Peter A. Tyler

13. Endemism in freshwater algae

Across the world there is a prevailing view that freshwater algae are cosmopolitan. The notion has seldom been tested and is unlikely to be true in genetic terms. Nonetheless, some morphospecies of several groups of algae do have a worldwide distribution. Others have restricted distributions and may be regarded as endemic to a region. However there is always the possibility that they will be discovered in far away places. Australia has a rather large element of endemicity in its algal flora. From the early days of Australian phycology many new genera and species of freshwater algae have been described. Some are of such distinctive appearance or novelty as to be regarded as ‘flagship’ taxa. There is little doubt about their endemicity and their existence increases the probability of less-distinguished species also being endemic. The degree of endemicity is probably masked by the ‘force-fitting’ of European names to Australian species.Some Australian endemics are robust and are widely distributed in a variety of types of water body. Others, the frail endemics, the ones of greatest novelty and phylogenetic significance, have a very restricted range with their strongholds in dystrophic coastal lagoons where tracts or remnant patches of native vegetation survive. Their survival and the conservation of their biodiversity depends on recognition of the significance of coastal lagoons and swamps.

Analysis of fossil pigments from algae and bacteria in meromictic Lake Fidler, Tasmania, and its application to lake management

Lake Fidler is an ectogenic meromictic lake with a monimolimnion maintained by periodic incursions of brackish water from the lower Gordon River estuary. A dam across the middle reaches of the Gordon River has restricted these incursions of brackish water and meromictic stability has rapidly declined. A palaeolimnological study was carried in order to assess the historical development of meromixis and the impact of the dam on the microbiological communities in the lake. Fossil pigments in a 17 m sediment core were analysed using reverse phase high performance liquid chromatography (rp-HPLC) and mass spectrometry (MS). In addition, taphonomic studies of pigment production, deposition and degradation in the water column and surface sediments were used to identify planktonic and benthic pigment degradation processes and constrain the stratigraphic interpretation. Results comparing the pigment composition of pelagic sediment traps and littoral surface sediments indicated that the core from the centre of the lake would permit a historical reconstruction of planktonic bacterial and algal communities. Marked increases in prokaryotic pigments ca 3500 yr B.P. suggested the possible colonisation of a chemocline by phototrophic bacteria. Further changes in chlorophyll: carotenoid ratios and changes in relative abundances of both chlorophyll a and bacteriochlorophyll c derivatives also indicated that a change in the depositional environment had occurred; possibly due to altered stratification or anoxia. From this we infer the onset of either intermittent or permanent meromixis. Further increases in prokaryotic pigment abundance suggested that the present state of permanent meromixis was firmly established by 2070 ±50 14C yr B.P., and diatom analysis confirmed the development of a stable mixolimnion. High resolution studies of the top 10 cm of sediments measured pigments in mean concentrations of 15.1 ng g-1 with a mean S.D. of only 2.78 indicating little change in pigment abundance since the construction of the dam. Thus, Lake Fidler still retains most of the features of meromixis. However, evidence from nearby Lake Morrison and Sulphide Pool has shown that any further declines in meromictic stability will cause a rapid reversion to holomixis. Palaeolimnological evidence from the early stages of meromictic development of Lake Fidler suggests that such reversion to holomixis may not permanently eliminate all the microbiological communities, and that, given time, they may return and prosper with re-establishment of a suitable chemocline. These studies will guide recommendations for a management strategy to prevent the further decay of meromixis in the Gordon River lakes.

A lakeland from the dreamtime the second founders' lecture

The mountainous wilderness of Tasmanias World Heritage Area and contiguous land is a district of lakes and rivers of immense beauty and interest. A congruence of change in climate, relief, geology, soils and vegetation divides the island into western and eastern provinces. A jagged, western land of ancient rocks is mantled by peat-forming rainforest and sedgeland, where creeks run, unenriched with minerals, to topaz, red-window lakes. Eastwards lies a younger, flatter land, covered by sclerophyll forests of Eucalyptus. Minerals from the soluble rocks give the lakes distinctive chemistry compared with the brown dilute sea-water which drains the western quartz. No peat extracts stain these eastern lakes and they lie crystal clear with deep green windows. In this wilderness is a rich diversity of rare microscopic organisms. Some, long forgotten, have been rediscovered there. Others, new and novel, turn up with every cast of the net. Among the richest sites are the coastal, fresh-water lagoons which the Abor...

