Marine communities of North Sea offshore platforms, and the use of stable isotopes to explore artificial reef food webs

Abstract

Stable isotope methods offer a powerful means of investigating trophic interactions, allowing assessment of the relative importance of multiple nutrient sources to biological assemblages, as well as estimation of the trophic positions of consumers. Differences in the isotope ratios of consumers between habitats can thus indicate differences in the structures of food webs, or the contributions of different food sources to those food webs. Isotope methods were used to compare the food web of an artificial reef located off the south coast of England with that of a nearby natural reef system, revealing a similarly complex food web, with similar trophic structure, and similar inputs from the available food sources. Isotope methods should be incorporated into more artificial reef studies, where they have been seldom applied. Offshore oil and gas platforms in the North Sea are artificial reefs, hosting substantial assemblages of sessile invertebrates and other associated fauna, and attracting large numbers of fish and motile invertebrates. Structural survey footage provided by the oil and gas industry allowed the investigation of the marine life associated with several of these structures, of varied ages and in various locations in the North Sea. At least thirty‐six taxa of motile invertebrates and fish were observed in association with the structures, most of which were present on all platforms surveyed. While most reef‐associated fish were observed around the base of the larger platforms, many thousands of fish were also observed in the water column around these structures at other depths. A small number of sessile taxa dominated the fouling assemblages, in places achieving total coverage of the available surfaces. Fouling composition changed with depth, but this pattern was not identical on all platforms. Platform age and location both affected the fouling assemblages present, but these two factors did not fully explain all the variation.