Utilization of detritus by the copepod, Acartia tonsa1

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Abstract
Ingestion, survivorship, and growth experiments were conducted with the marine calanoid copepod, Acartia tonsa, various concentrations of the diatom, Thalassiosira weissflogii, and detritus derived from the macrophyte, Thalassia testudinum. Copepod ingestion rates of detritus increased with detritus concentration from 1,700 µg C·liter−1.Copepod survival in detritus suspensions was significantly greater than in filtered seawater controls. The instantaneous mortality coefficient, z, of A. tonsa was a linear (negative) function of the diatom concentration (r2 = 0.7831). When T. weissflogii suspensions were supplemented with detritus (1,000 µg C·liter−1), the copepod instantaneous mortality rate decreased (0.3002–0.1362 in 50 µg C liter−1 T. weissflogii; 0.1345–0.0406 in 200 µg C·liter−1 T. weissflogii). The growth rate of A. tonsa was a linear function of diatom concentration (r2 = 0.8816). When the diatom suspensions were supplemented with T. testudinum detritus, the growth rate of the copepod increased.Thalassiosira weissflogii contained 12 × the protein, 8 × the fatty acids, and a greater amount and diversity of amino acids and polyunsaturated fatty acids per unit dry weight than T. testudinum detritus. Although A. tonsa could not grow from egg to adult on a detrital diet, T. testudinum detritus did supplement algal diets to increase copepod production rates.