SEASONAL-VARIATION IN TISSUE DRY BIOMASS AND ITS RELATIVE ASH AND ORGANIC-CARBON AND NITROGEN-CONTENT IN THE FRESH-WATER MUSSEL DREISSENA-POLYMORPHA (PALLAS)

The documentation of the dry soft tissue biomass and its relative ash, organic carbon and nitrogen content in adult, standard D. polymorpha from the meso-oligotrophic Lake Maarsseveen I in The Netherlands is presented for the period September 1989 to September 1990 inclusive. The dry weights displayed a seasonal pattern of increase to a maximum value in April, followed by a decrease in summer. No significant seasonal changes in ash content were apparent. When the dry weight is maximal, the relative carbon content is maximal and the relative nitrogen content is minimal. As a consequence, the C : N ratio is high then. This indicates that the annual dry weight cycle was caused by gain and loss of C. The literature on bivalves makes clear that the nutritional conditions for growth and reproduction, as well as the nature of the transfer of organic biomass for production and maturation of gametes are poorly understood. The timing of both depends on phytoplankton dynamics and latitude.