Meiovent Succession

Deep-sea hydrothermal vents are globally wide-spread extreme environments located at the mid-ocean ridge system of the largest mountain chain on Earth. Driven by in situ primary production via chemosynthesis, a special vent fauna thrives under highly fluctuating conditions along a gradient of temperature and toxic chemicals such as hydrogen sulfide. Meiofauna - the small-sized animal and protist community - of the 950`N East Pacific Rise region is a prominent component of all known vent communities there and has been found in low diversity and low abundance. As the volcano of this region erupted early 2006 and destroyed most of the living beings there, this gives us the unique opportunity to study the sofar completely unknown successional patterns of meiobenthos. Using artificial settlement devices and control natural collections in a variety of benthic locations with and without vent flux in the axial summit collapse trough, as well as in the pelagial on moorings, we will investigate the temporal and spatial hydrothermal vent communities over a time course of about 6 months to 3 years post eruption. This study on succession, the non-seasonal, directional continuous pattern of colonization and extinction will include the description of new species, the identification, and quantification of the specific meiofauna communities of selected hydrothermal vent habitats in terms of species richness, diversity, and abundance in conjunction with an assessment of the abiotic conditions as well as of the bacterial abundance and particulate organic matter measurements serving as food for this exclusively primary consumer community. In addition, this study will include the search for vent meiobenthic species in the pelagial in the vicinity the 950`N EPR region. This will study will be the first of its kind and will lead to a better understanding of the processes and underlying mechanisms of vent meiofauna succession.

Deep-sea hydrothermal vents are globally widespread, extreme environments located at the mid-ocean ridge system of the largest mountain chain on Earth. Independent of sunlight, a special vent animal fauna lives on primary production through bacterial chemosynthesis under stressful environmental conditions with fluctuating temperature and toxic chemicals in the crater of volcanoes. One of these volcanoes in the 9o50N region of the East Pacific Rise has been very well studied before it erupted in early 2006. Meiofauna the small-sized animal community has been found low in abundance and low in diversity. The majority of meiofauna species, such as copepods and nematodes, were not restricted to vents but lived also on the basalt surrounding the vents. In contrast, macrofauna the large-sized animal communities was also low in diversity but high in abundance. The majority of macrofauna species, such as gastropods and polychaetes, were specialized to vents but many of them can also live on basalt as juveniles while they grow up and then need to migrate to vents for more food and to reproduce. After the eruption, which killed most animal communities, we studied the colonization and succession of animal communities at vents and surrounding basalt using artificial colonization devices and collections of natural communities as well as dispersal of meiofauna in the water column using sediment traps in the first four years after the eruption. We conducted this study with the submersible Alvin and the research vessel Atlantis. This is the first time that primary succession of entire animal communities was studied at a deep-sea hydrothermal vent. The data are based on counting more than 250 000 and identifying about 100 000 animals. Less than one year after the eruption, an animal community in the early successional stage was present. Surprisingly, communities in vent flow and outside of vent flow on the basalt were similar in diversity, despite the facts that the primary production was restricted to vents and stress was much higher at vents than at basalt. Shifts in community composition, however, were apparent. Thus initially, neither the environmental conditions nor the productivity appear to be responsible for the communities establishing. Colonization was through dispersal in the water column from further away populations, but while macrofauna disperses as larvae only, meiofauna disperses as larvae, juveniles, and adults. In addition, many pelagic animals initially colonize the fresh basalt and are later replaced by benthic animals. A comparison prior to post eruption revealed that diversity was similar between meiofauna and macrofauna during early succession but macrofauna diversity increased during late succession at vents and meiofauna diversity increased during late succession at basalt. Thus, different components of the animal fauna are the driving forces for diversity patterns during succession.