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Abstract Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea. Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton, and in particular Calanus finmarchicus and Calanus helgolandicus , over the last 40 years as measured by the Continuous Plankton Recorder survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow and outflow across a section between Orkney and Utsira in Norway as well as netflow (sum of Baltic outflow, runoff and Channel inflow), have been derived from runs of the NORWECOM model for two integrated depth intervals: surface to 150 m and >150 m. A comparison is made between the physical model output and plankton results for the period 1958–99. Distinct plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and earlier plankton studies over approximately the last 100 years. [ABSTRACT FROM AUTHOR]

Abstract Recently, large-scale changes in the biogeography of calanoid copepod crustaceans have been detected in the northeastern North Atlantic Ocean and adjacent seas. Strong biogeographical shifts in all copepod assemblages were found with a northward extension of more than ° in latitude of warm-water species associated with a decrease in the number of colder-water species. These changes were attributed to regional increase in sea surface temperature. Here, we have extended these studies to examine long-term changes in phytoplankton, zooplankton and salmon in relation to hydro-meteorological forcing in the northeast Atlantic Ocean and adjacent seas. We found highly significant relationships between (1) long-term changes in all three trophic levels, (2) sea surface temperature in the northeastern Atlantic, (3) Northern Hemisphere temperature and (4) the North Atlantic Oscillation. The similarities detected between plankton, salmon, temperature and hydro-climatic parameters are also seen in their cyclical variability and in a stepwise shift that started after a pronounced increase in Northern Hemisphere Temperature anomalies at the end of the 1970s. All biological variables show a pronounced change which started after circa 1982 for euphausiids (decline), 1984 for the total abundance of small copepods (increase), 1986 for phytoplankton biomass (increase) and Calanus finmarchicus (decrease) and 1988 for salmon (decrease). This cascade of biological events led to an exceptional period, which is identified after 1986 to present and followed another shift in large-scale hydro-climatic variables and sea surface temperature. This regional temperature increase therefore appears to be an important parameter that is at present governing the dynamic equilibrium of northeast Atlantic pelagic ecosystems with possible consequences for biogeochemical processes and fisheries. [ABSTRACT FROM AUTHOR]

Trends in basking shark (Cetorhinus maximus ) fishery catches off Achill Island, west Ireland between 1949 and 1975 were examined in relation to zooplankton (total copepod) abundance in four adjacent sea areas over a 27-year period. The numbers of basking sharks caught and copepod abundance showed downward trends and were positively correlated (r -value range, 0.44–0.74). A possible explanation for the downward trend in shark catches was that progressively fewer basking sharks occurred there between 1956 and 1975 because fewer copepods, their food resource, occurred near the surface off west Ireland over the same period. We suggest that the decline in basking sharks may have been due to a distributional shift of sharks to more productive areas, rather than a highly philopatric, localized stock that was over-exploited. [ABSTRACT FROM AUTHOR]