An overview of plankton ecology in the North Sea

The purpose of this report is to give an overview of plankton ecology in the North Sea, and the processes that effect it, as derived from current research. The Sir Alister Hardy Foundation has extensive data for the North Sea area, and other sources have also been used to provide information for this report. Shortfalls in current research have also been highlighted. The information contained herein is to be contributed towards an information base for the Strategic Environmental Assessment. The North Sea is an extension of the North Atlantic that has an area of 574,980 km2. The deepest area is off the coast of Norway (660m), with a number of shallow areas, such as the Dogger Bank (15m). The North Sea represents a large source of hydrocarbons that have been exploited since the early 1970s. The aim of this study is to provide the Department of Trade and Industry with biological data on the planktonic community of the North Sea, as a contribution towards the Strategic Environmental Assessment (SEA 2). An overview of phyto- and zoo- plankton community composition, plankton blooms, Calanus, mero-, pico- and megaplankton, sensitivity to disturbance / contamination, phytodetritus and vertical fluxes and the resting stages of phytoplankton is made using the results of the survey database. Additional published literature has also been used, and gaps in available data have been highlighted. 1.3 The Continuous Plankton Recorder (CPR) survey provides a unique long-term dataset of plankton abundance in the North Atlantic and North Sea (Warner and Hays 1994). The survey has been running for almost 70 years, using ‘ships of opportunity’ to tow CPRs on regular, and incidental routes, sampling at a depth of 10 m. Each sample represents 18 km of tow and approximately 3 m3 of filtered seawater. Over 400 taxa of plankton are routinely identified by a team of taxonomists. The samples are also compared to colour charts to give an indication of ‘greenness’, which provides a visual index of chlorophyll value. CPRs have been towed for over 4 million nautical miles, accumulating almost 200,000 samples. The design of the CPR has remained virtually unchanged since sampling started, thus providing a consistency of sampling that provides good historical comparisons. By systematically monitoring the plankton over a period, changes in abundance and long term trends can be distinguished. From this baseline data, inferences can be made, particularly concerning climate change and potentialanthropogenic impacts.

Continuous Plankton Records - Seasonal-Variations In The Distribution And Abundance Of Plankton In The North-Atlantic Ocean And The North-Sea

Charts are presented of the seasonal variations in the distribution of four phytoplankton and five zooplankton taxa in the North Atlantic and the North Sea. The main factors determining the seasonal variations appear to be the distribution of the main overwintering stocks, the current system and, in some instances, temperature control of the rate of population increase. Information is presented about the variation with latitude (over the range from 34° N to 65 ° N) of the seasonal regime of the plankton. On the assumption that there is a relationship between nutrient supply and vertical temperature stratification the main features of this variability can be interpreted. In the south (to about 43° N) nutrient limitation plus grazing appear to be dominant, resulting in a bimodal seasonal cycle of phytoplankton. North of about 60° N the system appears to be limited by the size of the phytoplankton stocks being grazed primarily by Calanus Finmarchicus and Euphausiacea. In an extensive zone, from about 44° N to 60° N, it would appear that the spring bloom of phytoplankton is under-exploited by grazing while in summer the zooplankton graze the daily production of the phytoplankton, the stocks of which are probably maintained by in situ nutrient regeneration. The implications, for at least this mid-latitude zone, that rates and fluxes of processes, as opposed to density dependent interactions between stocks, play a major role in the dynamics of the seasonal cycle is consistent with previously reported observations suggesting that physical environmental factors play a major role in determining year-to-year fluctuations in the abundance of the plankton.

Trophodynamics and stability of regional scale ecosystems in the Northeast Atlantic

This study addresses the long-term stability of three trophic groupings in the Northeast Atlantic at regional scales. The most abundant taxa representing phytoplankton, herbivorous copepods, and carnivorous zooplankton were examined from the Continuous Plankton Recorder database. Multivariate control charts using a Bray–Curtis similarity metric were used to assess whether fluctuations within trophic groupings were within or beyond the expected variability. Two evaluation periods were examined: annual changes between 1960 and 1999 (2000–2009 baseline) and recent changes between 2000 and 2009 (1960–1999 baseline). The trends over time in abundance/biomass of trophic levels were region-specific, especially in carnivorous copepods, where abundance did not mirror trends in the overall study area. The stability of phytoplankton was within the expected limits, although not in 2008 and 2009. Higher trophic levels were less stable, perhaps reflecting the added complexity of interactions governing their abundance. In addition, some regions were consistently less stable than others. Correlations in stability between adjacent trophic levels were positive at large marine ecosystem scale but generally non-significant at regional scales. The study suggests that certain regions may be particularly vulnerable to periods of instability in community structure. The benefits of using the control chart method rather than other multivariate measures of plankton dynamics are discussed.

Ecological Investigations with the Continuous Plankton Recorder: The Zooplankton (other than Copepoda and Young Fish) in the Southern North Sea, 1932-37.

I. The report describes the main monthly changes in the distribution and abundance of the zooplankton, other than Copepoda and young fish (dealt with in separate reports), over the southern part of the North Sea from 1932 to 1937. The work is part of the survey carried out by Continuous Plankton Recorders towed at a depth of 10 metres on regular steamship lines between England and the Continent. 2. The limitations to the sampling method are discussed, and it is shown to be unsuitable for recording Mysidacea and Euphausiacea on account of their marked diurnal variation due presumably to vertical migration; they are omitted from the report. 3. The changing distribution of Sagitta, Limacina, Clione, Lamellibranch larvae, Cladocera, Caprellid Amphipoda, Decapod larvae, Echinoderm larvae and Oikopleura are shown in a series of monthly charts while their seasonal fluctuations are compared in time-chart histograms. 4. The Alima larvae of Squilla are recorded on a few occasions in the regions where the Channel opens into the North Sea. 5. The distributional characteristics of the different forms, i.e. their tendencies to even or " patchy " production, are compared.