The palaeolimnology of Lake Fidler, a meromictic lake in south-west Tasmania and the significance of recent human impact

Three meromictic lakes in the World Heritage Area of south-west Tasmania possess unusual microbiological communities. Their meromixis is maintained by periodic incursions of brackish water from the nearby Gordon River which, in its lower reaches, is a salt-wedge estuary. In 1977 the construction of a dam in the middle reaches of the river restricted penetration of the salt-wedge and meromixis rapidly declined in all three lakes. A palaeolimnological study was carried out on one of the lakes, Lake Fidler, firstly to determine the history of meromixis and its associated microbiological communities, and secondly to assess whether the recent and rapid decline of meromixis is inconsistent with natural rates of development of the Gordon River meromictic lakes. One part of this study included the analysis of the stratigraphy of fossil diatoms from a 17-metre sediment core dating back 8000 yrs. Detrended Correspondence Analysis and Analog Matching were used to compare diatom species assemblages in core samples with diatom samples from a reference dataset consisting of a selection of lake and river sites in the lower Gordon River valley. Five distinct stratigraphic zones were identified in the core. These zones indicated specific stages in the development of the Gordon River lakes from river backwaters to ectogenically-maintained meromictic lakes which will, finally, become terrestrialised by encroaching rainforest. The onset of a stratified water column was identified by the emergence of a dominant freshwater algal flora which suggested that the lake had developed a mixolimnion and become meromictic ca. 2070 ± 50 14C yrs ago. In the context of this long history of meromixis, the rapid demise in meromictic stability following construction of the dam is judged to be inconsistent with natural rates of development. The palaeolimnological studies, of which this paper is one part, prompt recommendations for a management strategy to prevent the further decay of these meromictic lakes in the World Heritage Area.

The Microanatomy and Ecology of ‘Chlorochromatium aggregatunf in Two Meromictic Lakes in Tasmania

SUMMARY: The motile ectosymbiotic consortium “Chlorochromatium aggregatum” occurs in large numbers in two meromictic lakes in Tasmania. In its structure it resembles specimens previously described, except that vesicles or mesosomes are present in the central bacterium. The population occupies a narrow stratum near the chemocline, but may occur either above or below it, in microaerobic or anaerobic conditions, respectively. Its presence under aerobic conditions need not invalidate previous hypotheses concerning the mutualistic relationship between the two partners of the consortium.

Palynological evidence for Holocene palaeoenvironments from the lower Gordon River valley, in the World Heritage Area of southwest Tasmania

A Holocene palaeoenvironmental history from the World Heritage Area of southwest Tasmania is reconstructed using an 8000-year palynological record from Lake Fidler, a small meromictic lake adjacent to the lower reaches of the Gordon River. The sequence indicates that cool temperate rainforest has remained dominant in the region for at least the last 8000 years, confirming the wilderness value of this important conservation area. There is little evidence for fire in the region throughout this period and no discernible evidence for anthropogenic impact until approximately 1815 when small-scale convict logging activities commenced along the Gordon River. The record demonstrates the long-term presence of stands of one of the worlds oldest living trees, Huon pine (Lagarostrobos franklinii), with significant increases in this species in the mid-to late Holocene. This expansion is evident in several Tasmanian records and is associated with declines in other important Tasmanian plant species. It is proposed that it represents a regional phenomenon possibly related to climate change. Examination of the climate signal from other Australian Holocene pollen records provides some support for this interpretation.

Morphology and taxonomy of Cyclotella tasmanica spec. nov, a newly described diatom from Tasmanian lakes

A species of Cyclotella with an elliptical valve outline has been found in several Tasmanian lakes and is herein described and named C. tasmanica nov. sp. Morphologically, it is similar to C. stelligera and, to a lesser extent, to C. radiosa. The valve has coarse, clearly alveolate, marginal striae and a central rosette. Unlike other elliptical forms, the central area is always more or less circular. The nearest similar species is C. rhomboideo-elliptica.

The recent palaeolimnology of Lake Nicholls, Mount Field National Park, Tasmania

Analyses were carried out for diatoms, spherical carbonaceous particles, and magnetic minerals on a short sediment core from a small cirque lake, Lake Nicholls, in the Mount Field National Park, south-west Tasmania.