DEPARTMENT for ENVIRONMENT, FOOD and RURAL AFFAIRS CSG 15 Research and Development Final Project Report (Not to be used for LINK projects)

Two hard copies of this form should be returned to: Research Policy and International Division, Final Reports Unit DEFRA, Area 301 Cromwell House, Dean Stanley Street, London, SW1P 3JH. An electronic version should be e-mailed to [email protected]

Project title The benthic ecology of the Western

DEFRA project code AE1143

Contractor organisation CEFAS and location Remembrance Avenue Burnham-on-crouch Essex CM0 8HA

Total DEFRA project costs £ 125436

Project start date 01/10/02 Project end date 31/12/04

Executive summary (maximum 2 sides A4)

The main objective of this work is to provide a strategic evaluation of the status of the benthic communities of the western North Sea in relation to natural and anthropogenic influences, as a timely contribution to the DEFRA-led ‘State of the Seas’ assessment for UK waters, due for publication in 2005. This has been achieved through the generation of up-to- date information on the occurrences and densities of benthic in the northern North Sea, by capitalising on sampling effort in 2001 by FRS, Aberdeen, accompanied by completion of a grid of benthic sampling stations off the English east coast, sampled (under NMMP auspices) by CEFAS, leading to coverage of the entire western North Sea.

The outcome has particular benefit in providing a wider context for more localised appraisals of environmental quality status, and inter-relationships between assessment scales (both in space and time) were explored by reference to additional data sources, including those from established NMMP stations, and more site-specific surveys, such as those relating to disposal at sea and aggregate extraction. The generation of new data for coastal and offshore waters of the eastern UK has the additional and important benefit of contributing to an ongoing international evaluation of benthic community status in the North Sea, under ICES auspices, thereby providing a third (sea-wide) tier to the assessment of spatial pattern and the causative influences. DEFRA sponsorship of the proposal therefore had two complementary advantages, namely the servicing of a national need (the UK ‘State of the Seas’ report) and, through the provision of new data, further consolidation of a leading role for UK marine science in ongoing and future assessments of the quality status of the North Sea as a whole.

Macrobenthic samples from 89 stations in the western North Sea were analysed for species occurrences, densities and biomass, in order to assess the current status of the western North Sea benthos. Evaluation of patterns against a suite of natural environmental factors identified sediment type and tidal current strength as the most influential in governing the distribution of contemporary species assemblages.

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Data from the present study were also compared to those from the 1986 ICES North Sea benthos survey. Whilst there were subtle differences in species assemblages resulting mainly from an increase in the dominance of certain taxa, the species assemblages were seen to be similar between sampling occasions.

The effects on benthic communities and sediments of anthropogenic influences such as those arising from oil and gas installations, aggregate extraction and dredged material disposal were not identifiable on the relatively coarse scale of the present sampling grid, indicating that, as might be expected, the consequences of these activities when considered on a case-by-case basis are much more localised. However, it may also be concluded that there is no evidence of a cumulative ‘footprint’ associated with concentrations of these activities, e.g., gas platforms and aggregate extraction sites off the English east coast. Similarly, there was no evidence of deleterious effects associated with demersal fishing activity, which operates on a much wider spatial scale. As with the other sources of anthropogenic activities investigated, the disposition and size of areas of relatively intense fishing effort are, individually, beyond the resolving power of the present survey design, and so this is not to imply the absence of any effects within the survey area.

The outcome of the present study demonstrates the utility of periodic surveys to evaluate the broadscale status of the benthic communities of UK waters, especially in providing a wider context for the numerous ongoing environmental assessments conducted over smaller spatial scales.

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Scientific report (maximum 20 sides A4)

1.0 Introduction

During 2000-2002, 89 stations were sampled for the benthic macrofauna and sediments (thereafter referred to as “2000 survey”, Figure 1). CEFAS work involved the re-sampling of stations off the English east coast occupied in 1986 as part of the ICES North Sea Benthos Survey (Kunitzer et al., 1992). Samples at five of these stations were kindly contributed by the Senckenberg Institute, Germany. FRS work involved stratified random sampling of the northern and eastern North Sea as part of an EU project (MAFCONS).

In 2002, DEFRA funded the work-up of these samples as a contribution both to the UK ‘State of the Seas’ report and to an international collaborative initiative to re-appraise the status of the North Sea benthos following an earlier (1986) survey, under ICES auspices. The present report relates to the first of these aims.

CEFAS stations were sampled using a 0.1m2 Hamon grab or Day grab; Senckenberg Institute stations were sampled with a 0.1m2 Van Veen grab; FRS stations were sampled with a 0.25m2 box core. A 1 mm mesh sieve was used in the processing of all benthos samples. Sediment sub-samples collected by CEFAS and FRS were analysed for particle size. Additionally, sub-samples at CEFAS stations were analysed for % organic carbon and nitrogen content and the concentrations of a range of trace metals.

Box core (FRS Aberdeen)

Day grab (CEFAS)

Hamon grab (CEFAS)

Van Veen (Senckenberg Institute) 0 150 300 kilometres

Figure 1. Locations of stations, principally in the western North Sea, sampled in the period 2000-2002

2.0 The Sedimentary Environment

2.1 Particle size All the sediments sampled in the 2000 survey were relatively coarse grained, with 90% containing < 10% silt/clay (< 63µm), and with most samples being predominantly sandy in nature. Gravelly sands and sandy gravels predominated in the south and east with the proportion of silt/clay increasing to the north (see Figure 2 for percentages of gravel, sand, silt/clay). This is consistent with the reported distribution of sediment types in the region and corresponds approximately to variations in bathymetry and tidal current velocities. The sources of sediment are varied and the present distribution has resulted from a complex interaction of modern processes (tides, waves and surges) with the effects of glaciations, changes in relative sea level, active sediment erosion, particularly of older Quaternary deposits, and relict features (Pantin, 1991; Basford et al., 1993; Nio et al, 1981; Irion and Zöllmer, 1999; Goldberg, 1973).

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0 100 200 % gravel kilometres % sand % silt/clay

Figure 2. Percentage distributions of gravel, sand, silt/clay

2.2 Metals Trace metal concentrations in sediments were determined using ICP-MS following HF extraction. HF attacks the crystal lattice of alumino-silicate minerals and the resulting metal concentrations reflect both the mineralogy of the sediment and metals adsorbed onto particle surfaces (including the contaminant fraction). Contaminant concentrations in sediments often show an inverse correlation with particle size (finer sediments have a much greater surface area for adsorption). To some extent this can be addressed by analysing a defined size fraction. In the present study the silt-clay fraction (<63µm) was separated and analysed. Earlier studies used a variety of size fractionations (e.g. < 2mm (‘whole sediment’), < 63 µm, < 20µm, < 16 µm; < 2 µm; Rowlatt and Lovell, 1994; Whalley et al., 1999; Rowlatt, 1996; de Groot and Allersma, 1973; Basford et al., 1993; Irion, 1994). In addition, the metal concentration can be normalised against a non-contaminant element such as aluminium or lithium, to account for lithogenic variability. The relative merits of using Al and Li, which vary differently with the mineralogy, have been discussed by Loring (1990). He concluded that Li was more appropriate for use in relatively high latitude regions, such as the NW European Shelf.

In the present study both Li and Al normalisation were used. The distribution patterns were not consistent. Higher concentrations of arsenic, cadmium, chromium, mercury, nickel, vanadium and zinc were observed in the northeast sector, although the extent was variable. Metal/Al ratios were compared with the published OSPAR background/reference concentrations (BRC; OSPAR, 1997) for Fe, As, Cd, Cr, Cu, Hg, Ni, Pb and Zn (Table 1). Eighty percent of the samples were below or within the 1997 BRC range for Fe, Cr, Cu, Hg, and Ni. As and Cd were below or within range for fifty percent of the samples. Pb and Zn showed relatively high concentrations across the whole area. This is most likely to be an historical artefact of mining and industrial activity in northeast England in the previous century. Pb is also introduced into the North Sea as a result of atmospheric fallout (Förstner and Witmann, 1979), although there have been substantial reductions as a result of the phasing out of lead additives in petrol. The BRC's are being re-evaluated (Bignert et al., 2004), as more data become available, particularly to take account of regional variations due to differences in the background geochemistry, but these have not been finalised.

