Microplastic contamination in brown shrimp (Crangon crangon, Linnaeus 1758) from coastal waters of the Southern North Sea and Channel area.

In Limfjorden, Denmark, an extensive mussel fishery exploits the wild stocks of Mytilus edulis with annual landings of 80,000–100,000 t of mussels. During the last 10 years the impact of mussel dredging on the ecosystem has been studied, including the effect of resuspension of sediment and nutrients and the impoverishment of in- and epi-fauna assemblages. Furthermore, dredging changes the physical structure and complexity of the seabed which affects mussel growth and interactions among zoobenthic species. The blue mussel constitutes the dominant fraction of the zoobenthic suspension feeders, and is important for the transport of material and energy from the pelagic to benthic systems and the control of phytoplankton biomass. In order to evaluate the impact on clearance capacity of a reduction in mussel densities due to mussel dredging, mussel filtration activity measured in situ has been related to the mixing of the water column and the amount of near-bed phytoplankton. Fishery practice for mussel dredging in Limfjorden is discussed in relation to its known impact on the ecosystem and the ecological role of the mussels, and modifications towards an ecosystem management approach and a more sustainable fishery are suggested. The suggested modifications include: a fishery practice where the mussel beds are thinned out when the mussels have attained good quality, and a transplantation practice of mussels from areas with a high mortality to areas with a high growth rate. Both practices intensify the production in a certain area, leaving other areas open for alternative production or for permanent closure for the benefit of the benthic flora and fauna. In addition, other shellfish species represent interesting new resources for fishing or aquaculture. Habitat restoration, such as the relaying of mussel shells from the mussel industry, is another important management tool that should be included in an ecosystem management approach of the mussel fishery.

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Evaluation of the Danish mussel fishery: suggestions for an ecosystem management approach

A large scale BACI experiment to test the effects of prawn trawling on seabed biota in a closed area of the Great Barrier Reef Marine Park, Australia

This study was part-funded by the EU FP 7 project BENTHIS (grant no. 312088). It does not necessarily reflect the views of the European Commission and does not anticipate the Commission’s future policy in this area. We are grateful for the logistic support of VLIZ, the fishermen of TX43 and TX29 and crew members of RV ISIS and RV Simon Stevin during the sea trials and NIOZ for the use of their box corer. ADR and LRT were partly supported by the project “Impact assessment pulsvisserij”. We are indebted to the skippers and Eddy Buyvoets for drawing the net plans of the trawls. We thank John Aldridge for his insights in sediment transport in relation to natural dynamics; Bavo De Witte for conducting the particle size analysis; Daniel Benden for assisting SPI analyses; Miriam Levenson for English-language editing and Julie Bremner and Stefan Bolam for their critical review. We also wish to thank 3 anonymous reviewers for their constructive comments on earlier drafts of this manuscript.

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Comparison of mechanical disturbance in soft sediments due to tickler-chain SumWing trawl vs. electro-fitted PulseWing trawl

http://laurentgodetpagepersonnelle.a.l.f.unblog.fr/files/2009/05/toupointal2008.pdf

Does Manila clam cultivation affect habitats of the engineer species Lanice conchilega (Pallas, 1766)?

The short-term effect of mussel dredging in a brackish Danish sound was studied. A commercial dredging track was identified and an analysis of the species composition inside the track and at an adjacent control area showed that dredging changed the community structure by reducing the density of polychaetes. In order to investigate the extent and the duration of the dredging impact experimental dredging was conducted. The experimental dredging removed 50% of the mussels in two dredged areas. Immediately after dredging, a significantly lower number of species was measured inside the mussel beds in dredged areas compared to control and boundary areas. This effect lasted for at least 40 days. The analysis of the species composition showed that the dredged area had a significantly lower density, particularly of polychaetes compared to the boundary area. An increased number of species was recorded outside the mussel beds just after dredging, but this effect lasted for less than 7 days. After dredging, brown shrimps, C. crangon invaded the dredged areas. This species is an important predator of smaller invertebrates, and it is suspected that it was feeding on small vulnerable polychaetes exposed at the sediment surface after dredging. The dredging process was observed to form 2–5-cm deep furrows in the seabed, but the sediment texture and the organic content of the sediment was not affected. The biomass accumulation of individual blue mussels was significantly lower in the dredged area compared to the boundary area. This indicates that the disturbance of the mussel bed structure reduced growth and that the lowering of intraspecific food competition caused by a reduced density of mussels did not increase the accumulation of biomass in the mussels which remained in the dredged area.

M.L. Christiansen

Papers

Short-term impact of blue mussel dredging (Mytilus edulis L.) on a benthic community