DIFFERENTIAL-EFFECTS OF ANABAENA-AFFINIS ON CLADOCERANS AND ROTIFERS - MECHANISMS AND IMPLICATIONS

Observations of plankton community structure in Star Lake, Vermont, indicated that blooms of the filamentous cyanobacterium Anabaena affinis were associated with low densities of Daphnia pulex and high densities of rotifers. A series of laboratory experiments indicated that a sensitive strain of D. pulex was inhibited by ingesting an A. affinis endotoxin. The pattern of different susceptibilities of the cladocerans and rotifers to A. affinis filaments is at least partially due to different sensitivities to the endotoxin, possibly reinforced by a similar pattern of different tendencies to ingest the filaments. The Star Lake strain of D. pulex was unaffected by the highest tested concentration of A. affinis filaments (5×103cells/mL), indicating a co-evolved resistance to the toxin, possibly a counter to an antiherbivore defense. -from Author