Tributylin (TBT) concentrations were determined on the whole sediment sub-samples and all were below the detection limit, except for one station on the East coast, where 0.013 ppm TBT was recorded.

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metal (ppm)/Al % BRC range calculated % samples within or % samples exceeding from: Sediment (metal/Al below range range (x10-4) ratio)

Fe 0.12 – 1.26 98 2 As 2 – 4.5 52 48 Cd 0.007 – 0.03 48 52 Cr 9 – 20 85 15 Cu 2.2 – 5.7 87 13 Hg 0.0034 – 0.006 98 2 Ni 4.4 9.1 96 4 Pb 1.8 – 4 2 98 Zn 8.8 – 18 28 72

Table 1. Recommended Background Concentrations (BRCs) for fine sediments or fine fractions of sediments and percentage of samples from the 2000 survey which either fell within or exceeded the BRC range.

2.3 Spatial and temporal variability & potential sources There have been a number of studies of trace metal distributions in this region in recent years. Direct comparison to establish trends is problematic in many cases because of differences in the particle size fraction used for the analysis. The 2000 western North Sea benthos samples were taken from the same sites occupied in the 1986 survey, up to 2.5º E, but trace metal concentrations in the 1986 samples were determined in the <2 µm fraction (Basford et al., 1993). The 1990/91 baseline survey, for the North Sea Task Force, covered the same region at a higher density of sampling locations, but metals were analysed on the <2 mm fraction (Rowlatt & Lovell, 1994; Rowlatt 1996; Rowlatt & Davies, 1995). The study concluded that there were relatively high concentrations of lead and mercury off the northeast coast of England, that copper and nickel were relatively uniformly distributed, but that Al-normalised cadmium and chromium concentrations were higher on the northern edge of the Dogger Bank. A comprehensive investigation of metal distributions and behaviour on and around the Dogger Bank concluded that cadmium cycling was associated with phytoplankton dynamics (Whalley et al., 2002). A more detailed study of arsenic was carried out using the 1990/91 baseline samples augmented by high-resolution sampling on the Dogger Bank in 1993 and 1995 (Whalley et al., 1999), again using the <2 mm fraction. Arsenic has a high affinity with iron and tends to co-vary. Higher arsenic concentrations were observed off the northeast coast, in the Thames and off northeast Norfolk. The first two cases may have a direct industrial source, although the high discharges to the Humber are not reflected in high levels offshore. Higher levels of particulate iron observed off the Norfolk coast (Whalley et al., 1999) may originate from the ironstone deposits exposed near Hunstanton, and sediments eroded on the Norfolk coast are transported eastwards (Irion and Zöllmer, 1999). This may provide a partial explanation for the higher arsenic levels, although transport from the Humber and offshore drilling activities (gas fields) may be contributory factors.

Trace metal concentrations from the present North Sea Benthos study were compared with two other CEFAS datasets which had been collected, processed and analysed by the same techniques: a set of National Marine Monitoring Programme (NMMP) samples, and a suite of sediment samples collected at and around the Tyne dredged material disposal sites (FEPA monitoring). The NMMP data included samples collected from outside the North Sea whilst the Tyne samples were taken from a region of known contaminant inputs. The resulting correlation matrices of metal vs. metal revealed few consistent patterns (Table 2). The only strong correlations (r > 0.5) which were consistent across all 3 datasets were: Zn vs. Pb, Zn vs. Cu, Fe vs. Al, Cr vs. Al, Cr vs. Fe and Ni vs. Cr. The 2000 survey and NMMP results both showed strong correlations of Li with Ni, Zn, Al, Cr and Fe. The Tyne samples had high correlations between Pb, Zn, Cu and Hg which is thought to be due to the direct disposal of contaminated harbour sediments. The Tyne disposal site also exhibited relatively high TBT concentrations, which were not found further afield.

Ecotoxicological Assessment Criteria (EACs) for trace metals (as well as for PCBs, PAHs, TBT and some organochlorine pesticides) have been adopted by OSPAR (1997) to identify potential areas of concern. These are shown in Table 3 together with the mean, standard deviation and 95% confidence limits for the 2000 survey, NMMP and Tyne datasets. It is noted that the measured concentration means and upper bounds exceeded the EACs. However, the analyses were conducted on the < 63µm fraction, representing generally < 10% of the particle size range, and the mean concentrations for the whole sediment are likely to be much lower. It is not thought that these levels, when considering the probable whole sediment concentration, will have a significant impact on biota. Offshore oil and gas production represents a potential point source of trace metals in the region. However, an earlier evaluation (dti, 2001) concluded that such impacts were unlikely to occur more than 500m from installations, and so would be unlikely to be detected at the resolution of sampling achieved in the present study.

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NSB data n = 54 As Pb Cd (ppm) Cr (ppm) Cu (ppm) Fe (%) Hg (ppm) Li (ppm) Mn (ppm) Ni (ppm) 2000 data Al(%) (ppm) (ppm) As (ppm) 0.02 Cd (ppm) -0.05 -0.35 Cr (ppm) 0.61 0.1 0.15 Cu (ppm) 0.27 0.37 0.01 0.4 Fe (%) 0.55 0.45 -0.2 0.7 0.51 Hg (ppm) 0.22 0.09 0.18 0.35 0.36 0.18 Li (ppm) 0.67 0.16 -0.16 0.63 0.5 0.75 0.2 Mn (ppm) 0.38 0.57 -0.21 0.43 0.23 0.62 0.12 0.42 Ni (ppm) 0.58 0.21 -0.06 0.7 0.51 0.64 0.06 0.77 0.39 Pb (ppm) 0.37 0.51 -0.01 0.47 0.48 0.59 0.3 0.37 0.81 0.33 Zn (ppm) 0.47 0.55 -0.07 0.64 0.51 0.81 0.3 0.63 0.77 0.51 0.85

Monitoring data: NMMP As Pb Cd (ppm) Cr (ppm) Cu (ppm) Fe (%) Hg (ppm) Li (ppm) Mn (ppm) Ni (ppm) 2000 data Al (%) (ppm) (ppm) As (ppm) -0.02 Cd (ppm) 0.14 0.15 Cr (ppm) 0.7 0.33 0.18 Cu (ppm) -0.35 0.31 0.18 -0.03 Fe (%) 0.73 0.25 0.42 0.67 -0.1 Hg (ppm) 0.3 0.19 0.07 0.4 0.3 0.11 Li (ppm) 0.52 0.57 0.3 0.76 0.06 0.65 0.32 Mn (ppm) 0.13 0.44 0.18 0.26 0.08 0.12 0.34 0.31 Ni (ppm) 0.43 0.48 -0.18 0.68 0.08 0.31 0.25 0.48 0.29 Pb (ppm) 0.13 0.17 0.23 0.25 0.44 0.19 0.56 0.14 0.36 0.3 Zn (ppm) 0.18 0.67 0.38 0.57 0.55 0.45 0.53 0.59 0.46 0.55 0.63

Monitoring data: Tyne As Pb Cd (ppm) Cr (ppm) Cu (ppm) Fe (%) Hg (ppm) Li (ppm) Mn (ppm) Ni (ppm) 2000 data Al (%) (ppm) (ppm) As (ppm) 0.06 Cd (ppm) -0.38 0.14 Cr (ppm) 0.57 0.26 0.08 Cu (ppm) -0.24 0.05 0.7 0.11 Fe (%) 0.53 0.35 -0.1 0.61 0.2 Hg (ppm) -0.16 0.28 0.77 0.36 0.68 0.1 Li (ppm) -0.04 0.25 0.35 0.15 0.71 0.21 0.61 Mn (ppm) 0.34 0.25 -0.35 0.35 -0.37 0.4 -0.39 -0.38 Ni (ppm) 0.48 -0.09 0.15 0.69 0.21 0.61 0.22 0.03 0.09 Pb (ppm) -0.27 0.19 0.92 0.19 0.68 -0.1 0.86 0.48 -0.4 0.07 Zn (ppm) -0.39 0.15 0.98 0.11 0.7 -0.1 0.81 0.34 -0.35 0.12 0.93

Table 2. Metal vs. metal (ppm) correlates for 2000 survey, Tyne and NMMP datasets.

