Use of the Pisces IV Submersible for Zooplankton Studies in Coastal Waters of British Columbia

Abstract

This study evaluates the usefulness of a small submersible for observations of the plankton. A method for calculating plankton densities from estimates of mean interanimal distances is described. Estimates made by this method were compared with estimates based on net sampling and were found to be in fair general agreement with them. Fragile gelatinous forms were better counted from the submersible, small organisms by netting. Some delicate species, known to be abundant from submersible observations, were never recognized in net samples. Submersible observations also gave important insights into vertical distribution of the plankton. Several species were found to exist within unexpectedly narrow and sharply defined layers, often at densities greatly surpassing density estimates based on net samples. In Saanich Inlet, B.C., plankton distribution was studied in relation to the seasonal formation and dispersion of the oxygen-deficient basin water. Other data deal with behavior, color change, bioluminescence, and vertical migration of planktonic organisms. We conclude that submersible observations are potentially valuable in plankton research, and we make recommendations regarding instrumentation and observer training as an aid in planning future dives.