Australian Estuaries Research Articles

Relationship between diatoms and water quality (TN, TP) in sub-tropical east Australian estuaries

Nutrient over-enrichment of estuarine environments is increasing globally. However, it is difficult to determine the eutrophication trend in estuaries over long periods of time because long-term monitoring records are scarce and do not permit the identification of baseline environmental conditions. In this study, preliminary diatom based transfer functions for the inference of total phosphorus (TP) and total nitrogen (TN) in east-Australian sub-tropical estuaries were developed to address the deficiency in knowledge relating to historical estuary water quality trends. The transfer functions were created from a calibration set consisting of water quality and associated surface sediment diatom assemblage data from fifty-two sub-tropical estuaries in New South Wales and Queensland, Australia. Following data screening processes, Canonical Correspondence Analysis confirmed that TP and TN both explained significant, independent variation in the diatom assemblages. Variance partitioning, however, indicated that the TP was confounded with and may receive some strength from TN. WA and WA-PLS 2 component models for TP that included all calibration set sites yielded statistically weak results based on the jack-knifed r 2 scores $$ \left( {r_{\text{jack}}^{{^{ 2} }} \, = 0.22\;{\text{and}}\;0. 2 2 {\text{ respectively}}} \right) $$ . Removal from the calibration set of 12 sites that had all PO4, NH4, NO2, and NOx concentrations below detection limit resulted in a substantial improvement in WA-PLS 2 component TP model scores $$ \left( {r_{\text{jack}}^{{^{ 2} }} \; = \;\,0.69} \right) $$ , indicating that this model is statistically robust, and thus suitable for down core nutrient reconstructions. Caution, however, is required when developing diatom based inference models in Australian estuaries as nutrient cycling processes may have the potential to influence diatom based transfer functions. The model reported on here provides a foundation for reconstructing nutrient histories in eastern Australian sub-tropical estuaries in the absence of monitoring data.

Phytoplankton composition in the coastal Magnetic Island lagoon, Western Pacific Ocean (Australia)

1 - Coastal lagoons have traditionally been considered as transitional systems between continental and marine domains. The phytoplankton plays a key role in these aquatic environments, forming the base of the food web and having a substantial function in nutrient dynamics and in the carbon biogeochemical cycle. 2 - Due to their short life cycle, planktonic algae respond quickly to environmental changes and they are thus a valuable indicator of water quality. It is essential to investigate the development of phytoplankton populations to understand the biological functioning and to detect changes in aquatic systems. 3 - Phytoplankton studies in the Australian estuaries and lagoons are relatively scarce. This study has provided a broad perspective and preliminary information on taxonomic structure of phytoplankton guilds for the Magnetic Island Lagoon (Queensland, Australia). This work may provide valuable information of interest to later ecological studies. 4 - In the whole sampling a total of 143 taxa were identified. In terms of species richness, diatoms (Bacillariophyceae, Coscinodiscophyceae, Fragilariophyceae) and dinoflagellates (Dinophyceae) were the most important groups. In taxonomic terms, diatoms were the major contributor to the phytoplankton composition (~ 70%) whereas Dinophyceae were moderately abundant (~23%). Diatoms are a very important component in estuarine and shallow coastal wetlands and they are increasingly being utilized as indicators of environmental change.

Fluctuations in natural and synthetic estrogen concentrations in a tidal estuary in south-eastern Australia