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Pb As (ppm) Cd (ppm) Cr (ppm) Cu (ppm) Hg (ppm) Ni (ppm) (ppm) Zn (ppm) EAC 1-10 0.1-1 10-100 5-50 0.05-0.5 5-50 5-50 50-500 Mean 2000 survey 32 0.23 98 22 0.13 35 92 129 NMMP 17 0.16 94 23 0.15 31 66 104 FEPA Tyne 1999 21 0.56 123 58 0.35 53 137 208 2000 survey 22 0.13 22 7 0.07 12 72 40 Standard deviation NMMP 8 0.1 24 11 0.08 11 41 26 FEPA Tyne 1999 3 0.41 10 13 0.09 6 37 93 95% confidence that mean fits in this range 2000 survey 26-38 0.2-0.27 91-104 20-24 0.11-0.15 31-38 71-114 117-140 NMMP 15-19 0.13-0.18 88-100 21-26 0.13-0.17 29-34 56-76 98-110 FEPA Tyne 1999 21-22 0.43-0.69 120-126 54-62 0.32-0.38 51-55 125-148 179-238

Table 3. Ecological Assessment Criteria for trace metals compared to the 2000 survey, NMMP and Tyne datasets.

3.0 Current Status of Macrobenthic Assemblages (2000 survey)

3.1 Data Issues Taxonomic spelling and synonyms were checked using the Marine Conservation Society species directory (Howson and Picton, 1997). Species that are only transiently associated with the seabed (e.g., chance occurrences of pelagic species) were removed. Taxa were pooled to the appropriate higher level where there was uncertainty in identification to species level (e.g., due to the presence of juveniles or damaged specimens). For data analysis, all species occurring in only one sample were removed from the list to reduce the opportunity for skewed results due to random occurrences. Colonial taxa were also removed, as they were not adequately sampled in the 1986 North Sea Benthos survey (see Section 4). The final data set for the 2000 western North Sea survey contained 458 species.

The data from replicate samples collected by grabs in the 2000 survey were pooled at each station. The area sampled (0.2 – 0.3m2) was therefore approximately equivalent to that for single core samples in the northern part of the survey area (see Figure 1). All counts were then raised to individuals per metre2.

Core samples were collected at stations principally in the northern North Sea (Figure 1). It may be anticipated that proportionately greater numbers of species will be collected by the deeper-penetrating core samples (see Section 4.1), indicating the need for some caution in making quantitative comparisons of diversity across the survey area.

Regarding timing, the 2000 survey embraced samples collected principally in May/June, with a subset of five collected by the Senckenberg Institute in August (see Figure 1). Also, samples were collected across years (2000-2002).

3.2 Univariate analyses All univariate analyses were conducted using PRIMER version 5 software (Clarke and Gorley, 2001) and Microsoft Excel. Key findings are presented below; a full account of analytical outcomes is in preparation for peer-reviewed publication.

3.2.1 Latitudinal gradient From 51oN to 61oN, the number of species varied from 11-120, and generally increased with increasing latitude. Species diversity (H’) also increased with latitude. A variable diversity was found south of 54oN, coinciding with a dataset composed of Hamon grab and Day grab samples.

160

140

120

100

80

60

40

20

0 50 52 54 56 58 60 62

Lati tude (°N)

Figure 3. Correlation between latitude vs. depth

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Since the Hamon grab samples were collected (mainly) from gravel beds in the Southern North Sea (East English coast), diversity was significantly increased by the presence of epifaunal species. The strong latitudinal gradient within the macrobenthos is likely to be explained by other environmental variables that are known to be correlated with latitude, e.g., depth (Figure 3) and changes in sediment type (Figure 2). Numbers of individuals ranged from 63-6658 per m2 but did not correlate with latitude.

3.2.2 Species distributions Distributions of the 10 most numerically abundant species are illustrated in Figure 4a-j. All species belonged to the major groups Polychaeta or Echinodermata with the exception of Phoronis spp. (Figure 4i), which belongs to a separate phylum. The polychaete Spiophanes bombyx was the most abundant and most widely distributed, ranging from the Thames Estuary to the Shetland Isles (Figure 4j). The remaining nine species were generally located from the Wash northwards and appear to be concentrated in the central North Sea, approximately between Flamborough Head and the Firth of Forth. Exceptions to this are the polychaete species Galathowenia oculata (Figure 4e), Paramphinome jeffreysii (Figure 4h) and the echinoderm species Amphiura chiajei and Amphiura filiformis (Figures 4a and 4b respectively) which were also present in large numbers in the northern North Sea from the Firth of Forth to the Shetland Isles. The polychaete Lanice conchilega (Figure 4g) was prevalent around the Dogger Bank area, most likely due to the sandy substratum preferred by these species.

a b c

d e f

g h i

j

Figure 4. Distributions of the 10 numerically dominant species in the 2000 NSBP survey (a) Amphiura chiajei (b) Amphiura filiformis (c) Echinocyamus pusillus (d) Echinoid spp. (e) Galathowenia oculata (f) koreni (g) Lanice conchilega (h) Paramphinome jeffreysii (i) Phoronis spp. (j) Spiophanes bombyx.

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3.3 Multivariate analyses – patterns in species assemblages and links to environmental variables Group average cluster analysis using the Bray-Curtis similarity coefficient was applied to fourth root transformed data. The dendogram arising from this analysis (Figure 5) was utilised to identify seven main species assemblages (Figure 6):

• two principally in the southern North Sea (south of Flamborough Head), namely an impoverished offshore assemblage associated with clean sands (cluster A) and a species-rich inshore assemblage associated with gravelly substratum (cluster G). Two samples which fell into cluster B were also identified in this region, indicating the heterogeneous nature of the substratum. Note that cluster G may be further sub-divided into a northern and southern assemblage, linked at the 20% similarity level (Figure 5/6) • three in the central North Sea, all of which were characterised by high abundance of the polychaete Spiophanes bombyx (clusters B,D,E,) and other species indicative of a sandy substratum such as the polychaete Scoloplos armiger, the brittlestar Amphiura filiformis and the amphipod Bathyporeia elegans. Cluster B was generally seen to coincide with the Dogger Bank area, whilst cluster D extended towards the east of the Dogger Bank and cluster E to the north. • two in the northern North Sea (Clusters C and F), which were dominated by several species of tube-dwelling . Samples from cluster F were widely distributed from the Firth of Forth northwards and there was also a discrete cluster in the Tyne region. Cluster C was a discrete set of 3 stations which coincided with deep water (134-146 m) with a high % silt/clay content in the vicinity of the Fladen Ground. The northerly-distributed polychaete Paramphinome jeffreysii was characteristically abundant in clusters C and F.

A full listing of the dominant species present in each cluster along with a summary of substratum type, tidal current strength and depth can be found in Appendix 1.

Figure 5. Outcome of cluster analysis using fourth-root transformed data; colour-coded according to cluster.

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A non-parametric multi-dimensional scaling (MDS) ordination technique was employed, and a range of environmental variables were superimposed onto the outcome as an aid to the interpretation of patterns. In Figure 7a the cluster groups (A-G) have been superimposed. Figure 7b-f shows MDS output in relation to environmental variables. Particle size (Figure 7b-d), depth (Figure 7e) and tidal flow (Figure 7f) all appear to exhibit gradients associated with patterns in the benthic fauna. Analysis of relationships between the environmental variables and the biological samples, using BIOENV (Clarke and Gorley, 2001), supports these observations (Table 4). For this analysis, we employed summary statistics derived from the cumulative % particle size distributions, and sorting and median diameter were especially influential. This accords with the findings of Rees et al. (1999) for the benthos at NMMP stations around the England and Wales coastline.

Figure 6. Location of samples collected in 2000 with contouring according to cluster groups in Figure 5. Stations corresponding with NMMP stations are marked with an asterisk (see Section 6).

