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Spatial and temporal distribution of invertebrate organisms inhabiting the Chara zone Humphreys, Robert David

Abstract

Two methods of collection were employed in the investigation of the density, distribution, and movements of invertebrates inhabiting the Chara zone of lakes: (1) Chara samples were obtained at regular depth intervals over the Chara shoals with the aid of Scuba gear, partitioning the Chara stand into two approximately equal vertical halves - top half and bottom half; (2) a long-handled dipnet was used to sample the surface of the Chara stand and the waters above the stand. Sampling with the dipnet on a 24-hour basis provided data on the diel movements of organisms in the Chara zone. The density of the invertebrate populations was lowest in June due to the reduction of stocks over the winter months by predation and other causes of death. The high numbers in September were attributed to the results of early summer reproduction. Fluctuations in density over the summer months were traced to the changing interplay between hatching and emergence of various invertebrate groups. Eradication of fish from one of the lakes resulted in an increase in numbers of the major fish-food organisms, indicating predation by fish as an important factor controlling density of invertebrate stocks. The distribution of invertebrate organisms over the Chara shoal from shore to the limit of the vegetation offshore and vertically within the Chara bed itself was remarkably homogeneous. Minor differences in distribution of several invertebrate groups were demonstrated by statistical means. Daily vertical and horizontal movements of many of the organisms were shown to produce large density fluctuations on the Chara surface.

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