Estuaries are often the final repositories for aquatic pollutants but how estuarine hydrology influences the availability of marine- and freshwater-derived pollutants is not well understood, particularly for micro-pollutants such as endocrine disrupting chemicals. To address this knowledge gap, this study measured natural and synthetic estrogen concentrations within the Little River, a tidal estuary in close vicinity to the major discharge point of Melbourne's largest waste water treatment plant (WWTP), the Western Treatment Plant. Quantitative enzyme-linked immunosorbent assays (ELISA) were used to determine concentrations of natural estrogens (ES: ∑E1 (estrone), E2 (17β-estradiol), E3 (estriol)) and the synthetic estrogen, 17α-ethinylestradiol (EE2). The highest concentrations were measured in samples taken from the WWTP effluent discharge channel (29.0 ng/L and 0.35 ng/L, respectively). Within the estuary, concentrations of ES (2.25–23.16 ng/L) varied somewhat between locations and sampling periods (p < 0.05), however patterns were not consistent. Significant spatial variation was observed on only one sampling occasion, and likewise temporal variation was only observed once. In the upstream freshwaters, ES (2.95–7.26 ng/L) concentrations were lower than in the estuary, although their presence suggests an additional source of ES to the environment, most likely of agricultural origin. The EE2 concentrations measured in both the estuarine and freshwater areas were all low (mostly below 0.20 ng/L), which created difficulties in interpretation due to problems associated with trying to measure such low concentrations with confidence. However, some patterns did emerge, with EE2 concentrations exhibiting significant temporal and tidal variation (p < 0.05), with concentrations greatest during low and flooding (incoming) tides. Physico-chemical properties explained 30% of the variation in ES concentrations, whereby concentrations increased with decreasing pH and DO and increasing salinity. Given the higher concentrations observed during flooding tides and the association of higher estrogen concentrations with increased salinity and low DO, we suggest that estrogens might accumulate in estuarine bottom waters and upon disturbance from the incoming tidal flows, may be a contributing source of estrogens into the estuary. This study contributes the first comprehensive investigation of estrogen dynamics in an Australian estuary, and provides the foundation for further research aimed at identifying which compounds are present in estuarine waterways, where they are coming from and how their concentrations vary through space and time.

FORAMINIFERAL FAUNA AND BIOTOPES OF A BARRIER ESTUARY SYSTEM: ST GEORGES BASIN, NEW SOUTH WALES, AUSTRALIA

A 66-sample study of estuarine foraminifera within St Georges Basin identified 30 species from three biotopes that are divided almost equally in diversity between calcareous and agglutinated forms. The latter, however, are twice as abundant as the former, and the species Ammobaculites exiguus, Portatrochammina sorosa, Rhumblerella subconica , and Ammonia aoteana represent 78% of the fauna. The main driver of biotope distribution is water depth or factors related to it. Faunal composition and biotope distribution are similar to those found in other estuaries in the region, suggesting the possibility of a “standard fauna” for Australian estuaries with limited connections to the open ocean.

Characterizing the biological traits and life history of Acanthopagrus (Sparidae) hybrid complexes: implications for conservation and management

This study examined the spatio-temporal reproductive patterns, population structure, maturity and growth of Acanthopagrus hybrid complexes, which comprise mainly black bream Acanthopagrus butcheri and the hybrids they form with yellowfin bream Acanthopagrus australis, in two Australian estuaries (Coila and Brou Lakes, NSW). There were no differences between pure A. butcheri and hybrids in terms of their population structure, growth and maturity, suggesting that these two breeds have similar life histories and may therefore be managed as single, naturally cohesive units. Sexual variation in size structure was only observed for the complex in Coila Lake. Although there was significant variation in age structure between estuaries, both complexes exhibited dominance of only a few year classes indicating episodic recruitment and high fishing mortality. Acanthopagrus eggs occurred in higher numbers within upstream creek habitats compared to lake habitats, thereby highlighting the need to protect these spawning habitats. Although maturity in the complexes was not influenced by gender or estuary, differences in growth were detected between the genders and estuaries.

Replacement of native seagrass with invasive algal detritus: impacts to estuarine sediment communities

