Eutrophication
Although the CPR monitors plankton populations at a lower frequency than automated instruments such as the Cefas Smartbuoy, its long time-series and comprehensive spatial coverage combined with the measurement of 500 plankton taxa allow CPR data to reveal long-term changes missed by smaller scale instruments. Crucially, CPR data can provide baselines against which to measure changes. For example, there has been a considerable increase in phytoplankton biomass (Phytoplankton Colour Index) over the last decade in certain regions of the North-East Atlantic and North Sea, particularly over the winter months. Increased phytoplankton biomass may be an indicator of eutrophication; however, similar patterns of change have been found in both coastal and offshore waters. In the North Sea a significant increase in phytoplankton biomass has been found in both heavily anthropogenically-impacted coastal waters and the comparatively less-affected open North Sea despite significantly decreasing trends in nutrient concentrations. The increase in biomass appears to be linked to warmer temperatures and evidence that the waters are also becoming clearer (i.e., less turbid), thereby allowing the normally light-limited coastal phytoplankton to more effectively utilise lower concentrations of nutrients (Limnology and Oceanography (2007) 52: 635-648). These results may indicate that climatic variability and water transparency may be more important than nutrient concentrations to phytoplankton production in the North Sea. Despite the overriding influence of climate, elevated nutrient levels may be of concern in some localised areas around European seas.
Read more: McQuatters-Gollop, A., Raitsos, D.E., Edwards, M., Pradhan, Y., Mee, L.D., Lavender, S.J. and Attrill, M.J., 2007. A long-term chlorophyll dataset reveals regime shift in North Sea phytoplankton biomass unconnected to nutrient levels. Limnology and Oceanography, 52: 635-648.
Edwards, M., Reid, P.C. and Planque, B., 2001. Long-term and regional variability of phytoplankton biomass in the Northeast Atlantic (1960-1995). ICES Journal of Marine Science, 58: 39-49.
Contact at SAHFOS: Abigail McQuatters-Gollop
(left) Year/month plot of PCI for the central North Sea. (right) Phytoplankton Colour Index recorded by the CPR survey in the NE Atlantic by decades.
