Michael C. Geddes

A Ramsar wetland in crisis – the Coorong, Lower Lakes and Murray Mouth, Australia

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 Basin is a large river basin with such problems encapsulated in the crisis of its Ramsar-listed terminal wetland, the Coorong, Lower Lakes and Murray Mouth. Prolonged drought and upstream diversion of water dropped water levels in the Lakes below sea level (2009–2010), exposing hazardous acid sulfate soils. Salinities increased dramatically (e.g. South Lagoon of Coorong >200 g L–1, cf. modelled natural 80 g L–1), reducing populations of waterbirds, fish, macroinvertebrates and littoral plants. Calcareous masses of estuarine tubeworms (Ficopomatus enigmaticus) killed freshwater turtles (Chelidae) and other fauna. Management primarily focussed on treating symptoms (e.g. acidification), rather than reduced flows, at considerable expense (>AU

On the chemistry and biota of some saline lakes in Western Australia

2 billion). We modelled a scenario that increased annual flows during low-flow periods from current levels up to one-third of what the natural flow would have been, potentially delivering substantial environmental benefits and avoiding future crises. Realisation of this outcome depends on increasing environmental flows and implementing sophisticated river management during dry periods, both highly contentious options.

Effects of diet on the growth, survival, and condition of sea-caged adult southern rock lobster, Jasus edwardsii

Several limnological studies of Australian salt lakes have been made. Most relate to Victorian waters (reviewed by Williams 1978), but Bayly (1970) and De Deckker & Geddes (1980) have studied a number of (mostly) ephemeral salt lakes near the coast of south-eastern South Australia. Many similarities occur between lakes in these two regions, the only major differences being the presence of dense angiosperm beds (Ruppia and Lepilaena) and several invertebrates with marine affinities in some of the South Australian lakes.

Survival, growth and yield of the Australian freshwater crayfish Cherax destructor in extensive aquaculture ponds

Abstract Live‐holding of fisheries‐caught adult southern rock lobster (Jasus edwardsii) presents a means of value‐adding to the South Australian commercial catch through strategic marketing and product enhancement. This study investigated the effects of live mussel and three manufactured diets on the survival, growth, and condition of sea‐caged adult J. edwardsii held for an extended period of 29–30 weeks during the closed fishing season. Two trials were conducted in existing industry cage systems. All four diets tested were successful in keeping lobsters alive, promoting growth at moult, and maintaining/improving the condition of lobsters. Unfed lobsters had lowered survival, negative or zero growth at moult, and lowered condition. All lobsters moulted during the trials. Addition of 1% mussel mince to pellets as a feeding stimulant did not increase survival or growth. Males showed substantially greater weight gain at moult than females (means of 8% for females and 17% for males). Biomass of male lobsters increased by up to 16% in one trial treatment, where growth of individual lobsters more than compensated for weight loss caused by mortality. Two different levels of carotenoid (0.15% and 0.25%) proved sufficient to maintain and/or improve colour. Where females were held separate from, but adjacent to, males there was some spawning activity (up to 14%). The one negative outcome of the study was that tail fan damage was found to be a major problem, occurring in both trials and across all diets without apparent pattern. The causes and management of tail fan damage need to be addressed before a long‐term live‐holding industry can be developed. However, in terms of survival and weight gain, results were very encouraging as improvements in pellet formulation, pellet production, and food delivery can be expected.

Acid brine shrimp: Metabolic strategies in osmotic and ionic adaptation

Abstract In April 1989 juvenile Cherax destructor (mean weight 3.9 g) were stocked at densities of 3 and 9 m −2 into four 0.2 ha ponds in which a forage crop was planted. At harvest in February 1990 mean weights were 24.9, 33.7, 36.6 and 40.0 g with final mean weight lower in the high density ponds. There was wide variation in individual growth, with weight at harvest varying from 10 to 80 g and only 10.7% of yabbies harvested were premium market size (>50 g). Reproduction in the ponds provided a second generation of juveniles and large numbers of berried females at harvest. Only 22 to 44% of yabbies stocked were collected at harvest but refilling and further harvesting showed that perhaps 30% of the population had avoided harvest by burrowing. Yabbies below 50 g were restocked to grow-on ponds and more than 50% achieved market size in the period February–June. The biomass harvested after 10 months varied from 406 to 689 kg ha −1 . After grow-on and carry-over harvests, total yield from the original cohort was 666 kg of which 405 kg comprised individuals above 50 g. This yield was from an area approximately equivalent to 1 ha of ponds. Extensive aquaculture using forage crops can produce modest yields of premium size C. destructor . Yields may improve with further development of forage management and harvesting methods.

The brine shrimps Artemia and Parartemia

Acid salt lakes are found in several regions of Australia but are uncommonly abundant in the Yilgarn Block area of southwestern Australia. The chemical properties of the acid salt lakes are in general similar to those of shallow ephemeral alkaline salt lakes found in adjacent regions except for having a higher hydrogen ion concentration and an absence of carbonate and bicarbonate ions. The Australian brine shrimp, Parartemia, is the major zooplankter living in these salt lakes. Present investigation on two species of larval Parartemia reveal P. zietziana nauplii having high salt tolerance (LD50> 225‰ TDS) but a narrow pH range with an optimum lying near pH 8. In contrast, P. contracta collected from acid salt lakes had a more restricted salt tolerance (LD50< 100‰ TDS) but a wider range of pH tolerances with substantial survival below pH 3.5. Both species, P. zietziana and contracta, when placed in ouabain-laden salines, demonstrated decreased survival and indirectly indicated the presence of a ouabain-sensitive sodium pump. Direct enzymatic assay of the sodium pump (Na, K-ATPase) in nauplii of P. zietziana gave specific activity values of 2.9 µM Pi/hr/mg protein supporting our working hypothesis that the nauplii of Parartermia have an osmoregulatory system similar to that found in larval Artemia which is dependent upon having large quantities of ATP to support the sodium pump. In Artemia larvae, the production of ATP is enhanced through a facultative pathway involving an aerobic glycolysis linked C-4 dicarboxylic shunt. The major CO2 source for the C-4 acid shunt for alkaline brine shrimp has been found to be the dissolved bicarbonate/carbonate ions. In highly acidic saline lakes, these ions are missing. If acid brine shrimp are to survive in low pH ephemeral saline lakes, they must have evolved an additional proton pump and devised a mechanism to produce ATP from endogenous CO2 substrates.

