Phytoplankton are among the most important life-forms on Earth: they produce an amount of oxygen comparable to all land plants and are crucial because of their functions in marine ecosystems. We use numerical simulations to investigate the dynamics and distribution of both motile and non-motile phytoplankton transported by ocean turbulence. In particular we study how the presence of turbulent flows can affect sedimentation statistics and lead to non-trivial spatial patterns. In recent years, significant efforts have been devoted to understand the mechanisms underlying the phytoplankton patchiness formation, since the latter has profound effects on the ecology of the oceans. These patterns play a fundamental role in microorganisms population composition, modulating cells activities such as the encounter rate, the predation and the reproduction. We first investigate the role of motility in non-trivial spatial pattern formation, then we move our attention on non-motile microorganisms that have developed different strategies to actively control their buoyancy, in order to behave simply like passive tracers.