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Introduction
Keith Walker died suddenly on the 27th February 2016.
For more than 40 years, Keith worked on the fauna (including freshwater mussels), flora and ecology of rivers and floodplains, especially in the Murray-Darling Basin. He was an inspirational teacher, supervising many honours and PhD students, many of whom have gone on to make significant contributions.
This researchgate page will be maintained so that others can continue to access his substantial contribution to ecology.
Current institution
Additional affiliations
January 2008 - present
January 1975 - December 2007
Position
- Professor (Associate)
Description
- Research Methods (incl biostatistics) Invertebrate Zoology Freshwater Ecology
January 1997 - December 1999
Australian Agency for International Development (AusAID)
Position
- SubProgram Leader
Publications
Publications (259)
The conservation biology of Australasian freshwater mussels is hindered by lack of a taxonomic framework that employs molecular data as a complement to shell characters, larval forms and internal anatomy. The fauna includes more than 32 known species (30? Hyriidae, 2 Unionidae), but has not been revised for 55 years, despite minor amendments. The h...
In Australia, New Guinea, Solomon Islands and New Zealand, freshwater mussels are represented by the families Hyriidae and Unionidae. The Hyriidae includes 27 species in 8 genera, in the subfamilies Cucumerunioninae, Hyridellinae, Lortiellinae and Velesunioninae (a fifth subfamily, the Hyriinae, is endemic to South America). Two other species (one...
For species to persist on floodplains and in temporary wetlands in arid climates, where large and unpredictable water level fluctuations are common, at least one life history stage must be able to survive inundation. We investigated the survival and performance (RGR, total biomass and above-to-belowground biomass (A:B)) of three common and often co...
The natural flow regime of the Murray River in south-eastern Australia has been fundamentally altered through regulation and extraction, with fewer, shorter floods, changing seasonality of flows and reduced floodplain connectivity. Ecosystems which evolved over millenia show serious stress and decline under the regulated regime. Environmental water...
Common carp, Cyprinus carpio L., a destructive invasive pest of the Murray–Darling Basin, Australia, move from rivers into wetlands to spawn, making them vulnerable to trapping, but traps may also capture and affect access for native species. This study trialled a trap designed to separate carp from native fish entering wetlands by exploiting their...
Regionalisations based on species assemblages are a useful framework for characterising ecological communities and revealing patterns in the environment. In the present study, multivariate analyses are used to discern large-scale patterns in fish assemblages in the Murray–Darling Basin, based on information from the Murray–Darling Basin Authority’s...
There are high rates of regional and global extinctions among freshwater species and few chances for recovery. We report here on the rediscovery after 30. years of a small fish, the southern-purple spotted gudgeon (Mogurnda adspersa), once widespread in the southern Murray-Darling Basin of south-eastern Australia. The rediscovery was in a region, t...
Colloff et al. (2015). Marine and Freshwater Research examined time-series data for flow-dependent vegetation, invertebrates, fish, frogs, reptiles and waterbirds in the Murray-Darling Basin, 1905 2013. They concluded that temporal patterns fluctuated, declining during droughts and recovering after floods. They suggested that major changes in land...
Colloff et al. in Marine and Freshwater Research (http:dx.doi.org/10.1071/MF14067) examined time-series data for flow-dependent vegetation, invertebrates, fish, frogs, reptiles and waterbirds in the Murray–Darling Basin, 1905–2013. They concluded that temporal patterns fluctuated, declining during droughts and recovering after floods. They suggeste...
The Riverland Ramsar site in south-eastern Australia has Limits of Acceptable Change (LAC) derived on the basis of hydrological regimes and vegetation requirements. This study evaluated LAC for the site against trajectories of environmental change including increasing river regulation and changing climate. The study identified a high likelihood of...
Conservation status assessment of the 'Glenelg Freshwater Mussel' Hyridella glenelgensis, from western Victoria, Australia - assessed as CR - Critically Endangered.
Conservation status assessment of the 'Southern River Mussel' Hyridella narracanensis from south-eastern Australia. Assessed as Near Threatened.
Conservation status assessment of the 'South Esk Freshwater Mussel' Velesunio moretonicus, from Tasmania, Australia, assessed as NT - Near Threatened.
Conservation status of 'Carter's Freshwater Mussel' Westralunio carteri, from south-western Australia, assessed as VU - Vulnerable.
Conservation status assessment of the 'Australian River Mussel' Cucumerunio novaehollandiae, from eastern Australia, assessed as LC - Least Concern.
Increased hydraulic diversity could be a means to promote fish diversity in rivers, but little is known of the behaviour of fish in hydraulic environments. This study concerns the behaviour of two species of small native Australian freshwater fish in variable hydraulic environments and ecological habit, with regard for (a) whether the apparent diff...
