Food selection by copepods: discrimination on the basis of food quality |
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Authors: | T. J. Cowles R. J. Olson S. W. Chisholm |
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Affiliation: | (1) Woods Hole Oceanographic Institution, 02543 Woods Hole, Massachusetts, USA;(2) Ralph M. Parsons Laboratory, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts, USA;(3) Present address: College of Oceanography, Oregon State University, 97331 Corvallis, Oregon, USA;(4) Present address: Woods Hole Oceanographic Institution, 02543 Woods Hole, Massachusetts, USA |
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Abstract: | The copepod Acartia tonsa displayed nearly two-fold higher ingestion rates on faster-growing cells of the diatom Thalassiosira weissflogii compared to ingestion rates on slower-growing cells of that species at the same cell concentration. Ingestion rates on slow-growing cells were also enhanced by the addition of cell-free aliquots of algal exudate to the experimental feeding chambers. In addition, the faster-growing algal cells were selectively ingested by the copepod when the two cell types were mixed together in different proportions, indicating that physiological differences between growing cells are a critical factor in the food detection/selection process of zooplankton. Consideration of cell carbon, nitrogen, and protein composition suggests that the copepods are maximizing nitrogenous ingestion (total protein and/or nitrogen). Selectivity for cells with higher protein content results in a higher daily protein ration, even if the selection process results in a decreased rate of ingestion in mixtures of cell types. |
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