Quantitative analysis of a deep-water bryozoan collection from the Hebridean continental slope

Bryozoans were collected from nine stations between 369 and 1278m depth on the Hebridean continental slope north-west of Lewis. The 21 species recorded from 1544 colonies included three species new to the British fauna. The bryozoan fauna, growing on pebbles, cobbles and small boulders, was dominated by species with encrusting, spot or ribbon-like colony morphologies. The few erect species were rare. Colony density on available rock substrata declined from 569 to 855 m, but was high at 1278 m, where the nodular species Tubicellepora boreale occurred on pebbles as small as I cm diameter. Cyclostomates made up > 90% of the colonies in the shallowest sample and were present in lower numbers to 855 m. None were recorded at 1278 m. In the 569-855 m depth range, diversity and evenness were lowest at 569 m but relatively constant at the other stations. A species accumulation curve suggests that the 20 species recorded is a good estimate of the total fauna in this depth range.