Biological invasions modify the quality and supply of detrital subsidies to aquatic and terrestrial ecosystems. Where the invader has very different traits to native species, major changes in associated consumer communities may result, as a consequence of differences in their nutritional value and effects on the sedimentary habitat. We assessed how the replacement of seagrasses with the invasive alga Caulerpa taxifolia in modified Australian estuaries influences invertebrate communities of mudflats that are subsidized by detritus from submerged aquatic vegetation. Two months after experimental enrichment of sediments with high (60 g dry weight per 0.25 m2 plot) or low (30 g dry weight) quantities of either non-native C. taxifolia or native Posidonia australis or Zostera capricorni detritus, there were positive effects of detrital addition on invertebrate abundance that occurred irrespective of the resource added. By 4 months after addition, however, detritus from invasive C. taxifolia had produced effects on benthic communities that could not be replicated by detritus from either of the native seagrasses. Plots receiving the high loading of C. taxifolia detritus contained fewer invertebrates than plots of the other treatments, perhaps due to the induction of sediment hypoxia. The pattern, however, reversed at low detrital loading, with the plots receiving 30 g of C. taxifolia containing more invertebrates and more taxa than the other plots, presumably due to the greater resource availability for detritivores. Our results demonstrate that replacement of native seagrass with invasive algal detritus can have large impacts on sediment-dwelling communities.

Giant mud crab (Scylla serrata): relative efficiencies of common baited traps and impacts on discards

Abstract Butcher, P. A., Leland, J. C., Broadhurst, M. K., Paterson, B. D., and Mayer, D. G. 2012. Giant mud crab (Scylla serrata): relative efficiencies of common baited traps and impacts to discards. – ICES Journal of Marine Science, 69: . This study was initiated in response to a scarcity of data on the efficiency, selectivity and discard mortality of baited traps to target Scylla serrata. Five replicates of four traps, including “hoop nets”, rigid “wire pots”, and collapsible “round” and “rectangular” pots were deployed for 3, 6 and 24 h in two Australian estuaries. Trapped S. serrata were “discarded” into cages and monitored with controls over 3 d. All S. serrata were assessed for damage, while subsets of immediately caught and monitored individuals had haemolymph constituents quantified as stress indices. All traps retained similar-sized (8.1–19.1 cm carapace width) S. serrata, with catches positively correlated to deployment duration. Round pots were the most efficient for S. serrata and fish—mostly Acanthopagrus australis (3% mortality). Hoop nets were the least efficient and were often damaged. No S. serrata died, but 18% were wounded (biased towards hoop nets), typically involving a missing swimmeret. Physiological responses were mild and mostly affected by biological factors. The results validate discarding unwanted S. serrata for controlling exploitation, but larger mesh sizes or escape vents in pots and restrictions on hoop nets would minimise unnecessary catches, pollution and ghost fishing.

Development and validation of fish-based, multimetric indices for assessing the ecological health of Western Australian estuaries

We describe the development of the first fish-based, multimetric indices for assessing and monitoring the health of Australian estuaries, and their application to the nearshore (<2 m depth) and offshore (>2 m depth) waters of the Swan Estuary, Western Australia. Suites of fish community metrics, including measures of species composition, diversity and abundance, trophic structure and life history function, were selected via a novel weight of evidence approach on the basis of their sensitivity to detect inter-annual change in estuarine condition. For each selected metric, seasonally-adjusted reference conditions were established for each spatial management zone of the Swan Estuary using 30 years of standardised historical fish assemblage data. This extensive data set provided a sound basis for determining the ‘best available’ standard of biotic integrity recorded over that time period and thus a reliable benchmark against which the current and future health of the estuary may be assessed and compared. The nearshore and offshore indices were robust to the effects of natural, intra-seasonal variability in environmental conditions, and so provide reliable tools for quantifying and classifying the ecological health of the Swan Estuary and its constituent management zones. The response of the nearshore index to an algal bloom confirmed that it is sufficiently sensitive to quantify ecological health responses to local-scale environmental perturbations and to track the subsequent recovery of the system following their removal. The indices provide managers with a reliable, quantitative method for assessing and communicating the health of the Swan Estuary and, similarly, of other estuaries across south-western Australia.

