Epibenthic diversity in the North Sea

Quantitative analysis of fish and invertebrate assemblage dynamics in association with a North Sea oil and gas installation complex

Decommissioning of offshore infrastructure has become a major issue facing the global offshore energy industry. In the North Sea alone, the decommissioning liability is estimated at £40 billion by 2040. Current international policy requires removal of offshore infrastructure when their production life ends; however, this policy is being questioned as emerging data reveal the importance of these structures to fish and invertebrate populations. Indeed, some governments are developing 'rigs-to-reef' (RTR) policies in situations where offshore infrastructure is demonstrated to have important environmental benefits. Using Remotely Operated Vehicles (ROVs), this study quantified and analysed fish and invertebrate assemblage dynamics associated with an oil and gas (O&G) complex in the Dogger Bank Special Area of Conservation (SAC), in the North Sea, Germany. We found clear depth zonation of organisms: infralittoral communities (0-15 m), circalittoral assemblages (15-45 m) and epi-benthic communities (45-50 m), which implies that 'topping' or 'toppling' decommissioning strategies could eliminate communities that are unique to the upper zones. Sessile invertebrate assemblages were significantly different between structures, which appeared to be driven by both biotic and abiotic mechanisms. The O&G complex accommodated diverse and abundant motile invertebrate and fish assemblages within which the whelk Buccinium undatum, cod fish Gadus morhua and lumpsucker fish Cyclopterus lumpus used the infrastructure for different stages of reproduction. This observation of breeding implies that the structures may be producing more fish and invertebrates, as opposed to simply acting as sites of attraction (sensu the 'attraction vs production' debate). At present, there are no records of C. lumpus spawning at such depth and distance from the coast, and this is the first published evidence of this species using an offshore structure as a spawning site. Overall, this study provides important new insight into the role of offshore O&G structures as habitat for fish and invertebrates in the North Sea, thereby helping to inform decommissioning decisions.

Full-coverage spatial distribution of epibenthic communities in the south-eastern North Sea in relation to habitat characteristics and fishing effort

Full-coverage spatial data of occurrence and a detailed description of habitat requirements of epibenthic communities are needed in many conservation and management contexts. In the North Sea the focus has so far been on small benthic infauna, whereas structure and ecosystem functions of larger epifaunal communities have been largely ignored. This study provides a comprehensive analysis of epibenthic community structure in the south-eastern North Sea, including a detailed inventory of species, diversity and spatially contiguous distribution of communities. Data from nearly 400 stations were compiled for the study, enabling us to describe epibenthic community structure at unprecedented spatial resolution. Eight distinct epibenthic communities were found in the south-eastern North Sea by using multivariate analysis. Distribution modelling with eight environmental variables (bottom temperature and salinity, temperature differences between summer and winter, mud content of sediments, maximum bottom shear stress, stratification, water depth and annual primary production) and one human pressure (fishing effort) was used to extrapolate probable spatial distributions and to identify associated habitat characteristics of the communities in the south-eastern North Sea. Three large epibenthic communities "Coast", "Oysterground" and "Tail End" reflect a gradual habitat change from the coast towards offshore regions, expressed in gradients of bottom salinity, seasonal temperature differences and stratification as the dominant environmental factors. Five smaller communities ("Amrum Bank", "Frisian Front", "Deeps", "Dogger Bank" and "Dogger Slope") outline specific habitats in the south-eastern North Sea. The "Dogger Slope" community has not been recognized before, but has a predicted spatial extent of 7118 km². Due to the high occurrence of long-lived, sessile species such as sponges this community is very sensitive to demersal fishing.

When molecules support morphology: Phylogenetic reconstruction of the family Onuphidae (Eunicida, Annelida) based on 16S rDNA and 18S rDNA

Onuphid polychaetes are tubicolous marine worms commonly reported worldwide from intertidal areas to hadal depths. They often dominate in benthic communities and have economic importance in aquaculture and recreational fishing. Here we report the phylogeny of the family Onuphidae based on the combined analyses of nuclear (18S rDNA) and mitochondrial (16S rDNA) genes. Results of Bayesian and Maximum Likelihood analyses supported the monophyly of Onuphidae and its traditional subdivision into two monophyletic subfamilies: Onuphinae and Hyalinoeciinae. Ten of 22 recognized genera were monophyletic with strong node support; four more genera included in this study were either monotypic or represented by a single species. None of the genera appeared para- or polyphyletic and this indicates a strong congruence between the traditional morphology-based systematics of the family and the newly obtained molecular-based phylogenetic reconstructions. Intergeneric relationships within Hyalinoeciinae were not resolved. Two strongly supported monophyletic groups of genera were recovered within Onuphinae: ((Onuphis, Aponuphis), Diopatra, Paradiopatra) and (Hirsutonuphis, (Paxtonia, (Kinbergonuphis, Mooreonuphis))). A previously accepted hypothesis on the subdivision of Onuphinae into the Onuphis group of genera and the Diopatra group of genera was largely rejected.