The ecological communities of the River Murray and its floodplain wetlands and woodlands are adapted to a highly variable flow regime. Today, the Murray is intensively regulated for irrigation and other uses, and is a vital water resource in a dry region. Flow regulation and diversions increased rapidly in the latter half of the 20th Century, but g...
The ecological communities of the River Murray and its floodplain wetlands and woodlands are adapted to a highly variable flow regime. Today, the Murray is intensively regulated for irrigation and other uses, and is a vital water resource in a dry region. Flow regulation and diversions increased rapidly in the latter half of the 20th Century, but g...
Environmental Water Allocations (EWAs) are used to enhance native flora and fauna in regulated rivers, but may also benefit alien invasive species like common carp (Cyprinus carpio). We examined the invasion and spawning risk posed by adult common carp during an EWA delivered from the River Murray to a flow-through wetland in South Australia from J...
Access to offstream habitats is vital for many freshwater fish, but details of their lateral movements are scarce. We describe the movements of fish between the channel of the River Murray and six perennially inundated wetlands in South Australia from August to November 2006. At this time there were unprecedented low flows in the river owing to the...
The state of global freshwater ecosystems is increasingly parlous with water resource development degrading high-conservation wetlands. Rehabilitation is challenging because necessary increases in environmental flows have concomitant social impacts, complicated because many rivers flow between jurisdictions or countries. Australia’s Murray–Darling...
Swimming ability tests can inform physiological, biological and ecological studies, but there are few such data available for Australian freshwater fish. Here, an incremental velocity test was used to assess the swimming ability of three common species, namely Australian smelt, common galaxias and flat-headed gudgeon. Body form is one indicator of...
![Fig. 7. Valleys ranked by SR Macroinvertebrate Index (SR]MI) scores....](profile/Keith-Walker-13/publication/248887762/figure/fig3/AS:671507260903436@1537111215805/alleys-ranked-by-SR-Macroinvertebrate-Index-SRMI-scores-Symbols-as-for-Fig-6-For_Q320.jpg)
The Sustainable Rivers Audit (SRA) is a systematic assessment of the health of river ecosystems in the Murray–Darling Basin (MDB), Australia. It has similarities to the United States’ Environmental Monitoring and Assessment Program, the European Water Framework Directive and the South African River Health Program, but is designed expressly to repre...
Includes
Climate change and water allocation planning: biotic perspective: pp. 25-44
Molecular genetic information should be a pre-requisite when evaluating conservation priorities in highly structured species
such as freshwater fishes. Nuclear (allozyme) and mitochondrial (cytochrome b) markers were used to investigate phylogeographic structure in the Yarra pygmy perch Nannoperca obscura (Klunzinger), a threatened freshwater fish...
Physa acuta (Draparnaud), an invasive species from Europe, is the most abundant freshwater snail in the Lower River Murray. Its ascendancy follows a general decline of native species, including the morphologically and ecologically similar Glyptophysa gibbosa (Gould). We began with two hypotheses. The first required comparisons of the salinity and t...
Freshwater ecosystems are a foundation of our social, cultural, spiritual and economic well being. The degraded condition of many of Australia’s river ecosystems is testament to our failure to manage these resources wisely. Ecosystem science involves the holistic study of complex biophysical systems to understand the drivers that influence ecologic...
1.Hyridella glenelgensis is a small freshwater mussel that occurs in the Glenelg–Wannon river system in south-western Victoria and is listed as ‘threatened’ under the state Flora and Fauna Guarantee Act 1988. The species has rarely been reported since its discovery in 1898, and there are no records from the late 1920s until 1990, and again in 2000,...
Abstract – Fragmented populations of freshwater fish may develop genotypic and phenotypic differences as adaptations to local habitat conditions. These differences contribute significantly to biological diversity and may lead to speciation. In the Murray–Darling Basin, Australia, the Murray hardyhead Craterocephalus fluviatilis, listed as ‘endange...
Plant communities on the River Murray floodplain, South Australia, are degraded by flow regulation and salinization, with up to 95% of eucalypt trees being dead or dying from water stress. This paper describes the floodplain seed bank and its capacity to respond to floods or managed ‘environmental flows’. The soil seed bank contained mainly annual...
Salinisation in lowland areas of the Murray–Darling Basin, Australia, has had noticeable effects on fish. The endangered endemic Murray hardyhead Craterocephalus fluviatilis is distributed patchily and confined mainly to saline waters (0.4–20 g L–1), whereas the unspecked hardyhead C. stercusmuscarum fulvus has a more continuous distribution but is...
