Quantitative differences in the fauna of boreal mud associations

Summary

The fauna of a muddy area in the northern North Sea (the Fladen ground) is compared with that of a similar area in a Scottish west-coast sea loch (Loch Nevis). These areas were selected because certain similarities in environmental features and in fauna, coupled with their marked difference in biomass, make them particularly suitable for studies of the factors affecting benthic production.

For macrobenthos samples (from a grab) a coarse sieve with round holes of 1-3 mm diameter and a fine sieve with meshes of 0-5 mm side were used. Meiobenthos samples (from a corer) were sieved through a 0124 mm mesh and the total residue stained in rose bengal.

The Fladen ground, depth 140 m, had annual bottom temperatures between 6-31 and 8-22 C and salinities between 35-20 and 35-2.50. The deposit was mainly of coarse silt with abundant tests of small Foraminifera. The fauna is redescribed. The characteristic species was the foraminifer Saccammina sphaerica. By separating empty tests from living specimens it is shown that this species was not so abundant as had been thought. The main lamellibranch was Thyasira equalis, not T. flexuosa as recorded in previous work. Other important species were the polychaetes Paraonis gracilis, Myriochele heeri, Spiophanes kroyeri, Tharyx sp., Lumbrineris impatiens, and Nephthys incisa. The standing crop of macrobenthos was 6-42 g/m2 wet weight.