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The physical oceanographic factors governing the plankton distribution in the British Columbia inlets LeBrasseur, Robin John

Abstract

The major constituents of the plankton, phytoplankton, cladocera, copepods and chaetognaths, sampled in the 1951 oceanographic survey of the British Columbia Inlets are reported in concentrations per cubic meter of water. Horizontal plankton tows sampled four depths, 5, 21, 32 and 47 feet, respectively. The distribution of each group is discussed in relation to the hydrographic data and the present theory of inlet circulation. The inlets investigated fall into two general groups, (a) those which are long and have a large freshwater discharge at the head and (b) those which have a small freshwater discharge and are short. The data from six inlets making up the former have been grouped together and are discussed as the Average Inlet. Those inlets making up the latter group are classified under the general heading of atypical inlets; each is discussed separately. In the Average Inlet the plankton volumes were the greatest at the mouth, particularly towards the surface. The concentration of plankton is shown to be a result of local phytoplankton production. In the absence of currents the phytoplankton are shown to be limited vertically by density. The zooplankton are divided into three groups on the basis of their response to the physical factors. The distribution of cladocera indicates that it is positively phototropic while that of the copepods and chaetognaths indicate that that they are negatively phototropic. The chaetognaths are found to be absent from all the atypical inlets, the cladocera from three. The copepods are concentrated at the depth which is associated with the compensation light intensity. Attention is drawn to the fact that this report is a qualitative description of the relationship between the distribution of the plankton and the physical oceanographic conditions. Future surveys will have to sample more extensively and intensively.

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