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Environmental variable ρ value Sorting, Median phi, tidal current 0.636 Sorting, Median phi, tidal current, % Organic Nitrogen 0.635 Sorting, Median phi 0.613 Sorting, Median phi, % Organic Nitrogen 0.612 Sorting, tidal current 0.609

Table 4. The top 5 combinations of environmental variables that best explain the patterns in biological communities (Figure 6) in the 2000 survey

F a B b E EE C D D C D F DF F C E D F D F F F D F F D D FD F F FFF B FF EB F B B B E E E E F F B D F F B B B E B B E B E D E D D G A G G A G G A B A G A A G G A A G G G G G G

c d

e f

Figure 7. Multi-Dimensional Scaling ordinations of: all samples collected in 2000-2002 (a), superimposed upon which are values for % gravel (b) % sand (c) % silt/clay (d) depth in metres (e) peak tidal flow in knots (f). Stress value = 0.18

3.4 Biomass Wet weight data were converted to ash-free dry weight (AFDW) using appropriate conversion factors (Rumohr et al., 1987). Because of the larger surface area and greater penetration depth (potentially leading to higher frequencies of larger, deeper-burrowing fauna) of the 0.25m2 box-core used to sample soft sediments in the northern North Sea, direct comparisons between data are not possible. Therefore, the biomass of each major group (Polychaeta, Crustacea,

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Mollusca, Echinodermata and “other groups”, i.e., species which do not fit into the remaining four major groups) is presented as a percentage of the total sample weight (Figure 8a-e). While having some benefit in improving comparability between stations, it is acknowledged that this expression of the data will not compensate for any skewness associated with occasional heavier, deep-burrowing organisms from core samples. Data indicate a decrease of total biomass from south to north, which was also evident in the earlier 1986 survey (Heip et al., 1992). The exception to this is an increase in mollusc biomass with increasing latitude. This may be explained by the presence of certain large and heavy mollusc species such as Arctica islandica and Lucinoma borealis, which were present in large numbers in some northerly located stations. Overall, polychaetes (Figure 8a) are the most dominant in terms of biomass throughout the western North Sea. Echinoderm biomass (Figure 8b) is highest in the central North Sea and particularly in the Dogger Bank area where the sediment is dominated by sand. (Figure 8c) are dominant at only a few coastal stations. Mollusc biomass (Figure 8d) is generally greatest in the Wash and the deeper waters of the northern North Sea.

Polychaeta % AFDW Echinodermata % AFDW 75 to 100 75 to 100 50 to 75 25 to 50 50 to 75 0 to 25 25 to 50 0 to 25

a b

Crustacea % AFDW Mollusca % AFDW

75 to 100 75 to 100 50 to 75 50 to 75 25 to 50 25 to 50 0 to 25 0 to 25

c d

Other groups % AFDW 75 to 100 50 to 75 25 to 50 0 to 25

e

Figure 8. Biomass of macrofaunal groups. (a) % contribution of the group Polychaeta (b) % contribution of the group Echinodermata (c) % contribution of the group Crustacea (d) % contribution of the group Mollusca (e) % contribution of “other groups”

4.0 Comparison between 1986 and 2000 western North Sea Benthos data

4.1 Data issues To make data from the 2000 survey comparable for later analysis with the 1986 survey, which were only available as individuals per metre2 (we were unable to access the data for individual samples), replicate samples from the 2000 survey were pooled at each station. Pooled counts were then raised to individuals per metre2. It is accepted that this adjustment cannot compensate for differences in the frequency of occurrence of rare species between stations arising from variability in the area sampled (see below).

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There are several issues that affect our ability to compare directly between 1986 and 2000 data. In 1986 cores and/or Van Veen grabs were used to collect samples. Although less versatile than grabs, core samplers are generally more efficient at collecting a greater number of species and individuals in soft sediments due to greater penetration depth (Heip et al., 1985). As they were used at the majority of stations off the eastern English coast in 1986 it might be anticipated that a greater range of species would be encountered when compared to the grabs used in the 2000 survey.

A further difference between the two studies is the number of replicates utilised in the 1986 North Sea Benthos survey, which ranged from 2-12. The number of stations at which more than 3 replicates were collected in 1986 amounted to 15, i.e., about 30% of the survey area, and these were located principally at stations on the eastern (offshore) edge of the grid, and at stations to the south of the Humber estuary. It may be expected that those stations at which >3 samples were collected will show a proportionally greater number of species when compared to the 2-3 replicate samples that were taken in 2000, due to the well-established species-area effect (e.g., Holme, 1953).

Other factors that may explain differences in the data include the timing of the two surveys, variability in methodologies adopted in the processing of samples at sea and in the laboratory and taxonomic issues. Regarding timing, the 2000 survey embraced samples collected principally in May/June, with a subset of five collected by the Senckenberg Institute in August (see Figure 1). Also, samples were collected across years (2000-2002). For the earlier ICES survey, all samples were collected in April 1986.

One useful statistical method to identify any differences between the two sampling occasions is rarefaction. This involves estimation of the number of species expected in a sub-sample of individuals selected at random from a larger census or collection (e.g., Hurlbert, 1971; Heck et al., 1975). This technique can be used to standardise collections of different sample sizes, to treat them as if they are the same size, and to make more informative comparisons among them. Rarefaction produces a hyperbolic curve that portrays the expected number of species (ES(n)) for a given sample size. It has been employed in many ecological studies, especially for comparison of species diversity or species richness among different communities, habitats or areas (see Hsieh and Li, 1998 for an example). In our case, the resulting rarefaction curves are used to compare data obtained in 1986 and 2000.

Rarefaction measurements were generated using DIVERSE in PRIMER (Clarke and Gorley, 2001). Figure 9 illustrates that the expected number of species is indeed higher in the 1986 North Sea Benthos survey than the 2000 survey. In addition, the 95% confidence limits do not overlap each other unless the samples contain less than 20 or more than 500 individuals indicating significant differences. However, the magnitude of the differences are not great. These are likely to be a function of the different sampling gears employed, with greater numbers of species collected by the deeper- penetrating cores, and indicate that some caution is required in making quantitative comparisons of diversity between sampling occasions. The same consideration applied to comparisons between stations at which cores or grabs were collected in the 2000 survey (Section 3).

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50

45 1986 40

35 2000

30

25 ES(n) 20

15

10

5

0 0 100 200 300 400 500 600 700 800 Number of individuals

Figure 9. Rarefaction curves derived from the 1986 and 2000 datasets. Bars indicate 95% confidence limits.

Taxonomic spelling and synonyms were checked using the Marine Conservation Society species directory (Howson and Picton, 1997). Species that are only transiently associated with the seabed (e.g., chance occurrences of pelagic species) were removed. Taxa were pooled to the appropriate higher level where there was uncertainty in identification to species level (e.g., due to the presence of juveniles or damaged specimens). For data analysis, all species occurring in only one sample were removed from the list to reduce the opportunity for skewed results due to random occurrences. Colonial taxa were also removed, as they were not adequately sampled in the 1986 North Sea Benthos survey. The stations selected from the 1986 North Sea Benthos survey for a comparison with the 2000 data contained 385 species, and the combined dataset contained 573 species.

4.2 Univariate analyses The ten most dominant species in each year of survey were ranked to determine any changes between 1986 and 2000 (Table 5). Distributions are shown in Figures 10-17.

Four species were common to both surveys. These were the tube-dwelling polychaetes Spiophanes bombyx, Galathowenia oculata, and Scoloplos armiger, and the echinoderm Amphiura filiformis. The 2000 data show an increase in the abundances of Spiophanes bombyx (Figure 10) and Galathowenia oculata (Figure 11) since 1986. Densities and distribution of Scoloplos armiger (Figure 12) and Amphiura filiformis (Figure 13) have declined since 1986. The increase in numbers of the polychaetes Lagis koreni and Lanice conchilega in the 2000 survey compared to the 1986 survey is due to a large increase in abundance off the Thames Estuary. Conversely, the amphipod Bathyporeia elegans (Figure 14) and bivalve Mysella bidentata (Figure 15) listed in the top ten dominant species in the 1986 survey but not in the 2000 survey show a reduction in their abundance and distribution since 1986. Paramphinome jeffreysii (Figure 16), a known northerly-distributed species which was present only in small numbers at six stations in the1986 survey, occurred at higher densities and at a greater number of stations in 2000. A decrease in distributions or densities of certain echinoderm species was also seen between 1986 and 2000. This was particularly noticeable in the heart urchin Echinocardium cordatum (Figure 17).

