Ref ID : 6989
Christine Ferrier and Fereidoun Rassoulzadegan; Density-dependent effects of protozoans on specific growth rates in pico- and nanoplanktonic assemblages. Limnol.Oceanogr. 36(4):657-669, 1991
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We experimentally assess nutrient feedback of oligotrichous ciliates and phagotrophic flagellates on growth in naturally occurring Mediterranean autotrophic microbial populations as well as on the microphytoplankton. Dialysis bags were used the separate cultured protozoa from the <7-µm plankton filtrates yet allow nutrient exchange. Growth rates in microbial autotrophic populations increased with protozoan densities added to bags. Microbial growth half-saturation constants, expressed in terms of protozoan densities added, varied from 11 to 17 ciliates ml-1 and 2-5x10E3 flagellates ml-1. The "transdialysis contact" of protozoa with microbial planktonic populations led to growth rates 2 to >10 times higher than those observed without added protozoa. These findings suggest that in situ, autotrophic pico- and nanoplanktonic growth is limited by protozoan standing stocks. Lower generation times and half-saturation constants were obtained for autotrophic nanoplankton (~3 hr, K(µ)=10 ciliates ml-1 and 1.7x10E3 phagotrophic flagellates ml-1, respectively). Microphytoplankton (e.g. diatoms and dinoflagellates) showed no significant functional responses to the additions of microprotozoa, suggesting a possible dependence of the latter on new rather than on recycled nutrients.