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

Abstract

The influence of turbulence on the incidence of infection of the diatom Coscinodiscus granii by the parasitoid nanoflagellate Pirsonia diadema was investigated experimentally with two initial host densities. Independently of the initial diatom densities of 7 and 44 cells ml-1, under calm conditions 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 into 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 infections may effectively prevent the mass development of host diatoms.