Rank 1986 2000 1 Amphiura filiformis Spiophanes bombyx 2 Spiophanes bombyx Echinocyamus pusillus 3 Bathyporeia elegans Lanice conchilega 4 PELECYPODA juv. Galathowenia oculata

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5 Magelona spp. Lagis koreni 6 Mysella bidentata OPHIUROIDEA juv. 7 Galathowenia oculata Amphiura filiformis 8 Phoronis spp. Pisidia longicornis 9 Scoloplos armiger Paramphinome jeffreysii 10 Nephtys cirrosa Scoloplos armiger

Table 5. The ten dominant species from each year of survey, ranked in order of decreasing contribution

Largest circle = 1100 individuals per metre2

Figure 10. The densities (per m2) and distribution of the polychaete Spiophanes bombyx in 1986 (left) and 2000 (right).

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Largest circle = 640 individuals per metre2

Figure 11. The densities (per m2) and distribution of the polychaete Galathowenia oculata in 1986 (left) and 2000 (right).

Largest circle = 260 individuals per metre2

Figure 12. The densities (per m2) and distribution of the polychaete Scoloplos armiger in 1986 (left) and 2000 (right).

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Largest circle = 550 individuals per metre2

Figure 13. The densities (per m2) and distribution of the brittlestar Amphiura filiformis in 1986 (left) and 2000 (right).

Largest circle = 640 individuals per metre2

Figure 14. The densities (per m2) and distribution of the amphipod Bathyporeia elegans in 1986 (left) and 2000 (right).

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Largest circle = 410 individuals per metre2

Figure 15. The densities (per m2) and distribution of the bivalve mollusc Mysella bidentata in 1986 (left) and 2000 (right).

Largest circle = 260 individuals per metre2

Figure 16. The densities (per m2) and distribution of the polychaete Paramphinome jeffreysii in 1986 (left) and 2000 (right).

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Largest circle = 79 individuals per metre2

Figure 17. The densities (per m2) and distribution of the heart-urchin Echinocardium cordatum in 1986 (left) and 2000 (right).

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4.3 Multivariate analyses – patterns in species assemblages and links to environmental variables Stations located in the western North Sea which had been sampled in both 1986 and 2000 were analysed and cluster analysis performed on fourth root-transformed data. The clusters were mapped and contoured (Figure 18) to allow a comparison of the nature and distribution of species assemblages between the two surveys. Patterns were broadly similar between the years. To the south, the cluster analysis distinguished between a diverse assemblage associated with mixed substrata (cluster F) and an impoverished assemblage associated with sandy substrata (cluster A in 2000). In the 1986 North Sea Benthos survey coarser substrata were not sampled at a number of locations off the eastern English coastline, presumably due to the unsuitability of the sampling gear (corer and Van Veen grab).

In the central North Sea, north of Flamborough Head, clusters B and E generally coincided in both years with, respectively, the Dogger Bank and nearshore regions. Stations within clusters C and D were generally located further offshore to the north of the Dogger Bank, although in neither year did they form spatially coherent groups, which might reflect the relative uniformity of the physical environment in this region (see Figure 2).

Divisions between assemblages are similar to those reported by Kunitzer et al. (1992). They further identified southerly stations as being divided into those with coarser or finer sediments which correspond with the clusters A and F in Figure 18. Kunitzer et al. (1992) also distinguished between assemblages at and to the north of the Dogger Bank, with stations close to the English coast having a different fauna to those further offshore. Huys et al. (1992) also found similar patterns in meiofaunal communities.

The contribution of individual species to the observed faunal patterns was investigated utilising the similarity percentages (SIMPER) routine within PRIMER. No major differences in the community structure were detected, indicating that assemblage types have generally remained similar. To further explore the similarities between the stations from the two surveys, the RELATE routine in PRIMER was employed. This tests the significance of differences between species assemblages collected from the same stations in 1986 and 2000. A Spearman rank correlation coefficient of 0.524 (p=0.001) was obtained indicating significant similarity between the two years of sampling.

a b

Figure 18. The distributions of species assemblages A-F in 1986 (a) and 2000 (b)

As with the 2000 data, correlation analysis using the BIOENV procedure was applied to the 1986 North Sea benthos data and a suite of environmental variables. As would be expected, environmental variables that best explain the observed species distribution patterns (Table 6) were similar to those identified for 2000 data (see Table 4). The following environmental variables were tested: median (phi), % silt/clay, % sediment>2mm, depth (metres) and tidal current (knots)

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as these were available for the majority of stations. (It is recognised that measures of sediment properties are inter- related to varying degrees). The influence of variability in tidal current strengths is especially notable.

Environmental variable ρ value Median phi, % silt/clay, % sediment >2mm, tidal current 0.608 Median phi, % silt/clay, % sediment >2mm 0.604 % silt/clay, % sediment >2mm, tidal current 0.601 Median phi, % sediment (>2mm), tidal current 0.601 % silt/clay, % sediment (>2mm) 0.597

Table 6. The top 5 combinations of the environmental variables tested which best explain the patterns in assemblages in the 1986 survey

4.4 Biomass In the 1986 survey, the majority of biomass data was derived directly from determination of AFDW, but for the 2000 data, wet blotted weights were determined and then converted to AFDW using the conversion factors of Rumohr et al. (1987). Biomass data are notoriously difficult to standardise between laboratories and previous intercalibration exercises have revealed differences of up to 50% between estimates of AFDW (Duineveld and Witte, 1987). Similar observations have been made by the UK NMBAQC. Further differences between 1986 and 2000 are likely to arise from the type of equipment which was used to collect macrofaunal samples (see 4.1., above). These methodological constraints preclude a direct quantitative comparison of biomass values obtained in 1986 with those reported from the 2000 survey. There is reported evidence for no marked overall decline in biomass from long-term studies annual studies in the Dutch sector of the North Sea commencing in 1986 (Daan and Mulder, 2001; 2002; 2003).

However, it is possible to make general comments on differences in the proportional contributions of the major groups. The most noticeable change between the two surveys was the proportional increase in polychaete biomass in 2000, particularly in offshore northern areas of the North Sea. There was also a large increase in polychaete biomass in the Thames Estuary in 2000 due to high abundances of the polychaete worms Lanice conchilega and Lagis koreni. Echinoderm biomass appears to have remained constant over time in the central and northern North Sea. However, off the northern Norfolk coast, there appeared to be a reduction both in biomass values and species occurrences of echinoderms between the two surveys, particularly Echinocardium cordatum. In 1986, mollusc biomass was high offshore in the northern part of the sampling grid and lower elsewhere. In 2000 biomass offshore was much reduced; the Wash supported highest mollusc biomass. Changes in the distribution of biomass are harder to define, as the high biomass values in the southern North Sea in 2000 were encountered at stations not sampled in 1986. ‘Other groups’ appear to have remained relatively constant between 1986 and 2000 with the exception of an increase in biomass in the Thames Estuary in 2000 due to high abundances of the polychaete worms Lanice conchilega and Lagis koreni.

5.0 Anthropogenic influences

In an evaluation of relationships between the benthos of the western North Sea and anthropogenic activities, GIS overlays were produced of the distributions of dredged material disposal sites, aggregate extraction sites and oil and gas installations (Figure 19). The effects on benthic communities of anthropogenic influences such as those arising from oil and gas installations, aggregate extraction and dredged material disposal were not identifiable on the relatively coarse scale of the present sampling grid, indicating that, as might be expected, the consequences of these activities, when considered on a case-by-case basis, are much more localised. However, it may also be considered that there is no evidence of a cumulative ‘footprint’ associated with concentrations of these activities covering wider spatial scales e.g. gas platforms and aggregate extraction sites off the English east coast.

