Palaeoecology of tube-dwelling polychaetes on a Late Cretaceous rocky shore, Ivö Klack (SkÃ¥ne, southern Sweden)

The tube-dwelling polychaete fauna from a late early Campanian rocky shore at Ivö Klack, southern Sweden, comprises 10 genera and 17 species, plus eight unidentified taxa. Spirorbins predominated on the shore and are considered opportunistic forms, well adapted to a wide range of environmental conditions. Factors controlling the settlement of polychaete larvae on different kinds of hard substrate are water energy, competition for space, and substrate size and stability. Four different kinds of hard substrate, a large gneiss boulder, an oyster valve, a pectinid valve, and a bone fragment are mapped in order to document species composition, density, orientation and distribution of encrusting serpulids and sabellids. The location of tubes appears to be important because different species chose different positions on different substrates. Orientation of tube apertures, however, is random on all kinds of substrate probably reflecting that food was not a limiting factor. Very large serpulids were confined to a life encrusting boulders, which provided the only substrate which was sufficiently large and stable. Smaller species encrusted all kinds of substrate but were dependent on its stability and on the surrounding environment. The high density of tube-dwelling polychaetes which inhabited the rocky shore makes it possible to obtain an insight into settlement strategies of Late Cretaceous polychaetes.