Interannual variability

Abstract

There is a relative dearth of good long-term phytoplankton data as it is difficult to sustain the necessary effort using consistent methods of sampling, counting and identification. Many of the earlier sampling and counting methods did not adequately enumerate the smaller flagellates and nanoplankton but merely concentrated on the net phytoplankton fraction. In other cases inconsistencies in the siting of sampling stations, analytical methods and changes in personnel have rendered the interpretation of long-term data sets difficult or impossible. Also, regrettably, there seems to be a general lack of appreciation of the value of long-term routine monitoring which, in a time of financial stringency, has made it difficult to sustain the effort in recent years. It has, perhaps, also been difficult to justify long-term monitoring because the direct results of such activities were not apparent until recently. In recent years there have been a number of published accounts of long-term monitoring and of similar long-term climatological data. Such results have, no doubt, contributed to the unease with equilibrium theory, as it is clear when a number of years of data are analysed that the world is an inconstant and inconsistent place. Time cannot be ignored. The best long-term records are probably those from fishing activities as catch records have existed for centuries. Direct, quantitative sampling of phytoplankton and zooplankton populations has only been carried on on a continuous basis since the 1930s and there was much disruption during the war. Despite the problems and the paucity of data there are now a sufficient number of accounts in existence from both marine and freshwater environments to demonstrate both the nature of the biological processes involved and the necessity of long-term data collection. For example, long-term data records exist for certain English Lakes, the Laurentian Great Lakes, the North Sea and the English Channel. Conveniently these data span a wide range of basin scales from small lakes to oceanic basins. Some common mechanisms and properties will however be identified.