Importance of trophodynamics and functional traits in the structure of macrobenthic Southern Ocean shelf communities under methane seepage influence

Overview

Methane is confirmed as one of the potent climate change gases with a global warming potential higher than carbon dioxide. Marine methane in the Southern Ocean (SO) is estimated to comprise about a quarter of the Earth’s marine methane. In recent years, first records of methane seepages from the seafloor and raised methane concentrations in the overlying water column have been reported from sub-Antarctic islands and the Antarctic shelf. Research to date has focussed on the Arctic, with investigations on the origins, amounts and effects on the ecosystem of methane emissions, but there has been minimal research in the SO. More specifically, significant gaps exist in relation to the responses of the SO benthic faunal communities to methane and their role in whether seepage areas are sources or sinks.
To date research on methane as a climate change gas with global warming potential has focussed on terrestrial methane. Marine methane in the SO could play an important role in a) climate change and b) may also impact SO biodiversity and ecosystem function as a result of the increased marine methane seepage caused by warming of the Antarctic continental shelf.
Evidence of methane seepage has come from a number of sources including the detection of raised methane in sediments at the eastern Antarctic Peninsula, gas flares on the Kerguelen Plateau, gas hydrate in the South Georgia shelf and methane seepage including bacterial mats in nearshore, shallow waters of the Ross Sea. However, to date no living chemosynthetic mega- or macrofauna, generally associated with deep-sea methane seepage have been reported from the SO seepage sites. At South Georgia, there were raised abundances of SO infaunal taxa in sediments saturated with methane, but neither community composition nor trophic interactions have been fully investigated across the full range of methane seepage conditions. In the eastern Antarctic Peninsula, benthic fauna from carbon-enriched sites suggests that these are from opportunistic taxonomic groups, which are often found in association with methane seepage but are not dependent on it. This pattern has been observed in other areas of the ocean where methane seepage occurs but lacks charismatic megafauna which are often observed in methane seep habitats. This suggests that the role of methane sustaining marine benthic food webs is being underestimated, and that identifying seepage locations may be too reliant on larger, visual cues.
The proposed work will investigate the community composition, functional traits and trophodynamics of benthic fauna from hydrocarbon and carbon enriched habitats in the SO, which are hypothesised or known to be influenced by methane seepage. The research will use a combination of the biogeochemical techniques (e.g. stable isotope and lipid analyses) to elucidate the food source of benthic fauna and establish the degree of dependence on methane sources; morphological analysis to identify species and establish potential functional traits; and statistical analysis to understand the response of the benthic communities to varying sediment geochemical conditions. There will be an emphasis on understanding the role of bivalves as potential indicator species of hydrocarbon- and carbon-enriched habitats in the SO, which will lead to a biogeographical analysis and the identification of potential future exploration sites.

Methodology

The student will undertake a combination of laboratory-based data acquisition and analysis of large datasets. Samples and associated environmental data will come from a series of sources: South Georgia and Antarctic benthic samples collected during previous expeditions (e.g. JR17003a, M134), biodiversity.aq database, and new material from SG methane seepage collected through K Linse’s collaboration with Prof S Kasten on PS133-2 in November 2022. The latter material is not required to fulfil this PhD.

The student will use the following methodologies
• Ecological community statistical analyses techniques
• Morphological, morphometric, and potentially molecular species determination techniques
• Stable isotope and lipid analysis on frozen and ethanol-fixed macrofauna
• Functional trait analyses
• Biogeographic analysis using ArcGIS
• Public data mining for review on shallow water hydrocarbon habitats and species
• No fieldwork is required for this PhD to enable a successful PhD even if pandemic conditions continue. The supervisors, especially Dr Katrin Linse, have secured regular, international expedition participation for their teams and we would hope to expect similar during the length of this PhD to enable time on a research vessel for the student.