Indeed, studies of oil platforms have shown that areas affected are very small, approximately 1km wide and 1-3km long and on the scale of the entire North Sea the impacted area is likely to be less than 0.5% of the total (Davies et al., 1984; Gray et al., 1988). Similarly, disposal operations and aggregate extraction have been shown to affect discrete areas of the seabed in the near-vicinity of the activity (see MEMG, 2003; Boyd and Rees 2003). In contrast, the spatial extent of beam-trawling effort exceeds that of other human activities. An examination of the spatial pattern of fishing effort in 1998 (Callaway et al., 2002) showed that beam trawling was concentrated in the southern North Sea both near- and offshore. They identified that otter-trawling effort was highest north of the Humber Estuary and was concentrated near-shore in English waters and slightly further offshore in Scottish waters. However, it is understood that the distribution of fishing effort has been steadily increasing over time and that effort has tended to shift from otter to beam trawling. Furthermore, recording techniques between countries remain different, and hence effort is likely to be under-recorded (Jennings et al., 1999).

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Using the data of Callaway et al. (2002), variability in the intensity of commercial beam trawling does appear to correlate with patterns in numbers of species and species richness. However it should be noted that beam-trawling activity follows a latitudinal gradient with decreasing effort from south to north, and such a gradient is confounded with those of several other environmental variables which correlate with patterns in the benthic fauna (Table 4). The fact that fishing pressure appears to be concentrated in the shallower areas of the southern North Sea, which, in the present study, have been shown to be very diverse in species assemblage and substratum does not appear to concur with conjecture that intensive fishing activity has a large scale effect. It is therefore probable that the observed correlation is an artefact of a natural shift in fishing practices. The distribution of otter trawling effort does not appear to correlate with spatial differences in species composition.

Recent CEFAS effort to collate more comprehensive fishing effort data has produced a measure of fishing intensity based on satellite information for the locations of all UK vessels and Dutch beam trawlers over 24 metres. The analysis assumes that, on average, areas that are more highly impacted will have a higher incidence of recorded presences (derived from satellite tracking) than those that do not. These data were analysed within a GIS to facilitate estimation of impact intensity and allow for a higher resolution of fishing effort to be obtained, but does not differentiate between types of fishing. Other caveats are that some vessel positions may have been lost due to the vessels having no gear type classification. Also, only vessels over 24 metres in length were recorded which means that total effort is likely to be under-recorded, particularly in coastal areas. Finally, vessel speed was used to filter out steaming (i.e. travelling to and from locations). However, some vessels may still have been steaming inside the boundaries set or fishing at steaming speeds.

Values of fishing effort were obtained for the 1km square surrounding each position in the NSBP 2000 survey for the years 2001 and 2002. Compared to the Callaway et al. (2002) data which was based on effort per ICES rectangle (approximately 3350km2), it was anticipated that this higher resolution data might provide a clearer picture of the impacts of fishing activity. The data from both years showed that effort was concentrated in the central North Sea area, particularly the Dogger Bank region with lower effort in nearshore areas due to the recording of vessels over 24m length. These values of fishing effort were then correlated with patterns in species assemblages using the BEST routine in PRIMER. Very low correlations of –0.055 and 0.069 were seen for the 2001 and 2002 data respectively indicating there was no significant negative or positive correlation of fishing effort with species assemblages.

The effects of intensive fishing on the benthos are well documented for relatively localised spatial scales (Frid et al., 2001; Jennings et al., 2001; Kaiser and Spencer, 1994). For the present survey, there was no evidence of wider effects within the western North Sea region arising from fishing activity using either type of fishing effort data. However, in common with consideration of the effects of other activities such as those associated with oil and gas installations, there is a mis-match between the resolving power of the relatively coarse grid employed in 2000, and the localised (often patchy) distribution of intensive fishing effort, which mitigates against the identification of more localised effects, as noted by Jennings et al. (1999).

≅≅ ≅ ≅ ≅ ≅≅≅≅≅≅ ≅≅ ≅≅≅≅≅ ≅ ≅ ≅≅ ≅≅≅ ≅≅≅≅≅≅ ≅ ≅≅≅ ≅≅≅ ≅ ≅≅ ≅≅ ≅ ≅ ≅ ≅≅ ≅≅≅≅ ≅ ≅ ≅≅≅ ≅ ≅ ≅≅ ≅ ≅≅≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅≅≅ ≅ ≅ ≅ ≅≅ ≅≅≅≅≅≅≅ ≅ ≅ ≅≅ ≅≅≅ ≅≅≅ ≅ ≅ ≅≅ ≅≅≅ ≅≅ ≅≅ ≅≅≅≅≅ ≅ ≅ ≅ ≅ ≅≅ ≅≅ ≅≅≅≅≅≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅≅ ≅≅ ≅ ≅ ≅≅ ≅≅≅≅ ≅≅ ≅≅≅ ≅ ≅≅ ≅≅ ≅≅≅ ≅ ≅ ≅ ≅ ≅ ≅≅ ≅ ≅ ≅ ≅≅≅ ≅≅≅≅≅ ≅ ≅≅≅ ≅≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅ ≅≅ ≅ ≅≅≅≅≅≅≅ ≅ ≅ ≅≅ ≅ ≅≅ ≅ ≅ ≅≅≅ ≅≅≅≅≅ ≅ ≅ ≅ ≅≅≅ ≅ ≅ ≅≅≅≅ ≅≅≅ ≅≅ ≅ ≅ ≅ ≅ ≅ ≅≅≅≅≅≅≅≅≅ ≅≅≅≅≅ ≅≅≅ ≅≅≅≅≅≅≅ ≅ ≅ ≅≅ ≅≅≅≅≅≅≅≅ ≅ ≅ ≅≅≅≅ ≅ ≅ ≅ ≅≅ ≅≅≅≅≅≅≅≅≅≅ ≅≅ ≅≅≅≅≅≅≅≅≅ ≅ ≅≅ ≅≅≅≅≅≅≅ ≅≅≅≅≅≅≅≅≅≅ ≅≅≅ ≅≅≅ ≅≅≅≅≅ ≅≅≅≅ ≅≅≅ ≅ ≅ ≅≅ ≅ ≅ ≅≅ ≅≅ ≅ Current disposal sites ≅≅≅≅ ≅≅≅≅ ≅ ≅ ≅ Current aggregate extracion licences ≅≅≅

≅ Oil and Gas Platforms 500 0 250 ≅ kilometres

Figure 19. Distribution of selected human activities in the North Sea (excluding fishing)

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6.0 Comparison of site-specific and larger-scale survey outcomes

The relatively coarse sampling grid limits the scope for identifying human impacts which arise from more localised activities. For example, the majority of dredged material disposal sites are located inshore of the sampling grid. Further offshore, analyses provided no evidence of wider-scale ‘footprints’ arising from the cumulative impacts of regional oil and gas developments or of marine aggregate extraction activities. However, the inclusion of site-specific survey data from existing surveys, where localised impacts have been identified, provides an interesting insight into scale-related perceptions of their significance.

Macrofaunal datasets derived from small-scale surveys of the effects of human impacts, which were analysed in conjunction with data from the present North Sea grid, were as follows:

• Survey in 2000 of a current dredgings disposal site off the River Tyne (TD) • Survey in 2000 of a relinquished aggregate extraction site in the Cross Sands area off Lowestoft (CS) – Cooper et al. In prep. • Survey in 2002 of a recently disused dredgings disposal site (Roughs Tower) in the outer Thames Estuary (RT)

These were selected to provide a wider spatial context for the evaluation of species assemblages within or in the near vicinity of the relevant local human activity. The outcome of combined analysis using MDS is given in Figure 20.

As expected, the samples from the southern North Sea, namely Cross Sands and Roughs Tower, tended to form discrete groups. In particular, the Cross Sands samples were associated with those from impoverished sands and gravel from the western North Sea grid, whilst the Roughs Tower samples clustered with the richer gravels. The ‘impacted’ samples from the Roughs Tower and Cross Sands surveys were generally isolated from the ‘non-impacted’ samples (labelled N) from the same survey and also the western North Sea benthos samples, indicating that the degree of alteration in assemblage structure finds no parallel with any natural equivalents. In contrast, the Tyne samples were biologically more similar to those collected in the northern North Sea (Firth of Forth northwards) than those collected offshore of the Tyne region. Thus, the degree of impact associated with some of these samples was apparently not sufficient to distinguish them from natural assemblages in the region.

