Ecology of bathyal polychaete fauna at an Arctic–Atlantic boundary (Faroe–Shetland Channel, North-east Atlantic)

Abstract

By reference to a series of 15 sampling stations spanning the West Shetland Slope (150–1000 m; Faroe–Shetland Channel, North-east Atlantic) we examined the potential environmental controls on the standing stock, diversity and composition of the polychaete fauna. In contrast to the majority of studied bathyal environments, the Faroe–Shetland Channel has a highly complex and dynamic hydrographic regime, particularly notable for extreme thermal variability at mid-slope depths (i.e. 7°C range at ca. 500 m). Contrary to general expectation, polychaete biomass increased (rather than decreased) with depth. Species diversity exhibited a parabolic pattern with depth, maximum diversity occurring at depths of 350–550 m, rather shallower than observed in other bathyal studies, and possibly linked with a maximum in habitat temperature range. Multivariate analyses of faunal composition suggested a separation of the sampling stations into a shallower and a deeper group, with temperature exerting a major control on polychaete species distributions. The decline in diversity below 600 m (i.e. the descending limb of the parabolic relationship) may be a result of historically limited immigration/recolonization of the thermally isolated Arctic deep-water basins that feed the cold-water flow through the Faroe–Shetland Channel. The bathymetric distribution of polychaetes and other benthos in this region appears to be intimately linked with the thermal regime, having a long-term impact (geological timescales) on the deep-water species pool and leading to local enhancement of diversity where cold- and warm-water masses meet and mix.

Keywords:

• Bathymetric distribution
• diversity
• Faroe–Shetland Channel
• macrobenthos
• North-east Atlantic
• polychaetes
• Scotland
• standing stock

Acknowledgments

The authors wish to thank the Atlantic Frontier Environmental Network (AFEN) for funding this study. AFEN comprises: AGIP (UK) Ltd, Amerada Hess Ltd, BG E&P Ltd, BP Amoco, Chevron UK Ltd, Conoco (UK) Ltd, Enterprise Oil plc, Marathon Oil UK Ltd, Phillips Petroleum Company UK Ltd, Shell UK Exploration and Production Ltd, Statoil Ltd, Texaco North Sea UK Company, TotalFina, Veba Oil and Gas UK Ltd, Department of Trade and Industry, Joint Nature Conservation Committee and the Scottish Executive – Environment and Rural Affairs Department. We would also like to thank the crew of the RRS Charles Darwin for their help in collecting the samples. This work was based on PhD studies of the lead author undertaken at the Scottish Association for Marine Science and the School of Ocean and Earth Sciences, University of Southampton.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Editorial responsibility: Tore Høisæter