Statement |
Existing swath bathymetry data were used to assist in the interpretation of seabed habitats. Through the Southeast Regional Coastal Monitoring Programme, the inshore 1 km zones of the northern and southern coasts of the Isle of Wight were surveyed in 2011 and Christchurch Bay in 2010. Further offshore, Poole and Christchurch Bays were surveyed in 2012 as part of the MCA UK CHP. The bathymetric data from these two areas were collected as four individual surveys and processed in accordance with the International Hydrographic Organisation (IHO) Standards for Hydrographic Surveys - Order 1a (Special Publication 44, Edition 5). The individual acoustic datasets were available to Ordnance Datum and combined into a single raster in ArcGIS for analysis with the lowest value taken as the depth where datasets overlap. Although previously surveyed by Natural England, data from an area in the south-western corner of the rMCZ were not available and therefore acoustic coverage of the site was not complete.
Ground truth samples were collected by the EA MMS aboard the Solent Guardian in September 2014 (CruiseID: 2GDK70914B). Benthic grabs were used at 33 stations to collect sediments and infauna. An underwater camera system was deployed at 64 stations to collect video and still images of the seabed. Of the 64 samples, 51 could be used to describe BSH (Figure 2; Appendix 1).
A mini-Hamon grab with a sampling area of 0.1 m2 was deployed from the stern gantry of the vessel to collect sediment from the seabed, as described by Ware and Kenny (2011). Sampling positions were recorded (fixed) using TrimbleHYDROpro data acquisition software when the gear made contact with the seabed, with the midpoint of the vesselÔÇÖs stern gantry used as the default offset for position fixing. Once recovered, the sample was emptied into a suitable container, photographed, and the sample volume measured. A sub-sample (approx. 500 ml) of sediment was taken from each sample for particle size analysis (PSA). The remaining sample was washed over a 1 mm mesh sieve to retain the faunal fraction. Retained material was preserved with buffered 8% formaldehyde solution for transfer ashore to a specialist laboratory for analysis.
The SES SeaSpyder camera system was deployed from the stern of the Solent Guardian. Real-time navigation data acquisition and manual position fixing when the gear contacted the seabed was captured via Trimble HYDROpro software and logged by the survey officer. The video footage was annotated with time and position using a SIMRAD MX512 DGPS referenced video overlay. For further detail on ground truth sample collection see The Needles rMCZ Survey Report (Arnold et al., 2014).
All new maps and their derivatives have been projected to WGS84 datum. An indicative broadscale habitat map for the site was produced by analysing and interpreting the available acoustic data collected through the SERCMP, the MCAÔÇÖs UK CHP, and the additional groundtruthing data collected during the dedicated 2014 survey of the site.
The BSHs ÔÇÿA5.1 Subtidal coarse sedimentÔÇÖ and ÔÇÿA5.4 Subtidal mixed sedimentsÔÇÖ were the most widespread habitat types, occupying the majority of the rMCZ site (Figure 4; Table 5). The BSH ÔÇÿA3.2 Moderate energy infralittoral rockÔÇÖ occupies approximately a tenth of the site. The remainder of the site comprises a combination of BSHs ÔÇÿA4.2 Moderate energy circalittoral rockÔÇÖ, and ÔÇÿA5.2 Subtidal sandÔÇÖ. ÔÇÿA5.1 Subtidal coarse sedimentÔÇÖ was identified in the south-western corner, and covering the nearshore rock platform and ridges. The BSH ÔÇÿA5.2 Subtidal sandÔÇÖ is the offshore extension of the sandy beaches on the northwest shoreline of the Isle of Wight. The BSH ÔÇÿA5.4 Subtidal mixed sedimentsÔÇÖ is identified covering the rock platforms and extends to the flanks of the offshore deep water channel and westwards to the southern flank of the extensive offshore bank. The BSH ÔÇÿA4.2. Moderate energy circalittoral rockÔÇÖ occurs on a few isolated north-facing slopes of rock ridge outcrops at the north of the Needles. |