Effects of small-scale turbulence on marine microzooplankton

Abstract

We investigated the effects of turbulence on growth and ingestion rates of 4 dinoflagellates (Oxyrrhis marina, Gyrodinium dominans, Peridiniella danica, and Karlodinium armiger) and one ciliate (Mesodinium pulex). These protists display different feeding mechanisms: K. armiger feeds with a peduncle; G. dominans, O. marina and M. pulex engulf the prey, the first two being active swimmers and M. pulex being an ambush predator; P. danica possesses a microtubular basket, typical of tube-feeders, but its feeding mechanism has not been fully described yet. We used an oscillating grid to generate two intensities of turbulence (Low = 1 10-2 cm2 s-1, open waters conditions; High = 2.5 10-1 cm2 s-1, coastal conditions) and a plankton wheel (0.2 r.p.m.) to reproduce still conditions. As food, we used Rhodomonas salina for the dinoflagellates and Heterocapsa rotundata for the ciliate. After 48 h preconditioning to food and turbulence, O. marina and M. pulex ingestion rates were unaltered by any of the two levels of turbulence; however, M. pulex growth rates were negatively affected at the highest intensities. G. dominans displayed a negative response in grazing activity only to the highest intensity of turbulence; the effect was not apparent in growth rates. P. danicum growth and ingestion rates were negatively affected by both intensities of turbulence. K. armiger escaped the oscillating grid and remained close to the bottom of the experimental tank at both intensities of turbulence. We think that the different responses to small-scale turbulence are related to the particular feeding mechanisms of each species