An official website of the United States government
As biodiversity loss accelerates globally, understanding environmental influence over biodiversity–ecosystem functioning (BEF) relationships becomes crucial for ecosystem management. Theory suggests that resource supply affects the shape of BEF relationships, but this awaits detailed investigation in marine ecosystems. Here, we use deep-sea chemosynthetic methane seeps and surrounding sediments as natural laboratories in which to contrast relationships between BEF proxies along with a gradient of trophic resource availability (higher resource methane seep, to lower resource photosynthetically fuelled deep-sea habitats). We determined sediment fauna taxonomic and functional trait biodiversity, and quantified bioturbation potential (BPc), calcification degree, standing stock and density as ecosystem functioning proxies. Relationships were strongly unimodal in chemosynthetic seep habitats, but were undetectable in transitional ‘chemotone’ habitats and photosynthetically dependent deep-sea habitats. In seep habitats, ecosystem functioning proxies peaked below maximum biodiversity, perhaps suggesting that a small number of specialized species are important in shaping this relationship. This suggests that absolute biodiversity is not a good metric of ecosystem ‘value’ at methane seeps, and that these deep-sea environments may require special management to maintain ecosystem functioning under human disturbance. We promote further investigation of BEF relationships in non-traditional resource environments and emphasize that deep-sea conservation should consider ‘functioning hotspots' alongside biodiversity hotspots.
more »
« less
Discovery of deep-sea cold seeps from Argentina host singular trophic linkages and biodiversity
Chemosynthetic ecosystems host unique geological, biogeochemical, microbial and faunistic settings, which provide key ecosystem services for human wellbeing. In the Argentine continental margin, the existence of chemosynthetic ecosystems is still unknown. We present the first finding of chemosynthetic ecosystems in the Argentine deep sea. We assessed and compared biological and geological settings for cold seeps at Malvinas Basin and Colorado Basin and a control site (no gas) at Colorado Basin. We found two cold seeps with crater-like geomorphic features (pockmarks) of 500-m and 1000-m diameter at depths of ⁓500 m. Both cold seeps exhibited methane gas bubbles trapped at the surface of the seafloor, one exhibited seepage into the water column. Cold seeps hosted dense benthic macroinvertebrates (≥300 μm) assemblages consisting mainly of polychaetes, peracarid crustaceans and mollusks. The fauna from Argentinean seeps exhibited δ13C and δ15N stable isotope signatures indicative of multiple trophic levels, supported by both chemosynthetic and photosynthetic sources of energy. The difference in bubbling to the water column was not associated with different trophic input of chemosynthetically-derived sources of energy, suggesting that gas input is mediated by the bubbles trapped in the seafloor sediments. The presence of gas bubbles trapped in the surface sediments of the ocean floor allowed the detection of ecological and trophic characteristics of active chemosynthetic ecosystems. Integration of the sub-bottom dimension can help improve our understanding of the interactions of chemosynthetic ecosystems with seafloor fluid flow in a more reliable manner than the gas plumes. These cold seeps host significant biodiversity and ecosystem functions of the deep ocean. They fall within areas tendered for oil and gas industry development, but have not been a focus of conservation efforts to date. Information provided here can inform effective conservation actions and improve our understanding of the distribution of chemosynthetic ecosystems worldwide.
more »
« less
- Award ID(s):
- 2048720
- PAR ID:
- 10530169
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Deep Sea Research Part I: Oceanographic Research Papers
- Volume:
- 211
- Issue:
- C
- ISSN:
- 0967-0637
- Page Range / eLocation ID:
- 104361
- Subject(s) / Keyword(s):
- Deep sea, methane seep, Argentina, stable isotopes
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The Southern Hydrate Summit 1 Seafloor study site, situated on the continental slope off the coast of Oregon at a water depth of ~775 meters, hosts abundant deposits of gas hydrates (methane ice) that are buried beneath, and sometime exposed at, the seafloor. The deposits vent methane-rich fluids and bubbles that escape through seeps on the ocean bottom and can rise in plumes several hundred meters above the seafloor, also fueling dense communities of microbes and animals with chemosynthetic symbiotes. These seeps provide a unique opportunity to study ocean chemistry, quantify chemical fluxes from the seafloor, and observe the impacts of methane release on overlying seawater and biota. Methane is a powerful greenhouse gas and, therefore, quantifying the flux of methane from the seafloor into the hydrosphere is critical to understanding carbon-cycle dynamics and the impacts of global warming on methane release, particularly following seismic events. This Low-Power junction box (LJ01B) contains geophysical and near-seafloor water column instrumentation, and is attached to an electro-optical cable that provides significant power and 1 Gb two-way communications bandwidth. This junction box is also co-located with a Medium-Power junction box that collects a complementary suite of seafloor and water column measurements.more » « less
-
