Blue-green algal inhibition of diatom growth: transition from mesotrophic to eutrophic community structure.

Cell-free filtrates of axenic or bacterized cultures of the dominant blue-green algae from a freshwater lake inhibited the growth of diatoms isolated from the same lake. Lake waters, collected during blue-green algal blooms, also inhibited diatom growth. In situ observations over a 5-year period indicate that diatom bloom populations vary inversely with the levels of the preceding blue-green algal populations. Blue-green algal dominance of eutrophic lakes is attributed to this allelopathy, and dilution is proposed as one cause for the limited occurrence of blue-green alga dominance in marine waters.