Predicting sea pen (Pennatulacea) distribution on the UK continental shelf: evidence of range modification by benthic trawling

Abstract

Sea pen communities are United Nations General Assembly-designated Vulnerable Marine Ecosystems which occur worldwide in soft-bottom sediments where trawling often occurs. However, the ability of marine managers to assess, monitor and mitigate impacts to sea pens at national scales has been constrained by a limited understanding of their environmental requirements, geographical distribution and responses to trawling. In this study, we used random forest species distribution modelling (SDM) to predict the distribution of suitable habitat for 3 sea pen species (tall sea pen Funiculina quadrangularis, slender sea pen Virgularia mirabilis and phosphorescent sea pen Pennatula phosphorea) on the UK continental shelf, exploring the results relative to the distribution of fishing activity. Occurrence of all 3 species corresponded to areas of low current and wave velocity, where suspended matter in the water column was also low. However, for F. quadrangularis, the largest species, the models indicated substantially different drivers of distribution between the Greater North Sea and Celtic Seas ICES Ecoregions. This disparity appears to reflect modification to the range and realised niche of this species in the Greater North Sea, due to trawling impacts. P. phosphorea and V. mirabilis appear to be more resilient to trawling, with no clear negative relationships observed. Our findings illustrate the value of broadscale qualitative comparisons between SDMs and human activity data for insights on pressure-state relationships. When combined with robust distribution maps, this improved understanding of vulnerability will enable marine managers to make ecologically sound, defensible decisions and deliver tangible conservation outcomes for sea pen communities.