Inter-annual variability of the epibiotic community on Pagurus bernhardus from Scotland

Epibiont communities of Pagurus bernhardus and its inhabiting shell collected in the same month of two consecutive years near the Isle of Cumbrae (Scotland) were analyzed. The epibionts found were: (1) the protozoans Acineta, Conchacineta, Corynophrya, Zoothamnium, Cothurnia mobiusi, Cothurnia longipes, Chilodochona, Cryptacineta, Ephelota gemmipara and Ephelota plana; (2) the hydrozoans Leuckartiara, Clytia and Phialella; (3) the entoproct Barentsia; (4) the cirripeds Balanus balanus and Balanus crenatus; (5) the polychaetes Pomatoceros triqueter, Circeis amoricana paguri and Hydroides norvegica. Among these epibionts, a protozoan (E. plana), two hydrozoans (Leuckartiara, and Phialella), and the entoproct (Barentsia) have not been described previously as epibionts on crustaceans. The protozoan, entoproct and hydrozoan epibiont species found on P. bernhardus represent the first mention of their presence on this hermit crab. The protozoan epibionts were found only on the crab, while the hydrozoan epibionts were observed on the shell and on the crab. The cirriped species were observed only on the external surface of the shell, and the polychaete species were observed on the external and internal surfaces of the shell, although Circeis was found only internally. An analysis of the distribution and density of each epibiont species on the anatomical units of the crab, as well as on the different shell areas were made. The comparison between the data of the two years showed differences with respect to the size of crabs, diversity of epibiont groups and density of epibionts. There was a significant difference between the two years with respect to the distribution of epibionts on the anatomical units of the crab, both in terms of density and biomass. The influence of some environmental parameters on these differences is considered.