Environmental Management
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Item The restoration of mud flats invaded by common cord-grass (Spartina anglica, CE Hubbard) using mechanical disturbance and its effects on the macrobenthic fauna(Aquatic Conservation: Marine and Freshwater Ecosystems, 1999) Frid, C.L.J.; Chandrasekera, L.W.H.U.; Davey, P.1. The growth of the common cord-grass, Spartina anglica, across many temperate coastlines has resulted in a reduction in the extent of tidal flats. Its colonization has reduced the abundance of macrobenthic fauna and hence has had a direct effect on the feeding of shorebirds. Although the use of chemical methods has proven successful in controlling Spartina swards on tidal flats, factors such as environmental and human health concerns have stimulated a search for alternative control methods. However, any such control method must not impact the macrobenthic fauna. 2. The effectiveness of a physical disruption to control Spartina swards on tidal flats was investigated in the saltmarsh at Lindisfarne NNR, UK. The sediment was disturbed by a light-weight tracked vehicle until the Spartina swards were dislodged and buried within the sediment. The post-disturbance dynamics of the infauna in the disturbed area was investigated 1, 12, 31, 92 and 384 days after the disturbance. 3. In spite of the drastic change brought about in the flora, there was no evidence that the infauna were impacted by the disturbance at any sampling time. Two possible mechanisms to explain the absence of changes in the abundance of the infauna are discussed with special reference to the unconsolidated nature of the sediment and the high mobility of the adult infauna. The abundance of Spartina swards in the disturbed area was lower than that in the undisturbed area. Physical disturbance to Spartina swards by the tracked vehicle seems to be an appropriate method for its control in tidal flats which obviates the need, with associated financial costs and environmental risks, of chemical control.Item Alaboratoryassessment of the survival and verticalmovement of twoepibenthicgastropodspecies, Hydrobia ulvae (Pennant) and Littorina littorea (Linnaeus), afterburial in sediment(Journal of Experimental Marine Biology and Ecology, 1998) Chandrasekera, L.W.H.U.; Frid, C.L.J.Physical disturbance may result in the burial of the epibenthic fauna in sediment. The patches thus created undergo a `recovery' which may include 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 twoepibenthicgastropodspecies, Hydrobia ulvae and Littorina littorea, under various sediment temperature regimes. Their ability to regain the sediment surface under simulated winter (i.e. 7.5�C) and summer (i.e. 20.3�C) temperature conditions was studied in relation to the depth and the duration of burial. The effects of sediment silt and water content was also examined in a separate experiment. The proportion of H. ulvae surviving burial in natural sediment to 5 cm depth decreased with increasing duration of burial and sediment temperature. Burial to 5 cm was fatal to L. littorea within 24 h at all the temperatures 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 individuals 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 reduced the surface regaining ability of L. littorea while it had no effect on H. ulvae. The survival and the escape behaviour of buried H. ulvae and L. littorea is discussed in relation to their respiratory metabolism and the oxygen stress in the sediment. The potential contribution of the buried fauna to the recovery of soft-bottom patches is assessed.Item Effects of human trampling on tidalflat infauna(Aquatic Conservation: Marine and Freshwater Ecosystems, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.1.?Human trampling has been shown to be detrimental to the survival of fauna of terrestrial habitats and on rocky coastal areas. However, its effects on saltmarsh benthic infauna were not known. 2.?The abundance of macro-benthic fauna at five locations on a transect across a footpath on the emergent marsh and on the tidalflat at Lindisfarne NNR were sampled during the summer 1994 and winter 1995. 3.?The abundances of dominant taxa increased in summer in the intensely trampled path on the unvegetated tidalflat leading to a change in the community structure. These changes were not apparent when the trampling intensity was lower in winter. 4.?The abundances of dominant taxa at a less intensively trampled site in the vegetated emergent marsh did not change in either season. 5.?The susceptibility of the saltmarsh infauna to human trampling depends on the intensity of trampling disturbance and on the nature of the habitat. The possible effects of human trampling on the macrofauna in these intertidal habitats are discussed with reference to coastal management.Item The effects of Relic fauna on initial patch colonisation in a British saltmarsh(Netherlands Journal of Aquatic Ecology, 1996) Chandrasekera, L.W.H.U.; Frid, C.L.J.When a disturbance impacts an area it rarely leads to a complete defaunation, some individuals survive forming a relic fauna. Relic fauna in azoic patches in an intertidal soft-bottom habitat were simulated by the separate introduction of individuals ofNereis diversicolor, Hydrobia ulvae andLittorina littorea into defaunated cores. These were exposed in the field for 24 hours and the effects of relics on colonisation were assessed separately for colonisation via the sediment surface and colonisation via the surface and laterally through the sediment. After 24 hours all the species in the ambient community were recorded from at least some experimental cores. Densities of the most abundant infaunal taxa,Corophium volutator, Enchytraeus buchholzi, Manayunkia aestuarina, Tubificoides benedeni and nematodes, varied between 1% and 279% of ambient. MDS ordinations showed significant differences in the fauna of experimental cores, a result of the lack of full colonisation by some species and the presence of other species at densities in excess of ambient. Comparisons (ANOSIM and ANOVA) of the fauna of the relic addition cores vs. no-addition cores showed an influence ofN. diversicolor on colonisation. However, this relic effect appeared to be masked by the high degree of variation in colonisation. Densities ofL. littorina andH. ulvae were not maintained in all of the experimental cores and there was no significant difference in the fauna of cores in which the treatments were maintained. It therefore seems that initial colonisation of patches in the emergent saltmarsh is controlled by the (i) supply of colonists and (ii) attraction to under-exploited organic matter and that any relic fauna exerts little influence on the early stages of the colonisation process.