Because of their microscopic size, phytoplankton and microzooplankton are difficult to study, especially at the species level. Oceanographers often use chemical techniques which can be quite sensitive in identifying plankton. For example, chlorophyll a is produced only by photosynthetic organisms and therefore can be used as a general marker for phytoplankton biomass. Chlorophyll a is converted to degraded forms called pheopigments when phytoplankton are consumed by zooplankton. Therefore pheopigments can serve as markers for the grazing activity of zooplankton.
Photosynthetic organisms produce many pigments other than chlorophyll a .
Some of these pigments are unique to specific algal groups. We are also studying a unique group of phytoplankton called prochlorophytes .