Doctoral Programme on Marine Ecosystem Health and Conservation
 The MARES Researchers and their Research
Global change effects on the carbon metabolism of seagrasses and on their role as carbon sinks
PhD Code: MARES_12_04:
  • Host institute 1: P5 - University of Algarve
  • Host institute 2: P7 - University of Plymouth
Research fields:
  • T1 - Future Oceans: temperature changes - hypoxia - acidifation
  • Santos Rui
  • Hall-Spencer Jason
Contact Person and email: Santos Rui -

Subject description
Questions to be assessed
1) What are the ecophysiological responses of seagrasses to short and long-term CO2 enrichment?
2) How do increasing CO2 levels affect the ecological functioning of seagrass beds?
3) Can seagrass habitats be harnessed to combat ocean acidification?
Seagrasses form an important component of coastal ecosystems worldwide, being an important global sink of carbon (Kennedy et al 2010). An understanding of their sensitivity to ocean acidification and warming is important in planning for the wider impacts of global environmental change on coastal ecosystems (Bjork et al 2008).  A combination of laboratory, mesocosm and field surveys have revealed that ocean warming and acidification will likely cause a major reorganization of seagrass communities along the coastlines of Europe since fundamental processes like photosynthesis, nutrient uptake, growth and reproduction are affected (Palacios et al 2007, Diaz-Almela 2007, Jiang et al 2010, Alexandre et al in press). Little is known about the consequences of these changes for ecosystem function although it has been suggested that seagrass habitats may help combat acidification, as their photosynthesis makes water less corrosive to calcified organisms (e.g. coralline seaweeds, corals, mussels, oysters, Semesi et al 2009). On the other hand, global change effects might weaken the role of seagrass ecosystems as carbon sinks (Macreadie et al 2012). The proposed studentship will address these questions using a combination of laboratory and field experiments.
The student will carry out field campaigns to volcanic vents in the Mediterranean to undertake incubation experiments with seagrasses (Posidonia oceanica and Cymodocea nodosa) along natural CO2 gradients (Arnold et al. 2012). Net community metabolism, community calcification and dissolved organic carbon (DOC) fluxes will be measured by monitoring the oxygen evolution, total alkalinity and DOC within the chambers before and after the incubation (Santos et al. 2004, Semesi et al 2009). Community respiration will be measured in the dark. Models of gross community production (GCP) vs photosynthetic active radiation (PAR) will be developed by measuring GCP and DOC along the daily variation of PAR. Photosynthetic production vs PAR curves will also be obtained by incubating isolated shoots along the daily variation of PAR, to assess seagrass contribution to the whole community production.
Seagrass samples (leaves and rhizomes) will be collected to measure the sugar, amino acids, soluble proteins, phenols, starch and total C and N contents to assess the effects of CO2 levels on their carbon metabolism and plant storage. The stable isotope ratios of N and C of the surface sediments of seagrass meadows along the CO2 gradient near the vents, and of the main primary producers, benthic consumers and particulate organic matter of the water column will be measured to assess the proportional contribution of seagrasses to the surface sediment organic carbon pool (Kennedy et al, 2011), i.e. how will CO2 increase affect the carbon sink capacity of seagrass meadows. The analytical work will be developed at the Center of Marine Sciences (CCMAR) of the University of Algarve, Portugal.
The student will use cultivation chambers at CCMAR, with temperature and CO2 controls. The within chamber CO2 concentration will be maintained by bubbling CO2 with desired concentration from a gas tank. Short-term experiments to test the synergistic effects of elevated CO2 and temperature on seagrass production will be done to compare with field results. These chambers will be deployed in P oceanica and C nodosa meadows located near field stations both at CCMAR (C. nodosa) and at Stareso field station in Corsica.
This work will be developed within the framework of the COST Action ES0906 “Seagrass productivity: from genes to ecosystem management”, chaired by the host partner of this proposal. The student will be integrated in this network and will have the possibility to apply to Short Term Scientific Mission grants to develop the fieldwork planned at Stareso station. This proposal is also aligned with the FP7 MedSeA work, which will help the student become integrated into this wide program, with training opportunities and permission to join in on expeditions to CO2 vent sites in Greece and Italy.
In an initial 9-month training period the student will review the literature and refine the laboratory and field-based methods needed for this project, at CCMAR. The student will receive training at the host lab and practice and test these techniques in Ria Formosa lagoon in C. nodosa meadows.
  • Alexandre A, Silva J, Buapet P, Björk M and Santos R (in press). Long-term effects of CO2 enrichment on photosynthesis, growth and nitrogen metabolism of the seagrass Zostera noltii. Ecology and Evolution.
  • Arnold, T., Mealey, C., Leahey, H., Miller, a. W., Hall-Spencer, J. M., Milazzo, M., & Maers, K. (2012). Ocean Acidification and the Loss of Phenolic Substances in Marine Plants. (R. K. F. Unsworth, Ed.) PLoS ONE, 7(4), e35107. doi:10.1371/journal.pone.0035107
  •  Björk, M., Short, F., Mcleod, E., & Beer, S. (2008). Managing Seagrasses for Resilience to Climate Change. IUCN, Gland, Switzerland. 56pp
  •  Diaz-Almela E, Marbà N and Duarte CM (2007), Consequences of Mediterranean warming events in seagrass (Posidonia oceanica) flowering records. Global Change Biology, 13: 224–235.
  • Jiang ZJ, Huang XP, Zhang JP (2010) Effects of CO2 enrichment on photosynthesis, growth and biochemical composition of seagrass Thalassia hemprichii (Ehrenb.) Aschers. Journal of Integrative Plant Biology, 52, 904-913.
  • Kennedy, H., Beggins, J., Duarte, C. M., Fourqurean, J. W., Holmer, M., Marbà, N., & Middelburg, J. J. (2010). Seagrass sediments as a global carbon sink: Isotopic constraints. Global Biogeochemical Cycles, 24(4), 1–8.
  • Macreadie, P. I., Allen, K., Kelaher, B. P., Ralph, P. J., & Skilbeck, C. G. (2012). Paleoreconstruction of estuarine sediments reveal human-induced weakening of coastal carbon sinks. Global Change Biology, 18(3), 891–901.
  •  Palacios SL, Zimmerman RC (2007) Eelgrass (Zostera marina L.) response to CO2 enrichment: possible impacts of climate change and potential for remediation of coastal habitats. Marine Ecology Progress Series, 344, 1-13.
  • Santos R, Silva J, Alexandre A, Navarro N, Barrón C and Duarte CM (2004). Ecosystem metabolism and carbon fluxes of a tidal-dominated coastal lagoon. Estuaries 27:977-985.
  • Semesi, I. S., Beer, S., & Björk, M. (2009). Seagrass photosynthesis controls rates of calcification and photosynthesis of calcareous macroalgae in a tropical seagrass meadow. Marine Ecology Progress Series, 382, 41–47.

Expected outcomes
This studentship has been designed to provide integrated doctoral training across two leading European marine research institutes. 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 international conferences. Close co-operation and exchange with international projects, the COST Action ES0906 “Seagrass productivity: from genes to ecosystem management” and the FP7 MedSeA project, will help the student become integrated into these wide program, with training opportunities an permission to apply to Cost specific grants and to join in on expeditions to CO2 vent sites in Greece and Italy. This will ensure that the outcomes of the Ph.D. project will be recognized 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.

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