The effects of ocean acidification on demersal zooplankton in coral reefs: Using natural CO2 seeps in Papua New Guinea as a window into the future


  • Host institute 1: P2 – Universität Bremen
  • Host institute 2: P7 – University of Plymouth

Research fields:

  • T1 – Future Oceans: temperature changes – hypoxia – acidifation
  • T2 – Understanding biodiversity effects on the functioning of marine ecosystems

Subject description

Streams of CO2 bubbles naturally emerge from the shallow coral reefs in eastern Papua New Guinea (Fabricius et al. 2011). They offer the opportunity for an exiting PhD Project to observe the effects of elevated seawater CO2 levels on the composition and food web dynamics of demersal zooplankton, providing an insight into how rising atmospheric CO2 concentrations may impact reef associated zooplankton communities in 50-100 years time.

In eastern Papua, three natural volcanic vent fields release gas bubbles of nearly pure CO2, providing natural gradients in pH from ambient waters away from the seeps (8.1 units) down to pH ~7.2 units in the center of these seep areas. Along the pH gradients, carbonates in sediments, calcareous algae and the structurally complex corals increase in abundance (Fabricius et al. 2011). A similar shallow site near the island Ischia in the Mediterranean has been instrumental in confirming concerns that sustained elevated levels of seawater CO2 have a negative impact on the condition and in fact on the presence or absence of calcifying species (Hall-Spencer et al. 2008).

Demersal plankton is an important food source for many of the reef building corals. Demersal plankton resides in reef sediment substrata during the day, emerging into the water column predominantly at night. Preliminary anecdotal observations suggest that both the biomass and species composition of this plankton may differ strongly between the high CO2 and control sites. This may have strong implications for the future trophic status of coral reefs.

The objectives of this PhD Project are twofold:

  1. To investigate the biomass and composition of demersal plankton along the CO2 gradients. This study will establish thresholds for individual taxonomic groups of plankton, and allow predicting which reef associated groups of demersal plankton can live at elevated CO2 and which can’t. It will also show how CO2 will alter plankton availability for corals as a food source.
  2. To investigate trophic fluxes and food webs within the plankton community, using fatty acids and 13C as biomarkers. The biomarkers will be investigated within the bulk of the highly diverse mixed-species communities, by size fractioning plankton communities, and additionally by choosing a few select plankton taxa that occur in sufficient numbers to conduct repeated analyses along the CO2 gradients. The volcanic CO2 are almost free of 13C isotopes, so plankton entering the seep area from the open ocean are likely to have another isotopic ratio compared with demersal plankton that predominantly depend on reef primary production as food source. Using gas chromatography – mass spectrometry, and compound specific stable isotope analysis (gas chromatography-combustion isotope ratio mass spectrometry), we can take advantage of this natural label to investigate relative contributions of local versus offshore carbon sources to the food webs.

The successful MARES PhD candidate will join up to two expeditions to visit the seep sites in Milne Bay, as part of an interdisciplinary team of scientists led by Katharina Fabricius at the Australian Institute of Marine Science (AIMS). K. Fabricius has already coordinated two expeditions to the seep sites, and will continue to do so throughout the duration of this PhD project. She has with long-standing expertise in coral reef studies and the assessment of changes in biotic communities along environmental gradients, with over 80 publications in peer reviewed journals. The student will spend a significant proportion of the time at the Townsville branch of AIMS (located at the central Great Barrier Reef) for development of a detailed work plan, preparation of all equipment and gear for the expeditions, testing of the equipment at local reefs in the Great Barrier Reef, and afterwards to process the plankton samples. The PhD candidate will also work across the laboratories at the University of Bremen and the Alfred Wegener Institute in Bremerhaven (Profs Wilhelm Hagen, Holger Auel, Claudio Richter), benefiting from their expertise in zooplankton research (e.g., Genin et al. 2005), in using fatty acids as biomarkers for trophic links (e.g., Dalsgaard J et al. 2003), and to conduct compound specific mass spectrometry. Additional co-supervision by Dr Jason Hall-Spencer, University of Plymouth, will create linkages to the ocean acidification research groups who work at CO2 seeps in the rocky shore communities of the Mediterranean. The three European institutions are all home to one or more of the ocean acidification research programs, BioAcid, UK-OA, ECO2, MedSea and EPOCA.

The candidate will have to be highly motivated, willing to spend time in Australia, and to conduct ship based field work (with diving or snorkeling, depending on qualification) in Papua New Guinea. The project will also entail extensive time in the laboratory to process the plankton samples, and will require strong numerical skills for data analyses.


  • Dalsgaard J, St John M, Kattner G, Müller-Navarra D, and H. W. 2003. Fatty acid trophic markers in the pelagic marine environment. Adv. Mar. Biol. 46:225-340.
  • Fabricius, K., C. Langdon, S. Uthicke, C. Humphrey, S. Noonan, G. De’ath, R. Okazaki, N. Muehllehner, M. Glas, and J. Lough. 2011. Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change 1:165–169.
  • Genin, A., J. Jaffe, R. Reef, C. Richter, and P. Franks. 2005. Swimming against the flow: the mechanism of zooplankton aggregation. Science 308:860-862.
  • Hall-Spencer, J. M., R. Rodolfo-Metalpa, S. Martin, E. Ransome, M. Fine, S. M. Turner, S. J. Rowley, D. Tedesco, and M. C. Buia. 2008. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454:96-99.

Expected outcomes

The candidate is expected to publish the results of the project together with the supervisors in peer-reviewed scientific journals. He/she will present the outcomes at two international conferences. Close co-operation and exchange with other international research projects, e.g. BIOACID, CALMARO, will ensure that the outcomes of the Ph.D. project will be recognised by the scientific community. Since ocean acidification is a burning issue of global concern, it is expected that the outcomes of this project will be of high relevance for a wider audience and also gain interest of the general public.

MARES, PhD opportunity.

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