Tube worms promote community change

Dense lawns of tube worms modify their immediate environment, They alter sediment properties, offer refuge from predation and provide a settlement surface for larvae and small organisms. The terebellid polychaete Lanice conchilega is among the tube dwellers that, when present at high densities, alter the community structure of other benthic fauna. However, L. conchilega often occurs individually or at low densities over large areas, and it is not known whether single tubes also affect the surrounding fauna. In this study a low density population of L. conchilega (15.7 +/- 15.6 m(-2)) was investigated on an exposed beach in South Wales, UK, from May 1998 to April 1999. Effects of single tubes and small groups of 2 to 5 tubes on the benthic community were examined over 1 yr. The relationship between L, conchilega and an associated amphipod (Urothoe poseidonis) was studied more closely in the field and the laboratory. Of a total of 56 species, 27 were found exclusively in samples with L. conchilega tubes. In comparison with tube-free samples, species richness and abundance of individuals was significantly higher in samples containing L. conchilega tubes. The community structure differed significantly between samples containing groups of tubes and tube-free samples in 10 out of 11 cases and in 9 of 11 cases for samples with 1 tube compared to samples with no tubes. Throughout the year, the polychaete Eumida sanguinea and the haustoriid amphipod U. poseidonis benefited from the presence of L. conchilega. E. sanguinea lives among the fringe filaments of the tube top, and U. poseidonis inhabits areas deep in the sediment in close vicinity to the tube. Laboratory experiments indicated that, unlike other haustoriids, the amphipod is not prone to benthopelagic migration but remains in the sediment for long periods of time and may benefit from an improved oxygen supply arising from L. conchilega's activity inside the tube. It is concluded that not only groups of tubes, but also single polychaete tubes bioengineer their environment.