Publication Abstract

Chronic bottom trawling alters the functional composition of benthic invertebrate communities on a sea basin scale

H.M. Tillin, J.G. Hiddink, M.J. Kaiser and S. Jennings

Bottom trawling causes widespread physical disturbance of sediments in shallow-shelf seas and affects benthic communities by  removing target and non-target species and  altering habitats. One aspiration of the ecosystem approach to management is to conserve function as well as biodiversity, but trawling impacts on benthic community function need to be understood before they can be managed. The effects of chronic trawling disturbance on the functional composition of epifaunal benthic invertebrate communities  were investigated at 6- 13 sites in four contrasting regions  of the North Sea. Each site was subject to known levels of trawling disturbance. This was the first replicated study of the effects of trawling on the functional structure of benthic communities at the scale of the fishery. Information on the life history  and ecological functional traits of the taxa sampled was translated into fuzzy coding and used to analyse the relationship between life history and functional roles within the ecosystem. Multivariate analyses were used to examine changes in the distribution of traits over gradients of trawling intensity. Changes in the functional structure of the community due to the effects of long-term trawling were identified in  three of the four areas sampled. Filter-feeding, attached habitat-forming and larger animals were more abundant in lightly trawled areas, while areas with higher levels of trawling were characterised by higher biomass of mobile animals like infaunal and scavenging invertebrates. Univariate analysis of selected traits confirmed the patterns observed in multivariate analysis.  These results demonstrate that bottom trawling can lead to shifts in the functional composition of benthic communities,  with likely effects the functioning of coastal sea ecosystems.

Reference:

H.M. Tillin, J.G. Hiddink, M.J. Kaiser and S. Jennings (2006) Chronic bottom trawling alters the functional composition of benthic invertebrate communities on a sea basin scale. Marine Ecology Progress Series, 318: 31-45