Energy flow and food webs in deep seafloor ecosystems: a multifaceted approach to testing deep-sea models with biochemical observations


  • Supervisors: Dr Rachel Jeffreys, University of Liverpool
    Prof Andrew Hirst, University of Liverpool


  • External Supervisors: Brian Bett, NOC, Southampton
    Jennifer Durden, NOC, Southampton
  • Contact:

    Dr Rachel Jeffreys, University of Liverpool Rachel.jeffreys@liverpool.ac.uk

  • CASE Partner:

Application deadline: 10 January 2020

Introduction:

Deep-sea habitats at water depths over 2000 m cover ~60% of the Earth’s surface and are the largest and least explored environment on the planet (Smith et al. 2009). Deep-seafloor communities are sustained by the flux of particulate organic carbon, which originates from primary producers in the euphotic zone. A small fraction (<5%) of the POC fixed in the surface ocean reaches the seafloor. Recent work at two abyssal observatories has demonstrated that deep-seafloor communities are sensitive to changes in this flux (Smith et al. 2009). This food supply is likely to be impacted by climate change, which is predicted to impact surface ocean primary production leading to a reduction in the POC flux (Yool et al. 2017). Modelling predicts that a reduction in POC flux will lead to a substantial reduction in biomass at the deep seafloor (Yool et al. 2017). Deep-seafloor communities play an important role in remineralising POC to nutrients and dissolved inorganic carbon, over time periods of days to months. A small fraction of that POC is not remineralised by deep-seafloor communities and is sequestered by seafloor burial, an important process over geological timescales. Therefore, changes in deep-seafloor communities will have direct and indirect impacts on biologically controlled processes, ecosystem functioning, biogeochemical cycling and carbon burial. This project aims to bring together empirical measurements, theory and modelling to better understand energy flow and ecosystem function in deep-seafloor communities.

Project Summary:

You will study pattern and process in energy transfer through seafloor communities by constructing food webs using novel stable isotope biomarker approaches and examining body-size spectra in deep-seafloor communities at the Porcupine Abyssal Plain sustained observatory (PAP-SO, depth 4850 m) in the NE Atlantic. The abyssal seafloor community and water column biogeochemistry have been routinely studied at this site for the last three decades, providing a unique historical dataset on POC flux, benthic biomass and abundance. The site will be accessed via annual research cruises 2019-2023. 

Body size is thought to be of primary importance in controlling energy flow through biological communities (Brown et al. 2004). Across geometric body-size classes, animal abundance appears to decline as a -3/4 power function. Given that metabolic rate scales as a +3/4 power function of body mass, then the total energy used by a size class will be approximately constant at steady state (Damuth’s rule or the energetic equivalence rule; Damuth 1981). The theory provides a numerical framework to link organism physiology, activity, and abundance with energy flows through the ecosystem (e.g. Durden et al. 2019). Your project will test and apply these linked theories in the case of deep-seafloor communities. In order to do this, you will use a multifaceted approach combining your stable isotope biomarker data (e.g. Jeffreys et al. 2015) with extensive data from the PAP-SO and numerical frameworks. 

References:

Brown et al. 2004. Ecology, 85, 1771-1789.

Damuth 1981. Nature, 290, 699-700.

Durden et al. 2019. Ecology, 100(1), e02564.

Jeffreys et al. 2015. Biogeosciences, 12(6), 1781-1797 doi: 10.5194/bg-12-1781-2015

Smith et al. 2009. Proc.Natl Acad Sci USA, 106, 19211-19218.

Yool et al. 2017. Global Change Biology, 23, 3554-3566.

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