Polar Biol (2007) 30:487–492 DOI 10.1007/s00300-006-0207-5 123 ORIGINAL PAPER Extraordinary abundance of hydrocorals (Cnidaria, Hydrozoa, Stylasteridae) in shallow water of the Patagonian fjord region Verena Häussermann · Günter Försterra Received: 6 June 2006 / Revised: 23 August 2006 / Accepted: 28 August 2006 / Published online: 18 November 2006  Springer-Verlag 2006 Abstract During two scuba-diving expeditions in 2005 and 2006, stylasterids were documented and sam- pled from fjords and channels in the Central Patago- nian Zone, Chile. At 15 of a total of 33 sampling sites we found colonies of Errina antarctica. We discuss the observed distribution patterns and the variability of colony shapes. In some regions we found E. antarctica to occur in extraordinary high densities on primary and secondary hard substratum below 10 m. In the archi- pelago Madre de Dios we discovered large colonies of E. antarctica covering areas of more than 10,000 m² with coverage exceeding 80%. The dense accumula- tions of E. antarctica have reef-like structure and form complex habitats. At one site we observed extensive mechanical damage to the corals that may result from coral extraction by divers and/or from boat anchors. Slow growth, fragility, scarceness and the lack of knowledge on their ecology make these spectacular and unique biocenoses very susceptible for damages and require protection and further studies. Keywords Stylasteridae · Southern Chile · Patagonia · Shallow water · Benthos · Fjords Introduction After the scleractinians, stylasterinae (Cnidaria, Hydrozoa) are the next large group of calciWed cnidari- ans in number of species (Cairns 1999). They can be found in all oceans, in shallow water as well as in the deep sea, but most of the approximately 250 described species worldwide, live between 200 and 500 m depth (Cairns 1983b, 1984, 1992). Nevertheless, comparably few publications deal with stylasterids. Of the 13 stylasterid species recorded for Chile, 10 were exclusively found south of Cape Horn in depths between 87 and 2,355 m depth, with only some records of Errina labiata shallower than 200 m; only two spe- cies are recorded from the Chilean coast proper, Errina antarctica form moseleyi from 18 to 119 m in the southern Chilean fjords (50–55°S) and Allopora pro- funda from 631 m in the Golfo de Penas (48°S) (Cairns 1983a). Errina antarctica is also known from the Falk- land Islands and the Burdwood Bank in the Scotia Arc (approx. 54°S; 57–62°W) down to 771 m, but occurs rarely deeper than 300 m. Errina antarctica form mose- leyi, originally described as Labiopora moseleyi by Ridley (1881), is characterized by having larger, more erect colonies with thick, Xattened branches and distin- guishable anterior and posterior sides. It is recorded from shallow water between Punta Rosario, Madre de Dios Arquipelago and Tierra del Fuego. The Central Patagonian Zone between Golfo de Penas and the Straits of Magellan (Pickard 1973; Vivi- ani 1979; Stuardo and Valdovinos 1992) is one of the least studied marine regions in the world (Arntz 1999; Escribano et al. 2003), mainly due to its remote loca- tion, diYcult accessibility and harsh weather condi- tions. The hard bottom benthos is largely unknown and V. Häussermann (&) · G. Försterra Huinay ScientiWc Field Station, Casilla 462, Puerto Montt, Chile e-mail: vreni_haeussermann@yahoo.de G. Försterra e-mail: gunter_forsterra@yahoo.com V. Häussermann · G. Försterra Universidad Austral de Chile, Campus Isla Teja, Avda. Inés de Haverbeck 9, 11 y 13, Casilla 467, Valdivia, Chile