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.

Prey landscapes help identify potential foraging habitats for leatherback turtles in the NE Atlantic

Identifying key marine megavertebrate habitats has become ever more important as concern increases regarding global fisheries bycatch and accelerated climate change. This will be aided by a greater understanding of the patterns and processes determining the spatiotemporal distribution of species of conservation concern. We identify probable foraging grounds for leatherback turtles in the NE Atlantic using monthly landscapes of gelatinous organism distribution constructed from Continuous Plankton Recorder Survey data. Using sightings data (n = 2013 records, 1954 to 2003) from 9 countries (UK, Ireland, France, Belgium, The Netherlands, Denmark, Germany, Norway and Sweden), we show sea surface temperatures of approximately 10 to 12 degree C most likely indicate the lower thermal threshold for accessible habitats during seasonal foraging migrations to high latitudes. Integrating maps of gelatinous plankton as a possible indicator of prey distribution with thermal tolerance parameters demonstrates the dynamic (spatial and temporal) nature of NE Atlantic foraging habitats. We highlight the importance of body size- related thermal constraints in structuring leatherback foraging populations and demonstrate a latitudinal gradient in body size (Bergmann's rule) where smaller animals are excluded from higher latitude foraging areas. We highlight the marine area of the European continental shelf edge as being both thermally accessible and prey rich, and therefore potentially supporting appreciable densities of foraging leatherbacks, with some suitable areas not yet extensively surveyed.