Testing tools for the assessment of phytoplankton biológical status and eutrophication, within the basque coast (southeastern bay of biscay)

Resumen

In regard to the benefits and needs of evaluating eutrophication in the Basque coast (southeastern Bay of Biscay), due to the high anthropogenic pressure and the lack of a specific and integrative method to evaluate it, two objectives have been proposed in this thesis: (i) to develop methods for those policies that implicitly address eutrophication, specifically phytoplankton composition indicators for the European Water Framework Directive (WFD); and (ii) to develop an integrative and specific method for those policies that explicitly address eutrophication.For the first objective, different phytoplankton attributes were studied based on different data acquisition tools. These attributes included the size fractionated phytoplankton biomass based on chlorophyll ¿a¿ (chl-a) concentration measurements, the abundance of picophytoplankton and nanoflagellates using epifluorescence microscopy, the biomass of major taxonomic groups based on High Performance Liquid Chromatography (HPLC) together with the CHEMTAX program and the abundance and size-spectra of particles within the nano- and microplankton size range using the FlowCAM (Flow cytometer and microscope).Among the four methods tested the fractionated chl-a and the HPLC together with the CHEMTAX program could be good candidates to be included in extensive monitoring networks and to develop phytoplankton composition indicators because they are practical and reproducible techniques. Additionally, some of the phytoplankton groups studied with these techniques showed significant correlations with anthropogenic nutrient pressure (a requisite to develop an indicator).Regarding the second objective, the new method (WFD-BC) was useful to evaluate the risk of eutrophication in Basque estuaries. In addition, the comparison with a specific and well-known method to assess eutrophication (Assessment of the Estuarine Tropic Status, ASSETS) confirmed the effectiveness of the WFD-BC method to assess the susceptibility and pressure of the systems. However, some improvements were suggested for the evaluation of the state component. These included the reconsideration of the weighting of the macroalgae and zoobenthos elements.