Topic: Defining the bio-energetic limits of Symbiodinium sp.’s host-symbiont relationship under future climate scenarios.
Supervisor: Associate Professor Peter Ralph, Dr Ross Hill, UTS
PhD conferred: 2013
Many Cnidaria of the class Anthozoa, and some other invertebrates, are known to be associated with unicellular photosynthetic dinoflagellates from the genus Symbiodinium sp. Freud. These symbioses are driven by the exchange of photosynthate translocated from the symbionts to the host organism and the transfer of metabolic endproducts such as CO2, ammonia, urea and polyphosphates from the host to the symbionts. The mechanisms involved in the maintenance and regulation of these symbioses remain elusive. In the past decades coral reefs worldwide have suffered mass-bleaching events as a result of global warming. Prolonged periods of elevated water temperatures can lead to the expulsion of the symbionts from the host and in some cases this can result in the death of the coral. Temperature-induced coral bleaching is just one phenomenon where an environmental change can tip the balance of a finely equilibrated symbiosis to the limit. Other abiotic influences such as light intensity, UV impact and low salinity are considered to threaten the symbiotic relationship of Symbiodinium sp. and its host organisms. It remains uncertain whether or not these organisms are robust enough to withstand the challenges of future climate change.
This project aims to understand the mechanisms which control the bio-energetically equilibrated symbioses between Symbiodinium sp. and its host Cnidarian by:
(1) Defining physiological characteristics of the host organism and photobiological parameters of Symbiodinium sp. under varying simulated climate scenarios (short-term and long-term approach)
(2) Examining the intercellular communication of the host organism and its interaction with Symbiodinium sp. under varying climate scenarios
(3) A system comparison approach between different host organisms associated with the same Symbiodinium sp. clade, in order to determine the degree of impact of predicted climate change scenarios.
A novel approach will be to focus on the internal mechanisms of the host organism in order to understand the driving and limiting factors for maintaining the symbiosis with Symbiodinium sp. To date, technology has limited our research and understanding of the intercellular responses within the host tissue towards stress. In my project, I will be able to use state-of-the-art microscopy techniques in order to clarify cellular communication of the host-symbiont relationship.
Experimental setups will be used to simulate future ocean scenarios based on modelled parameters. Elevated temperature regimes, intense light and lowered pH levels (a result of increased CO2) will be the parameters I will simulate in stress experiments. To get a broad picture, I will examine different species hosting Symbiodinium sp. and expose them to the aforementioned modified parameters. Experiments will be run for short-term exposure (days), to examine immediate stress response as well as long-term (months), to examine if and how acclimation takes place.
Verena in the news
C3 PhD coral reef research rewarded (January 2010)
Schrameyer V., Krämer W., Hill R., Jeans J., Campbell D. A., Larkum A.W.D., Bischof K., Ralp P.J., Photo-repair - a matter for coral resilience? (in preparation)
Schrameyer V., Gademann R., Hill R., Larkum, A.W.D., Behrendt L., Kühl M., Ralph P.J., A closed chamber system to quantify photosynthesis, respiration and bioenergetic fluxes of aquatic phototrophs (in preparation)
Schrameyer V., Wangpraseurt D., Hill R., Kühl M., Larkum A.W.D, Ralph P.J., Light respiratory processes and gross photosynthesis in two scleractinian corals. (in preparation)
Tonk L., Sampayo E.M., Schrameyer V., Chai A., Hoegh-Guldberg O., Host identity and SST drive low Symbiodinium diversity in invertebrate hosts from inshore marginal reefs of the southern Great Barrier Reef, Australia. (in review)
Slavov C., Schrameyer V., Reus M., Ralph P. J., Hill R., Larkum A.W.D., Holzwarth A.R., Photoprotective mechnisms of Symbiodinium under thermal stress - implications for coral bleaching. (in review)
Tonk L., Sampayo, E. M., LaJeunesse, T.C., Schrameyer, V., Hoegh-Guldberg, O., 2014. Symbiodinium (Dinophyceae) diversity in reef-invertebrates along an offshore to inshore reef gradient near Lizard Island, Great Barrier Reef. Journal of Phycology, DOI: 10.1111/jpy.12185
Krämer W., Schrameyer V., Hill R., Ralph P. J., and Bischof K., 2012. PSII activity and pigment dynamics of Symbiodinium in two Indo-Pacific corals exposed to short-term high-light stress. Marine Biology, Vol 160, Issue 3, pp. 563-577.
Hill R., Larkum A.W.D., Schrameyer V., Gustafsson M., Ralph P.J., 2012. Response to Biogeoscience Discussion: 9, pp: 8111-8139. 2012.
Behrendt L., Schrameyer V., Qvortrup K., Lunding L., Sorensen S., Larkum A.W.D., Kühl M., 2012. Biofilm growth and near infrared radiation-driven photosynthesis of the chlorophyll-d-containing cyanobacterium Acaryochloris marina. Applied Environmental Microbiology 78: 3896-3904.
Jupiter S., Roff G., Marion G., Henderson M., Schrameyer V., Hoegh Guldberg O., 2008. Linkages between coral assemblages and coral proxies of terrestrial exposure along a cross-shelf gradient of the southern Great Barrier Reef. Coral Reefs, Vol. 27, pp. 887- 903.