Variability at all scales and its effect on the ecosystem - an overview

In many ways, ICES was founded to explore the link between environmental change and ecosystem response. As early as 1890, Otto Pettersson and Gustav Ekman began the process of applied hydrographic monitoring in the Baltic and North Seas, and it was the utility of Pettersson’s scheme that prompted the founding of ICES in 1902. Though these early initiatives were invaluable in establishing a basis for the long-term detection of "change", it required something more for this to develop into the wealth of decade-to-century time-series that today form so much of the focus, interest, and expertise of ICES. That extra stimulus was provided by the large-scale, long-period shifts in ocean climate that have successively worked their way through ICES waters during much of the present century: the "Warming in the North", the "Russell Cycle", the "Great Salinity Anomaly", and the varied effects of the North Atlantic Oscillation (NAO). This paper is built around four case studies which describe the growth of our understanding in contrasting aspects of biophysical change. In the first, we are concerned with the vertical circulation in the sea and the key developments in critical depth theory by which Gran and Braarud and Sverdrup were able to postulate and then demonstrate the seasonal changes which control the spring phytoplankton bloom, before we go on to discuss the "match-mismatch" theory of Cushing by which the interannual variability of "production" is related to the success of fish stocks. The second pair of cases illustrates the dramatic dislocation of ecological distributions that can result when the effects of climatic change spread through the large-scale ocean circulation. Two contrasting examples are discussed: 1) the rise and spread of the West Greenland cod stock and fishery as a wave of warming passed through the Northern Gyre in the middle decades of the 20th century, and 2) the equally dramatic dislocation of the traditional pattern of herring migration in the Nordic Seas in the 1960s- 1990s as extremes of NAO activity forced fundamental changes in the position of the Oceanic Polar Front. The third case study concerns ways in which perturbations of the intermediate-scale flow fie ld might contribute to the success of fish stocks through space-time variations in the loss or retention of larvae. The fourth and final example is reserved for a description of ocean temperature and its variability, both as a key control variable on the success of fish stocks and as a proxy for others. Subtle shifts in the marine climate may have important effects on the ecosystem. To mitigate these or even to be aware of them, our prime requirement is the continuation of our long hydrobiological time-series, and the need to continue these series is the main conclusion of this paper.

Article from Marine Science Symposia Vol. 215 - 100 years of science under ICES. To access the remaining articles please click on the keyword "MSS Volume 215".