Gastropod assemblages associated with Himantothallus grandifolius, Sarcopeltis antarctica and other subtidal macroalgae

Gastropods are an important component of subtidal Antarctic communities including in common association with macroalgae. Nonetheless, limited data exist detailing their abundance and distribution on macroalgal species. This study documents the abundance and species composition of gastropod assemblages on the two largest, blade-forming Antarctic macroalgae, Himantothallus grandifolius and Sarcopeltis antarctica, sampled across two depths (9 and 18 m) at four sites for each species off Anvers Island, Antarctica. Gastropods were also enumerated on Desmarestia anceps, Desmarestia antarctica and Plocamium sp. but were not included in the main analyses because of small sample sizes. There were major differences between the gastropod assemblages on deep vs shallow H. grandifolius and S. antarctica with much higher numbers of individuals and also greater numbers of gastropod species at the greater depth. Differences between the gastropod assemblages on H. grandifolius and S. antarctica across sampling sites were apparent in non-parametric, multivariate analyses, although depth contributed more than site to these differences. Within common sites, assemblages on H. grandifolius were significantly different from those on S. antarctica at 18 m depth but not at 9 m depth, indicating that the host species can be but is not always more important than site in influencing the gastropod assemblages.