Effects of the tube-building polychaete Lanice conchilega (Pallas) on benthic macrofauna and nematodes in an intertidal sandflat

Biogenic habitat structures play a major role for distribution pattems of benthic fauna. Tube-dwellingpolychaetes provide one of the main features in the otherwise relatively low structured sandy intertidal. Theaim of this study was to investigate the effect of the tube-dwel[ing sand-mason Lanice conchilega on macrofaunaand nematodes in an intertidal sandflat in the Wadden Sea area off the German coast. Field studiesand experiments were carried out on the associated macrobenthic fauna of natural L. concbilega aggregatesand of artificial tubes. Furthermore, the distribution of nematode species at increasing distances alongtransects arising from individual L. conchilega tubes, was investigated.Natural as well as artificial tubes had positive effects on numbers of macrofaunal species and individuals.Yet, juvenile Mya arenaria were the only species appearing in higher numbers in both L. conchilegaaggregates and artificial tube fields. They used the tube structure to attach themselves with their byssusthreads. The polychaete Malmgreniella lunulata only occurred in natural L. conchilega aggregates and wasoften found inside the polychaetes' tubes. It is possibly a commensal associated to L. conchilega. In artificialtube fields, opportunistic spionids and Capitella capitata settled in higher numbers. This might be due tocolonisation of sediment accumulating in the tube fields, utilisation of the tubes as an attachment suffaceor refuge from predation. However, two predatory polychaetes, Eteone longa and Nereis diversicolor, werealso found in higher abundance in natural or artificial tube fields.Nematode abundances were considerably higher next to individual L. conchilega tubes ata distance of0.5 cm. This distribution was mainly caused by a group of threadlike species with a thin cuticle, which arethought to be adapted to epidermal uptake of dissolved organic matter.It is suggested that there might be a linkage between predatory polychaetes and the distribution patternfound for nematodes around the tubes of L. conchilega