Bottom trawling can change food availability for benthivorous demersal species by (i) changing benthic prey composition through physical seabed impacts and (ii) by removing overall benthic consumer biomass increasing the net availability of benthic prey for remaining individuals. Thus trawling may both negatively and positively influence the quantity and quality of food available. Using δ 13C and δ 15N we investigated potential diet changes of three commercially exploited species across trawling gradients in the Kattegat (plaice, dab and Norway lobster (Nephrops)) and the Irish Sea (Nephrops). In the Kattegat, trawling affected primarily the biomass of benthic consumers, lowering competition. Nephrops showed significant positive relationships for δ 13C and a domed relationship for δ 15N with trawling. In the Irish Sea, intense trawling had a negative effect on benthic prey. δ 13C and δ 15N thus showed the inverse relationships to those observed in the Kattegat. Plaice from the Kattegat, showed a significant relationship with trawling intensity for δ 13C, but not for δ 15N. No relationship was found for dab. Changes of δ 13C and δ 15N correlated with changes in condition of species. The results show that the removal of demersal competitors and benthos by trawling can change the diets of commercial species, ultimately affecting their body condition.

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Echiura (commonly called spoon worms) are derived annelids that have an unsegmented sausage-shaped body with a highly extensible anterior end (i.e. a proboscis). Echiura currently contains two superfamilies: Echiurioidea (with Echiuridae, Urechidae and Thalassematidae) and Bonellioidea (with Bonelliidae, and Ikedidae). Ikedidae contains only Ikeda, which is distinctive in having a huge trunk, a highly elongate proboscis with stripes or dots, and numerous gonoducts. A recent molecular phylogeny of Echiura recovered Ikedidae as the sister group to Bonelliidae. However, due to relatively low support values for the monophyly of Bonelliidae, this relationship remains problematic. In this study, we reinvestigated the relationship of Bonelliidae and Ikedidae using an expanded dataset with more taxa and genes. In contrast to the previous results, our analyses strongly support that Ikeda is nested within Bonelliidae due to the placement of Maxmuelleria. On the basis of this result, we synonymise Ikedidae with Bonelliidae and transfer Ikeda to the latter, the diagnosis of which is amended. In addition, we synonymise Urechidae with its sister group Echiuridae because they share the synapomorphy of having anal chaetae rings. Furthermore, considering that recent phylogenetic studies have consistently recovered Echiura as the sister group to Capitelliidae within Annelida, we drop the rank of the echiuran clade to family-level and propose a revised classification: Thalassematidae with two subfamilies, Thalassematinae (with two tribes Echiurini and Thalassematini) and Bonelliinae. In addition, we identified a sample collected from the deep sea (~1820 m) of Monterey Bay, California, based on its molecular data. This terminal unexpectedly formed the sister group to the eight genera of Thalassematini, most members of which are inhabitants of littoral zones.