Topic: Modelling macromolecular synthesis and flux in scleractinian coral
Supervisors: Professor Peter Ralph and Dr. Mark Baird
PhD conferred: 2014
Coral reefs are one of the world’s most complex and productive type of ecosystems. Scleractinian coral (reef building) usually acts as a foundation for these ecosystems. Effects of climate change such as increasing sea surface temperatures and ocean acidification have been shown to have adverse effects on coral health and growth. Corals are foremost found in oligotrophic marine environments and their success is largely dependent on their symbiotic relationship with dinoflagellate algae from the genus Symbiodinium often referred to as ’zooxanthellae’. The main function of the host-algal relationship is based on the host providing the symbiont with a protected environment within its tissue as well as inorganic nourishment including nitrogen, phosphorus and carbon. The zooxanthellae in turn provide the host with glycerol, glycerides and amino acids which are essential to the host’s metabolic processes. Corals’ internal response to stress induced by climate change is still poorly understood. The purpose of this project is to develop the first energetic model of the macromolecular synthesis and flux in scleractinian coral. The goal is to construct a model which can predict the effect of external forcing both in terms of tissue composition and in terms of how acquired energy is spent on various physiological processes such as growth, lipid storage, reproduction and mucus production. The major focus will be on evaluating the processes of the synthesis and flux of protein, lipids and carbohydrates between different parts of the cnidarians host and the symbiotic algae.
To achieve the purpose of this project a number of processes and fluxes within the coral has to be assessed. The objectives will therefore be to:
• Determine the changes in macromolecular composition within host and symbiont tissues under different temperature, nutrient, light, CO2 and feeding regimes.
• Assess the exchange rate of different compounds within and between host, symbiont and the environment under different temperature, nutrient, light, CO2 and feeding regimes.
• Assess the overall use of energy (i.e. how much energy is used for processes such as growth, reproduction or mucus production) under different temperature, nutrient, light, CO2 and feeding regimes.
• All these components should then be incorporated into the model, which should be rigorously tested.
The macromolecular model will initially be based on the dynamic energy budget (DEB) model constructed by Muller et al. (2009). The DEB model provides a good basic framework for the host-algae relationship which we can build on and incorporate additional aspects of scleractinian physiology.
A range of methods will be used to assess synthesis and fluxes of different macromolecular compounds between the host, symbiont and environment. Fourier transform infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) are two of the methods that may be used to determine the macromolecular composition within host and symbiont tissues. Prior to this analyses the coral tissue will be separated into three fractions; epidermis, gastrodermis and algae which are analyzed individually.The flux measurements can hopefully be acquired using the OMX microscope. Other measurements such as feeding rates and photosynthetic rates will also be obtained and used to improve the model.