The effects of turbulence on marine ecology are studied by performing direct numerical simulations of motile microorganisms in isotropic homogeneous turbulence. We show that in a fully turbulent flow the patchiness and clustering is reduced respect to simple laminar and vortical flows. Micro-organisms in presence of gyrotaxis tend to accumulate if spherical in shape while elongated swimmers are more randomly distributed because of their sensitivity to the local shear. These results suggest that purely hydrodynamic phenomena can influence the marine life of microorganisms when the type of flow and their shape are changed.