Oil and gas platforms as artificial substrates for epibenthic North Sea fauna: Effects of location and depth

Offshore oil and gas platforms, shipwrecks and wind farms are known to act as artificial reefs, attracting a broad range of marine species such as algae, invertebrate species and fish. Using Remotely Operated Vehicle (ROV) videos made for technical inspection of eight Dutch and nine Danish oil and gas platforms, we characterize the abundance and diversity of invertebrates and fish species found on or around these artificial hard substrates. Dutch platforms located in the southern part of the North Sea were at depths ranging from 26 to 46 meters, whereas Danish platforms located about 400 km further north were deeper (40 – 66 m). A total of 38 taxa were identified. The most common species were Mytilus edulis (Mollusca), Metridium senile (Cnidaria) and Asterias rubens (Echinodermata). One non-indigenous species was identified: Mnemiopsis leidyi (Ctenophora). A significant clustering of species communities was found based on geographical location: a southern cluster close to the Dutch shoreline and a northern cluster near Denmark (p=0.01). Species diversity was not significantly different between geographical clusters; however, average Braun-Blanquet abundance was significantly higher on in the northern cluster (p<0.05). Invertebrate and fish communities did not change significantly with depth. However, depth zone was a significant clustering factor (p=0.01): communities closer to the seafloor (maximum depth minus 5 m) were characterized by higher species diversity and species richness compared to communities found closer to the surface (<10 m). Future research should focus on the potential role of habitat complexity, substrate orientation and type, and inter-specific relations in explaining the different communities on offshore platforms.