Phaeocystis

Phaeocystis is a genus of single-celled marine algae in the haptophyte group, widespread as phytoplankton across a wide range of temperatures and salinities in both open ocean and sea ice environments. Its defining trait is the ability to form extensive floating colonies of hundreds of cells embedded in a shared polysaccharide gel matrix, which can expand dramatically during blooms; the most substantial blooms occur in polar regions, where Phaeocystis pouchetii dominates northern waters and Phaeocystis antarctica dominates southern seas, while Phaeocystis globosa blooms in temperate and tropical waters. These blooms significantly affect marine ecosystems and human activities, generating foul-smelling foams on beaches as they decline and substantially contributing to ocean carbon cycling, and the genus produces dimethyl sulfide, a compound that plays a role in the global sulfur cycle and cloud formation.