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

Aim Encrusting faunal communities on rocks were examined from Southern Ocean intertidal and subtidal (6 m) zones to investigate potential change with latitude. Location The site locations were South Georgia (54°S sub-Antarctic]), Signy Island (60.5°S maritime Antarctic]) and Adelaide Island (68°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 composition and interactions. Spirorbid polychaetes (Annelida) and cheilostomatid bryozoans were the principal components. The community simplicity and dominance of unitary (compared to colonial) fauna increased with latitude. Mean annual mortality of subtidal cheilostomatids also significantly increased with latitude. The number of bryozoan species and potential aspects of community complexity increased with latitude. The growth of the bryozoan Inversiula nutrix increased with latitude reversing the general trend of decreased growth rate. Conclusions These findings suggest that disturbance may significantly increase with latitude within the Southern Ocean. The apparent reversal of typical latitudinal growth trends is probably a result of classical island biogeography, with species decreasing away from a centre of high diversity.