Authigenic carbonate precipitation associated with methane seepage is typically mediated by anaerobic oxidation of methane (AOM). This microbial process produces massive amounts of carbonate rock, introducing habitat heterogeneity to continental margins and providing a major repository for methane-derived carbon released from the sea floor. This study will investigate the extent to which these carbonate substrates form a distinct ecosystem within the seep environment by characterizing associated microbial, foraminiferal, macrofaunal and megafaunal communities in a successional context. Surveys and sampling of carbonate will take place at 4 bathyal locations on the Costa Rica margin (730-1300 m) and at Hydrate Ridge North on the Oregon margin (590 m).
Location differences and associated water depth, oxygenation, seep megafauna and carbonate formation variation are expected to influence community composition. This study will characterize assemblages inhabiting carbonates subject to active, weak and no methane seepage, and conduct rock colonization and transplant experiments to address the following main hypotheses:(1) Under conditions of active seepage at the seafloor-water interface, authigenic carbonate functions as a distinct ecosystem fueled by AOM, with its own sources of (chemosynthetic) primary and secondary production; (2) Seep carbonate faunal communities undergo succession driven by methane supply and microbial activity; (3) Sessile seep carbonate assemblages include mainly microbial, protozoan and metazoan species that are taxonomically and evolutionarily distinct from the biota of surrounding seep sediments, but ecologically and evolutionarily related to deep-sea, hard-substrate and reducing faunas, including those from seeps, vents, coral mounds and whale bones.
Single rocks will be split and sectioned for carbonate mineralogy and isotopic analysis, FISH-SIMS analyses of endogeneous microorganisms and their respective delta 13C signatures, faunal (protozoan and metazoan) taxonomic, lifestyle and position studies. Stable isotopic and lipid analyses of foraminifera and metazoan protoplasm, delta 18O and delta 13C signatures of foraminiferan tests and mollusk shells will be linked to microbial and carbonate signatures to assess trophic pathways and paleo proxies for methane release. Archaea and AOM are hypothesized as key to both. Defaunated carbonate substrates will be deployed at active and inactive sites for 1 year to examine early faunal succession and the role of external seepage. Rocks transplanted between inactive and active sites, with appropriate manipulation controls, will provide additional information about faunal reliance on seepage and persistence of AOM in the absence of seepage. Community comparisons will be drawn with seep sediments, other biotic substrates (mussels, clams, tubeworms) and with other deep-sea reducing and hardground systems (vents, whales, deep-water corals). Macrofaunal assemblages will be DNA and selected annelid and foraminiferan taxa will be targeted for phylogenetic analyses to assess evolutionary affinities with fauna from other hardground-reducing ecosystems (vents).
Broader Impacts: Benefits of this research to society include: (1) an understanding of seep carbonate ecosystems for improved marine resource management and more comprehensive assessments of seafloor biodiversity, carbon cycling, and adaptations to extreme environments; and (2) a model for successional changes in carbonate ecosystems and the use of their faunas as proxies to more accurately assess past methane release and paleoclimate change. Education and outreach will include local school presentations; web site development and interdisciplinary, hands-on, at-sea training of future scientists at undergraduate, graduate, and post-doc levels, including under-represented groups (women; first-generation university students from rural communities) recruited through SURF, STARS and REU programs. Research results will be incorporated into lectures, exercises and field trips for deep-sea biology, microbiology, geology, paleontology, oceanography and benthic ecology courses, and onto websites and databases managed by the Census of Marine Life and the SIO Benthic Invertebrate Collection.
Public Statement. The deep ocean is vast and much of it remains unexplored. While there are parts of the deep ocean we have never visited, detailed study of areas previously visited can reveal new secrets and lessons of great value in understanding life in the ocean. This project explored the life forms associated with carbonate rocks in two regions with methane seepage on the continental margins: one off Costa Rica (400-1850 m) and one off Oregon (500-900m water depth). We used the submersible ALVIN and the remotely operated vehicle JASON to observe, sample and conduct manipulative experiments intended to examine the roles of seepage activity, ocean conditions, and substrate type in shaping microbial and animal communities. In the process we discovered that carbonate rocks, themselves created by an exotic consortium of microbes, host a wealth of previously unknown bacteria, archaea, and small animals – effectively forming their own distinct, dynamic ecosystem. These communities are greatly influenced by proximity to methane seepage. In the processes of conducting these studies we discovered (a) the first animal known to derive nutrition primarily from the kingdom archaea, (b) the first yeti crab representative from methane seeps and only the second member of this family known (Kiwa puravida), (c) the first evidence of a dimorphic (two stage) lifestyle for the largest known bacteria, Thiomargarita, (d) the first (fungal-like) microsporidia ever reported from the deep sea, found in nematodes on seep carbonates and (e) new-found examples of animals and protists living in symbiosis with methane eating microbes. We discovered a novel deep-sea habitat type at 1800 m off Costa Rica that blends attributes of a hydrothermal vent and methane seep; we called this a hydrothermal seep. This study has yielded the first description of active and abundant microbes (methane-oxidizing archaea and sulfate-reducing bacterial partners) living inside methane seep carbonates. It has also yielded a wealth of new biodiversity, with over forty undescribed animals species. Descriptions of new worms, clams, mussels, snails, brittle stars and crabs are made or in progress. What is so remarkable is that our two study regions had been visited numerous times by other scientists before we got there. Taken together our findings reveal exquisite biological communities on margins of the E. Pacific Ocean, living in tight dependence on their environment and other organisms, and vulnerable to disturbance from human activities. Equally important, we have managed introduce a large number of undergraduates, graduate students, postdoctoral scientists, and a rural science teacher, to the wonders of deep- sea science, contributing to the next generation of deep-ocean explorers and researchers.
