Marine Ecology Progress Series 239:1

ABSTRACT: Long-term changes in the plankton of the North Sea are investigated using data from the continuous plankton recorder (CPR) survey. During the last 4 decades, there appears to have been 2 large anomalous periods within the plankton data set, one that occurred in the late 1970s and the other in the late 1980s. These anomalous periods seem to be largely synchronous with unusual ocean climate conditions that have occurred episodically over a timescale of decades. The unusual ocean climate conditions prevailing at these 2 time periods appear to contain important hydrographical elements that involve oceanic incursions into the North Sea. This paper, using data from the CPR survey and providing evidence from other studies, focuses on the relationship between the long-term changes in the biology of the North Sea and these 2 exceptional hydro-climatic events. Here, we suggest that while atmospheric variability and associated changes in regional temperatures have a dominant effect on the marine environment, oceanic influences on the ecology of a semi-closed environment such as the North Sea may have been underestimated in the past. KEY WORDS: North Sea · Plankton communities · Long-term trends · Continuous plankton recorder · Great salinity anomaly · Ocean climate Resale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 239: [1][2][3][4][5][6][7][8][9][10] 2002 to such an extent they can take the form of notable biological shifts The CPR survey, which was started in the North Sea in 1931, is one of only a few long-term biological monitoring programmes and the only one at a spatial scale that gives a systematic coverage of the North Sea in space and time. Using biological data recorded by the CPR survey, several planktonic time series were examined, including an assessment of phytoplankton biomass/structure, and components of the holozooplankton and meroplankton communities. This paper focuses predominately on the response of phytoplankton populations to the ocean climate anomalies. Other biological components of the ecosystem and independent studies from single-point stations are also discussed to corroborate and highlight the manifestation of this response through the various marine trophic levels. We found that although these studies also noticed an abrupt change in the North Sea ecosystem during these 2 periods, they did not have the benefit of regional comparisons MATERIALS AND METHODS The CPR survey is a long-term marine plankton monitoring programme which consists of a network of CPR transects, towed monthly across the major geographical regions of the North Atlantic. On certain standard routes, there is a virtually unbroken monthly coverage going back to 1948. The CPR is a high speed sampler (usually towed between 10 and 18 knots), sampling at a depth of approximately 7 m using a filtering mesh size of 270 µm. After each tow, the CPR is returned to the laboratory for routine analysis involving the recorded estimate of phytoplankton biomass (phytoplankton colour index), and the identification (up to 450 different taxa) and quantification of zooplankton and phytoplankton taxa For the assessment of trends in the phytoplankton community, principal component analysis (PCA) was performed separately on the diatom and dinoflagellate assemblages. This procedure gave a summary of the dominant information within the phytoplankton data set by explaining the largest amount of variation in the phytoplankton assemblage. The phytoplankton data set included those species recorded at a frequency above 1% in CPR samples (approximately 20 dinoflagellate and 30 diatom species). Although there are large variances in the sizes of diatoms and dinoflagellates sampled by the CPR survey, this is not thought to bias the sampling, as the percent retention is roughly constant within each species RESULTS AND DISCUSSION The late 1970s cold-boreal event If a cold body of water was advected into the North Sea during the late 1970s, there should be some evidence from indicator species recorded by the CPR survey. Although one of the possible explanations for the presence of these species in the North Sea is through advection, probably, entering the North Sea at depth along the Norwegian trench, it is unlikely that they were advected from the northwest Atlantic following the route of the GSA advective hypothesis suggested by The late 1980s warm-temperate event In contrast, the late 1980s warm-temperate event was, as the name would suggest, the reverse of the late 1970s cold-boreal event, with the North Sea characterised by high salinities and temperatures as opposed to cold, low salinity conditions seen in the late 1970s. From 1988 onwards, the NAO index increased to the highest positive level observed in the 20th century. This, coupled with evidence for an increased inflow of relatively warm Atlantic water into the North Sea, conspired to produce an extremely warm oceanic climate for the North Sea during the late 1980s and early 1990s period. While SST changes in the North Sea can be explained chiefly by local air-sea exchange processes, which depend on the North Atlantic atmospheric circulation (measured by the NAO index), larger SST anomalies (positive or negative) are related to salinity anomalies in the eastern North Atlantic and North Sea The biological response to the late 1980s and early 1990s event was exceptional. In 1989, phytoplankton 7 Mar Ecol Prog Ser 239: [1][2][3][4][5][6][7][8][9][10] 2002 biomass measured by the CPR survey was nearly 3 standard deviations above the long-term mean Data on fish stocks also suggest that there was an increased inflow of oceanic water, originating from along the continental slope, into the North Sea. For example, researchers have noticed the northward progression of tropical species along the continental shelf west of Ireland since the late 1980s (e.g. CONCLUSIONS While atmospheric variability plays a key role in the overall long-term and regional patterns of plankton From the evidence presented in this paper, major ecosystem changes took place around both of these physically anomalous periods that affected all trophic levels from phytoplankton to fish. The 2 periods seem to have been characterised by oceanic incursions into the North Sea, one boreal in origin the other lusitanian. While the largely synchronous changes in the ecosystem of the North Sea around these 2 periods may suggest a link between the biology and oceanic inflow into the North Sea, it is largely unclear as to which mechanisms are responsible for the observed changes. For example, it is still open to question as to whether the biological changes are associated with a temperaturemediated response, circulatory changes within the North Sea, chemically driven changes via oceanic influxes or a combination of many factors. There is certainly strong evidence to suggest that large structural changes observed in the macrobenthos community of the southern North Sea can be explained by the severity (late 1970s) and mildness (late 1980s) of winters Acknowledgements. The CPR survey is supported by a funding consortium comprising: Intergovernmental Oceanographic Commission (IOC), United Nations Industrial Development Organisation (UNIDO), the European Commission and agencies from Canada, Denmark, The Netherlands, United Kingdom and USA. The survey depends on the voluntary co-operation of owners, masters and crews of merchant vessels which tow the CPRs on regular routes. We wish to thank CPR survey team past and present

50th Annual Feeders Day Progress Report

Feeding pastured calves protein supplements weekly instead of daily during the winter made little difference in either winter or summer gains, according to research results to date. Two sources of protein were used in the trial. (I) Second cutting alfalfa hay was fed at the rate of four pounds per head daily. One group of calves was fed four pounds per head daily and one group was fed 28 pounds per head once each week. (2) Forty percent protein, pellets or cake, was fed at the rate of one pound per head daily. One group was fed one pound per head daily and one group was fed seven pounds per head once each week. Approximately equal amounts of protein were provided by the alfalfa and 40% supplement as fed