The use of large volume,transparent, enclosed sea-surface water columns in the study of stress on plankton ecosystems

A brief account is given of the Controlled Ecosystem Pollution Experiment (CEPEX) program, with results from a recent experiment disigned to ascertain effects of mercury on planktonic ecosystems. The experimental modules are 1300 m³ transparent, flexible, polyethylene cylinders 9.5 m in diameter and 23.5 m deep, floating for periods up to three months at the sea surface of Saanich Inlet, British Columbia. Groups of three cylinders are filled simultaneously by being raised to the surface from 35 m, a procedure shown to produce biological replicability. An experiment is described in which mercury at 1 and 5 g l^–1 was added to two modules, with a third serving as a control. In both polluted modules temporary reductions in heterotrophic activity of micro-organisms and carbon assimilation of phytoplankton were observed, followed by a return to control levels. Only at the higher mercury concentration were any effects observed in the zooplankton, which included reduced feeding inCalanus, mortality and molting failure ofPseudocalanus and decreased growth in young fish.