Assessment of the re-habilitation of the seabed following

6,01

MB

marine aggregate dredging

156

stron

3612

ID

Centre for Environment, Fisheries & Aquaculture Science

2004

rok

Contents

1. Executive Summary 5

2. Introduction .9

2.1 Objectives 11

2.2 Selection of survey sites 11

2.2.1 Area 222 .11

2.2.2 Area 408 .12

2.2.3 Hastings Area X and Y .13

3. Methods 15

3.1 Sampling design 15

3.2 Sample collection .15

3.3 Acoustic and video surveys 15

3.4 Macrofaunal sample processing 16

3.5 Sediment particle size analysis .16

3.6 Data processing .16

3.6.1 Sediment variables 16

3.6.2 Macrofaunal assemblage structure .17

4. Temporal investigations of the physical and biological status of Area 222 18

4.1 Methods .18

4.1.1 Study site 18

4.1.2 Sampling design .18

4.2 Results .20

4.2.1 Sediment characteristics 20

4.2.2 Acoustic surveys 22

4.2.3 Underwater video surveys .30

4.2.4 Macrofaunal assemblage structure 30

5. Temporal investigations of the physical and biological status of Hastings Areas X and Y .36

5.1 Methods .36

5.1.1 Study site 36

5.1.2 Sampling design .38

5.2 Results (Hastings Area X) 39

5.2.1 Sediment characteristics 39

5.2.2 Acoustic and underwater camera surveys 40

5.2.3 Macrofaunal assemblage structure .50

5.3 Results (Hastings Area Y) 55

5.3.1 Sediment characteristics 55

5.3.2 Sidescan sonar surveys 56

5.3.3 Macrofaunal assemblage structure .61

6. Temporal investigations of the physical and biological status of Area 408 .65

6.1 Methods .65

6.1.1 Study site 65

6.1.2 Sampling design .65

6.2 Results .66

6.2.1 Sediment characteristics 66

6.2.2 Sidescan sonar and underwater camera surveys .69

6.2.3 Macrofaunal assemblage structure .76

6.3 Comparison with other studies undertaken at Area 408 78

7. Spatial investigations of Area 222 82

7.1 Introduction 82

7.2 Methods and materials .82

7.3 Results .83

7.4 Discussion 89

8. Spatial investigations of the Hastings Shingle Bank 92

8.1 Methods .92

8.1.1 Sampling design .92

8.1.2 Sidescan sonar surveys 92

8.1.3 The use of Electronic Monitoring System (EMS) data 92

8.1.4 Benthic survey 92

8.2 Results .92

8.2.1 Sidescan sonar survey .93

8.2.2. QTC AGDS survey .96

8.2.3 Multibeam bathymetry survey .97

8.2.4 Sediment characteristics and environmental variables .98

8.2.5 Macrofaunal assemblage structure .98

8.3 Discussion 102

9. Synthesis of fi ndings from temporal investigations 104

10. Discussion of the outcome of fi eld surveys 109

11. Conclusions and recommendations .116

12. Future work 119

13. References .120

14. Annex I - Indices of natural environmental variability 126

14.1 Introduction 126

14.2 The HR Wallingford study 126

14.2.1 Aims 126

14.2.2 Selection of sites .126

14.2.3 Tidal currents 126

14.2.4 Wave climates 127

14.2.5 Bed shear stresses .128

14.2.6 Sand mobility 130

14.2.7 Sensitivities .132

14.2.8 Bed materials 133

14.3 Future work 134

14.4 Summary and conclusions .134

14.5 References .135

15. Annex II - The effects of dredging activity on epifaunal communities – surveys following

cessation of dredging .136

15.1 Introduction 136

15.2 Methodology 137

15.3 Results 140

15.4 Discussion 149

15.5 References .151

16. Annex III - Steering Group Members .