Are we there yet? Management baselines and biodiversity indicators for the protection and restoration of subtidal bivalve shellfish habitats.

Biodiversity loss and degradation of natural habitats is increasing at an unprecedented rate. Of all marine habitats, biogenic reefs created by once-widespread shellfish, are now one of the most imperilled, and globally scarce. Conservation managers seek to protect and restore these habitats, but suitable baselines and indicators are required, and detailed scientific accounts are rare and inconsistent. In the present study the biodiversity of a model subtidal habitat, formed by the keystone horse mussel Modiolus modiolus (L.), was analysed across its Northeast Atlantic biogeographical range. Consistent samples of 'clumped' mussels were collected at 16 locations, covering a wide range of environmental conditions. Analysis of the associated macroscopic biota showed high biodiversity across all sites, cumulatively hosting 924 marine macroinvertebrate and algal taxa. There was a rapid increase in macroinvertebrate biodiversity (H') and community evenness (J) between 2 and 10 mussels per clump, reaching an asymptote at mussel densities of 10 per clump. Diversity declined at more northern latitudes, with depth and in coarser substrata with the fastest tidal flows. Diversity metrics corrected for species abundance were generally high across the habitats sampled, with significant latitudinal variability caused by current, depth and substrate type. Faunal community composition varied significantly between most sites and was difficult to assign to a 'typical' M. modiolus assemblage, being significantly influenced by regional environmental conditions, including the presence of algal turfs. Within the context of the rapid global increase in protection and restoration of bivalve shellfish habitats, site and density-specific values of diversity are probably the best targets for conservation management and upon which to base monitoring programmes.

The right place at the right time: Improving the odds of biogenic reef restoration.

Habitat restoration is an international priority. With this demand there is a need for ecological knowledge to underpin restoration projects to ensure their success and cost-effective delivery. This study is the first temperate marine restoration project to examine the role seasonality and location may have on restoration projects. The study found that the settlement of Serpula vermicularis, a rare biogenic reef forming species of conservation importance, was up to three times higher on materials deployed during July than other months. The results also found similar differences in settlement between restoration sites. These results suggest that the timing and location of a restoration effort could affect its overall success in the medium to long term. For the restoration of marine biogenic species of conservation importance, targeted spatial and temporal pre-restoration experiments can greatly increase a project's chance of success as well as making large-scale restoration programs more cost efficient.

Historic scale and persistence of drill cuttings impacts on North Sea benthos.

Despite its long history of hydrocarbon exploitation, the United Kingdom lacks scientific protocols to monitor ecological impacts of drill cuttings (mixtures between rocky material excavated from wells and drilling mud). The present study used the UK Benthos industry database to apply standardised variance partitioning and measure the scale and persistence of these effects at 19 sites across the UK sector of the North Sea. Generally, effects were limited to within 1 km from the platform, but two platforms historically drilled with oil-based mud were impacted up to 1.2 km away. Impacts persisted for at least 6-8 years in the northern and central North Sea, but were undetectable in the south where cuttings piles do not accumulate. This study underpins new recommendations to implement regional, phase-based approaches to drill cuttings monitoring, and to apply a precautionary approach in considering decommissioning options that will minimise disturbance to cuttings piles.