Ecosystem Dynamics of Hydrothermal Vent Communities

In the deep sea, hydrothermal vents are biologically important, harboring massive animal communities at densities that make them one of the most productive ecosystems on Earth. All this biomass exists thousands of feet below the sea surface and, unlike most communities, which rely on sunlight, the food web of hydrothermal vents is based on tiny chemosynthetic microbes (bacteria) which derive their energy from "breathing" vented chemicals. Hydrothermal vents typically arise where the movement of the plates that make up the surface of the Earth split and fissure, allowing geothermally heated water to escape through the planet’s crust (chemically enriched water that may reach temperatures of over 640°F).

Spreading centers in Western Pacific back-arc basins are geologically unique and the frequency of their tectonic or volcanic events are not well documented. The hydrothermal vent communities in these regions are also distinct, hosting endemic fauna, which are species that are not found anywhere else. Recent studies have further shown that these communities may harbor cryptic species that have yet to be described.

Mining and the need for research

Potential environmental impacts of industrial mining in deep sea environments remains poorly constrained, and our limited knowledge about hydrothermal vent ecosystems in the Western Pacific back-arc basins makes it difficult to create conservation strategies to effectively manage anthropogenic effects in this area. To date, Papua New Guinea, Fiji, and the Kingdom of Tonga have granted exploration licenses in their territorial waters for industrial mining of polymetallic sulfide deposits around hydrothermal vents. Current mining strategies and management plans are largely based on patterns and predictions derived from studies and observations at mid-ocean ridge vents in the Pacific (i.e., East Pacific Rise), which are likely not relevant to the geologically and biologically distinct hydrothermal vents of the Western Pacific. This is one of the primary reasons why the research vessel Falkor traveled to Fiji in April 2016, and embarked on an expedition to obtain new knowledge necessary for sustainable management of these natural resources.

The Vent Life expedition

The regional bathymetry between Fiji and Tonga and the six hydrothermal vent fields that were studied during the Vent Life expedition (grey circles; include long-term study sites). Insert shows global location.[/caption]

A team of interdisciplinary scientists led by principal investigators Dr Charles Fisher from Pennsylvania State University, Dr Peter Girguis from Harvard University, Dr Vicki Ferrini from Columbia University’s Lamont Doherty Earth Observatory, and Dr Roxanne A. Beinart from Woods Hole Oceanographic Institution embarked on a 28-day expedition onboard the R/V Falkor. The team revisited long-term study sites (some established over a decade ago) as well as newly discovered hydrothermal vent fields on the Eastern Lau Spreading Center and Valu Fa Ridge between Fiji and the Kingdom of Tonga.

The remotely operated vehicle (ROV) ROPOS traveled up to nine thousand feet to the deep seafloor of the Lau Basin. Once on the bottom, the extremely versatile ROV performed a range of scientific tasks including visual and sonar surveys, collecting specimens and samples, and taking environmental measurements.[/caption]

The remotely operated vehicle (ROV) ROPOS traveled up to nine thousand feet to the deep seafloor of the Lau Basin. Once on the bottom, the extremely versatile ROV performed a range of scientific tasks including visual and sonar surveys, collecting specimens and samples, and taking environmental measurements. All the research conducted on this hydrothermal vent expedition was facilitated by the remotely operated vehicle (ROV) ROPOS. From a sensor onboard ROPOS, scientists conducted high-resolution bathymetric surveys at six hydrothermal vent fields and looked for evidence of tectonic or volcanic events that alter the environment. These high-resolution bathymetric maps also provided insight into geological processes for more than two dozen long-term study sites members of the team established in 2005 and 2006. At each site, high-resolution two- and three-dimensional mosaicsand advanced in situ chemical and temperature sensors were used to document the fine-scale spatial ecology of hydrothermal vents, the effect vent animals have on the local water chemistry, and temporal ecosystem changes.

In conjunction with the field surveys and samples, scientists studied several of the most abundant vent species using high pressure aquaria and molecular tools to better understand the influence of particulate load on respiration (a potential influence of deep sea mining), symbiont activity, and survival. The observations contributed to predictive models for species-specific tolerance to changing conditions.

Benefits of this research

A close look at the diversity of life thriving on and around deep sea hydrothermal vents in the Lau Basin back-arc.[/caption]

This extensive study provided new insights into the level of volcanic and tectonic activity in the Lau basin, the ecology of hydrothermal vent communities, and the sensitivity of vent animals to potential anthropogenic stressors. The unique longevity of research at these study sites by the team provides a baseline with which to compare their findings, allowing them to make a more informed assessment of the potential impact of mining in the region, and provide a baseline for robust interpretation of post-mining monitoring of environmental impacts. Fisher, Girguis, Ferrini and Beinart believe that the results from these studies can inform impact assessment protocols and policies at deep sea sites in the Western Pacific biogeographic province that may be the target of future mining.

by Monika Naranjo González