Richness,abundance and shell use of subarctic and arctic hermit crabs

Hermit crabs are an obvious, common and abundant feature of global shallow water environments but almost nothing is known of their ecology at their extreme latitudinal ranges, the Arctic and southern South America. In this study, we report the first investigation on hermit crabs and their use of a key resource, gastropod shells, in a subpolar and a polar environment—amongst the most rapidly changing places on earth. Hypothesised low levels of richness were confirmed by surveys—only Pagurus pubescens was found in western Spitsbergen and only three pagurids were found in northern Norway. At the northern-most of their extent, hermit crabs were fairly common but Arctic abundances (1–5 m⁻²) were an order of magnitude lower than in many warm temperate or tropical localities. Along the open coast of Spitsbergen, the occurrence of P. pubescens was infrequent and very patchy, but it was more abundant in the fjords. In Isfjorden, the largest studied fjord, the population of P. pubescens was mainly represented by small individuals. Spitsbergen P. pubescens used few shell types and >87% just occurred in Margarites or Buccinum shells. The proportion of the gastropod shells, used by P. pubescens, which were damaged, was high and increased with shell size. These hermit crabs are at the edge of the range for both their species and Anomura. The extremes of their location are reflected by: They probably represent the least rich assemblage, with the lowest and most patchy typical abundances reported to date and are amongst the smallest individuals using the least diverse and most damaged gastropod shells.