Growth and somatic production estimates of Dosinia hepatica (Lamark) (Mollusca: Bivalvia) in the Swartkops estuary,South Africa

Regular and quantitative sampling for Dosinia hepatica was performed in the Swartkops estuary over a period of a year. The size of the D. hepatica recorded at LWMST was significantly (P<0,01) larger than that sampled at 0,4 m above LWMST This appeared to be a result of a spatial separation of large and small individuals. Size frequency analyses of the populations sampled and growth ring lengths were used to construct a growth curve for D. hepatica. The calculated growth rate was slow, with D. hepatica reaching a shell length of approximately 16,3 mm and a dry tissue mass of ca. 44 mg after three years. The potential life span of the bivalve was estimated to be 8-9 years. The annual somatic production (per m2) of the population sampled was calculated to be 0,58 g shell free dry mass or 8,63 kJ, while the production biomass (P/B) ratio was 0,3.