The mollusc fauna along a depth transect in the Faroe Shetland Channel: Is there a relationship with internal waves?

Abstract

From boxcore and dredge samples taken along a depth transect across the Faroe Shetland Channel (FSC) in 1997 and 1999, molluscs were sorted and identified. On the basis of their numerical abundance, the stations could be clustered into three groups, reflecting the depth extension of the main water masses in the FSC. Between 400 and 500 m depth, both the number of taxa per sample and the number of specimens, were highest. Bivalves were mainly caught by the boxcorer and the dredge was best suited to collect the epifaunal gastropods. According to the literature, at mid-slope depths, resuspension is increased by the action of internal waves, which leads to the development of intermediate nepheloid layers. This increased concentration of suspended matter may serve as a food source of low quality. Likewise the low amounts of suspended matter with a relatively high quality of particulate organic matter, such as from ∼400 and ∼700 m may act similarly and explain the relative high abundance of filter feeders at these depths. However, in the various multivariate analyses we could not distinguish the fauna from these depths from that collected from other sites. We observed, however, a pattern in the depth distribution of feeding guilds across the slope of the FSC. Deposit feeders demonstrated a trend of decreasing numbers with depth. Filter-feeding taxa were found to have peaks at depths of approximately 350 m, between 500 and 600 m and between 700 and 800 m. This observation supports the idea that the fauna at the deep sites reflects the locally high cross-slope currents and the subsequent increased amounts or availability of food with a better quality, which seems to be related to resuspension events.

Keywords:

• Community analyses
• Faroe Shetland Channel
• hydrography
• internal waves
• molluscs

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

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

Acknowledgments

This study has been made possible by NWO grant 589.12. The crew of RV Pelagia is thanked for their assistance in the collection of samples and Dr L. R. M. Maas is thanked for his help in understanding the basics of internal wave dynamics. Anonymous reviewer 2 is especially thanked for all suggestions that significantly improved this manuscript.

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