Possible latitudinal dines in Antarctic intertidal and subtidal zone communities encrusting ephemeral hard substrata

Aim Encrusting faunal communities on rocks were examined from Southern Ocea n intertidal and subtidal (6 m) zones to investigate potential change with latitude. Location The site locations were South Georgia (54 degrees S [sub-Antarctic ]), Signy Island (60.5 degrees S [maritime Antarctic]) and Adelaide Island (68 degrees S [high Antarctic]). Methods The number of taxa, degree of colonization and bryozoan growth and mortality were measured. Results The communities present were relatively simple in terms of composit ion and interactions. Spirorbid polychaetes (Annelida) and cheilostomatid b ryozoans were the principal components. The community simplicity and domina nce of unitary (compared to colonial) fauna increased with latitude. Mean a nnual mortality of subtidal cheilostomatids also significantly increased wi th latitude. The number of bryozoan species and potential aspects of commun ity complexity increased with latitude. The growth of the bryozoan Inversiu la nutrix increased with latitude reversing the general trend of decreased growth rate. Conclusions These findings suggest that disturbance may significantly incre ase with latitude within the Southern Ocean. The apparent reversal of typic al latitudinal growth trends is probably a result of classical island bioge ography, with species decreasing away from a centre of high diversity.