Microhabitat diversity of Svalbard Bryozoa

Bryozoans are one of the major macrofaunal groups of the high polar regions. Here we present data on the nature of bryozoan assemblages in the Svalbard Archipelago sampled over 6 years between 1997 and 2002. Samples were collected with use of Van Veen grab, dredge and Scuba diving at depths ranging from 0 to 268 m. Among examined material (5026 items) bryozoans were present on one type of abiotic (stones) and 40 types of biotic substrata. The biotic substrata we investigated included algae (12 taxa) and invertebrates (28 taxa: Hydrozoa, Gastropoda, Bivalvia, Polychaeta, Crustacea, Ascidiacea, other Bryozoa). Both a priori ANOSIM (Global R = 0.512, P = 0.001) and cluster analyses reveal differences between the assemblages on different types of substrata. Cluster analyses distinguish two distinct groups of substrata. The first (stable) included stones, molluscs and Balanus balanus whilst the second (flexible) consisted of algae, hydrozoans and bryozoans. Bryozoan assemblages which colonized different substrata, varied in terms of species composition and their dominance. Bryozoan species were categorized as generalists, low-specificity epibiotic species or locally abundant background species. No species were found to be substratum-specific to any type. Among substrata with the richest bryozoan fauna were stones (156 taxa), Chlamys islandica (68) and Balanus balanus (62). There were clear patterns in the distribution of substrata colonized by bryozoans within the fjord system: those shallow near the mouth were rich whilst those in deeper water were depauperate. We consider environmental gradients such as siltation and processes related to depth to be responsible for such patterns.

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