Morecambe Bay SAC subtidal cobble and Boulder skear communities drop-down video survey: final report.
Abstract
This report aims to present the results of a drop-down video survey in order to inform condition monitoring of the subtidal cobble and boulder skear communities within the Morecambe Bay SAC. The attributes to be assessed during the survey were: (1) extent and distribution of subtidal boulder and cobble skear communities; (2) extent and distribution of characterising biotopes; (3) species composition of reef characterising biotopes; and (4) spatial arrangement of biotopes within the Walney / Piel channel. A total of 71 transects were attempted throughout the survey areas, with focus on four Priority Areas assigned by Natural England, using Seastar Survey's own HD Freshwater Lens Camera System (FLCS), with a total of 528 discrete video clips achieved, 500 of which yielded usable data. Results showed that the most commonly identified broad habitat was SS.SSa (sublittoral sands and muddy sands) with 35.5 % of seabed contacts assigned to either the broad habitat SS.SSa or the biotope complex SS.SSa.CMuSa (circalittoral muddy sand). Circalittoral mixed sediments (SS.SMx.CMx) were also frequently observed. Cobble (and, less frequently, boulder) skear communities were frequently observed throughout the survey area. Where potential cobbles and boulder skear habitats were observed, epifauna was dominated by the non-native, cryptogenic colonial ascidian Molgula manhattensis. The condition monitoring attribute species Mytillus edulis was not identified at any location across the surveyed area. In order to further future condition monitoring, it is suggested that the biotope CR.HCR.XFa.Mol be included as a characterising biotope attribute of the Annex I sub-feature 'cobble and boulder skear'.