Russell J. Shiel

Occurrence of aquatic invertebrates of the wheatbelt region of Western Australia in relation to salinity

The wheatbelt region of Western Australia has been extensively cleared of indigenous vegetation for agriculture and is now severely affected by dryland salinity. Wetlands that were once freshwater are now saline and others are under threat, as are the animals and plants that inhabit them. Rising groundwater is also affecting the many naturally saline playas. To provide a framework for setting conservation priorities in this region a biological survey was undertaken, including sampling of aquatic invertebrates at 230 wetlands. In this paper, we have used data from the survey to summarise occurrence of species in relation to salinity. Total species richness at a wetland showed no response to salinity below 4.1 g l−1 and then declined dramatically as salinity increased. When halophilic species were excluded from consideration, species richness was found to decline from 2.6 g l−1. These patterns are compared to previous studies of richness-salinity relationships. There is some evidence that the freshwater invertebrate fauna of the wheatbelt may be comparatively salt tolerant, with 46% of freshwater species collected at salinities above 3 g l−1 and 17% above 10 g l−1, though these proportions differed between various invertebrate groups. While this tolerance will provide a buffer against the effects of mild salinisation, many species are at risk of regional extinction as salinisation becomes more widespread.

Distribution of rotifers in North Island, New Zealand, and their potential use as bioindicators of lake trophic state

The distribution and ecology of planktonic rotifers was investigated in 33 lakes in the North Island, New Zealand, between 1997 and 1999. A total of 79 species of monogonont rotifer were identified, with an average of 21 species per lake, a diversity which is high in comparison with many previous New Zealand studies. Most species recorded were cosmopolitan taxa, and were widespread in their distribution over the North Island. Multivariate analyses (Multi-Dimensional Scaling and Canonical Correspondence Analysis) did not distinguish distinct lake groupings based on rotifer communities, but rather gradients in assemblages, which were most highly associated with lake trophic state. Based on these responses, the development of potential rotifer bioindicator schemes for lake trophic state is described and discussed.

Freshwater zooplankton in the Hawkesbury-Nepean River: comparison of community structure with other rivers

The Hawkesbury-Nepean River is a regulated coastal river in New South Wales, Australia. Between March 1992 and March 1993, the freshwater portion of the river was inhabited by a taxonomically rich (total: 116 taxa) and dense (annual mean community density: up to 1024 animals l-1) microzooplankton community, comparable to that in some of the large regulated temperate rivers in the Northern Hemisphere. The common zooplankton taxa in the river were similar to those observed in other rivers at the genus or species level, with a characteristic increase in protists ( Vorticella spp.) towards the downstream reaches of the river. Zooplankton community density in the Hawkesbury-Nepean River was, to some degree, predictable from river environmental variables: density was significantly negatively correlated with river flow rate but positively correlated with temperature, turbidity, conductivity, total phosphorus and chlorophyll a. The results of the present study generally conform to the hypothesis of similar structure of zooplankton communities in rivers, relative to that in lakes.

Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy

Abstract Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size).

The composition of aquatic communities in saline wetlands in Western Australia

Macrophytes, plankton samples, salinity and depth data were collected from wetlands in October 1981. Species diversity and distributions are recorded and relationships drawn between macrophytes and plankton occurrence. An examination of the data of Geddes et al. (1981) enables comparisons of species composition in a similar range of Western Australian lakes in 1978 at a different stage in the seasonal cycle. Comparison with the biota of salt lakes in Australias eastern states and elsewhere lead to biogeographical speculations for the macrophytes and for some of the planktonic species.

Responses of billabong rotifer communities to inundation

Daily plankton collections were taken from a billabong of the River Murray for two weeks prior to inundation in March 1990, and continued for ten days after flooding. Quantitative responses of the plankton community and the component species were analysed against measured environmental variables and between species. Rotifers and copepod nauplii were the predominant net plankton (> 53 µm). Significant negative or positive responses to inundation were detected for most common taxa of 63 rotifer species recorded. A four-fold dilution from intrusion of river water masked rapid population increases. Opportunistic responses to inundation appear to be a survival strategy in the highly unpredictable billabong environment.

