Phytoplankton utilise sunlight energy and dissolved nutrients converting these into organic materials which are often consumed by higher life forms such as fish. As phytoplankton are short lived and derive their nutrients from the water; they are an ideal indicator of changing nutrient conditions and therefore useful for assessing pollution of coastal waters.
The TW phytoplankton tool enables an assessment of the condition of the quality element phytoplankton. The WFD requires that the assessment of the phytoplankton quality element considers composition, abundance, biomass and planktonic blooms.
The method is based on the principle that additional nutrients (especially nitrogen in coastal waters) can alter the amount of phytoplankton in transitional waters. Persistent and high counts of phytoplankton taxa are also seen as a measurement of disturbance in the phytoplankton community.