Peter Ralph's research

Research of Aquatic Photosynthesis Group (APG)


Ecophysiology of seagrasses Over the past 8 years we have been trying to find a unique stress signature to identify the possible type of pollutant impacting on seagrasses, based on the fluorescence response. To date we have not achieved this objective, however we now know a lot more about the photosynthetic response of several seagrass species (Halophila ovalis, Zostera capricorni and Cymodocea serrulata) to sub-lethal stressors. Most of these trials were laboratory-based and highly manipulative, however we are now using field-based trials. This research project is being undertaken by Cate Macinnis. Hormosira banksii – an accidental finding Our main interest in macroalgae has been with one unusual, but very common Australasian species, Hormosira banksii. Back in the early 90's, Peter was doing some fieldwork with a group of geologists in a small saltmarsh in the back of Jervis Bay, where a population of what appeared to be H. banksii was found, however it was 2-3 times the size of what is usually found on rock platforms. After measuring the dimensions of many thousands of receptacles, enough data had been gathered to support a paper where we separated it into at least 3 growth forms (ecotypes). Then an Honours student (Cate Macinnis) did a comprehensive survey of growth forms from the Queensland border through to Adelaide. We wanted to know whether it was genotypic or phenotypic variation in these widely distributed populations. Was there a physiological advantage to any of these growth forms? Toxicity testing Now we are looking into the use of H. banksii in fluorescence-based toxicity tests. While H. banksii is used in a number of existing toxicity bioassays, it is hoped that we will be able to provide a new, more powerful method of assessing toxicant impact on macroalgae populations. This research project is being undertaken by Cliff Seery. We are also examining the effectiveness of gross pollutant traps in reducing the toxicity of stormwater. This Honours project is using an innovative new instrument to assess toxicity, a Toxy-PAM. We measure the impact of stormwater on the photosynthesis of phytoplankton. This research project is being undertaken by Rachel Smith. Mechanistic uptake of uranium in freshwater macrophytes Uranium is a poorly understood heavy metal with respect to plant health, yet its mining and use generates wide public interest. We are looking at a range of issues associated with the uptake, toxicity and tolerance of a freshwater macrophyte to uranium. This research project is being undertaken by Amanda Charles. Community structure of phytoplankton in Gippsland Lakes Phytoplankton are important as the base of aquatic food chains, and any pollutant which impacts on the plankton will effect the higher order consumers, such as fish and invertebrates. We are looking at the phytoplankton ecology of the Gippsland Lakes coastal lagoon systems. An EPA-funded post doc has begun looking into the use of fluorometry to understand changes in these phytoplankton communities. Coral bleaching and photobiology At a first glance, a coral looks pretty uniform in its structure, however a polyp is not the same at the top and bottom of a branch. The coral colony is a highly variable group of tissues. Corals lend themselves to microscale investigations, at the macro-scale a branch has a multitude of microhabitats due to changes in light and current, so the physiology of a single polyp changes depending on its location within the colony. We are only just starting to understand the microscale variations of corals. We were able to measure the difference in photosynthesis of the zooxanthellae (algal symbionts) at the scale of 100 micrometres, that is a little thicker than a human hair. We have also looked into the photosynthesis of the zooxanthellae during a bleaching event. We have found that many of the expelled zooxanthellae are actually alive not dead as previously thought. Our coral research program is continuing to look into mechanisms of bleaching; triggers, responses, and possible recovery. For details on coral photokinetics, see Ross Hill's research page For details on the interaction of coral genetics and photokinetics, see Karin Ulstrup's research page See ABC News in Science for a recent article on this research project. Introduction to PAM fluorometry A lot of our research is associated with PAM fluorometers, these instruments measure the photosynthetic activity of a plant, seagrass, phytoplankton or coral. A fluorometer exposes a leaf to light and then measures the amount of light that is re-emitted from the leaf in the form of chlorophyll a fluorescence. The more light re-emitted, the less light has been used in photosynthesis, suggesting the plant is under photosynthetic stress. Click here to learn more about PAM fluorometry Publications