Project Timeline

Year 1

• Literature review on SO methane seepage systems (not hot vent ones) and macrobenthic communities as well as shallow water/shelf seepage systems
• Stable isotope lab work on macrofaunal communities from methane saturated sediments, active methane seeps and adjacent non-seepage areas from the South Georgia shelf
• Analysis of stable isotope data
• Morphological and functional trait assessment of the SG macrobenthic communities

Year 2

• Finish analysis and manuscript writing for macrobenthic SG community study using stable isotopes
• Analysis on morphological and functional traits and write-up to manuscript
• Stable isotope analysis of Duse Bay, Eastern Antarctic Peninsula, benthic community – an area under climate change and potentially carbon-rich environment – can methane seepage be detected by stable isotopes analysis?
• Biogeographic and morphometric data and lab work of selected macrobenthic bivalves from hydrothermal, carbon-enriched and “normal” SO environments across different functional groups (filter feeder, detritivores, carnivores)
• Stable isotope analysis of bivalve shells to detect hydrothermal/ chemosynthetic/ hydrocarbon enriched environments.

Year 3

• Finish analysis and manuscript writing of Duse Bay stable isotope work
• Finish and write up biogeographic and morphometric data analysis on selected macrobenthic bivalves from hydrothermal, carbon-enriched and “normal” SO environments
• Assemble data for review publication/chapter on “non-seep” organic rich environments vs hydrothermal seepage ones.
• Finish analysis and manuscript on bivalve shell stable isotope analysis

Year 3.5

• Analyse and write up review on “non-seep” carbon enriched environments
• Write introduction and conclusion chapter of PhD thesis, submit thesis.

Training
& Skills

IAPETUS offers a multidisciplinary package of training that is focused around meeting the specific needs and requirements of each of our students. The student will be eligible to training courses for research and soft skills offered across the IAPETUS’ partner organisations. The student will be registered at Newcastle University and hosted at the British Antarctic Survey, Cambridge. Specific training will include:

• Competence with univariate and multivariate data analysis techniques in R
• Biological trait analysis
• ArcGIS package
• Identification of macrobenthic Southern Ocean taxa
• Stable isotope preparation and analysis skills
• Lipid preparation and analysis skills

The student will gain important research skills such as scientific writing and oral presentation by attending appropriate courses. If possible, travel to international scientific meetings to present project results and network building will also be encouraged. While fieldwork is not required, if opportunities present, participation in expeditions will be considered

References & further reading

Römer, M., Torres, M, Kasten, S., Kuhn, G., Graham, A.G.C., Mau, S., Little, C., Linse, K., Pape, T., Geprägs, P., Fischer, D., Wintersteller, P., Marcon, Y., Rethemeyer, J., Bohrmann, G. and shipboard scientific party ANT-XXIX/4. 2014. First evidence of widespread methane emissions around a Sub-Antarctic island (South Georgia). ESPL 403: 166-177

Bell JB, Aquilina A, Woulds C, Glover AG, Little CTS, Reid WDK, Hepburn LE, Newton J, Mills RA. 2016 Geochemistry, faunal composition and trophic structuring in reducing sediments on the southwest South Georgia margin. Royal Society Open Science 2016, 3, 160284.

Bell, J. B., Reid, W. D. K., Pearce, D. A., Glover, A. G., Sweeting, C. J., Newton, J., and Woulds, C. 2017. Hydrothermal activity lowers trophic diversity in Antarctic hydrothermal sediments, Biogeosciences, 14, 5705–5725.

Bohrmann, G. et al. 2017. R/V METEOR Cruise Report M134, Emissions of Free Gas from Cross-Shelf Troughs of South Georgia: Distribution, Quantification, and Sources for Methane Ebullition Sites in Sub-Antarctic Waters, Port Stanley (Falkland Islands) – Punta Arenas (Chile), 16 January – 18 February 2017. http://nbn-resolving.de/urn:nbn:de:gbv:46-00106081-12

Linse K. 2019 RRS James Clark Ross JR17003a Cruise report. https://www.bodc.ac.uk/resources/inventories/cruise_inventory/report/16954/

Further Information

For further information, please contact Dr Katrin Linse (kl@bas.ac.uk) and Dr William Reid (william.reid@newcastle.ac.uk). Students are encouraged to contact Dr Linse and Dr Reid to discuss the PhD prior to application.

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