Stress: 0.22 SITE N N N NS N N N N N N N N N N N TD N N N N N N N CS N N N NNNN N N N N NN NN NN N N N N N N N RT N N I IN N N N N IN N N N N N N N N N N N N N N N N N N N N N N N N North of Flamborough Head N N N N N South of FlamboroughN Head I N N N N N I N N N I I N N N N I I N I N N N N LINCREASING LATITUDE LATITUDE LINCREASING NN SEDIMENTS BECOMING FINER N N N

N N

Figure 20. MDS plot of the large-scale western North Sea Benthos 2000 survey combined with the three site-specific surveys. N= ‘non-impacted’ in relation to the anthropogenic activities of dredged material disposal and aggregate extraction. I = samples which were considered to be impacted by these activities.

Six coastal/offshore NMMP stations off the English east coast are located at or very near to stations on the present sampling grid. These are adjacent to the Tyne, Tees, Humber/Wash and Thames (Figure 6) and form only part of a geographically widespread network of stations which extends into southern and western UK subtidal waters. The NMMP station off the Tyne estuary was located within assemblage type F identified from cluster analysis; offshore NMMP stations located east of the Tees and Humber estuaries belonged, respectively, to assemblage types B and D; NMMP stations located in the Wash, and in the vicinity of the outer Thames estuary all belonged to assemblage type G (Figure CSG 15 (1/00) 23

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6). It is concluded that: i. each station is representative of the prevailing regional pattern in the distribution of assemblage types: none was isolated in terms of faunal characteristics; ii. it is important to recognise this regional (rather than global) affinity, when interpreting trends in the data at individual stations in relation to natural and human influences.

Schratzberger et al. (2004) consider that the network of offshore NMMP stations are important for a number of reasons. They are generally deeper-water soft sediment communities that are depositional and therefore may act as a sink for contaminants. Furthermore, they are relatively stable and less likely to be influenced by short-term disturbances such as storms. These stations are therefore ideal candidates for a ‘reference’ or ‘baseline’ in terms of the structure and the degree of natural variability of the resident assemblages present against which perturbation effects can be evaluated.

7.0 Summary of conclusions

1. There is no evidence of major structural change in the benthic communities of the western North Sea between 1986 and 2000. 2. Spatial variations in the numbers of species and densities of the benthic macrofauna in both surveys are mainly accounted for by a trend towards increasingly fine substrata, increasing water depths and reduced tidal current strengths from south to north. Species-rich assemblages associated with gravelly substrata along parts of the southern English coast provide a notable exception to this general trend. Other environmental factors associated with this latitudinal gradient may be important, but are difficult to isolate due to confounding influences. 3. A comparison between the biomass of the major groups in 1986 and 2000 was problematic due to methodological constraints. However, there was evidence of reduced values (and occurrences) of echinoderms from areas off the Norfolk coast, although the cause of this is uncertain. 4. Changes in the distributions or densities of individual species are apparent between earlier (1986) and recent sampling effort, which is likely to reflect natural (short-term) variations in recruitment rather than longer-term changes in environmental processes. 5. Concentrations of a range of trace metals in offshore sediments provide little indication of the presence of levels of contamination that will impact on the distribution and densities of benthic species at the scale of survey effort employed in the 2000 survey. This is confirmed by the absence of any correlation between contaminant levels and benthic assemblages. 6. The concentrations of trace metals in sediments are not consistently distributed and comparison of the North Sea data with small-scale survey data from the NMMP and FEPA survey programmes also shows few consistent patterns. 7. Certain trace metal concentrations in the 2000 survey exceeded Ecological Assessment Criteria. However, the analyses were conducted on the < 63µm fraction, representing generally < 10% of the particle size range, and the mean concentrations for the whole sediment are likely to be much lower. It is not thought that these levels, when considering the probable whole sediment concentration, will have a significant impact on biota. 8. The absence of any ‘footprint’ associated with oil and gas installations (the most widely distributed anthropogenic activity, other than demersal fishing) adds weight to the view that adverse effects on the benthic macrofauna remain very localised in extent. It follows that, similarly, there is no evidence of large-scale cumulative consequences arising from oil and gas exploitation, or from the activities of aggregate extraction and dredged material disposal (at least offshore). 9. The distribution of commercial beam trawling effort is confounded with latitude, and hence with natural environmental factors such as substratum type and depth, as well as with trends in the benthic macrofauna. There is no evidence of any causal relationship between the distribution of benthic assemblages in the western North Sea and this activity, although more subtle effects cannot be dismissed. As with other human impacts and activities, more localised effects arising from intensive fishing activity could not be resolved by the present relatively coarse sampling grid. 10. The inclusion of site-specific biological and chemical survey data from the NMMP and FEPA programmes to assess, respectively, the representativeness of stations and the influence of spatial scale on evaluations of anthropogenic impacts have provided useful insights into scale-related perceptions of the “significance” of local activities and will be the subject of further analyses.

8.0 Recommendations

a. Periodic synoptic surveys are valuable as a means to evaluate the broadscale status and to provide a wider context for the numerous ongoing assessments of the benthic environment on smaller spatial scales

b. Future synoptic surveys should conform with the QA and AQC procedures adhered to in the present survey

c. The extension of such large-scale surveys into other UK waters, employing standard survey and analytical methodologies, would have strategic benefits for future quality assessments.

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d. Holistic assessments of marine environments are currently hampered by inadequate information on the dynamics and functional role of non-target species at the bottom of marine food webs and in particular microbiota and small-sized multi-cellular organisms (meiofauna). There would be benefits for expanding the scope of future survey effort to incorporate these poorly-studied benthic components to further our understanding of system function and it’s relationship to structure.

e. Further exploration of historic datasets for comparison with contemporary surveys are recommended in order to provide additional insights into the nature and causes of long-term change, particularly in relation to climate change.

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9.0 References

Basford, D.J., Eleftheriou, A., Davies, I.M., Irion, G., Soltwedel, T. (1993) The ICES North Sea benthos survey: the sedimentary environment. ICES Journal of Marine Science 50: 71-80.

Bignert, A., Cossa, D., Emmerson, R. Fryer, R., Full, C., Fumega, J., Laane, R., Martinez-Calls, H., McHugh, B., Miller, B., Millward, G.E. (Chair of B/RCs), Moffat, C.(ed.), Piijnenburg, J. (ed.), Roose, P., Ruus, A., Schmolke, S., Smedes, F., Strand, J., Stronkhorst, J., Thain, J., Tissier, C., Trass, T. (Chair of EACs) & Tronczynski, J.(2004). OSPAR/ICES Workshop on the Evaluation and Update of Background Reference Concentrations (B/RCs) and Ecotoxicological Assessment Criteria (EACs) and how these Assessment Tools Should be Used in Assessing Contaminants in Water, Sediment and Biota. Final Report to OSPAR/ICES, 106 pp.

Boyd, S.E. and Rees, H.L. (2003). An examination of the spatial scale of impact on the marine benthos arising from marine aggregate extraction in the Central English Channel. Estuarine Coastal and Shelf Science, 57:1-16.

Callaway, R., Alsvag, J., de Boois, E., Cotter, J., Ford, A., Hinz, H., Jennings, S., Kroncke, I., Lancaster, J., Piet, G., Prince, P., Ehrich, S. (2002). Diversity and community structure of epibenthic invertebrates and fish in the North Sea. ICES Journal of Marine Science 59:1199-1214.

Clarke, K.R. and Gorley, R.N. (2001) PRIMER v. 5 user manual tutorial. PRIMER-E Ltd, Plymouth, 91pp.

Cooper, K.M., Boyd, S.E. and Rees, H.L. (in prep.) An assessment of the impacts of a multiple aggregate extraction licence on seabed macro-invertebrate communities in an area off the east coast of the United Kingdom.

Daan, R. and Mulder, M. (2001). The Macrobenthic Fauna in the Dutch Sector of the North Sea in 2000 and a comparison with previous data. Netherlands Institute for Sea Research. NIOZ-RAPPORT 2001-2. 93 pp.

Daan, R. and Mulder, M. (2002). The Macrobenthic Fauna in the Dutch Sector of the North Sea in 2001 and a comparison with previous data. Netherlands Institute for Sea Research. NIOZ-RAPPORT 2002-1. 90 pp.

