A LABORATORY ASSESSMENT OF THE SURVIVAL AND VERTICAL MOVEMENT OF 2 EPIBENTHIC GASTROPOD SPECIES, HYDROBIA-ULVAE (PENNANT) AND LITTORINA-LITTOREA (LINNAEUS), AFTER BURIAL IN SEDIMENT

Physical disturbance may result in the burial of the epibenthic fauna in sediment. The patches thus created undergo a 'recovery' which may i nclude the buried fauna migrating through the sediment to regain their original position in the sediment. A series of laboratory experiments were carried out to investigate the effects of prolonged burial on tw o epibenthic gastropod species, Hydrobia ulvae and Littorina littorea, under various sediment temperature regimes. Their ability to regain t he sediment surface under simulated winter (i.e. 7.5 degrees C) and su mmer (i.e. 20.3 degrees C) temperature conditions was studied in relat ion to the depth and the duration of burial. The effects of sediment s ilt and water content was also examined in a separate experiment. The proportion of H. ulvae surviving burial in natural sediment to 5 cm de pth decreased with increasing duration of burial and sediment temperat ure. Burial to 5 cm was fatal to L. littorea within 24 h at all the te mperatures examined. In sediment mixtures which had, by dint of large interstitial spaces, a good supply of oxygen or which were very fluid (i.e. 'high silt-high water' sediment) a large proportion of H. ulvae and L. littorea regained the surface within 1 day of burial. No indivi duals of either species regained the surface in sediment mixtures with high silt and low water contents, this included the unaltered natural sediment treatment. In all cases, the depth of burial significantly r educed the surface regaining ability of L. littorea while it had no ef fect on H. ulvae. The survival and the escape behaviour of buried H. u lvae and L. littorea is discussed in relation to their respiratory met abolism and the oxygen stress in the sediment. The potential contribut ion of the buried fauna to the recovery of soft-bottom patches is asse ssed. (C) 1998 Elsevier Science B.V.