Colonization of habitat islands in the deep sea: recruitment to glass sponge stalks

Biogenic structures in the deep sea often act as hard substratum 'islands' for the attachment of encrusting fauna. At an abyssal station in the NE Pac ific, stalks of hexactinellid sponges in the genus Hyalonema are habitat is lands for species-rich epifaunal communities. An experimental study was con ducted to (1) determine the colonization rates of artificial Hyalonema stal ks, (2) compare the species composition and diversity of recruits to newly available substrata to that of the natural communities, and (3) examine the vertical distribution of recruits. Four sets of six artificial sponge stal ks, constructed of Hyalonema spicules, were deployed at 4100 m depth for 3- to 5-month periods. There was no difference in net colonization or immigra tion rate among the four deployments. Colonization rates were similar to th ose reported for other deep-sea, hard substratum recruitment experiments. T he taxa that recruited to the artificial stalks were a subset of the taxa f ound in natural communities. However, several taxa important in structuring natural communities did not recruit to the artificial stalks. The two taxa with the highest invasion rates, a calcareous Foraminiferan (Cibicides lob atulus) and a serpulid polychaete (Bathyvermilia sp.), also were the two ta xa with greatest relative abundance in natural communities. Vertical distri butions of Cibicides and an agglutinated foraminiferan (Telammina sp.) were skewed towards the top of the artificial stalks, potentially because of ac tive habitat selection. These results have several implications for natural Hyalonema stalk communities. Most importantly, species composition and abu ndance of individuals in the stalk communities appear to be maintained by f requent recruitment of a few common taxa and infrequent recruitment of many rare taxa. An argument is presented for temporal-mosaic maintenance of div ersity in these deep-sea, hard substratum communities. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.