Aggregations of the tube-building worms Lanice conchilega and Diopatra cuprea were studied on soft-sediment shores on the Isle of Anglesey, UK, and within the Barrier Island system of Wachapreague, Virginia, USA, respectively, with regards to their influence on the composition of the associated infauna! communities and sediment profiles. Species abundance, richness and diversity were all positively associated with the presence of tubes, however, no significant differences were found between the percentage of grain size fractions or organic
content of sediments inside and outside of tube patches. The abundance of small bivalves was higher inside tube aggregations, at both the UK and USA sites. A series of laboratory and tank experiments were carried out to examine potential mechanisms responsible for this pattern. These were identified as: 1) active habitat selection by the bivalves, 2) higher retention of clams inside tube patches in response to changes in water flow, 3) a refuge from predation within tube areas, 4) a combination of all or any two of mechanisms 1-3. The results of these studies indicate that tube-worms offer some refuge from crab predation by interfering with foraging behaviour, but that infauna! polychaete predators are not inhibited in such a way, and their levels of predation can actually be higher amongst tubes. No evidence was found to support the theory of active habitat selection by small bivalves, but their burrowing behaviour allows them some protection from being washed out of areas where sediments are being
eroded. In natural flow conditions the chances of being eroded and transported as bedload or suspended particles are less in patches of tubes where sediments may be more stable, but the exact nature of the tubes' impact is influenced by their size and distribution on the shore.
An opportunistic study was conducted to document changes in the infaunal community composition of a sandflat in the Barrier Island System of Wachapreague after Hurricane Isobel hit the Eastern seaboard of North America on 18 September 2003. An immediate effect of Isobel was a doubling in the number of species, a significant increase in invertebrate species diversity and a rise in opportunistic species and deposit feeders. Changes in the benthic infauna also took place over the subsequent 18 months which suggested a potentially positive medium-term effect of this hurricane perturbation. However, this study highlights potential problems in interpreting post-perturbation data when insufficient pre-perturbation data exist and when there is a lack of information pertaining to the relevant physical attributes of the sampled area.