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2009, Emu LImited, Sheringham Shoal, Benthic Ecology and Sabellaria Study

2009, Emu LImited, Sheringham Shoal, Benthic Ecology and Sabellaria Study

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Benthic Ecology
Sedimentology

Description

The principal objective of the survey was ascertain whether Sabellaria spinulosa reef had built up in the windfarm turbine areas, or in the associated cable route since previous surveys undertaken in 2008. The survey work presented here found no evidence to suggest that Sabellaria spinulosa reef had built up during that time. All of the sites found to support the biotope SS.SBR.PoR.SspiMx previously were found to support the same biotope. These were amongst 10 of the 16 sites surveyed which have remained the same as those assigned previously. Of the seven sites within the turbine area (6, 18, 21, 26, 30, 31 and 47) four have been assigned different biotopes; these are 6, 26, 30 and 47. For sites 6 and 26 the change is relatively minor between related biotopes. For sites 30 and 47 the apparent change in sediment from coarse to fine sands is more interesting. However, the same change was also seen at site 7 well outside the windfarm area and approximately three kilometers east of the main cable route. Hence these changes appear to be natural in the habitats prevailing in the area. Site 10 was the only location found previously for the SS.SCS.ICS.MoeVen biotope but is now, again uniquely, SS.SCS.ICS.Glap. These two biotopes are related, with the former grading into the latter where the sediment is subject to continual disturbance. Of the 44 video sites analysed, 42 did not register a score for either elevation or patchiness. Neither of the remaining 2 locations, site 4 and 21, scored for both elevation and patchiness. Site 4 had a score of ‘medium’ for patchiness, but the elevation was less than 1cm illustrating this was a thin crust only and would need to be more than twice this measure to register a score. Although not part of the grab survey an extra grab sample was taken at this location and inspected during the survey thus reinforcing the elevation measure here for those pebbles encrusted with Sabellaria spinulosa. Site 21 measured ‘low’ for elevation, but this assessment was based on a single loose pebble with an estimated tube length of 3cm. The grab samples at site 21 show the numbers of Sabellaria to be about 200m-2 well below Hendrick and Foster-Smith (2006) requirement of 500m-2 for a ‘low-grade’ reef score. Furthermore as the UK Biodiversity Group (1999) notes, crusts may only be seasonal features, easily broken up by winter storms and then reforming the following spring. As such they are ephemeral constructs only, unable to provide stable biogenic habitats for associated species and therefore cannot be considered true Sabellaria spinulosa reefs. The cable route video study identified three biotopes that are typical of robust sand and gravelly sand habitats, primarily supporting Pomatoceros sp. These findings are consistent with data results from previous surveys.

Dataset

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2009, Emu Limited, Sheringham Shoal Offshore Wind Farm, Benthic Ecology and Sabellaria Study, Appendices

Report

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2009, Emu Limited, Sheringham Shoal Offshore Wind Farm, Benthic Ecology and Sabellaria Study, Report