Process-driven and biological characterisation and mapping of seabed habitats sensitive to trawling.

The increase of anthropogenic pressures on the marine environment together with the necessity of a sustainable management of marine living resources have underlined the need to map and model coastal environments, particularly for the purposes of spatial planning and for the implementation of integrated ecosystem-based management approach. The present study compares outputs of a process-driven benthic habitat sensitivity (PDS) model to the structure, composition and distribution of benthic invertebrates in the Eastern English Channel and southern part of the North Sea. Trawl disturbance indicators (TDI) computed from species biological traits and benthic community composition were produced from samples collected with a bottom trawl. The TDI was found to be highly correlated to the PDS further validating the latter's purpose to identify natural process-driven pattern of sensitivity. PDS was found to reflect an environmental potential that may no longer be fully observable in the field and difference with in situ biological observations could be partially explained by the spatial distribution of fishery pressure on the seafloor. The management implication of these findings are discussed and we suggest that, used in conjunction with TDI approaches, PDS may help monitor management effort by evaluating the difference between the current state and the presumed optimal environmental status of marine benthic habitats

Widespread overspill from a saline density-current channel and its interaction with topography on the south-west Black Sea shelf

Seaward of the Bosphorus Strait, the south-west Black Sea shelf is dominated by the world's largest channel network maintained by a quasi-continuous saline (ca 35 -> 31 psu) underflow. Calculations indicate that >85% of the initial discharge of ca 10(4) m(3) s(-1) spills overbank before the shelf edge. This paper documents interaction of the overspill with sea bed topography using multibeam bathymetry, echo-sounder images of the water column, conductivity-temperature-depth profiles and sediment cores. Overbank spill is widespread, particularly through crevasse channels and on the middle shelf where confinement by channel banks is negligible. Towards the outer shelf, the wind-driven Rim Current advects mud along the shelf, contributing to levee successions and deposition on stoss sides of elongate transverse ridges. Echo-sounder profiles reveal metre-scale eddies over megaflutes, and breaking lee waves and internal hydraulic jumps over ridges. Megaflutes reach 600 m long and 7 m deep, yet form where the underflow, outside the flute, is no thicker than ca 2 to 5 m. Two types of elongate seaward-facing ridges are recognized. Type 1 ridges, 2 to 5 m high, consist of bivalve-rich muddy sand in low-angle (3.5 degrees to 6 degrees) cross-sets created by the underflow. Type 2 ridges, ca 5 m high, have crests up to 2 km long and a buried wedge-shaped foundation (the 'ridge-core') comprised of facies similar to Type 1 ridges. These ridge-cores are blanketed on the landward side by stratified muds, and are capped by obliquely oriented ribs supporting a diverse benthic community. This facies distribution is interpreted to result from stoss-side and lee-side velocity and turbulence fluctuations induced by internal hydraulic jumps and breaking lee waves in overspilling portions of the underflow. Experimental results published by W. H. Snyder and co-workers effectively explain ridge evolution and flow across the ridges, and therefore can be applied with confidence to less easily studied deep-marine settings swept by turbidity currents

Station locations for the three scientific surveys carried in the study area.

<p>Station locations for the three scientific surveys carried in the study area.</p

Results of PCA analysis of the taxonomic composition data with fragility, feeding, mobility, size, position.

<p>Disturbance (Dist), scope for growth (SfG), risk, TDI and abrasion are represented as supplementary variables.</p

Results of PCA analysis for PDS predictors and indices.

<p>Disturbance, Scope for Growth, Risk and seabed abrasion are shown as supplementary variables.</p

Results of PCA analysis of functional traits vs PDS indices, TDI and abrasion.

<p>Results of PCA analysis of functional traits vs PDS indices, TDI and abrasion.</p

Spearman correlation matrix between the functional sensitivity traits and the other factors.

<p>Spearman correlation matrix between the functional sensitivity traits and the other factors.</p

Localisation of the study area.

<p>Localisation of the study area.</p