Megafaunal bioturbation in organically enriched Scottish sea lochs  <B>Megafaunal bioturbation in organically enriched Scottish sea lochs</B><P><B>Lois A. Nickell</B><SUP>1</SUP><B>, David J. Hughes</B><SUP>1</SUP> <B>& R. James A. Atkinson</B><SUP>2</SUP><P> 1. <I>Dunstaffnage Marine Laboratory, PO Box 3, Oban, Argyll PA34 4AD, UK</I><BR> 2. <I>University Marine Biological Station, Millport, Isle of Cumbrae KA28 OEG, UK</I><B><P> Abstract</B><BR> Burrowing megafauna have long been recognized as powerful bioturbators in the marine environment, but the contributions of different species to rates of turnover of both particles and fluids are dependent upon the burrowing behaviour and trophic mode of each. These factors can in turn be influenced by the environmental conditions experienced by individual animals, such as sediment stability and organic carbon levels. In Loch Sween, a shallow sea loch on the west coast of Scotland, three thalassinidean shrimps, <I>Callianassa subterranea </I>(Montagu), <I>Jaxea nocturna</I> Nardo<I> </I>and <I>Upogebia stellata</I> (Montagu), and an echiuran worm, <I>Maxmuelleria lankesteri</I> (Herdman) were identified as part of the megafaunal community. Mechanisms of bioturbation by these species were examined through a combination of field and laboratory studies. Resin casting was used to elucidate burrow morphology, whilst burrowing behaviour and feeding modes were determined by direct observation and through the use of video techniques. Quantitative measurements of particulate and fluid movement are given for selected species and related to population density in the field in order to assess the contribution of each to bioturbation rates. Preliminary bioturbation data are also presented for <I>Thalassema thalassemum</I> (Pallas) from the Firth of Clyde. Effects of bioturbation by each of the five species are contrasted and the influence of sedimentary organic carbon upon bioturbatory activity is discussed.<I><P> Keywords</I>: Thalassinidea, Echiura, <I>Callianassa</I>, <I>Jaxea</I>, <I>Upogebia</I>, <I>Maxmuelleria</I>, <I>Thalassema</I>, megafauna, burrows, bioturbation, sea loch.<P>