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

Abstract

Bottom trawling causes widespread physical disturbance of sediments in seas and oceans 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. Here we present the large scale and long term impact of chronic trawling on the functional composition of benthic invertebrate communities using a comprehensive set of functional traits. The effects of chronic trawling disturbance on the functional composition of faunal benthic invertebrate communities, as sampled with a small beam trawl, were investigated at 6 to 13 sites in each of 4 contrasting regions of the North Sea. Each site was subject to known levels of trawling disturbance. Information on the life history and ecological function 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 3 of the 4 areas sampled. Filter-feeding, attached and larger animals were relatively more abundant in lightly trawled areas, while areas with higher levels of trawling were characterised by a higher relative biomass of mobile animals and infaunal and scavenging invertebrates. Univariate analysis of selected traits confirmed the patterns observed in multivariate analysis. These results demonstrate that chronic bottom trawling can lead to large scale shifts in the functional composition of benthic communities, with likely effects on the functioning of coastal ecosystems.

Mediation of nitrogen by post-disturbance shelf communities experiencing organic matter enrichment

“…Given the findings elsewhere that report higher mortality of suspension feeders at locations that are subject to fishing activity (e.g. Tillin et al 2006;van Denderen et al 2015), it is surprising that we found a higher ratio of suspension to deposit feeders in sand communities that experienced a higher frequency of chronic fishing. However, a clear trend that emerges from previous studies is that the degree of natural disturbance in which a community develops determines the degree to which it is affected by bottom fishing (Kaiser and Spencer 1996;Hiddink et al 2006;Sciberras et al 2013).…”

Marine long-term biodiversity assessment suggests loss of rare species in the Skagerrak and Kattegat region

“…Over the past decades, the impacts of major anthropogenic pressures on coastal and benthic marine biodiversity have been studied intensely. Here, especially field assessments investigated the negative effects arising from bottom trawling (Jennings and Kaiser 1998;Kaiser et al 2006;Tillin et al 2006;Worm et al 2006;Olsgard et al 2008), coastal nutrient loading (Rosenberg and Nilsson 2005;Quijon et al 2008), and climate change (Norderhaug et al 2015). However, since many of these drivers act on the ecosystems simultaneously and over long periods of time Halpern et al 2008), it is difficult to infer cumulative impacts from such assessments (Moksnes et al 2008;Robinson and Frid 2008).…”

Catch me in winter! Seasonal variation in air temperature severely enhances physiological stress and mortality of species subjected to sorting operations and discarded during annual fishing activities

“…The overexploitation of marine resources has been recognized to cause drastic impairments of the food web structure and the consequent alteration of the productivity (Pauly & Christensen, 1995). Besides, fishing has dramatic effects on the non-target species, and the different techniques employed have been proved to cause a wide range of alterations to biodiversity and community structure (Jennings et al, 2001;Queirós et al, 2006;Tillin et al, 2006). These aspects are reflected, for example, by the pronounced imbalance in terms of damage, physiological stress, and survival among the species subjected to trawling activities.…”