Availability: <http://search.informit.com.au/documentSummary;dn=588106192845597;res=IELENG>
ISBN: 0858257351.
Abstract
Diversions and regulation have reduced the frequency of flooding on the River Murray floodplain, causing the decline and death of floodplain vegetation. Now, after seven years without their key water source from flooding, river r...
Thickets of tangled lignum, a drought-tolerant perennial shrub, occur in flood-prone areas throughout central and eastern Australia, including large areas of the River Murray floodplain. In dry periods, lignum appears dry and lifeless, without leaves, flowers or green stems, but it recovers rapidly in response to flooding or rainfall. Little is kno...
Abstract – Comparative studies of related species may reveal the determinants of distribution and abundance, and elucidate the causes of fragmentation. The intensively regulated River Murray in south‐eastern Australia contains fragmented populations of several small fish species that have more common, widespread congeners. The Murray hardyhead Cra...
Trees on the River Murray floodplain in South Australia, particularly river red gum and black box (Myrtaceae: Eucalyptus camaldulensis, E. largiflorens), are increasingly water-stressed as the period since effective overbank flows extends to six years. As a result of declining health and dry conditions, recruitment rates in these species are insuff...
The smelt genus Retropinna nominally includes three small (<150 mm) freshwater fish species endemic to south-eastern Australia and New Zealand. For the two Australian species, the broad range of R. semoni (Weber) on the mainland suggests some vulnerability to isolation and genetic divergence, whereas the apparent confinement of R. tasmanica McCullo...
The lower Murray population of bony bream is subject to an annual epidemic of the oomycete Saprolegnia (principally S. parasitica) and the bacterium Aeromonas hydrophila. The epidemic is species-specific; it mainly affects adults whose susceptibility may be increased by stress due to winter cold. Lesions occur on the mid-flank and are characterized...
Salinisation in the Murray–Darling Basin, Australia, may affect aquatic flora and fauna, including the common carp, an alien species that has become the most common fish in the river system. This study describes the responses of juvenile carp (31–108 mm total length) to salinity levels that prevail in some wetlands of the lower reaches of the River...
For populations to persist, recruitment must keep pace with mortality. In variable environments, opportunities for reproduction occur patchily in time and space, and favourable conditions must occur sufficiently often to allow growth to maturity (hence ‘recruitment’). The risks of local extinctions may be increased by anthropogenic factors. This sc...
Tangled lignum (‘lignum’) is a dioecious, multi-stemmed woody shrub that is common in flood-prone areas of inland Australia, including the Murray–Darling Basin. It is often leafless during dry periods, but maintains vegetative growth by stem layering, and responds rapidly to rainfall or flooding by production of shoots, leaves and flowers. This stu...
In October 2000, the flow of the River Murray entering South Australia was increased from 32 000 to 42 050 ML day−1 by release of water from an offstream reservoir, and a downstream weir was raised by 500 mm to impound the flood and enhance local floodplain inundation. The flood was maintained for about two weeks, although the duration of inundatio...
Strandlines are mounds of organic matter deposited around lake edges by the action of waves and seiches. In the Menindee Lakes they form multiple discontinuous rings around the edges of the lakes. The strandlines and adjacent sediment of four lakes (three large regulated lakes and one small minimally impacted lake) in the Menindee Lakes system were...
Published data, recent surveys and studies of museum specimens are combined to provide a list of 84 fishes for South Australia in five drainage divisions. The list includes 58 native species (44 restricted to freshwater) and 26 alien species. Seven endemics are recognised, namely Chlamydogobius eremius (Zeitz), Chlamydogobius gloveri Larson, Crater...
Young-of-the-year (YOY) samples, gonadosomatic index (GSI) and the histological staging of ovaries were used to monitor the reproduction of common carp (Cyprinus carpio L.) in the lower River Murray, South Australia, from August 2001 to December 2002. Spawning occurred initially over 9 months from late September 2001 to May 2002, the longest period...
In the Lake Eyre Basin, the Australian hyriid genus Velesunio is represented by three undescribed species, each of which are highly divergent genetically, but morphologically similar to Velesunio wilsonii (Lea 1859). A fourth species, Velesunio ambiguus (Philippi 1847), occurs not only in the Lake Eyre Basin but throughout much of eastern Australia...
Gonado-somatic indices and macroscopic and histological changes to gonads were monitored in an aggregate sample of 231 male and female common carp Cyprinus carpio(359–755 mm total length LT) from the River Murray in South Australia between November 2001 and October 2002. Histological inspection was most accurate and macroscopic inspection was not p...
