Energetics of growth and reproduction in cockles (Cerastoderma edule): Seasonal and age-dependent variations

Seasonal patterns of growth were compared interannually between 1983 and 1985 for different ageclasses of an intertidal population of cockles,Cerastoderma edule L., in the Mundaka Estuary (Basque Country, North Spain). Growth data and simultaneous determinations of respiratory metabolism were integrated over defined periods of time in order to compute assimilation and net growth efficiency. Consistent differences between the exponents that scale both assimilation and metabolism to body size led to growth efficiency values that were a decreasing function of age. Total growth was partitioned into three components: somatic growth, reproductive output and reserve storage, and the corresponding effort indexes were calculated. Despite important differences in total growth, reproductive output was constant between years, indicating a higher reproductive effort under poorer growth conditions. Increased costs of reproduction that appeared to be associated with this higher reproductive effort did not affect somatic maintenance, since previously stored carbohydrate reserves were primarily used to fuel gametogenesis.