Community dynamics over a decadal scale at Logatchev, 14 degrees 45 ' N, Mid-Atlantic Ridge

Hydrothermal vent community dynamics over a ten year span was studied in the Logatchev area, 14 degrees 45'N on the Mid-Atlantic Ridge. On the SERPENTINE cruise in March 2007 with the RN Pourquoi pas? and the ROV Victor 6000 (IFREMER), composition, abundance and distribution of dominant megafauna at Logatchev were examined and compared to published data from 1997. Our results revealed notable changes in several community characteristics. The most significant changes evident in March 2007 compared to July 1997 were the increase up to by order of magnitude in the population density of predatory gastropods Phymorchynchus spp. at the site Irina-2 and disappearance of a live population of vesicomyids at the site Anya's Garden. Other notable differences between the two periods of observation were the overall increase in the abundance in 2007 of the mussel Bathymodiolus puteoserpentis and a high abundance of gravid females of the shrimp Rimicaris exoculata at Irina-2. It is suggested that the extinction of vesicomyids occurred owing to either a sediment slide at a steep slope of the Anya's Garden locality or instability of a biotope required for vesicomyids. Live vesicomyids were not found over a large area explored at Logatchev in 2007. Other changes observed in 2007 apparently were related to seasonal fluctuations in the community at Logatchev or fluctuations in the hydrothermal activity. Any successional stages over a decadal scale at Logatchev were not observed.