Carbon budgets for three autotrophic Australian estuaries: Implications for global estimates of the coastal air‐water CO2 flux

Estuaries are ‘hot spots’ in the global carbon cycle, yet data on carbon dynamics, in particular air‐sea CO2 fluxes, from autotrophic systems are rare. Estuarine carbon budgets were constructed for three geomorphically distinct warm temperate Australian estuaries over an annual cycle. All three estuaries were net autotrophic, with annual net ecosystem metabolism (NEM) ranging from 8 ± 13.4 molC m−2 yr−1 to 10 ± 14 molC m−2 yr−1. There was a net flux of CO2 from the atmosphere to the estuaries of between 0.4 ± 0.6 molC m−2 yr−1 and 2 ± 0.9 molC m−2 yr−1. Loading of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) to the estuaries varied markedly within and between the estuaries, and was directly related to freshwater inflow. While NEM was similar in all three estuaries, the ratio of benthic versus pelagic contributions to NEM differed, with NEM dominated by pelagic production in the river dominated system, benthic production dominating in the intermediate estuary, and equal contributions of benthic and pelagic production in the marine dominated lagoon. All three estuaries exported more organic carbon than was imported, fueled by additional organic carbon supplied by NEM. The estuaries essentially acted as bioreactors, transforming DIC to organic carbon. Burial of organic carbon ranged from 1.2 ± 0.3 molC m−2 yr−1 to 4.4 ± 1.2 molC m−2 yr−1 and represented up to half of NEM. The annual net uptake of atmospheric CO2 in these systems, along with previous estimates of the global estuarine CO2flux being based predominantly on heterotrophic, large river dominated estuarine systems, indicates that the global estimate of the estuarine air‐water CO2flux may be over‐estimated due to the lack of studies from autotrophic marine dominated estuaries.

Epiphyte grazing enhances productivity of remnant seagrass patches

Anthropogenic nutrient enrichment is increasingly modifying community structure and ecosystem functioning in terrestrial and aquatic ecosystems. In marine ecosystems, the paradigm is that nutrient enrichment leads to a decline of seagrasses by stimulating epiphytic algal growth, which shades and overgrows seagrasses. This ignores the potential for herbivores, which graze upon epiphytic algae, to partially or wholly counter such nutrient effects. We conducted a field experiment to assess the role that the trochid gastropod Calthalotia fragum plays in reducing nutrient impacts on the seagrass, Posidonia australis, in an urbanized Australian estuary, Botany Bay, Sydney. In a field experiment, where nutrient loading and grazer density were orthogonally manipulated, nutrient enrichment failed to promote epiphyte biomass or diminish growth and primary productivity of P. australis. To the contrary, nutrient enrichment enhanced photosynthesis of the seagrass in plots where the grazer was present at higher density. Epiphytic growth was negatively affected by increased C. fragum density, while P. australis shoot growth was positively influenced. Thus, in this study system, grazing appears to play a much greater role in determining seagrass primary productivity and above-ground growth than moderate nutrient loading, suggesting that the interaction between grazers and nutrients depends on the relative levels of each. Our study contributes to a growing body of literature suggesting that effects of nutrient loading on benthic assemblages are not universally negative, but are dependent on the biotic and abiotic setting.

The proteomes of Sydney rock oysters vary spatially according to exposure to acid sulfate runoff

Runoff from acid sulfate soils (ASS) has severe environmental and economic impacts on estuarine ecosystems. Oysters display reduced abundance, growth rate and shell thickness when exposed to ASS runoff, yet the molecular underpinnings of their responses have not been explored. We hypothesised that the proteomes of wild Sydney rock oysters, Saccostrea glomerata, would differ between populations recurrently exposed to ASS compared with those unaffected by runoff from ASS. We used two-dimensional electrophoresis to compare protein abundances in the gills of S. glomerata collected from two sites close to (acidified) and two sites away from (reference) major ASS outflow drains in a south-east Australian estuary. Approximately 5% of the proteome was differentially expressed between oysters from acidified and reference sites, with five protein spots more abundant and one less abundant at the sites close to drains. Another protein spot was present only in oysters from reference sites. This study is the first screening of spatial variation in the protein expression of S. glomerata with respect to discharge from ASS. Altered protein expression may underpin short-term inducible responses to ASS runoff, or genetic resistance acquired through recurrent exposure of populations to the stressor.