The Southern Hydrate Summit 2 Seafloor study site, situated on the continental slope off the coast of Oregon at a water depth of ~775 meters, hosts abundant deposits of gas hydrates (methane ice) that are buried beneath, and sometime exposed at, the seafloor. The deposits vent methane-rich fluids and bubbles that escape through seeps on the ocean bottom and can rise in plumes several hundred meters above the seafloor, also fueling dense communities of microbes and animals with chemosynthetic symbiotes. These seeps provide a unique opportunity to study ocean chemistry, quantify chemical fluxes from the seafloor, and observe the impacts of methane release on overlying seawater and biota. Methane is a powerful greenhouse gas and, therefore, quantifying the flux of methane from the seafloor into the hydrosphere is critical to understanding carbon-cycle dynamics and the impacts of global warming on methane release, particularly following seismic events. This Medium-Power junction box (MJ01B) rests on the seafloor adjacent to a highly active methane seep called Einstein’s Grotto. Instrumentation at this site is designed to monitor chemistry of the seep, image the seep and associated biota in detail, and image the bubble plume as it rises several hundred meters above the seafloor. This junction box is attached to an electro-optical cable that provides significant power and 1 Gb two-way communications bandwidth, and is co-located with a Low-Power junction box that collects a complementary suite of geophysical and near-seafloor water column measurements.more » « less
-
Abstract Ecotones have been described as “biodiversity hotspots” from myriad environments, yet have not been studied extensively in the deep ocean. While physiologically challenging, deep‐water methane seeps host highly productive communities fueled predominantly by chemosynthetic pathways. We hypothesized that the biological and geochemical influence of methane seeps extends into background habitats, resulting in the formation of a “chemotone” where chemosynthesis‐based and photosynthesis‐based communities overlap. To investigate this, we analyzed the macrofaunal assemblages and geochemical properties of sediments collected from “active,” “transition” (potential chemotone), and “background” habitats surrounding five Costa Rican methane seeps (depth range 377–1908 m). Sediment geochemistry demonstrated a clear distinction between active and transition habitats, but not between transition and background habitats. In contrast, biological variables confirmed the presence of a chemotone, characterized by intermediate biomass, a distinct species composition (including habitat endemics and species from both active and background habitats), and enhanced variability in species composition among samples. However, chemotone assemblages were not distinct from active and/or background assemblages in terms of faunal density, biological trait composition, or diversity. Biomass and faunal stable isotope data suggest that chemotones are driven by a gradient in food delivery, receiving supplements from chemosynthetic production in addition to available photosynthetic‐based resources. Sediment geochemistry suggests that chemosynthetic food supplements are delivered across the chemotone at least in part through the water column, as opposed to reflecting exclusivelyin situchemosynthetic production in sediments. Management efforts should be cognisant of the ecological attributes and spatial extent of the chemotone that surrounds deep‐sea chemosynthetic environments.more » « less
-
Abstract Methane seeps are highly productive deep‐sea ecosystems reliant on chemosynthetic primary production. They are increasingly affected by direct human activities that threaten key ecosystem services. Methane seepage often generates precipitation of authigenic carbonate rocks, which host diverse microbes, and a dynamic invertebrate community. By providing hard substrate, even after seepage ceases, these rocks may promote a long‐lasting ecological interaction between seep and background communities. We analyzed community composition, density, and trophic structure of invertebrates on authigenic carbonates at Mound 12, a seep on the Pacific margin of Costa Rica, using one mensurative and two manipulative experiments. We asked whether carbonate macrofaunal communities are able to survive, adapt, and recover from changes in environmental factors (i.e., seepage activity, chemosynthetic production, and food availability), and we hypothesized a key role for seepage activity in defining these communities and responses. Communities onin situcarbonates under different seepage activities showed declining density with increasing distance from the seep and a shift in composition from gastropod dominance in areas of active seepage to more annelids and peracarid crustaceans that are less dependent on chemosynthetic production under lesser seepage. Response to changing environmental context was evident from altered community composition following (1) a natural decline in seepage over successive years, (2) transplanting of carbonates to different seepage conditions for 17 months, and (3) defaunated carbonate deployments under different seepage regimes over 7.4 yr. Seep faunas on transplants to lesser seepage emerge and recover faster than transition fauna (characterized by native seep and background faunas, respectively) and are able to persist by adapting their diets or by retaining their symbiotic bacteria. The macrofaunal community colonizing defaunated carbonates deployed for 7.4 yr developed communities with a similar successional stage asin siturocks, although trophic structure was not fully recovered. Thus, macrofaunal successional dynamics are affected by habitat complexity and the availability of microbial chemosynthetic productivity. This multi‐experiment study highlights the interaction between biotic and abiotic factors at methane seeps at different time scales along a spatial gradient connecting seep and surrounding deep‐sea communities and offers insight on the resilience of deep‐sea macrofaunal communities.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.dsr.2024.104361
