Long term trends in the seas surrounding Sweden : Part two - Pelagic biology

This work presents trends in the phytoplankton community. Data on the occurrence of both chlorophyll a (hereafter Chl a) as well as phytoplankton community structure and biovolume are presented.Water transparency in terms of Secchi depth is also presented, as a secondary effect of phytoplankton occurrence. Due to differing water characteristics, 14 sea areas have been selected to represent the waters surrounding Sweden. These areas are identical to the ones chosen in the earlier nutrient report to facilitate comparison. In this report all available data up to and including 2008 are presented as graphs and tables. Each variable is divided into three different seasons: spring, summer and autumn. Trends are only shown for comparable depths. A classical linear regression method is used for phytoplankton groups, Chl a and Secchi depth. The trend magnitude and signifi cance are also calculated for Chl a and Secchi depth. Anoverview of the results are presented for Chl a and Secchi depth.The data presented in this report encourage further development of phytoplankton indicators that not only consider total biovolume or Chl a but rather consider different groups or species in the future. Thesechanges can be important indicators for both eutrophication but can also enhance the understanding of food web interactions