THE ECOLOGY OF THE CALANOID COPEPOD PSEUDOCALANUS MINUTUS KRØYER IN TESSIARSUK, A COASTAL MEROMICTIC LAKE OF NORTHERN LABRADOR

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A study of the ecology of the calanoid copepod Pseudocalanus minutus Krøyer in Tessiarsuk, a deep coastal meromictic lake of northern Labrador, was made in the summer of 1961 and spring of 1962. The lake, containing two basins, is separated from Anaktalik Bay by a shallow threshold and receives periodic volumes of tidal water. Maximum salinity at depth was 21.5‰, while surface salinity was less and increased through the season. Temperatures were stable in the monimolimnion but variable in the chemocline and mixolimnion. Gradual deoxygenation occurred with depth; the profundal waters contained only traces of oxygen. In both lake basins P. minutus produced two generations each year with a possibility that some animals might have been annual. Females in the spring spawned two broods in succession. An inverse relationship existed between water temperature and copepodite length. All stages were concentrated in the upper waters; the copepodites underwent a gradual seasonal descent. The salinity gradient produced a distinct spatial separation of Pseudocalanus from the other autochthonous calanoids, Acartia clausi and Eurytemora hirundoides.