Experimental studies on the transfer of 65Zn in high concentration by euphausiids

Abstract

The uptake and elimination of 65Zn by Euphausia pacifica, in ‘clean’ sea water and in several concentrations of radioactive phytoplankton food, have been measured at 10 °C. Measurement was done on time schedules to simulate those which vertically-migrating euphausiids would spend in and out of a hypothetical 65Zn pool at the sea surface at different seasons of the year in temperate latitudes. From a knowledge of the total 65Zn body burdens reached at any time t, and of the mechanisms and rates of loss of 65Zn in radioactive and non-radioactive water, transfer of 65Zn via euphausiids from the ‘hot’ surface pool to non-radioactive water below may be assessed. With inital concentrations of 25μ Ci 65Zn/l, equilibrium body burdens were achieved in ‘clean’ sea water in about four days under all time schedules. The level of equilibrium body burden was a function of time schedule (time spent in the radioactive solution). In radioactive food, equilibrium body burdens were not reached in five days. Below about 10 5 cells/ml, uptake through food was a function of food concentration, but was not apparently affected by food concentrations above 10 5 cells/ml. When uptake was from ‘clean’ sea water, elimination was by molting of the animal's chitinous exoskeleton and by exchange with non-radioactive water. When uptake was from labelled food, elimination was from fecal pellet deposition as well as molting and exchange. Molting, exchange, and fecal pellet deposition represented different percentage losses from total body burden, depending largely upon the time the animal spent in and out of 65Zn and the source of 65Zn (water or food). Summations of these losses have been used to estimate transfer of 65Zn by euphausiids from a ‘hot’ surface pool to waters below the pool.