in a minimum larval life of 3 weeks at 18°C, but this can be extended to 3 months depending upon endogenous and exogenous (environmental) factors. However, the planktonic larval stage and the immediate post-settlement stage are accompanied by high mortality rates (ca. 0.1 to 0.2 day −1). Therefore any factor that reduces growth rate, and thus extends the period of larval development in the water column will have a major effect on mortality and the chances of survival to the settlement stage and beyond. The effects of environmental factors, such as food availability, temperature, oxygen concentration, salinity, and pollutants, on the processes of feeding, metabolism and growth of mussel larvae are reviewed and discussed in this context. Once the larvae have reached the pediveliger stage and are ‘competent’ to settle, then the process of settlement and metamorphosis can be delayed for up to 7 weeks until a suitable substratum is found. However, any delay will result in a further decline in the number of offspring surviving.