Phytoplankton composition indicators for the assessment of eutrophication in marine waters: Present state and challenges within the European directives

Several legislations worldwide require assessing the health status of marine ecosystems. In Europe, the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD) demand the evaluation of the status with the overall objective of achieving at least “Good Status”, by 2015 and 2020, respectively. For this purpose, Member States are required to evaluate different biological, physico-chemical and hydro-morphological quality elements (WFD), or qualitative descriptors (MSFD). The assessments of both, the phytoplankton element and the eutrophication descriptor should include several attributes, namely phytoplankton biomass, composition, abundance and blooms. However, few composition-based indicators have been proposed. Principally, phytoplankton still relies on chlorophyll-a concentration measurements, mainly due to the high cost of collecting information on this element and the difficulties establishing significant pressure–impact relationships. This investigation describes the difficulties in the development of a phytoplankton community composition indicator, the state of the art and the main challenges for the future.