Virtual Posters

European Arctic is the Northern hemisphere region that is changing the fastest. Providing reliable and sufficient information on its actual status is essential for estimating impact of ongoing changes on marine biota. We used hermit crabs as it has been suggested that communities of species on their shells could be very useful as model organisms to study diversity patterns among geographic regions and to monitor sublittoral ecosystems. In order to establish an observing system for change in bottom-up processes we wanted to create present-day baseline data of Arctic mobile substrate community structure and diversity, check its inter-annul variability at a given locations and estimate the role of local species pool and annual recruitment composition in shaping these assemblages. Epibiotic assemblages on shells used by Arctic and sub-Arctic hermit crabs (Pagurus spp.) collected annually over five years (2005 - 2009) at Svalbard (West Spitsbergen, Isfjorden - S) and in Northern Norway (south of Tromso - T) were analyzed. Additionally rocks were collected in order to establish local species pool as well as settlement panels were deployed to estimate annual recruitment composition. In the first year of our studies we collected 250 individuals from the Arctic location to calibrate sampling strategy. In the following years due to time constraints comparable sampling efficiency was achieved gathering only 45 hermit crabs each time. They were hand-picked using SCUBA from ~10 m depth. Gastropod shells were identified to species, weighed and the external shell surface area was measured. All organisms that were directly attached to the shell, rock and panel larger than 1 mm were identified to the lowest possible taxonomic level. In total 27603 individuals of epibionts representing 105 taxa were found to occur on the shells. No clear differences in species composition and dominance structure of the assemblages between investigated years at both sites were observed. It resembled the community on rocks with cirriped (Semibalanus balanoides) at S and foraminiferans Lobatula lobatula and Discorbis rosacea at T as dominating species. There were however significant differences with respect to abundance, species richness, and diversity. This was most probably caused by fluctuations in annual recruitment as it was supported by the results obtained from settlement panels. All the investigated parameters were the highest in recent years. This study (1) provides the first overview of species associated with Arctic hermit crabs, shows that (2) invertebrate assemblages can be an important indicator of environmental changes but only in terms of community structure, indicates that (3) invertebrate assemblages on Arctic hermit crabs shells may be relatively persistent to changes over observation period of five years, (4) mobile epibiotic assemblages are highly dependent on the local species pool.