Patterns of hydroid (Cnidaria, Hydrozoa) species richness and distribution in an Arctic glaciated fjord

The consequences of global warming are particularly evident in high polar areas. Deglaciation phenomenon—negative mass balance of Svalbard glaciers and recession of tidal glaciers—results in landscape and shoreline change. These areas of very dynamic conditions are now open for primary colonists, among them hydroids, typical early colonists of the vacant substratum. This study aims to explore the patterns of Hydrozoan diversity and distribution in Hornsund (west Spitsbergen). Hydroids associated with shallow water kelp beds as well as those occurring on deeper subtidal soft bottom were collected at sites located along gradients of glacial disturbance (i.e., high mineral sedimentation, ice-berg scouring). Samples were collected by scuba diving (three sites of different distance to active tidal glaciers), van Veen grabs (two sites located in the inner and outer fjord basin), and dredges taken from along a fjord transect. Hydroid diversity differed significantly between sites located in the vicinity of glaciers fronts in glaciated bays and sites comparatively free from glacier disturbance. Glacial disturbance results in low frequencies of occurrence and high levels of rarity of hydroids at sites located close to glacier fronts. The species richness of hydroids colonizing the hard substrate elements present in deeper subtidal decreases along the fjord axis (i.e., along the glacial sedimentation gradient).