Habitat point records from 1987 UMBSM Loch Sween burrowing megafauna survey

Fieldwork, using SCUBA techniques, was carried out in June and August 1987, and showed that the muddy sediments of the upper arms of Loch Sween, Argyll, Scotland, were extensively bioturbated by megafaunal species that produced semi-permanent burrows. These were mostly decapod crustaceans (e.g. the Norway lobster, Nethrops norvegicus, and several species of thalassinid), but also included a gobiid fish, Lesueurigobius friesii, and an echiurid worm, Maxmulleria lankesteri. Fifteen sites were examined in detail (two in Caol Scotnish, one in Loch a'Bhealaich, six in Achnamara Arm and six in Sailean Mhor) and an additional two areas extending from Caol Scotnish to Loch a'Bhealaich were surveyed in less detail. In each case, the megafaunal burrows (if present) were identified, described and burrow densities were noted. At four sites, burrow structure and identity was confirmed by using polyester resin to take burrow casts. The resultant casts are illustrated and described. Hand-operated Senckenberg box corers (See Bouma, 1969) were used to take sediment and faunal samples at ten sites (sites 1,2,3,4,7,10,13 and 14) and hand-operated circular core tubes were used at two sites to collect faunal samples (sites 8 and 9). Four sites were chosen for casting burrows (site 2, 3 , 5 and 7). A 'slurp gun' was used in an attempt to extract animals from burrows at site 2 and an air-lift suction sampler was used in an attempt to identify deep burrowers at site 3. A light beam trawl (1.5m beam, 15mm cod end mesh) was used to collect epifaunal samples by night in the region of site 7. Data on the granulometry, redox characteristics and organic content of the sediments were obtained for most sites, together with quantitative and qualitative information on macrofaunal occurrence and abundance. The sediments were mostly silty clay muds, but sandy muds and muddy sand substrata also occurred. The sediments were poorly oxygenated and contained large amounts of organic matter. The sediments in Caol Scotnish were strongly reduced and contained the largest amounts of organic material. No megafaunal burrowers occurred in the anoxic north basin sediments, but a few megafaunal burrowers occurred in the south basin, including the little known thalassinid, Jaxea nocturna. Unlike the relatively flat sediment plain of Caol Scotnish, the bottom topography elsewhere in Loch Sween consisted of mounds and valleys. Mounds could be 50 cm in height, but were usually smaller. These sediment features were generated by three species, the thalassinid crustaceans Jaxea nocturna and Callianassa subterranea and the echirurid Maxmulleria lankesteri. Although these species also occcurred in Caol Scotnish they did not form sediment mounds there and their densities were lower than elsewhere (Loch a'Bhealaich, Achnamara Arm, Sailen Mhor) where several other burrowing megafaunal species also occurred. The sediment macrofauna included species which thrive in eutrophic conditions and most of the polychaete species sampled were relatively motile forms. This latter observation suggested that megafaunal bioturbation may have been influencing the structure of the macrofaunal communities by preventing the more sedentary species from becoming established. Macrofaunal abundance and diversity appeared to be relatively low. A number of inter-specific faunal associations were noted and are discussed. Most of these involved the utilization of megafaunal burrows by species additional to the original burrowers.

Organization: Joint Nature Conservation Committee