The Cold Zone – The Hydrothermal Vents Overlooked Cousin.

The Cold Zone – The Hydrothermal Vents Overlooked Cousin

Oases of life...

Unlike the extreme temperatures of the hydrothermal vent, their lesser known cousin – “The Cold Seep” emanates chemical-rich fluids from the seafloor, providing the nutrients to sustain lush chemoautotrophic communities. These seeps modify the local chemical and physical area around them allowing benthic assemblages to grow ranging from cm to km. This “deep-sea Oasis” of sorts directly influence the diversity and biomass of benthic communities.

Despite the first paper based on cold seeps being published a couple of decades ago; cold seeps are often overlooked and within the high-arctic regions are poorly explored. Along the coast of Svalbard there are a collection of cold seeps with many having been previously studied for the biogeochemical properties. However until this time no studies have explored the associated benthic community and its relation to the methane seeps.

The Study Itself

Åström et al., 2016 described the cold seep-associated communities and habitats  located on the shelf of western Svalbard and the western Barents Sea. Samples took place throughout June and July 2014 and May 2015, quantifying both the benthic communities and the sedimentary characteristics of 10 stations across three sites. Benthic fauna was quantified via; total abundance and biomass. While sediment properties included; Sediment grain size, total organic carbon (TOC), porosity, Density and Sediment Pigment concentrations.

The analysis of the results revealed the large localized impact that cold seeps have on the abundance and diversity of the benthic communities. The areas around the seeps are home to high levels of biomass however lacked diversity. Comprised of only a handful of taxa, the species present were adapted to the harsh environment often living as part of a symbiotic relationship, using the reduced chemicals as an energy source.

The studied cold Seeps were overwhelmed by Polycheates with the most abundant family being the Siboglinids, a tubeworm that thrives in reduced environments where reduced chemicals are present. Adult Siboglinids lack a mouth and digestive system and rely on symbiosis with chemoautotroph symbionts for their energetic requirements. This high abundance of chemosynthetic fauna indicates that in regions lacking photosynthtically derived organic matter chemosynthesis is an advantageous life strategy provides the organism a competitive advantage.

I would like to see further studies exploring cold seep communities located in areas that are more homogeneous, that lack the volatile hydrodynamic properties found off the coast of Svalbard. Along with a change in the location, future studies should carry out sampling with a more accurate sampling method due to the localized nature of the cold seeps as Åström et al., 2016 highlights that some grab samples were meters away from the seep, possibly resulting in a poor representation of the benthic communities.

What is the future for cold seeps?

These kinds of studies could provide a basis to help us explore and understand the delicate balance between biological, hydrographic and geological characteristics and how they impact benthic communities. The investigation of how ocean warming could influence these unique environments is an area that is becoming increasingly relevant and important all the time, yet lacks the studies to full understand the interaction. However the area is being progressed by a number of published researchers studying the destabilization of solid gas hydrates. These solid hydrates require an environment with high pressure and low temperature to form but due to ocean warming the limited environments that meet this requirements are diminishing; resulting in increase of methane emissions from dissociating hydrates. Future studies should focus on understanding the interactions and adaptations of benthic communities’ as well as the development of models to hopefully predict how such a large change could influence the benthic communities.

Citations:

EKL Åström, ML Carroll, WG Ambrose, J Carroll. Arctic cold seeps in marine methane hydrate environments: impacts on shelf macrobenthic community structure offshore Svalbard. Marine Ecology Progress Series, 2016; 552: 1 DOI: 10.3354/meps11773

Extra Reading

Hung, Chia-Wei et al. “Benthic Fluxes of Dissolved Organic Carbon from Gas Hydrate Sediments in the Northern South China Sea.” Scientific Reports 6 (2016): 29597. PMC. Web. 21 Oct. 2016.