ALGAE OF TWO SOMERSETSHIRE POOLS STANDING CROPS OF PHYTOPLANKTON AND EPIPELIC ALGAE AS MEASURED BY CELL NUMBERS AND CHLOROPHYLL A

Standing crops measured as cell numbers and as chlorophyll a content of phytoplankton and epipelic algal communities (those free-living on sediment surfaces) in 2 small water bodies of contrasted nutrient status were measured for 27 months. Mean yearly crops, on an areal basis, of phytoplankton were 4-13.4 times greater than those of epipelic algae in the nutrient-rich pool, but were only 0.65-1.8 times as great in the nutrient-poor pool, which, however, was shallower than the rich pool. The role of cells < 5 μ, in diameter in the composition of standing crops was minor. Effects of phytoplankton in limiting growth of epipelic algae by light attenuation are shown. Compilation of available data shows a direct relationship between epipelic algal crops in various water bodies and nutrient-status of the ambient water, similar to that already established for phytoplankton.