Phosphatase Activity in Freshwater Zooplankton

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Abstract
The activity of intra- and extracellular phosphatases and their relationship to the food sources of freshwater zooplankton were investigated. Daphnia magna from laboratory cultures, either without prefeeding or prefed with bacteria or bentonite, released phosphatases and protein into the external medium when starved for 24 h. When Daphnia were prefed with algae, however, a different pattern of extracellular release was noted, suggesting that starvation or prefeeding with bacteria or bentonite had the same effect on the animals. For natural, mixed zooplankton populations, collected during the Peridinium bloom in Lake Kinneret(Feb-July), acid phosphatase activity was low, whereas alkaline phosphatase activity was relatively high. The polyacrylamide gel electrophoretic band patterns of crude phosphatases from zooplankton and Peridinium were considerably different, enabling possible future identification of the source of free enzymes in the lake to be made. Alkaline phosphatase activity, measured within 20 min of collection, of isolated samples of Mesocyclops leuckarti was higher than that of Ceriodaphnia reticulata, although no phosphatase activities were detected in Bosmina longirostris. Acid and alkaline phosphatase may have different roles in zooplankton; the former unrelated to food type, the latter possibly related to the food quality of ingested particles. Zooplankton phosphatases are probably ecologically important.