Food web effects of human-made structures

The INSITE funded project entitled “Investigating food web effects due to human-made structures using COupled Spatial Modelling” (COSM) assessed the potential ecosystem effects of human-made structures in the North Sea, and forecasted what might happen to marine species communities if structures were to be removed through decommissioning^[1].

An Ecospace model was built for a published North Sea EwE model^[2] at 0.25 decimal degree resolution. Besides bathymetry and 5 natural habitat layers, proportional coverage of various classes of human-made submerged structures were brought in as non-natural habitats in the HFC model in addition to mean water column temperature. Species’ functional responses to the various types of man-made structures were determined through Generalized Additive Models (GAMs) analyses. The historical fishing effort for main fishing gears was also included.

Figure 1. – Effect of structure types on aggregated functional groups identified through statistical analyses of gridded survey data (significant relationships shown only). A positive (green bubble) effect indicates that the occurrence of the group is increased through the presence of structures, while negative effects (red bubbles) indicate the opposite. Bubble size is proportional to the change in probability of occurrence of the group in the region where the relevant structure type is present, thus independent of spatial coverage of the structures.

The model required a 10-year spin-up period, and the model ran for 40 years. The COSM study yielded interesting findings (Figure 1):

• Human-made structures affected local community compositions, which could disperse throughout the wider North Sea ecosystem;
• The removal of oil and gas platforms and pipelines may ultimately create losers (rays and sand eels) and winners (sharks, flatfish and roundfish);
• The presence of wrecks and wind turbines appeared to have a much greater impact than oil and gas infrastructure on rays, sharks, sand eels, flatfish and demersal roundfish;
• Importantly, all modeled effects of structures were minor compared to the potential effect of climate change (e.g., increase in temperature) or fisheries (increase in effort);
• Although the additional habitat provided by platforms and pipelines may be relatively small, they were assessed as important for some non-commercial species of conservation concern as refuges against natural variability.