Grazing characteristics and growth efficiencies at two different temperatures for three nanoflagellates fed with Vibrio bacteria at three different concentrations

Small inocula of one of the flagellates Paraphysomonas imperforata, Pterido monas danica,and Cafeteria roenbergensis were added to suspensions of the b acterium Vibrio natriegens at each of three concentrations between 10(7) an d 10(8) cells ml(-1) and incubated at each of the temperatures 10 degreesC and 25 degreesC. Samples were taken at intervals for counting the flagellat es and bacteria to determine the timing of the maximum of flagellate number s and the concentrations at that time. Measurements of the protein concentr ation of the suspensions during incubation were used to determine the gross growth efficiency (GGE) or yield of flagellate grazing in each experiment. The most effective grazer was Pteridomonas, followed by Paraphysomonas, wi th Cafeteria being least effective, as judged by the threshold bacterial co ncentrations at which flagellate multiplication ceased, which were about 2 X 10(5), 2 x 10(6), and 2 x 10(7), respectively, and by the finding that Pt eridomonas consumed 99%, Paraphysomonas about 95%, and Cafeteria only 60-70 % of the available bacteria in the experiments. Peak concentrations of flag ellates were reached later at the lower temperature, but the numbers of fla gellates produced and of bacteria eaten were of a similar order at the two temperatures and the GGE was only slightly higher at the lower temperature. The time taken to reach peak flagellate numbers changed little with a thre efold increase in bacterial concentrations, but the GGE increased and the n umbers of bacteria eaten to produce one flagellate decreased when the bacte rial concentration was increased. The three flagellates show clear evidence of niche specialization in differences in thresholds of bacterial prey con centration.