Differences in shell strength of native and non-native oysters do not extend to size classes that are susceptible to a generalist predator

Whether non-native species proliferate to pest status can depend on top-down control from native predators. Among epifaunal molluscs, the shell serves as a main line of anti-predator defence and shell strength may determine the ease with which generalist predators can penetrate prey. We assessed whether, in eastern Australia, the faster growth of the non-native Pacific oyster, Crassostrea gigas, than that of the native Saccostrea glomerata comes at the cost of reduced investment in shell thickening, rendering the non-native oyster more susceptible to a generalist predator, the muricid gastropod Morula marginalba. Laboratory tests confirmed that among larger (&gt;50-mm shell height) oysters, the shells of C. gigas were weaker than those of similar-sized S. glomerata. There were, however, no differences in shell strength or thickness between smaller S. glomerata and C. gigas of the size consumed by M. marginalba. In the absence of shell-strength differences among smaller oysters, M. marginalba preferentially consumed native over non-native oysters. When, however, M. marginalba had no choice of prey item, C. gigas was consumed at the same rate as the native oyster. Our results add to growing evidence that the invasion of C. gigas in eastern Australian estuaries is, at present, causing minimal disruption to trophic relationships.

Moderate acidification affects growth but not survival of 6-month-old oysters

Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata, were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods.

Palaeolimnology in eastern and southern Australian estuaries

Palaeolimnology has been widely used in freshwater environments, providing information for policy development and legislation (Bennion and Battarbee 2007; Battarbee and Bennion 2011). However, application of palaeolimnology in coastal environments remains challenging (Cooper 2010). The application of palaeolimnological techniques in coastal ecosystems was pioneered by Cooper and Brush (1991), Juggins (1992), Andren (1999) and Kerfoot et al. (1999). These methods have required some adaptations (Cooper 2000; Cooper et al. 2004), but have been effectively utilised in many Northern Hemisphere estuaries. For example, studies of the Baltic Sea (Kauppila et al. 2005; Clarke et al. 2006; Weckstrom 2006; Tuovinen et al. 2010), Chesapeake Bay (Cooper and Brush 1993; Cooper 1995, 1999, Cooper et al. 2004), Florida Bay (Wachnicka et al. 2010, 2011) and the Pearl River estuary in southern China (Zong et al. 2010) have produced results that provide information useful to managers. Yet, in the Southern Hemisphere, and in particular Australia, application of palaeolimnological methods in coastal environments remains in its infancy (Saunders and Taffs 2009). In general, palaeolimnology in Australia is underutilised, yet offers many possibilities for a continent that has experienced dramatic landscape change over a short period of time that is rarely fully documented. In particular, information on Australian estuaries is urgently required to assist management actions where there are substantial population pressures and multiple conflicting uses of coastal environments (Saunders and Taffs 2009). However, applying palaeolimnological techniques to Australian estuaries is particularly problematic because of the paucity of information on Australian estuary functioning. While it is well understood that estuaries are highly dynamic ecosystems (Cooper 1999), the variability of estuarine function across climatic zones is still being actively researched (Eyre and Balls 1999; Bowen and Valiela 2008). Australian estuaries function quite differently to their Northern Hemisphere counterparts (Davis and Koop 2006), hence palaeolimnological methods largely developed in the Northern Hemisphere need to be applied with some caution in Australia. The greatest cause of these differences is that rainfall frequency is much lower, with episodic rain events controlling chemical and biological functioning (Davis and Koop 2006). Hence, average water residence time is often higher than in less variable ecosystems with equivalent freshwater inputs, resulting in a dominance of internal nutrient cycling. J. Tibby (&) Geography, Environment and Population, University of Adelaide, Adelaide, SA 5005, Australia e-mail: john.tibby@adelaide.edu.au

Benthic carbon metabolism in southeast Australian estuaries: habitat importance, driving forces, and application of artificial neural network models

