Hydrothermal vent meiofauna from the West Pacific

Deep-sea hydrothermal vents are one of the most extreme habitats on Earth. Highly fluctuating temperatures, toxic hydrogen sulfide emissions, and low oxygen concentrations characterize this ecosystem, where in situ primary production via chemosynthesis supports a highly abundant but low diverse macrofauna. Vent meiofauna research is still in its infancy, and knowledge on biogeography and underlying causes of diversity patterns is scarce. Previous studies were mostly carried out at the East Pacific Rise (EPR) and illustrated low meiofauna abundance and diversity. The central objective of this multidisciplinary study is to unravel meiofauna diversity patterns from the Lau Basin back arc spreading center in the West Pacific. This includes detailed in situ evaluation of the abiotic environment (temperature, oxygen, and sulfide concentration), quantification and identification of the meio- and macrofauna of three dominant megafauna aggregations thriving at different vent flux regimes (the snail Alviniconcha hessleri and Ifremeria nautilei, the mussel Bathymodiolus brevior). By using the same quantitative collection device for all samples and by obtaining the set within 3 days at the same site, sampling problems from the past were overcome, thereby excluding the possible effects of sampling size, location, and time on diversity. In addition, surrounding non-vent sediments and hard substrates are observed to investigate if vent meiofauna is facultative (similar to the observations at the 9NEPR, but dissimilar to the macrofauna being vent endemic) and if substrate type plays a pivotal role in meiofauna distribution. The copepod family Dirivultidae is chosen as a model to study cryptic diversity and diversification processes of vent meiofauna. This involves DNA-analyses of dirivultids from two biogeographic regions of different age, the EPR and the Lau Basin Center. This study will shed light on meiofauna diversity patterns from the West Pacific, a region where currently only six (!) species are described. The combination of molecular and traditional taxonomy will enable for the first time to estimate true meiofauna diversity and to get insight into diversification processes. New species will be described. By integrating the meio- and macrofauna diversity patterns and vent flux characteristics, drivers of ecological processes that control differently-sized communities at various vent flux regimes can be evoked. The study of non- vent sites will show if meiofauna is in general vent facultative. This work will greatly expand and change our current knowledge of vent ecology and biogeography.