Find in Library

Two contrasting estuarine copepods, <i>Acartia tonsa</i> and <i>Eurytemora carolleeae</i>, the former a broadcast spawner and the latter a brood spawner, were fed a constant carbon-based diatom diet, but which had a variable N:P content, and the elemental composition (C, N, P) of tissue and eggs, as well as changes in the rates of grazing, excretion, egg production and viability were measured. To achieve the varied diet, the diatom <i>Thalassiosira pseudonana</i> was grown in continuous culture at a constant growth rate with varying P supply. Both copepods altered their chemical composition in response to the varied prey, but to different degrees. Grazing (clearance) rates increased for <i>A. tonsa</i> but not for <i>E. carolleeae</i> as prey N:P increased. Variable NH₄⁺ excretion rates were observed between copepod species, while excretion of PO₄³⁻ declined as prey N:P increased. Egg production by <i>E. carolleeae</i> was highest when eating high N:P prey, while that of <i>A. tonsa</i> showed the opposite pattern. Egg viability by <i>A. tonsa</i> was always greater than that of <i>E. carolleeae</i>. These results suggest that anthropogenically changing nutrient loads may affect the nutritional quality of food for copepods, in turn affecting their elemental stoichiometry and their reproductive success, having implications for food webs.