Benthic gross primary productivity (GPP), net primary production (NP), and respiration (R) were measured seasonally in each of 12 major benthic habitats in 3 southeast Australian estuaries, along with a suite of biological, physical, and chemical parameters to construct a benthic carbon budget and to elucidate controls over benthic metabolism. We also tested the performance of an artificial neural network (ANN) model in predicting benthic metabolism from the suite of measured parameters, and compared model performance to traditional stepwise regression methods. Carbon budgets indicated that macrophyte communities made the greatest contribution to whole system benthic metabolism (51 to 79% of gross productivity and 38 to 74% of respiration), and net benthic metabolism of the 3 estuaries ranged from −25 to ~90 g C m−2 yr−1. Metabolism in non-macrophyte communities was tightly coupled to light, temperature, organic matter supply, and benthic algal biomass, and metabolism in macrophyte communities was coupled predominantly to temperature and light. ANN outperformed stepwise regression for all benthic metabolic parameters in both macrophyte and non-macrophyte habitats. Root mean square errors of ANN were up to 3-fold lower than stepwise regression models, indicating the potential use of ANN in modeling ecosystem-scale metabolism. We used ANN models to predict systemwide changes in benthic net production associated with an increase in temperature of 1 to 2°C. Model results indicate that system-wide net production increased with temperature, indicating that carbon burial in, and/or export from estuaries may increase as a result of increasing water temperature associated with climate change.

Meiobenthic community underneath the carcass of a stingray: a snapshot after natural death

The impact of large food falls and carrion on meiobenthic communities remains little understood. The objective of the present study was to investigate whether the carcass of a stingray, encountered fortuitously in an Australian estuary, affects the underlying meiobenthic community, in particular nematode assemblages. The integrity of the skeleton and the low redox values observed under the carcass suggest that the cadaver had been slowly and chiefly decomposed by microbes. The abundance and number of meiofaunal taxa, as well as nematode abundance and nematode- species richness, were significantly lower under the carcass when compared to samples outside the carcass. Nonetheless, a few nematode species, typical of hypoxic/anoxic sediments, were more abun- dant under the carcass. Interestingly, all these species were absent or rare in samples near, but not under, the carcass, suggesting that they may take advantage of the reduced environment created by the carcass and the consequent lack of competition to prosper. As observed for other marine environ- ments, carcasses in estuaries create a microhabitat that supports a characteristic meiobenthic fauna, distinct from those inhabiting the surrounding sediments, but similar to those of reduced habitats.

Ecosystem states: Creating a data-derived, ecosystem-scale ecological response model that is explicit in space and time

Increasing difficulties associated with balancing consumptive demands for water and achieving ecological benefits in aquatic ecosystems provide opportunities for new ecosystem-scale ecological response models to assist managers. Using an Australian estuary as a case study, we developed a novel approach to create a data-derived state-and-transition model. The model identifies suites of co-occurring birds, fish, benthic invertebrates and aquatic macrophytes (as ‘states’) and the changing physico-chemical conditions that are associated with each (‘transitions’). The approach first used cluster analysis to identify sets of co-occurring biota. Differences in the physico-chemical data associated with each state were identified using classification trees, with the biotic distinctness of the resultant statistical model tested using analysis of similarities. The predictive capacity of the model was tested using new cases. Two models were created using different time-steps (annual and quarterly) and then combined to capture both longer-term trends and more-recent declines in ecological condition. We identified eight ecosystem states that were differentiated by a mix of water-quantity and water-quality variables. Each ecosystem state represented a distinct biotic assemblage under well-defined physico-chemical conditions. Two ‘basins of attraction’ were identified, with four tidally-influenced states, and another four independent of tidal influence. Within each basin, states described a continuum of relative health, manifest through declining taxonomic diversity and abundances. The main threshold determining relative health was whether freshwater flows had occurred in the region during the previous 339 days. Canonical analyses of principal coordinates tested the predictive capacity of the model and demonstrated that the variance in the environmental data set was well captured (87%) with 52% of the variance in the biological data set also captured. The latter increased to >80% when long- and short-term biological data were analysed separately, indicating that the model described the available data for the Coorong well. This approach thus created a data-derived, multivariate model, where neither states nor transitions were determined a priori. The approach did not over-fit the data, was robust to patchy or missing data, the choice of initial clustering technique and random errors in the biological data set, and was well-received by local natural resource managers. However, the model did not capture causal relationships and requires additional testing, particularly during future episodes of ecological recovery. The approach shows significant promise for simplifying management definitions of ecological condition and, via scenario analyses, can be used to assist in manager decision-making of large, complex aquatic ecosystems in the future.