Zooplankton diversity and assemblages in arid zone rivers of the Lake Eyre Basin, Australia

The responses of zooplankton assemblages in arid zone rivers to seasonal changes, flow events, drying and water quality changes are fundamental to our understanding of these unregulated rivers. For three years the zooplankton and littoral microfauna in three rivers in the Lake Eyre Basin were studied. A diverse assemblage was discovered with a total of 398 identifiable taxa being recorded, consisting of 72 protist, 227 rotifer and 93 microcrustacean taxa. Zooplankton diversity was highest in a boom phase during, or in the summer following, a large flood. The rotifer assemblage dominated during, or soon after, periods of flow. However, during the winter and early summer, there was a decline in rotifer taxon richness and abundance accompanied by an increase in microcrustacean taxon richness and abundance. The winter samples occurred during the recession of a large flood and the early summer samples during periods of no flow. These changes suggested the involvement of a strong annual cycle of ecosystem structure evident within the longer term patterns of boom and bust driven by the timing and size of flood events. Multivariate and regression analyses found that salinity was a significant and independent driver of assemblage composition.

Diatom and micro-invertebrate communities and environmental determinants in the western Australian wheatbelt: a response to salinization

Diatom and micro-invertebrate communities were analyzed in 56 lentic wetlands from the wheatbelt of Western Australia. Sixteen water quality parameters were measured at each habitat and were tested as determinants of diatom and micro-invertebrate distribution. Nearly all waters were dominated by Na1+ and Cl1− and over half had low buffering capacity (<2 meq/L as TCO). Salinities ranged from <1 to > 240 mS/cm; some hypersaline habitats had pH values as low as 2.1, but most sites were alkaline.Diatoms (165 taxa) were present in all habitats, with indications that assemblages are correlated with land-use practices, i.e., historical clearing of native vegetation for dryland agriculture with resultant hydrological problems of salinization and water-logging. A non-metric multidimensional ordination showed pH, salinity, TCO, and total phosphorus to be significantly correlated with diatom community structure. Principal components analysis showed similar patterns. A salinity index was also developed for numerically important diatom taxa. Principal components analysis showed similar patterns. Certain tolerant Bacillariales, including Hantzschia amphioxys, Nitzschia hybrida, Tryblionella hungarica, and N.recta, were numerically important taxa in wetlands with visible signs of salinization.Micro-invertebrates (143 taxa) were present in habitats with salinities up to 200 mS/cm. Multidimensional ordinations showed salinity to be significantly correlated with micro-invertebrate community structure. The cladoceran Daphniopsis queenslandensis, ostracods Australocypris insularis, Mytilocypris tasmanica chapmani, and Platycypris baueri, and copepods Apocyclops dengizicus and Mesochra nr. flava were numerically important micro-invertebrates in moderate to high salinity environments, including those with signs of salinization. The diatoms, Navicula minuscula var. muralis and Pinnularia divergentissa var.subrostrata, and the copepod, Calamoecia trilobata, were common inhabitants of the extreme hypersaline (≥75 mS/cm), acidic (<4) habitats. Diatom communities were similar to those previously reported for other regions in Australia subjected to salinization; there were some differences in micro-invertebrate communities.

Monitoring change in aquatic invertebrate biodiversity : sample size, faunal elements and analytical methods.

Replication is usually regarded as an integral part of biological sampling, yet the cost of extensive within-wetland replication prohibits its use in broad-scale monitoring of trends in aquatic invertebrate biodiversity. In this paper, we report results of testing an alternative protocol, whereby only two samples are collected from a wetland per monitoring event and then analysed using ordination to detect any changes in invertebrate biodiversity over time. Simulated data suggested ordination of combined data from the two samples would detect 20% species turnover and be a cost-effective method of monitoring changes in biodiversity, whereas power analyses showed about 10 samples were required to detect 20% change in species richness using ANOVA. Errors will be higher if years with extreme climatic events (e.g. drought), which often have dramatic short-term effects on invertebrate communities, are included in analyses. We also suggest that protocols for monitoring aquatic invertebrate biodiversity should include microinvertebrates. Almost half the species collected from the wetlands in this study were microinvertebrates and their biodiversity was poorly predicted by macroinvertebrate data.

Tale of a Sleeping Beauty: A New and Easily Cultured Model Organism for Experimental Studies on Bdelloid Rotifers

We present the description of a new species of bdelloid rotifer, Adineta ricciae n. sp., which emerged from dry mud of Ryan’s billabong, Victoria, Australia. Its conspicuous frontal eyes easily diagnose the species; it differs from A. oculata (Milne) by the position of the eyes and its general habitus. The animal came to our attention because it is exceptionally easy to culture, so that the species already is being used in diverse experimental studies utilising bdelloid rotifers as model organisms.