Short cruise report of ALKOR journey 383 [AL383]

18.10. - 25.10.201

REMOTS sediment profiles around an exploratory drilling rig in the southern North Sea

During the Bremerhaven Workshop in the southern North Sea, REMOTS sediment profile lmages (SPI) were recorded in order to supplement the benthic component of the workshop and other environmentally relevant parameters investigated along a spatial gradient at an abandoned exploratory drilling site off the Dutch coast. The sampling stations were in accordance with the other studies, but due to bad weather conditions only a small proportion of the intended samples were taken. The profile data were supplemented by video recordings of the sediment surface features taken on a second cruise. The results presented here have important implications for the interpretation of other benthic and sediment samples, and may help to interpret some enigmat~cw orkshop data

Experimental evidence of damage to benthos by bottom trawling with special reference to Arctica islandica

In Kiel Bay (Western Bahic), benthos samples were taken at 20 m water depth using rectangular botanical dredges fixed to the otter boards of an 80 ft Sonderborg standard trawl to document possible effects of trawl fishery on the benthic fauna. Thin-shelled bivalves like Syndosmya (Abra) alba, Mya spp. and Macoma calcarea, as well as the starfish Asterias rubens were damaged by otter-boards to a high extent. Thick-shelled bivalves such as Astarte borealis and Corbula gibba, however, seem to be more resistant to mechanical stress of bottom-trawl fishery. Musculus niger, an epibenthic species, is probably only resuspended and dislocated. The rate of damage to Arctica islandica, Macoma baltica and Macoma calcarea is related to their body size. Large specimens are more affected than smaller specimens due to the unfavourable relationship between shell surface and shell thickness. The size distribution of Arctica islandica in heavily trawled areas of Kiel Bay shows reductions in the upper size class in these areas

Comparison of multivariate patterns: different taxonomic levels in macrofaunal analysis vs.sediment profiling imagery (SPI)

The multivariate patterns resulting from analyses of macrobenthic abundance data at different taxonomic levels are compared to the pattern derived from various measurements obtained through sediment profiling imagery (SPI). A time-series data set from 1 station in Kiel Bay (Western Baltic) at 22 m depth including macrobenthic and SPI replicates covering 8 yr (1989 to 1996) was analyzed by means of multidimensional scaling (MDS) ordination. The macrobenthos data showed similar patterns, and there was little information loss, with decreasing taxonomic resolution from species to phylum level. The multivariate pattern in the SPI data was not significantly correlated to any of the macrofaunal patterns. However, macrofaunal and SPI patterns seemed to be complementary since they emphasized different aspects of the long-term succession in the Southern Baltic Sea. While macrofaunal patterns were sensitive to anoxia events, changes of SPI-recorded seabed characteristics were primarily related to physical disturbances possibly due to variations in fishing intensity