ALBERT

Description: In the Arctic, the currently observed rising air temperature results in more frequent calving of icebergs. The latter derive from tidewater glaciers. Arctic macrozoobenthic soft-sediment communities are considerably disturbed by direct hits and sediment reallocation caused by iceberg scouring. With the aim to describe the primary succession of macrozoobenthic communities following these events, scientific divers installed 28 terracotta containers in the soft-sediment off Brandal (Kongsfjorden, Svalbard, Norway) at 20 m water depth in 2002. The containers were filled with a bentonite–sand mixture resembling the natural sediment. Samples were taken annually between 2003 and 2007. A shift from pioneering species (e.g. Cumacea: Lamprops fuscatus) towards more specialised taxa, as well as from surface detritivores towards subsurface detritivores was observed. This is typical for an ecological succession following the facilitation and inhibition succession model. Similarity between experimental and non-manipulated communities from 2003 was significantly highest after 3 years of succession. In the following years, similarity decreased, probably due to elevated temperatures, which prevented the fjord system from freezing. Some organisms, numerically important in the non-manipulated community (e.g. the polychaete Dipolydora quadrilobata) did not colonise the substrate during the experiment. This suggests that the community had not fully matured within the first 3 years. Later, the settlement was probably impeded by consequences of rising temperatures. This demonstrates the long-lasting effects of severe disturbances on Arctic macrozoobenthic communities. Furthermore, environmental changes, such as rising temperatures coupled with enhanced food availability due to an increasing frequency of sea-ice-free days per year, may have a stronger effect on succession than exposure time.