LAUSR

This study provides taxonomical and ecological accounts for the poorly known diversity of hydroids distributed over ~2,000 km of Argentinean Patagonian intertidal habitats (42°-54°S). Sampling was performed in 11 sites with tidal amplitude between 6-13 m dominated by rocky outcrops, breakwaters, and salt marshes. Samples were sorted and identified up to the species level and hydroid associations were analyzed by multivariate analyses. A total of 26 species were recorded. The most frequent species were Amphisbetia operculata , present in 8 of the 10 sites inhabited by hydroids, followed by Symplectoscyphus subdichotomus and Nemertesia ramosa . All recorded hydroids are geographically and bathymetrically widely distributed species, common at the austral hemisphere. Seven species ( Coryne eximia , Bougainvillia muscus , Ectopleura crocea , Hybocodon unicus , Halecium delicatulum , Plumularia setacea , and Clytia gracilis ) were reported from intertidal fringes. Species richness differed according to the composition of the bottom, topographical complexity and density of mytilid communities. Some muddy intertidal fringes dominated by the glasswort Sarcocornia perennis had an unexpected hydroid fauna composition, never reported for salt marsh habitats, representing a remarkable novelty for the hydroid literature. The lack of studies on the hydroid fauna from these particular habitats represented a substantial gap for our biodiversity knowledge.