Grazing by Mayorella sp (Protozoa: Sarcodina) on cyanobacteria

The feeding selectivity and reproductive rates of a Mayorella sp., an amoeba isolated from a salt marsh in Morecambe Bay, Lancashire, UK and fed on the cyanobacteria Anabaena cylindrica Hemmerman, Anabaena sp., Nostoc sp. and Calothrix sp. and the green alga Chlorella, were investigated at 26 degrees C. Different rates of plaque extension and, in the case of cyanobacteria, reduced nitrogen fixation (acetylene reduction), occurred with different food species. Calothrix was not observed inside food vacuoles; its morphology prevented it from being ingested. When Calothrix was fragmented by an ultrasonic dis-integrator, Mayorella was observed ingesting the fragments which were retained and digested in the food vacuoles. As expected, amoeba reproductive rates varied in relation to diet, with generation times ranging between 41 6h and 100h, but the rates of reproduction did not relate to the rates of plaque extension or acetylene reduction on any given diet, thus suggesting varying degrees of digestive efficiency on different algal and blue-green diets. The ecological implications of feeding selectivity are discussed.