Particle size selection and tube structure of the polychaete Owenia fusiformis

Agglutinated tubes of the polychaete Owenia fusiformis Delle Chiaje and their adjacent sediment were analyzed with respect to grain size, particle composition and tube structure to assess whether these parameters reflect a specific relationship between tube and adjacent sediment. Tubes and sediments were sampled southwest off Helgoland Island (southeastern North Sea) in water depth of 35–37 m. Particle selection was studied using settling velocity and component analysis. Both methods clearly showed that O. fusiformis actively selects coarse particles for tube building. The ability for size selection seems to be fully developed immediately after the transition from pelagic to benthic life, as considerable differences in the composition of tube and adjacent sediments occurred over the whole sampled sediment depth. In both tube and surface sediments quartz was the dominating component (>80%). In contrast, heavy minerals, the second frequent component of the surface sediments, were used less frequently for tube building. Biogenic components (e.g. shell material, echinoid fragments, foraminifera) occurring rarely in the sediment are nevertheless preferred as components for tube building. As underlying selection criteria a combination of size and the existence of at least one flattened surface that can be attached to the tube may be assumed.