||1 : IFREMER, Ctr Brest, REM, EEP,LEP,ZI Pointe Diable, CS10070, F-29280 Plouzane, France.
The main objective of the present study was to investigate invertebrate colonization processes at deep-sea hydrothermal vents in response to environmental factors and to the presence of complex artificial substrata (i.e., synthetic sponges). We set out a pilot experiment at 1700 m depth on the Lucky Strike vent field (Eiffel Tower, Mid-Atlantic Ridge). Synthetic sponges were deployed in 2011 at five sites along a gradient of hydrothermal activity and were recovered in 2013, and the composition of macro- and meiofauna was assessed on four of them. The influence of temperature and fluid inputs on colonizer faunal abundance and diversity was analyzed. Faunal abundance and diversity decreased with increasing distance from vent emission. The colonizers were represented by a subset of species characterizing the natural populations at the Eiffel Tower edifice. Some taxa (e.g., pycnogonids, ophiuroids, cnidarians, foraminiferans) represented new records not yet found on deployed substrata on the Eiffel Tower. Synthetic sponges harbored a high percentage (from 17.5% to 55%) of juveniles and larval stages of polychaetes, molluscs, and copepods. A mature nematode community (mainly Cephalochaetosoma and Halomonhystera) in a reproductive stage was found. Variability in faunal composition was significantly correlated with distance from fluid emission. We hypothesize that the complex structure of inorganic sponge substrata may have favored settlement of juveniles and larvae. Sponge substrata may, therefore, help sample a wider range of organisms than other substrata, and, thereby, provide a more complete picture of vent biodiversity. The results provided in this study might improve our understanding of mechanisms that govern faunal colonization processes at vents.