Size grading did not enhance growth, survival and production of marron (Cherax tenuimanus) in experimental cages

Brine shrimps of the genus Artemia are a major faunal element of saline lakes throughout the world. Presently the taxonomy of the genus is under review and what was once considered a single species, Artemia salina, appears to be several sibling species. In some cases chromosome number differs between sibling species causing reproductive isolation (Halfer-Cervini et al. 1968; Barigozzi 1974) while some populations are parthenogenetic; in fact Artemia is a classic example of polyploidy and parthenogenesis in animals. Recent work on laboratory crosses with populations and on electrophoretic variation between populations has shown that even where chromosome number is the same, several brine shrimp populations are reproductively isolated from one another (Clark & Bowen 1976; Bowen et al. 1978; Abreu-Grobois & Beardmore 1979).

Evidence for multiple year classes of the giant Australian cuttlefish Sepia apama in northern Spencer Gulf, South Australia

Abstract The necessity for size grading prior to stocking in marron culture is not clear. In this study, production characteristics of marron of three size-graded groups (15.2, 78.3 and 157.6 g) and one mixed group were tested in 24 experimental cages (6×3×2 m) with six replicates for each treatment. After 258 days, mean weight of small marron in the graded group increased from 15.2 to 40.1 g, while small marron in the mixed group increased from 14.8 to 46.4 g. Mean weight of medium marron in the graded group increased from 78.3 to 129.5 g, while medium marron in the mixed group increased from 76.7 to 132.6 g. Mean weight of large marron in the graded group increased from 157.6 to 218.9 g, while the large marron in the mixed group increased from 165.3 to 223.7 g. Size grading of marron did not lead to improved growth. Marron survival rate was not improved by grading either. Instead, survival rate of medium and large individuals was significantly greater in the mixed group than in the graded group. Size specific growth rates were size-dependent and small marron grew faster than either medium or large individuals. The sequence of standing biomass of different sized groups at harvest was medium size (3080 kg/ha)>mixed size (2941 kg/ha)>mall size (2482 kg/ha)>large size (2037 kg/ha). The sequence of net production of different sized groups was small size (1374 kg/ha)>mixed size (1042 kg/ha)>medium size (756 kg/ha)>large size (−275kg/ha). Marron size grading during growout seems to be an unnecessary operation to improve the growth and survival.

Causes of tail fan necrosis in the southern rock lobster, Jasus edwardsii

Giant Australian cuttlefish form a mass spawning aggregation at a single site in northern Spencer Gulf (NSG) in South Australia every austral winter. Samples of cuttlefish were collected from this region over three consecutive years. Analysis of regular growth increments in the cuttlebones of these individuals, revealed a polymorphism in growth pattern for both sexes. Three distinct “bone patterns” were identified based on the variation in increment widths over the lengths of the bones. All bones analysed conformed to one of the three bone patterns, and the increment width patterns were consistent between years. Interpretation of the patterns, suggested that Sepia apama have two alternative life cycles. The first involves rapid juvenile growth during the first summer after hatching, with maturity reached within 7–8 months. These individuals return to spawn in their first year as small individuals. The second life cycle involves much slower juvenile growth during the first summer, with maturity deferred until their second year, when they return to spawn as much larger individuals. Thus, the age compositions of populations of S. apama in the NSG appear to consist of two year classes for both sexes.

An enclosure for experimental field studies with fish and zooplankton communities

Abstract Tail fan necrosis (TFN) is a recognised constraint on the advancement of the South Australian rock lobster (Jasus edwardsii) liveholding industry because of a reduction in value of afflicted lobsters. Trials were run in the laboratory and at a shore‐based experimental live‐holding facility (LHF) to determine the influence of at‐sea post‐harvest handling, feeding frequency (LHF only), density (LHF only), and temperature (laboratory only) on the advent of the condition. Lobsters were caught during normal fishing operations and either immediately placed in protective fine‐mesh nylon bags and stored in the boats well or placed unbagged in the well. At the laboratory, the tail fans of half the bagged lobsters were deliberately damaged with sterile instruments. At the LHF the TFN level increased significantly over 4 months. The bagged treatment showed significantly less late‐stage TFN than unbagged daily or weekly‐fed treatments with 60% of bagged lobsters showing no TFN at 4 months. With unbagged lobsters, 50% showed erosion in the <25% category and 30% showed erosion of >25% of the tail fan. Lobster density and feeding frequency had no effect on TFN incidence. In the laboratory, bagged and bagged‐damaged treatments had no advanced TFN after the 6‐week period suggesting that post‐harvest bagging minimises TFN and that inflicting physical damage to lobster tail fans with aseptic instruments does not lead to its development. Temperature had no effect on TFN development. The highest incidence of TFN was found in lobsters given normal post‐harvest handling, that is, communal holding in boat holds and tanks (i.e., without bags). These conditions are normally associated with physical damage inflicted by conspecifics. Such damage will presumably also involve infection of wounds by the bacterial flora of the crayfish exoskeleton, leading to development of TFN.