Species abundance data for benthic communities, collected during 1971–1988 off Northumberland on the north-east coast of England (western North Sea) and the Skagerrak (eastern North Sea), and pelagic data collected in corresponding areas during 1958–1988 by the Continuous Plankton Recorder (CPR) survey have been subjected tomulti-dimensional scaling ordination. Changes in community structure at the two benthic stations show a high degree of similarity, characterised by a transition in the late 70s. Similarly, there is a less marked transition between the 70s and 80s in pelagic community structure from the eastern North Sea but pelagic data from the western North Sea shows no discernible patterns. Benthic community biomass data, available only for the Skagerrak station, enabled abundance/biomass comparison curves to be constructed which demonstrated a change from un-disturbed communities in the early and mid 70s to moderately disturbed communities in the late 70s and 80s. North Sea macrofaunal abundance, and, in the Skagerrak, macrofaunal biomass appear to co-vary with phytoplankton colour and total zooplankton abundance, although there are insufficient data for statistical testing. A number of factors including eutrophication and/or pollution may be responsible for these changes in community structure.

Simple community parameters, such as number of species caught and the species diversity of a planktonic group (in this case Ostracoda), have been found to be stable enough in time and space to detect shifts in these parameters likely to be generated by interannual and decadal variation, especially if sampling is conducted at mesopelagic depths. At this time scale, changes in spatial variability will be expressed most clearly as shifts in zoogeographical boundaries. The clearest boundary to be detected in the North-east Atlantic occurs in the vicinity of 40°N, across which is a rapid equatorwards reduction in the total available nutrient as a result of a reduction in the depth of the mixed layer in winter. The boundary at 40°N is marked in satellite images by a sharp reduction in seasonality of surface chlorophyll concentrations. In the planktonic ostracods there is a sharp decline in both species numbers and diversity on the poleward side to a depth of at least 2000 m. If these changes are related to the degree of seasonality in the production cycle, then they can be expected to be climatically controlled. Monitoring this boundary will give an unambiguous signal of any future climate change, natural or anthropogenic, having a significant biological impact on the oceanic ecosystem and on fluxes of material within the water column.

Each summer, in the oceanic north-east Atlantic, a drop in the catch of albacore (Thunnus alalunga Bonnaterre, 1788) is observed for 8 to 10 days at the beginning of August. This temporary decrease of catch per unit effort (CPUE) is related to a relaxation of wind for 5 to 8 days during the previous 8 to 15 days. A similar and significant relationship is also observed in the Atlantic sardine (Sardina pilchardus Walbaum) fishery in a coastal area in the north-east of the Bay of Biscay (France). This indicates that a general ecological process is involved in this relationship between wind and CPUE of two pelagic fish, caught at the sea surface.

The timing of the response of the sardine and the albacore fishery to a relaxation of wind is interpreted in the light of a productivity model. The lack of wind-driven turbulent mixing provides a progressive decrease of the food organisms in the surface layer about 7 days after the wind event. Thus, fish disperse and become less susceptible to capture.

However, particular fertilization processes are involved at the continental shelf-break and the results of the association analysis were not found to be significant for the albacore fishery in this area.

The use of Superposed Epoch Analysis seems to provide a suitable method to analyse such a relationship with a daily time scale.

Comparison of the results of cross correlation analysis used in a previous work with a Superposed Epoch Analysis suggests that further considerations should be given to the use of the latter method infishery science.

Statistical methods for analysing changes in community structure fall under the three general headings of univariate, graphical/distributional and multivariate. These methods are applied to a variety of benthic community data (macrobenthos, meiobenthos, corals, demersal fish), from a variety of localities (intertidal/subtidal, temperate/tropical) and over both spatial and temporal scales. Four general conclusions emerge from this comparative study:

(1) The similarity between sites or times based on their univariate or graphical/distributional properties is usually different from their clustering in multivariate analyses.

(2) Species dependent (multivariate) methods are much more sensitive than species independent (univariate and graphical/distributional) methods in discriminating between sites or times.

(3) In examples where more than one component of the fauna has been studied, univariate and graphical/distributional methods may give different results for different components, whereas multivariate methods tend to give the same results.

(4) By matching multivariate ordinations from subsets of environmental data to an ordination of faunistic data, the key environmental variables responsible for community change may be identified.