On the freshwater crustaceans of the Central Plateau

Although the waters of the Central Plateau harbour a number of interesting planktonic crustaceans, in these notes we are primarily concerned with the large macroscopic crustaceans. Among the non-malacostracan crustaceans, the orders Anostraca, Notostraca, Conchostraca and sub-class Branchiura are not present on the Central Plateau

Aquatic invertebrate fauna of western Tasmania

Although there are close associations with the south-western fauna , there are nevertheless some aquatic invertebrates found predominantly in western Tasmania, and some biological problems best studied by reference to such animals; examples from two families of crustacea and two insect orders are discussed in this paper . Western Tasmania may be regarded as the freshwater crayfish ( Parastacidae) centre of the State , all four Tasmanian genera being found there . Each genus is discussed in turn ; the habitats utilised are considered and adaptation to these habitats is illustrated by particular reference to burrow systems , calcium distribution in the exoskeleton and where possible , breeding patterns . Data is also provided on distribut i on and associated zoogeographical questions are briefly considered . Two genera of the fami ly Koonungidae ( Syncarida) are found in the west - Micraspides and Koonunga . Their habitats �nd distribution are discus s ed and att ent ion is drawn to the need for more ecological data in order to formulate answers to the zoogeographical issues invo lved . The Odonata exemplify an insect order with g enerally good dispersal power s . Al l dragonfly species found in west ern Tasmania, t ogether with their nymphal habitats, are co llated and discussed. The mo st interest ing speci es are the co ld- c l imat e adapted species , especial ly archai cs such as Archipetalia auriculata and Synthemiopsis gomphomacromioides. At t ention is drawn to the probable importance of diapaus e as an adaptat ion to cold montane habitat s . Three component s are recogni sed in the odonatan fauna , - cosmopo l i tan groups , anci ent Aus tralasian groups , and very anc i ent Gondwanal and re lict s . The Plecoptera is an order demonstrat ing poor vagi l i ty and only 6 of 31 Tasmani an species are shared with mainl and Aus tral i a . The maj ori ty of Tasmanian speci es are cold c l imat e adapted forms and cons equent ly west ern wat ers have a part i cularly conspi cuous s tone fly fauna . Data on the habitats and di stribut ion of a l l speci es found in west ern Tasmania is co l l at ed and discussed. The influence of man on aquat ic environments in west ern Tasmania is bri efly cons idered . Environmental modi fication result s from mining act ivities , hydro -el ectri c deve l opmen t , fore s try practices and from the introduction of exotic speci es such a

Histological and histochemical observations of the cephalic neurosecretory system of the crab, Paragrapsus Gaimardii (H. Milne Edwards)

Anatomical, cytological and histochemical features of the neurosecretory system of the crab, Paragrapsus gaimardii are described, In the brain and the commissural ganglia, three types of neurosecretory cells are distinguished, The distribution of these cells in the brain and the commissural ganglia is described. In the eyestalk, four types of neurosecretory cells are identified and the distribution of these cells is described. The neurosecretory cells of the brain, the commissural ganglia, and of the eyes talks are all paraJdehyde fuchsin - positive (PFpositive), Their tinctorial properties with the chrome, haematoxylin phloxine technique are described. The neurohaemaJ organ of the eyestalk, the sinus gland, is described both as regards its anatomical characters and its staining properties. The presence of allochthonous cells in the sinus gland is revealed, The allochthonous neuroglial cells of the sinus gland do not appear to be active gliosecretory cells, However, some of the neuroglial cells of the brain, especially those of the protocerebrum, do appear to be active gliosecretory cells. The neurosecretory material of the cephalic neurosecretory system of P. gaimardii is proteinaceous with disulphide groups being markedly presen

A reconnaissance of pollution of the King River in the Comstock-Crotty area, west Tasmania

In November 1974 ,an investigation was made of the King River through the stretch from just above its junction with Comstock Creek to just above its junction with the Governor River. Sampling stations were selected at nine sites, six on the King River, one on Linda Creek, one on Comstock Creek and one on the Governor River. At each station, samples were taken of the water, of the sediments and of the benthic macro­invertebrates. Analysis of the sediment samples provided good evidence that the King River is polluted from Comstock Creek downstream, with copper and, to a lesser extent, lead and zinc. This pollution is clearly indicated in the distribution of the riffle-­dwelling macroinvertebrates and of trout. The Governor River and the King River up­stream of Comstock Creek are not polluted. A 24-hour sampling of the drift fauna in the King River just above and just below the entry of Comstock Creek showed a surprising drop in the abundance of the drift with the entry of pollution. The results of the survey are discussed in the light of overseas work on stream sediments and Australian and overseas work on the effects of metal pollution on stream fauna. The pollution, even if steps are made to abate it, is likely to persist for a very long time

