Zooplankton are heterotrophic consumers. Bacteria decompose organic matter into its non-living constituents. Below we focus on the key phytoplankton groups that contribute to ocean color. These algae occur as single cells, chains and colonies. Cell sizes range from 5 to 1000 micrometers.
Centric diatoms have circular, triangular, or pillbox shapes.
Pennate diatoms are elongate with bilateral symmetry . Diatoms may have spines or other projections and some are toxic . They usually occur as single cells. There are bioluminescent dinoflagellates and toxic species, too. Coccolithophores surround themselves with plates made of calcite.