Currents and topography drive assemblage distribution on an active hydrothermal edifice

Abstract

The deep sea is characterized by a wide range of landscapes, including complex features where topography and currents interact to form highly heterogeneous habitats. In addition to a complex topography, hydrothermal vent environments are characterized by strong environmental gradients that structure the spatial distribution of biological communities. The role of vent fluid temperature and chemical composition on species distribution is now well understood, but investigations on the effects of the complex sulfide edifice topography are scarce. Here, we used a novel approach combining 3D photogrammetric reconstruction, in situ environmental measurements and modeling to characterize assemblage distribution on the active edifice Eiffel Tower (Lucky Strike, Mid-Atlantic Ridge). Through the analysis of a high-resolution 3D model of the edifice, we show that assemblage distribution along with hydrothermal activity vary with their position on the edifice. Although physical terrain variables had a minor effect on assemblage distribution, the distance from fluid exits explained the distribution of most assemblages. However, these particular variables did not significantly explain the distribution of medium-sized Bathymodiolus azoricus mussels, the dominant assemblage on the edifice. Similarly, proximity to fluid exits only partially accounted for the distribution of microbial mats throughout the edifice. By modeling the current-driven dispersion of hydrothermal plumes around the edifice, we demonstrated that differences in mussel sizes may be due to differences in exposure time to currents bringing plume material. For the first time, we provide evidence that hydrothermal plumes can affect faunal assemblages meters away from fluid exits and that this relatively long-distance effect of vent plumes can fully account for microbial mat distribution throughout the edifice. Our findings extend the area of influence of hydrothermal plumes on vent communities considerably beyond previous estimations and suggest that the interactions between bottom currents, topography and smoker locations should be further investigated and considered as important structuring factors at vents. This novel approach, allowing to cover large areas of the seafloor, is particularly well suited for deep environments where topography and currents interact to form complex oceanographic patterns (e.g. canyons, seamounts). Its application to larger areas and various ecosystems can significantly enhance our understanding of benthic communities' distribution at large.

The EMSO Generic Instrument Module (EGIM): Standardized and Interoperable Instrumentation for Ocean Observation

“…Seawater temperatures measured by the EGIM and by SeaMon East are similar over the entire deployment period (i.e., 4-5 • C). The dispersion radius of vent particles is therefore significantly larger than the effect that vent plumes might have on seawater temperature, which confirms the key role of currents on the near vent dispersion of hydrothermal particles (Girard et al, 2020).…”

“…This example shows how the EGIM, measuring surrounding background oceanic conditions, can complement the array of instruments and bring valuable information on the dispersion of vent particulate matter, a key parameter for the distribution of hydrothermal habitats (Girard et al, 2020).…”

Population structure and environmental niches of Rimicaris shrimps from the Mid Atlantic Ridge

“…Additionally, distribution of R. exoculata and R. chacei juveniles further differ by their habitat topography, on steep chimney walls for R. exoculata nurseries and within flat areas or smooth slopes for R. chacei nurseries. As topography strongly influences the overall current hydrodynamics, with low topography areas generally associated with low mixing rates (Girard et al ., 2020), these structural differences in habitats might reflect the relative dependency of each species to the vent fluid mixing gradient essential to fuel their ongoing developing symbiosis (Methou et al ., 2020). Although our measurements were limited, this variability of the fluid chemistry between the nursery habitats of the two species could be observed in our dataset with lower H 2 S and Fe concentrations in R. chacei nurseries compared to R. exoculata ones.…”

Population structure and environmental niches of Rimicaris shrimps from the Mid-Atlantic Ridge

“…on steep chimney walls for R. exoculata nurseries and within flat areas or smooth slopes for R. chacei nurseries. As topography strongly influences the overall current hydrodynam-ics, with low-topography areas generally associated with low mixing rates (Girard et al 2020), these structural differences between habitats might reflect the relative dependency of each species on the vent fluid mixing gradient essential to fuel their ongoing developing symbiosis (Methou et al 2020). Although our measurements were limited, this variability of the fluid chemistry between nursery habitats of the 2 species could be observed in our dataset with lower H 2 S and Fe concentrations in R. chacei nurseries compared with R. exoculata ones.…”