Daan, R. and Mulder, M. (2003). The Macrobenthic Fauna in the Dutch Sector of the North Sea in 2002 and a comparison with previous data. Netherlands Institute for Sea Research. NIOZ-RAPPORT 2003-5. 94 pp.

Davies, J.M., Addy, J.M., Blackman, R.A., Blanchard, J.R., Ferbrache, J.E., Moore, D.C., Sommerville. H.J., Whitehead, A. and Wilkinson, T. (1984). Environmental effects of the use of oil-based drilling muds in the North Sea. Marine Pollution Bulletin, 15:363-370.

DeGroot, A.J. and Allersam, A. (1975). Heavy Metals in the Aquatic Environment. Int. Conf. Supplement Progress in Water Technol. 85-97.

Dti. (2001) Contaminant status of the North Sea. Technical report produced for strategic environmental assessment – SEA2, Technical Report TR_004.

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Heip, C., Basford, D., Craeymeersch, J., Dewarumez, J-M., Dörjes, J., de Wilde, P., Duineveld, G., Eleftheriou, A., Herman, Niermann, U., Kingston, P., Künitzer, A., Rachor, E., Rumohr, H., Soetaert, K., Soltwedel, T. (1992). Trends in biomass, density and diversity of North sea macrofauna. ICES Journal of Marine Science 49:13-22.

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10.0 APPENDIX ONE

Group Taxon Average Average Similarity Similarity Similarity Similarity Abundance Cumulative % sediment type % Contribution Overall Average average depth in metres with range in brackets Average peak tidal current (knots) A Nephtys caeca 1.80 7.25 26.79 26.79 27.04% Medium sand with 38 1.8 some shell and/or NEMERTEA 1.20 3.45 12.77 39.57 gravel (16-60) (1.4-2.0) Spiophanes bombyx 1.07 3.17 11.74 51.30

B Spiophanes bombyx 2.71 3.38 11.33 11.33 29.79 Slightly muddy sand 38 1.8 Magelona johnstoni 1.60 1.95 6.54 17.87 (16-60) (1.4-2.0) OPHIUROIDEA 1.94 1.87 6.27 24.14 Bathyporeia elegans 1.64 1.81 6.08 30.22 Fabulina fabula 1.40 1.42 4.77 34.99 Cirratulus caudatus 1.35 1.34 4.50 39.49 Scoloplos armiger 1.49 1.21 4.08 43.56 Sthenelais limicola 1.09 1.11 3.71 47.27 Polinices pulchellus 1.08 1.08 3.62 50.90

C Nephtys juv. 2.62 3.46 8.70 8.70 39.80% Sandy muds (high 139 0.8 silt/clay content) Levinsenia gracilis 2.86 2.95 7.41 16.10 (134-146) (0.6-0.9) Leucon nasica 2.07 2.43 6.12 22.22 Paramphinome jeffreysii 2.12 2.32 5.84 28.06 Eriopisa elongata 1.98 2.23 5.60 33.65 Lumbrineris gracilis 1.61 1.99 5.01 38.67 Heteromastus filiformis 1.71 1.94 4.88 43.55 Orbinia norvegica 1.76 1.94 4.88 48.43

D Spiophanes bombyx 3.37 1.76 4.84 4.84 36.25% Muddy sands 55 0.7 NEMERTEA 2.11 1.49 4.12 8.96 (29-128) (0.5-1.1) Phoronis 2.48 1.17 3.24 12.20 Amphiura filiformis 2.57 1.11 3.06 1.25 Chaetozone setosa 1.84 0.98 2.71 17.96 Scoloplos armiger 1.91 0.94 2.60 20.56 1.61 0.92 2.54 23.10 Lanice conchilega 1.65 0.88 2.43 25.53 Goniada maculata 1.56 0.87 2.40 27.93 Pholoe baltica 1.74 0.81 2.23 30.16 Lagis koreni 1.77 0.81 2.23 32.39 Anaitides groenlandica 1.52 0.81 2.23 34.62 Poecilochaetus serpens 1.77 0.81 2.23 36.84 ECHINOIDEA 2.00 0.74 2.04 38.88 Nucula nitidosa 1.67 0.74 2.03 40.92 Nephtys assimilis 1.25 0.71 1.97 42.89 Nephtys hombergii 1.52 0.71 1.95 44.83 Magelona filiformis 1.51 0.65 1.80 46.63 Edwardsia claparedii 1.40 0.61 1.70 48.33 Mysella bidentata 1.60 0.57 1.56 49.89

E Spiophanes bombyx 3.07 3.03 7.94 7.94 38.10% Slightly muddy sand 67 0.9 Paramphinome jeffreysii 2.34 2.48 6.51 14.45 (40-80) (0.6-1.7) Scoloplos armiger 1.91 2.10 5.52 19.97 NEMERTEA 1.87 2.05 5.37 25.35 Galathowenia oculata 2.15 1.89 4.96 30.31 Amphiura filiformis 2.02 1.81 4.76 35.07 Goniada maculata 1.69 1.66 4.36 39.43 Spiophanes kroeyeri 1.58 1.40 3.66 43.10

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Phoronis 1.69 1.38 3.62 46.72 OPHIUROIDEA 1.75 1.19 3.13 49.85

F Galathowenia oculata 3.05 1.60 4.09 4.09 39.16% 97 0.7 Goniada maculata 2.17 1.45 3.70 7.79 (58-107) (0.4-1.0) Spiophanes kroeyeri 2.08 1.30 3.33 11.12 Muddy sand Amphiura filiformis 2.26 1.27 3.25 14.37 Paramphinome jeffreysii 2.60 1.27 3.25 17.62 Diplocirrus glaucus 2.02 1.20 3.08 20.70 NEMERTEA 1.99 1.20 3.07 23.77 Harpinia antennaria 1.98 1.08 2.76 26.53 Amphiura chiajei 2.16 1.04 2.64 29.17 Chaetoderma nitidulum 1.69 0.93 2.37 31.54 Amphictene auricoma 1.63 0.92 2.34 33.88 Chaetozone setosa 1.61 0.85 2.16 36.05 Levinsenia gracilis 1.70 0.82 2.08 38.13 Owenia fusiformis 1.57 0.75 1.92 40.06 PELEPCYPODA 1.64 0.71 1.80 41.86 Anobothrus gracilis 1.42 0.68 1.74 43.60 Scoloplos armiger 1.59 0.65 1.66 45.26 Spiophanes bombyx 1.52 0.64 1.63 46.89 Phoronis spp. 1.42 0.62 1.57 48.86 Nephtys juv. 1.44 0.59 1.52 49.98

G NEMERTEA 2.22 1.35 5.11 5.11 26.38 Mixed – muddy 46 1.6 gravely sand/ Glycera lapidum 2.18 1.06 4.01 9.12 (21-136) (0.4-2.2) muddy sandy gravel OPHIUROIDEA 1.74 0.77 2.93 12.05 Pholoe spp. 1.64 0.77 2.93 14.99 Lumbrineris gracilis 1.62 0.72 2.72 17.71 Notomastus latericeus 1.67 0.70 2.64 20.34 Aonides paucibranchiata 1.63 0.62 2.34 22.68 Sabellaria spinulosa 1.97 0.61 2.33 25.01 Eteone flava 1.30 0.56 2.12 27.12 Mediomastus fragilis 1.45 0.54 2.04 29.16 Ampelisca spinipes 1.20 0.49 1.87 31.03 Leptochiton asellus 1.35 0.48 1.82 32.86 ANTHOZOA 1.21 0.47 1.79 34.65 Pisidia longicornis 1.60 0.47 1.77 36.42 Lanice conchilega 1.39 0.36 1.37 37.79 Polydora caulleryi 1.06 0.35 1.34 39.13 Laonice bahusiensis 1.19 0.35 1.33 40.66 Pomatoceros lamarcki 1.26 0.35 1.32 41.98 Polycirrus medusa 1.15 0.33 1.23 43.21 Scalibregma inflatum 1.13 0.32 1.23 44.34 Polycirrus norvegicus 1.08 0.30 1.14 45.49 Galathowenia oculata 0.93 0.29 1.08 46.57 Mysella bidentata 1.00 0.28 1.06 47.63 Urothoe elegans 1.03 0.27 1.03 47.66

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