Background Information Phytoplankton are a group of microscopic organisms that are found in the oceans and seas around the world. Taxonomically they are split into seven divisions. They range in size from 1 micrometer to over 100 micrometers in diameter.
Phytoplankton typically grow in the upper regions of the water column.
This allows them easy access to sunlight, as they require this radiant energy to carry out photosynthesis . All phytoplankton contain chlorophyll a . It can be extracted from the water sample and can be used to indicate the quantity of phytoplankton in a sample. The accessory pigments are specific to different taxonomic groups of organisms e.g. green algae contain chlorophylls a and b , but no c . Diatoms contain a and c but not b .