Forty carp larvae were reared from eggs spawned in the Torrens River, Adelaide, South Australia, and their otoliths were examined at the time of hatching or at 6, 10, 15 or 20 days after hatching (post-hatch). Using light- and scanning electron microscopy (SEM), otolith increments were counted and compared with known post-hatch ages. Typically, the...
First published 2002, published online 2004
The weeping willow Salix babylonica and crack willow S. fragilis dominate the riparian vegetation of the River Murray between Mannum and Wellington, South Australia, Australia. The presence of S. fragilis is confirmed, over-riding earlier, informal references to S. × rubens. In this region S. babylonica is represented by females and S. fragilis is...
Questions
Questions (4)
In reviewing research on Australian species (Hyriidae), I’ve encountered many examples where sex ratios are clearly biased towards males or females. These often are large samples, numbering in the hundreds, and most of the biases are statistically significant. I know that age and population density are implicated in research on species of Margaritiferidae and Unionidae, and that there may be differential mortality associated with dissolved oxygen levels (in that situation, brooding females are more vulnerable to hypoxia than males). The incidence of hermaphrodites may also need to be factored in.
In our Australian examples, the biases for any one species may differ between different times or places. There is little possibility of biased sampling, as these species are not sexually dimorphic.
Is anyone aware of published studies that shed more light on these seemingly haphazard shifts in favour of one sex or the other?
Pedal feeding is associated with juvenile freshwater mussels, yet some species (e.g. Margaritifera margaritifera) live in streams with a consistently low supply of suspended organic particles as food.
Are there any studies to show that pedal feeding is maintained (as a supplement to filter feeding) by the adults of species in highland streams and karst waters?
When collecting freshwater mussels in remote areas, it’s often impractical to use ethanol as a preservative. Especially for amateur collectors without access to laboratories.
Samples collected in the field might need to be stored briefly, then posted to a laboratory. The sample might consist of a snip of mantle tissue (possibly the whole body plus shell). On receipt, the tissue could be transferred to ethanol if necessary.
Some alternatives that have been suggested include overproof rum, whisky, vodka or other strong spirits, and car antifreeze.
Are there proven options for freshwater molluscs, including freshwater mussels?
This paper describes options for insects (ok for molluscs too?):
Steininger S, Storer C, Hulcr J & Lucky, A. (2015) Alternative preservatives of insect DNA for citizen science and other low-cost applications. Invertebrate Systematics 29, 468–472. Prevention of DNA degradation is essential to conducting molecular analyses of field-captured specimens. This is especially important for projects that incorporate participation of non-specialists in research, such as agency monitoring of pests, or citizen science, where standard methods of preservation may be inaccessible. We examined efficacy of three common alternative products as a substitute for 95% ethanol or pure propylene glycol in preserving DNA: alcohol based hand sanitiser and propylene and ethylene glycol-based automobile antifreeze. We subjected Xylosandrus compactus ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) to each preservative for two or seven days under direct outdoor exposure and assessed relative quantity of intact DNA by performing real-time polymerase chain reaction amplification of a single-copy nuclear marker. Amplification was observed in all treatments and electrophoresis of the amplified product showed clear bands of the appropriate weight. Successful amplification of the target gene was verified by sequencing the amplified control. No statistically significant differences were found between the cycle threshold values of any treatment. Our results suggest that alcohol-based hand sanitiser and automobile antifreeze can successfully preserve DNA for short-term storage and serve as effective substitutes for laboratory-grade preservatives in citizen science projects, large-scale trapping projects or by professionals.
With colleagues*, I’m intrigued by a situation in a karst spring in Australia where the shells of Hyridella narracanensis are thin and fragile, whereas in rivers that do not contain hard water the shells of this species are ‘normal’.
A related species, H. glenelgensis, occurs in an adjacent river that is fed by surface runoff and also contains hard water, and the shells of that species are ‘normal’.
Populations of crayfish living in both the spring and the river have normal shells.
The total hardness of water in the spring and the river generally is above 300 mg/L as CaCO3. The supply of calcium cannot be an issue, and perhaps the supply of organic matter is implicated, given that it is a significant component of mollusc shell. The water in the karst spring is very clear, with scarcely any plankton or other suspended particles, whereas the water in nearby rivers is laden with suspended material.
One way to gather support for this idea might be to compare the organic contents of shell material from the spring and river (say, by combustion in a muffle furnace at 550C).
We know that species of Margaritifera occur in hard water, yet have normal shells, and that other species like Unio crassus have thin shells in hard water and normal shells elsewhere.
Is anyone aware of research to explain more clearly why some molluscs (bivalves and gastropods) have thin shells in hard water?
[ * Mark Adams, Hugh Jones, Michael Klunzinger, Tarmo Raadik, Kevin Roe, Peter Unmack ]
