Infection of Coscinodiscus granii by the parasitoid nanoflagellate Pirsonia diadema: III. Effects of turbulence on the incidence of infection

The influence of turbulence on the incidence of infection of the diatom Cos cinodiscus granii by the parasitoid nanoflagellate Pirsonia diadema was inv estigated experimentally with two initial host densities. Independently of the initial diatom densities of 7 and 44 cells ml(-1), under calm condition s both diatoms and parasitoids became extinct within 6-9 days. Turbulence, however, led to the survival of diatoms at a reduced density of 0.1-2 cells ml(-1) for >30 days. A population-dynamic model is formulated that takes i nto account the non-homogeneous distribution of infecting flagellates among host diatoms. Application of the results to parasitoid-diatom interactions in natural waters suggests that, under turbulent conditions, endemic infec tions may effectively prevent the mass development of host diatoms.