Long Term Trends in the Occurrence of Phaeocystis Sp. in the North-East Atlantic

There is much current concern about increases in the inputs of nutrients to the sea. Onepossible effect might be to change the composition of the phytoplankton community.Such an effect has been suggested for certain regions of the North Sea, where an increasein flagellate algae has been observed. An apparent increase in the haptophycean algaPhaeocystis has also been implicated with increased nutrient inputs. In this study, longterm records (1946 to 1987) obtained from the Continuous Plankton Recorder Survey havebeen examined. These have revealed that the occurrence of Phaeocystis has undergone aconsiderable decline over the period in all open sea areas of the North-east Atlantic,including the North Sea; however, there is evidence for a reversal of the trend since 1980.Extreme nearshore regions are only poorly sampled by the Survey, thus data are notavailable for these areas. Principle components analysis of the data reveals an approxi-mate three-yearly cycle in the occurrence of Phaeocystis. This, together with the coinci-dence of the trends shown by both the zooplankton and total phytoplankton communi-ties, suggest that larger scale factors, such as climate, may be the dominant influenceaffecting the occurrence of Phaeocysti