Astacopsis gouldi Clark in streams of the Gog Range, northern Tasmania: the effects of catchment disturbance

Populations of the giant freshwater crayfish, Astrzcopsisgoufdi, were sampled in the Gog Range, northern Tasmania. Ten sites were sampled in relatively undisturbed and minimally disturbed areas, and in areas with a history of severe catchment disturbance. Larger numbers of A. gouldi were caught in two streams with undisturbed catchments than in three streams in heavily disturbed catchments. Thus, the abundance of A. gouldi in the Cog Range appears to have been adversely affected as a result of the disturbance of the original vegetation. Although the precise mechanism of the impact cannot be determined from this study, sedimentation and the presence of culverts may be preventing recolonisation of the disturbed streams. This study indicates the potential for catchment disturbance to affect populations of A. gouldi and highlights the need for proper management of land uses that may be detrimental to this species

Effects of a gradient in river regulation on the longitudinal trends in water quality and benthic algal and macroinvertebrate assemblages in the Hunter River, Australia

River regulation impacts lotic ecosystem processes; however, the effect of a gradient of regulation on these attributes has rarely been studied. This study examined the effects of a river regulation gradient on longitudinal trends in water quality and benthic algal and macroinvertebrate assemblages in three tributaries of the Hunter River, New South Wales, Australia. Longitudinal patterns were expected to differ across rivers, with recovery being proportional to its regulation gradient. Significant differences in longitudinal trends were tested using permutational multivariate analysis of variance (PERMANOVA) through exploration of the river by distance from source interaction. Multi-dimensional scaling (MDS) ordination plots identified sites responsible for any significant interaction observed. Similarity percentage analysis (SIMPER) analyses identified variables/taxa responsible for differences at sites below dams. BEST analyses identified environmental variables best explaining biological assemblage patterns. Significant differences in longitudinal trends were observed for all attributes. Increases in the regulation gradient most affected macroinvertebrate assemblages, followed by water quality and benthic algal assemblages respectively. Downstream recovery was absent in the heavily regulated river at its most downstream site, whereas recovery was observed on corresponding sites of the moderately regulated river. The study suggests that a gradient in river regulation increases the magnitude of disruption of lotic ecosystems, with recovery dependent on this gradient. © 2012 CSIRO

Zooplankton responses to freshwater inflows and organic-matter pulses in a wave-dominated estuary

Freshwater inflow events play a major role in structuring estuarine zooplankton communities. Freshwater inflow events affect zooplankton directly through advective forcing and changes in salinity, and indirectly through changes to resources by the delivery of organic carbon and nutrients that can stimulate microbial and primary production. Here, we investigate changes to estuarine zooplankton assemblage structure, density and δ13C stable isotopes during a period of highly variable freshwater inflow in the Bega River estuary, Australia. High inflows resulted in a reduction of salinity and a shift in the zooplankton assemblage structure from purely estuarine taxa towards freshwater taxa. The density of select genera of rotifers, cladocera and, in the upper estuary, copepods, increased following inflows, concurrent with increases in the concentration of dissolved organic carbon and bacterial biomass. Redundancy analysis found that environmental variables including discharge, dissolved organic carbon, salinity and bacterial biomass explained 66-73% of zooplankton variation. Stable isotope results indicated that all copepod and cladocera species tested were predominantly supported by allochthonous carbon from terrestrial sources. The present results have provided important evidence that freshwater inflows play a critical role in structuring zooplankton assemblages and supporting increased production through the delivery of allochthonous organic carbon

Disruption in water quality patterns along the river continuum by a large bottom release dam

© 2015 Environment Institute of Australia and New Zealand Inc. Understanding longitudinal variation in water quality along rivers and how they are influenced by large dams is important for both ecological theory and river management. This study examines longitudinal changes in water quality downstream of a large bottom release dam (Lake Copeton) on the Gwydir River, Australia. We compared longitudinal changes in water quality variables from sites upstream and downstream of Lake Copeton over a two-year period and a total river distance of approximately 200 km. Lake Copeton acted as a source of nitrogen as nitrogen oxides (NOx) and phosphorus as filterable reactive phosphorus (FRP). A significant increase in the concentration of NOx and FRP was evident downstream of the dam, particularly in summer with elevated concentrations detected up to 60 km downstream. Significantly lower chlorophyll a (Chl-a) concentrations and electrical conductivity (EC) were evident below the dam. Mean nutrient concentrations declined with increased distance downstream of Lake Copeton while Chl-a concentrations increased, suggesting uptake by autotrophs. This study suggests that Copeton Dam disrupts the river continuum for nutrients, Chl-a and EC as predicted by the serial discontinuity concept, with recovery occurring approximately 60 km downstream

