Interactive processes in a Lanice conchilega (Annelida: Polychaeta) dominated intertidal community
An investigation was conducted into the factors influencing a soft-sediment intertidal benthic community dominated by the large tube building polychaete Lanice conchilega (Pallas, 1766). The environmental and biological characteristics of a mid-shore sampling site on a relatively sheltered sandflat were monitored over a two year period. A total of 115 taxa were recorded. Temporal variability in the community is discussed in relation to the sporadic occurrence of macroalgae, harsh winter conditions and physical disturbance to the sedimentary environment. Lanice conchilega had a significantly contagious distribution on the shore. The population was analysed using width measurements of both worms and tubes. Recruiting Lanice conchilega juveniles observed during the first year of the study were initially randomly distributed, but as these individuals developed the overall distribution of the population returned to being contagious. The presence of excess tubes towards the end of the sampling period indicated that individual Lanice conchilega were dying, being removed by predation or emigrating. Further sampling was designed to investigate the macrofauna and meiofauna in areas of sediment containing different densities ofLanice conchilega tubes. A consistently significant positive correlation existed between tube density and macrofaunal abundance, which was attributed to sediment-mediated interactions. At higher tube densities, an increase in the depth of sediment above the underlying clay equated to an increase in the volume of available infaunal space. In addition, Lanice conchilega-derived mucus and its associated microbes potentially enhanced levels of food resources available to deposit feeders. Species living at or near the sediment-water interface would also have been positively influenced by any sediment stabilisation in high tube density areas. Possible causes of a positive correlation observed between tube density and Exogone hebes abundance are discussed. No significant relationship existed between tube density and the abundance of macrofaunal juveniles, indicating that any inhibitory or facilitatory Lanice conchilega-juvenile interactions were either insignificant or acting in opposition to to produce an overall neutral effect. Details of the developmental morphology of several polychaete species are described. Meiofaunal abundance (in particular nematode and harpacticoid abundance) was consistently greater in samples taken from areas of high tube density. Potential mechanisms responsible for this relationship include the provision of habitat heterogeneity and areas of refuge by tubes, and the enhancement of sediment stability and food resources by mucus. Particle accumulation in high tube density areas also potentially influenced meiofaunal settlement and resettlement patterns.