A SEASONAL ENERGY BUDGET FOR ZEBRA-MUSSELS (DREISSENA-POLYMORPHA) IN WESTERN LAKE ERIE

We constructed a balanced energy budget for zebra mussels (Dreissena p olymorpha) from the western basin of Lake Erie during the active growt h and reproductive season (May-October). We measured metabolic costs ( oxygen consumption and ammonia excretion), body mass change, and feces production weekly and marked mussels to quantify shell growth. Costs of reproduction were measured by inducing spawning four times using se rotonin and collecting gametes. After conversion to calories, all ener gy budget components were combined with published length-frequency dis tributions and mussel densities to estimate population consumption. We estimated that individual zebra mussel consumption averaged 3.16 cal. day(-1) (1 cal = 4.1868 J). Metabolic costs account for >90% of energy consumption. Mussels <15 mm increased in body mass whereas mussels >1 5 mm allocated energy to reproduction in lieu of somatic growth. Our e stimates of population consumption were sensitive to mussel size distr ibution, with the most abundant size-class responsible for the greates t proportion of population consumption. Based on published estimates f or primary production in western Lake Erie, our energy budget estimate d that zebra mussels (10 000 - 50 000 mussels.m(-2)) potentially consu me an equivalent of 10-50% of summer primary production.