SPATIAL VARIATION OF CRUSTACEAN PLANKTON IN LAKES OF DIFFERENT SIZE

The patterns of spatial distribution of planktonic crustaceans changed with increasing lake size. Greatest abundances were often found offshore in smaller lakes but nearshore in larger lakes. Interstation similarity of plankton, measured with Jaccard's and Renkonen's indices, was higher in small- to middle-sized lakes and lower in very small and very large lakes, indicating that mechanisms existed at both ends of the size spectrum which prevented plankton from mixing horizontally. The information content of a single central lake sample was evaluated against a lake average from 9-50 stations. To capture at least 80% of the species present, one station was sufficient only in smaller lakes, three to six stations were needed in the smallest and medium-sized lakes, and more than nine stations were needed in the largest lake. The single central station in small- and medium-sized lakes represented average total plankton abundance and dominant species relatively well but underestimated rare species. In larger lakes, lake average plankton was not well characterized by a single station. In Lake Superior, the central station reflected the offshore but not the nearshore community. Neither plankton abundance nor the number of species appeared related to lake size in the series of lakes investigated.