Biodeposit production by the mussel Mytilus edulis L. on rocky shores

Seasonal changes in the amount of biodeposit (faeces and pseudofaeces) produced by the mussel Mytilus edulis L., which is one of the representative suspension-feeders in the rocky intertidal and shallow subtidal regions of Mutsu Bay, were studied in the laboratory. The effects of water temperature, light, food concentration, flow rate, body size, age, and spawning on biodeposit production were investigated. More biodeposit was produced in summer than in other seasons. Throughout the year, the amount of biodeposit was positively correlated with body size. Relatively more biodeposit was produced by smaller than by larger individuals. A M. edulis population living in one square meter was estimated to produce 9.20 kg of faeces and 2.71 kg of pseudofaeces per year (dry wt). More biodeposit was produced at water temperatures of 17.6–20.2° C than at 4.5–7.6° C and 25.2–26.0° C. The optimum temperature for biodeposit production was found to be ≈ 20.0 °C. When kept in the dark, M. edulis produced more biodeposit than in the light. When food concentration is increased, more psuedofaeces are produced; the amount of faeces, however, remains constant. With increasing flow rate, the amount o f biodeposit per h increased but the biodeposition rate decreased. Larger amounts of faeces and smaller amounts of pseudofaeces were produced by younger mussels than by older ones of a similar size. Spawning also affected biodeposit production.