Potential effects of climate change on Australian estuaries and fish utilising estuaries: a review

Estuaries are especially vulnerable to the impacts of climate change because changes in climatic and hydrologic variables that influence freshwater and marine systems will also affect estuaries. We review potential impacts of climate change on Australian estuaries and their fish. Geographic differences are likely because southern Australian climates are predicted to become warmer and drier, whereas northern regions may see increased precipitation. Environmental factors, including salinity gradients, suspended sediment, dissolved oxygen and nutrient concentrations, will be influenced by changing freshwater input and other climate variables. Potential impacts will vary depending on the geomorphology of the estuary and the level of build-up of sand bars across estuarine entrances. Changes to estuarine fish assemblages will depend on associated changes to salinity and estuarine-mouth morphology. Marine migrants may be severely affected by closure of estuarine mouths, depending on whether species ‘must’ use estuarine habitat and the level of migratory v. resident individuals. Depending on how fish in coastal waters locate estuaries, there may be reduced cues associated with estuarine mouths, particularly in southern Australia, potentially influencing abundance. In summary, climate change is expected to have major consequences for Australian estuaries and associated fish, although the nature of impacts will show significant regional variation.

Post-release survival and physiology of angled luderick (Girella tricuspidata) after confinement in keeper nets in an Australian estuary

AbstractButcher, P. A., Broadhurst, M. K., Hall, K. C., and Cooke, S. J. 2011. Post-release survival and physiology of angled luderick (Girella tricuspidata) after confinement in keeper nets in an Australian estuary. – ICES Journal of Marine Science, 68: . The study was initiated in response to concerns about the post-release welfare of angled luderick (Girella tricuspidata) after protracted confinement in keeper nets. In all, 111 fish were angled and confined for 2–250 min before being released into holding cages (with 87 controls) and monitored for 4 d. Blood was taken from fish angled and brought on board immediately (n = 11), angled and held in keeper nets (n = 25), and angled and held in monitoring cages for 4 d (n = 12). Blood was also taken from controls held in monitoring cages for 4 d (n = 12). No controls and only one angled fish died. Compared with immediately sampled angled fish, those confined in keeper nets had significantly elevated cortisol, glucose, lactate, chloride, sodium, and aspartate aminotransferase. Most of the variables returned to pre-stress levels in caged fish after 4 d. Despite this recovery, the short-term stress associated with capture and keeper-net confinement has welfare implications and justifies avoiding such a practice and/or reducing the personal daily angling quota of the species.

Impacts of detritus from the invasive alga Caulerpa taxifolia on a soft sediment community

Invasive primary producers can dramatically reorganize food webs through detrital sub- sidies. This study assessed (1) contributions of the invasive alga Caulerpa taxifolia to detrital resources of temperate Australian estuaries, and (2) effects of these contributions on sediment- dwelling invertebrates. In an invaded estuary, sampling of an intertidal shore indicated C. taxifolia fragments were consistently present in organic matter deposits and were particularly abundant fol- lowing storms. Sampling of the alga across 6 invaded estuaries showed that the ratio of organic car- bon to nitrogen (C:N) in fresh tissue varied between 7 and 16. To determine how C. taxifolia detritus influences benthic macrofaunal assemblages and whether this influence depends on the quantity and C:N ratio of C. taxifolia detritus, a manipulative field experiment was performed. On a sheltered intertidal mudflat, 0.25 m 2 plots of sediment were experimentally enriched with either a high (90 g DW) or low (30 g) loading of high C:N (14) or low C:N (7) C. taxifolia detritus. Experimental enrich- ment negatively affected the total abundance and species richness of macroinvertebrates relative to controls, and these effects increased with detrital loading. For some macrofauna, reducing the C:N ratio tended to exacerbate negative effects on abundances, whereas it moderated these effects for other species. Given that organic matter derived from invasive species can be transported beyond the distribution of live invaders, greater consideration should be given to the potential broad-scale effects of invasive primary producers on detrital pathways.