Diversity, structure and interactions of encrusting lithophyllic macrofaunal assemblages from Belgica Bank, East Greenland

Abstract

Drop stones with lithophyllic macrofauna from Belgica Bank, Greenland Sea (79–81°N and 5–17°W) were collected during the Polarstern cruise in August 2000. The investigation focussed on species richness, diversity, abundance, and interactions of organisms colonizing rocks. On 101 stones collected by 10 dredges from nine sites, 113 taxa (58 genera, 38 families, 12 orders and 8 phyla) were recognized. Among the most abundant groups of organisms were foraminiferans, bryozoans and polychaetes, while the least abundant were anthozoans and ascidians. Abundance ranged from 1239 to 11,383 individuals m−2 of rock surface area. Bryozoans were the most species-rich group, while anthozoans and ascidians were represented by the least number of species. Colonization occurred at various topographical levels and was classified into two categories. Stones were classified as primary space and were colonized by erect membranous, erect flexible, erect rigid, and flat encrusting organisms. The second level of colonization by epibionts occurred on erect forms of organisms (e.g. erect bryozoans) and was classified as a secondary space. Species composition and abundance between faunal assemblages of primary and secondary space differed greatly. Colonization occurred only on the top of stones and was considered a special adaptation to avoid burial by sedimentation and to enhance food supply. Only 3% of recruits were involved in any competitive interactions. Competition was considered to be of minor importance in structuring lithophyllic assemblages.