Release and cycling of nutrients between planktonic algae and herbivores1

Efforts to quantify nutrient release by zooplankton in situ are usually complicated by simultaneous uptake of the nutrients by phytoplankton. Either separating the animals from their food or severely concentrating the zooplankton assemblage before measuring nutrient release introduces biases. Results are reported from experimen ts in which uptake and regeneration of nutrients were measured simultaneously in an intact alga‐herbivore assemblage. Short term responses to perturbations of both nutrients and zooplankton were followed and grazing rates as well as the nutrient fluxes quantified. Magnitudes of uptake and recycling depend on the nutritional status of the algal cells, with nutrient‐deficient cells displaying faster rates of uptake and lower rates of remineralization than nutrient‐sufficient cells for both phosphate and ammonia. The recycled nutrients are rapidly sequestered by the algae and contribute substantially to growth rates of the cells.