Terrestrial dissolved organic carbon subsidizes estuarine zooplankton: An in situ mesocosm study

© 2016 Association for the Sciences of Limnology and Oceanography. Freshwater inflows play an important role in delivering dissolved organic carbon (DOC) to estuaries. Episodic inputs of DOC may support increased bacterial production. However, the role of DOC in supporting zooplankton production is widely debated. To evaluate this role we performed an in situ mesocosm experiment in the Bega River estuary, Australia. We added a DOC leachate derived from terrestrial vegetation to 400 L mesocosm bags as treatments of +1.5, +3, and +16 mg C L-1 and monitored changes in carbon, nitrogen, phosphorus, bacteria, chlorophyll a (Chl a), and zooplankton over 22 d. Bacterial biomass peaked at day 2 and was highest in the +16 mg C L-1 treatment. Chl a was not significantly different between treatments. Mesozooplankton was dominated by copepodites of Gladioferens pectinatus and Sulcanus conflictus between days 5-9 and by adults between days 9-15. Significantly higher numbers of copepods were present in the +16 treatment followed by the +3 mg C L-1 treatment compared with the controls. Stable carbon isotope signatures of copepods in the +16 mg C L-1 treatment were significantly different from the control and showed leachate carbon supported between 29.3% and 55.8% of copepod biomass. These results suggest that the impact of allochthonous DOC loading events on estuarine zooplankton occurs over short periods, and that the magnitude of response is, in part, controlled by the quantity of bioavailable DOC loaded to the system. Our findings underscore the importance of microbial dynamics stimulated by DOC loading events from freshwater inflows as a trophic path in estuarine food webs

Food utilisation and digestive ability of aquatic and semi-terrestrial crayfishes, Cherax destructor and Engaeus sericatus (Astacidae, Parastacidae)

Both Engaeus sericatus and Cherax destructor are omnivorous crayfishes consuming a variety of food items. Materials identified in the faeces of both E. sericatus and C. destructor consisted of mainly plant material with minor amounts of arthropod animals, algae and fungi. The morphology of the gastric mill of C. destructor suggests that it is mainly involved in crushing of food material while the gastric mill of E. sericatus appears to be better suited to cutting of food material. Given this, the gastric mill of E. sericatus may be better able to cut the cellulose and hemicellulose fibres associated with fibrous plant material. In contrast, the gastric mill of C. destructor appears to be more efficient in grinding soft materials such as animal protein and algae. Both species accumulated high amounts of lipids in their midgut glands (about 60% of the dry mass) which were dominated by triacylglycerols (81&ndash;82% of total lipids). The dominating fatty acids were 16:0, 16:1(n-7), 18:1(n-9), 18:2(n-6), and 18:3(n-3). The two latter fatty acids can only be synthesised by plants, and are thus indicative of the consumption of terrestrial plants by the crayfishes. The similarity analysis of the fatty acid patterns showed three distinct clusters of plants and each of the crayfish species. The complement of digestive enzymes, proteinases, total cellulase, endo-&beta;-1,4-glucanase, &beta;-glucosidase, laminarinase and xylanase within midgut gland suggests that both C. destructor and E. sericatus are capable of hydrolysing a variety of substrates associated with an omnivorous diet. Higher activities of total cellulase, endo-&beta;-1,4-glucanase and &beta;-glucosidase indicate that E. sericatus is better able to hydrolyse cellulose within plant material than C. destructor. In contrast to E. sericatus, higher total protease and N-acetyl-&beta;-d-glucosaminidase activity in the midgut gland of C. destructor suggests that this species is better able to digest animal materials in the form of arthropods. Differences in total cellulase and gastric mill morphology suggest that E. sericatus is more efficient at digesting plant material than C. destructor. However, the contents of faecal pellets and the fatty acid compositions seem to indicate that both species opportunistically feed on the most abundant and easily accessible food items.<br /