:Patterns of Horizontal Distribution of Uroglena americana

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In order to clarify the patterns of horizontal distribution of Uroglena americana, investigations were conducted in the water area where the plankton accumulated in the northern basin of Lake Biwa in 1979. Small wings and a tail plane were set on an in situ fluorometer (Variosence II) with a thermistor and the instrument was towed by a ship with the speed of 4 knots at the depth 1 or 1.5 m. The following remarkable variations of patterns were found in the horizontal distribution of chlorophyll a and water temperature : 1) Chlorophyll a concentration changes in reverse proportion to water temperature. 2) Chlorophyll a concentration changes parallel with water temperature. 3) Chlorophyll a concentration changes independently with water temperature. As the cause why these various patterns were found, it was suggested that the types of vertical distributions of both U. americana and water temperature, the buoyancy of the plankton, the convergence and sinking of surface water, the convergence and upwelling of subsurface water, and so on, affected greatly the accumulation of the plankton and the formation of horizontal distribution patterns.
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