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Phytoplankton past and present : ecology and biodiversity of marine microalgal communities with particular emphasis on Antarctic ecosystems
thesisposted on 2023-05-27, 22:17 authored by McMinn, A
Dinoflagellate cysts and Diatoms. I have been working with the microalgal Divisions, Bascillariophyta (diatoms) and Dinophyta (dinoflagellates) since I began my PhD project on Late Cretaceous Dinoflagellate cyst biostratigraphy of northwestern Australia in 1978. Fossil microalgae, principally diatoms, dinoflagellates and coccolithophoroids have been used extensively in palaeoecology and biostratigraphy throughout the world. As a result of regional endemism, Australian communities were often different from those elsewhere. This is clearly demonstrated in northern Australia during the Mesozoic (papers 1, 10) and Neogene (papers 9, 15) and in the Neogene of southern Australia (paper 8). Using dinoflagellate cysts I was able to establish regional biostratigraphies of the late Cretaceous (1) and Neogene (9, 15) of northern Australia and the Neogene of southern Australia (8). In order to better understand the palaeo environmental implications of dinoflagellate distributions I began to work on modern, living dinoflagellate communities in 1988. Dinoflagellates and diatoms both respond rapidly to changes in the environment and this allows them to be used in detailed reconstructions of past environmental and climate change. In Australia changes in dinflagellate cyst distributions have been used to demonstrate changes in water temperature, salinity and urbanization. My early work concentrated on determining the relationship between the distribution of dinoflagellate cysts and environmental gradients; in particular temperature and latitude (papers 4, 6, 26), salinity (papers 5, 6, 8) distance from shore (paper 9) and with particular water bodies (papers 17, 22). This information was then used to characterize Quaternary and Holocene climate change around Australia (papers 2, 3, 5, 8, 11, 12, 15, 16, 29, 68). This work was reviewed in paper 68. The dinoflagellate Gymnodinium catenatum produces the paralytic shellfish toxin, saxitoxin, which has been associated with many human shellfish poisonings. It produces a fossilizable cyst, which enables its presence to be detected in modern and ancient sediments. In 1988 it was detected for the first time in the Derwent River, Hobart. I was able to demonstrate that the species was not endemic to the area but had been introduced via ballast water (paper 33). This was the first conclusive evidence anywhere of a genuine ballast water introduction. We were subsequently able to demonstrate further introductions at Port Lincoln, South Australia (paper 54) and in North Island New Zealand (paper 71). We are continuing to look at the effect of ballast and hull fouling organisms on Antarctic and SubAntarctic environments (paper 72). Diatom remains can also be used to interpret past environmental conditions. They are particularly valuable in Antarctica, where they usually dominate marine and lacustrine sediments. By identifying living diatom communities associated with 5 different types of sea ice in near shore marine environments I have been able to use diatom remains to interpret past sea ice conditions (papers 14, 20, 21, 24, 27, 49). This has then allowed inferences to be made about changes in climate over the last 10,0000 years (papers 52, 60, 61, 65). A close examination of sea ice algal ecology also revealed how sea ice communities utilize and recycle nutrients and 13C (paper 41). This enabled a model to be developed that can interpret past nutrient levels and rates of productivity (paper 44). High latitude lakes provide a particularly valuable archive of recent climate change. By developing high precision transfer functions based on the salinity preferences of diatoms in Antarctic saline lakes (papers 28, 36, 38, 42), and by modeling lake basin hydrology (paper 48) we have been able to reconstruct changes in atmospheric temperatures, evaporation rates and precipitation (papers 53, 63, 86). A correlation with ice core records demonstrated the value and utility of this approach (paper 58). Antarctic microalgal ecology. Each year sea ice expands to cover over 20 million square kilometers of the Southern Ocean. This sea ice contains an immense biomass of microalgae, which contributes between 20-50% of the primary production of the seasonally ice covered areas of the Southern Ocean. Conventional methods of measuring primary production destroy the ice environment of the sea ice algae and lead to an over estimation of photosynthesis. I have developed a novel method, which uses the flux of oxygen across the ice-water boundary layer to estimate photosynthetic rates (papers 37, 51, 66, 77). The theory and practice have been modified from work on sediment microbial mat communities. This work has been very successful and is continuing to be used in sea ice productivity studies from both the Arctic and the Antarctic. This use of microsensors allows photosynthesis to be measured in situ and without impacting the algal community at all. Recently we have also used a customized Pulse Amplitude Modulation (PAM) fluorometer to investigate in situ sea ice and benthic microalgal photosynthesis (papers 80, 84, 87) in Antarctica and the Arctic. This will form the basis for an ongoing study on the effects of global climate change on Antarctic coastal primary production. I have also examined the effects of nutrient limitation (McMinn et al. 1999), ultra violet radiation (papers 18, 35, 45, 67, 80), currents (51) and oxygen toxicity on sea ice algal photosynthesis. During the early part of my career I also worked on Australian and Antarctic fossil palynolgy. These studies are only distantly related to the main themes of my subsequent research and so are listed separately (A1-A25). I have also been involved in a number of studies of Antarctic fauna which are unrelated to algae and these are also listed separately (B1-B5).
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