Temporal, spatial and substrate-dependent variations of Danish hard-bottom macrofauna

Abstract.

Detailed knowledge of the Danish hard-bottom fauna is at present limited because of sampling problems. In this study, two different sampling units were used to yield quantitative results of the fauna on two stone reefs in Kattegat: natural holdfasts of Laminaria digitata and plastic pan-scourers imitating the holdfasts. On the two reefs a total of 135 taxa (102 species) were identified, representing 12 phyla. One species, the bryozoan Cribrilina cryptooecium, has not previously been recorded in Denmark. The fauna was characterized by a mixture of a large number of rare species, yielding high values on the Shannon-Wiener diversity index, and it showed a high degree of spatial and temporal variation. ANOSIM analyses showed a significant difference in species compositions between both sampling location, time and substrate type. The plastic pan-scourers proved to be a valuable substrate for quantitative investigations of the fauna. In contrast, the Laminaria holdfasts were too small and variable to be suitable for such studies.