Phytoplankton forms the basis for all marine organisms, their food chain, and food web, which makes them an important group of organisms to study. In large areas of the world’s oceans, a distinct annual pattern in the composition of the phytoplankton community can be identified, driven mainly by the availability of light, nutrients, and temperature, although they can be sensitive to a host of additional abiotic environmental factors, such as salinity, dissolved oxygen, total suspended solids, pH, and environmental contaminants. Furthermore, they have very short generation times and quickly respond to changes in their environment. These make them ideal indicators of changes and therefore are included in the environmental impact assessment programs.

Zooplankton as the secondary producers occupy the next level in marine food web, as they feed on phytoplankton. Zooplankton themselves are an important food source for organisms in the higher trophic levels, such as fish which makes them relevant in fisheries research. In addition, some zooplankton, such as crab zoea, shrimp nauplii, and larval fishes, represent the early life history stages of species with high ecological and economical importance to fisheries.

In the CEMS projects, phytoplankton are key parameters in all EIA works, as part of water quality assessment (chlorophyll, TSS and nutrients). Zooplankton studies help the fisheries group to explain changes in catches, due to variations in the zooplankton biomass as a food source, as well as to identify important areas in Saudi waters of the Arabian Gulf that serve as nursery grounds for species that are important to fisheries.