Observations on the freshwater fish of a small Tasmanian coastal stream

Fish were collected on two occassions, May and December 1976, by electro-fishing from Parsons Bay Creek, a small coastal stream in southeastearn Tasmania

General Minimal Flavor Violation

A model independent study of the minimal flavor violation (MFV) framework is presented, where the only sources of flavor breaking at low energy are the up and down Yukawa matrices. Two limits are identified for the Yukawa coupling expansion: linear MFV, where it is truncated at the leading terms, and nonlinear MFV, where such a truncation is not possible due to large third generation Yukawa couplings. These are then resummed to all orders using non-linear sigma-model techniques familiar from models of collective breaking. Generically, flavor diagonal CP violating (CPV) sources in the UV can induce O(1) CPV in processes involving third generation quarks. Due to a residual U(2) symmetry, the extra CPV in B_d-\bar B_d mixing is bounded by CPV in B_s-\bar B_s mixing. If operators with right-handed light quarks are subdominant, the extra CPV is equal in the two systems, and is negligible in processes involving only the first two generations. We find large enhancements in the up type sector, both in CPV in D-\bar D mixing and in top flavor violation.Comment: 5 pages and no figure

Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances

Gravitational collapse with tachyon field and barotropic fluid

A particular class of space-time, with a tachyon field, \phi, and a barotropic fluid constituting the matter content, is considered herein as a model for gravitational collapse. For simplicity, the tachyon potential is assumed to be of inverse square form i.e., V(\phi) \sim \phi^{-2}. Our purpose, by making use of the specific kinematical features of the tachyon, which are rather different from a standard scalar field, is to establish the several types of asymptotic behavior that our matter content induces. Employing a dynamical system analysis, complemented by a thorough numerical study, we find classical solutions corresponding to a naked singularity or a black hole formation. In particular, there is a subset where the fluid and tachyon participate in an interesting tracking behaviour, depending sensitively on the initial conditions for the energy densities of the tachyon field and barotropic fluid. Two other classes of solutions are present, corresponding respectively, to either a tachyon or a barotropic fluid regime. Which of these emerges as dominant, will depend on the choice of the barotropic parameter, \gamma. Furthermore, these collapsing scenarios both have as final state the formation of a black hole.Comment: 18 pages, 7 figures. v3: minor changes. Final version to appear in GR

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

The headwaters of karst rivers experience considerable hydrological variability, including spates and streambed drying. Extreme summer flooding on the River Lathkill (Derbyshire, UK) provided the opportunity to examine the invertebrate community response to unseasonal spate flows, flow recession and, at temporary sites, streambed drying. Invertebrates were sampled at sites with differing flow permanence regimes during and after the spates. Following streambed drying at temporary sites, dewatered surface sediments were investigated as a refugium for aquatic invertebrates. Experimental rehydration of these dewatered sediments was conducted to promote development of desiccation-tolerant life stages. At perennial sites, spate flows reduced invertebrate abundance and diversity, whilst at temporary sites, flow reactivation facilitated rapid colonisation of the surface channel by a limited number of invertebrate taxa. Following streambed drying, 38 taxa were recorded from the dewatered and rehydrated sediments, with Oligochaeta being the most abundant taxon and Chironomidae (Diptera) the most diverse. Experimental rehydration of dewatered sediments revealed the presence of additional taxa, including Stenophylax sp. (Trichoptera: Limnephilidae) and Nemoura sp. (Plecoptera: Nemouridae). The influence of flow permanence on invertebrate community composition was apparent despite the aseasonal high-magnitude flood events

Drought rewires the cores of food webs

Droughts are intensifying across the globe, with potentially devastating implications for freshwater ecosystems. We used new network science approaches to investigate drought impacts on stream food webs and explored potential consequences for web robustness to future perturbations. The substructure of the webs was characterized by a core of richly connected species surrounded by poorly connected peripheral species. Although drought caused the partial collapse of the food webs, the loss of the most extinction-prone peripheral species triggered a substantial rewiring of interactions within the networks’ cores. These shifts in species interactions in the core conserved the underlying core/periphery substructure and stability of the drought-impacted webs. When we subsequently perturbed the webs by simulating species loss in silico, the rewired drought webs were as robust as the larger, undisturbed webs. Our research unearths previously unknown compensatory dynamics arising from within the core that could underpin food web stability in the face of environmental perturbations