Impact of an artificial structure on the benthic community composition in the southern North Sea: assessed by a morphological and molecular approach

Abstract

Man-made structures in the North Sea are known to act as artificial reefs by providing a habitat for sessile epifauna in a predominantly soft sediment environment. This epifauna is hypothesized to cast a so-called “shadow” over the soft sediment ecosystem by altering the nutrient composition in the overlying water column. In addition, the structure itself could alter currents and thereby influence the deposition and erosion of the sediments in the wake of the platform. This study aims to assess the long-term effects of a gas platform in the southern North Sea on the surrounding benthic community by both morphological and molecular identification of benthic species. The species composition and a set of abiotic factors of the sediment around a gas platform were assessed along four transects. Differences for the abiotic factors were found in the closer vicinity of the platform in the direction corresponding to the predominant currents. The number of benthic fauna families found in the molecular approach were on average three times higher than for the morphological approach. Both approaches showed that small differences occurred primarily due to changes in sedimentary organic matter content. Differences in species composition were more pronounced between transects rather than between distances from the platform.

A Molecular Approach to Explore the Background Benthic Fauna Around a Hydrothermal Vent and Their Larvae: Implications for Future Mining of Deep-Sea SMS Deposits

“…The sieve residue of the water samples served as starting material for further molecular analysis of the pelagic larvae samples. The molecular analysis and subsequent bioinformatics analysis followed the protocols as described in Klunder et al (2018) using the F04 (5 -GCTTGTCTCAAAGATTAAGCC-3 ) and R22mod (5 -CCTGCTGCCTTCCTTRGA-3 ) primer pair (Sinniger et al, 2016) except for the DNA extraction of the larvae samples. Here, the DNEASY PowerSoil TM kit (MoBio Inc.) was used instead of the Powermax Soil TM kit.…”

Haven or hell? A perspective on the ecology of offshore oil and gas platforms

“…Finally, the production of faeces (and pseudo faeces) by associated biota combined with the action of sediment microorganisms and meiofauna, cycle nutrients, and organic matter back to primary producers [73].…”

“…Fourthly, the upper parts of platforms introduce new intertidal zones which allow the settlement of intertidal biota, including macroalgae, in offshore locations [111,112]. Finally, the presence of the platforms physically alters localised water flow and the seafloor conditions, leading to local scouring or changes in sedimentation patterns [73]. For example, all platforms on the Californian continental slope are sited on soft seafloors, although in some instances (e.g., Platforms Hidalgo, Grace, A, B, and C) natural reefs exist within a few kilometres of the platform.…”

“…Depth zonation of organisms on platforms in the Southern North Sea was also found to influence benthic communities [26] that concluded that "topping" or "toppling" decommissioning strategies could eliminate communities that are unique to the upper zones. Klunder and colleagues [73] investigated the long-term effects of a gas platform in the southern North Sea on the surrounding benthic community and reported clear variation in the grain size in the environment surrounding the gas platform, where a higher percentage of silt was found in the residual current direction (i.e., in the "shadow" area of the structure), while coarser sediment was found close to the artificial structure. This grain size variation affected the number of benthic fauna families and species composition in the vicinity of the platform and in the direction corresponding to the predominant currents.…”