2021 Publications (links to each paper available at read more)

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Image: Coorong Sunrise. Mac1745, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons 

Elemental concentrations of waters and bivalves in the fresh to hypersaline Coorong Lagoons, South Australia: Implications for palaeoenvironmental studies

Chamberlayne, BK, JJ Tyler, BM Gillanders. 2021. Estuarine, Coastal and Shelf Science

Element-to-calcium ratios of bivalve shells are potentially useful proxies for environmental change, provided the relationship between the environmental variable and element ratio are calibrated using modern specimens. In this study we investigate the utility of trace elemental ratios in the estuarine micromollusc Arthritica helmsi as (palaeo)environmental proxies. Sr/Ca, Mg/Ca and Ba/Ca ratios were measured in waters (n = 137) and live bivalves (n = 125) were collected along a salinity gradient from fresh to hypersaline in the Coorong Lagoon and Lake Alexandrina, at the terminus of the Murray River, South Australia. Water Mg, Sr and Ca exhibited linear relationships with salinity, while Ba showed no relationship. Mg/Ca and Sr/Ca in water both showed positive logarithmic responses to increasing salinity, while the response of Ba/Ca was best explained by a negative power function. The Sr concentration and Sr/Ca of water collected between 2016 and 2018 were elevated compared to a previous study conducted between 2007 and 2008, possibly due to a higher river flow regime in the more recent period. The range of Sr/Ca, Mg/Ca and Ba/Ca measured in A. helmsi were in agreement with previous studies, as were the range of partition coefficients. However, the incorporation of Sr/Ca, Mg/Ca and Ba/Ca did not correlate with water elemental ratios, temperature, salinity or pH and are therefore likely to be more heavily influenced by biological processes. As a consequence, while the elemental composition of other carbonate fossils within the Coorong system may hold potential to reconstruct past climate and environmental change, the trace element geochemistry of A. helmsi aragonite shells, and possibly other similar micro-bivalve molluscs, should be treated with caution as a palaeoenvironmental tracer.

 

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Image: Figure 3 from paper. Heat map of water salinity (top) and oxygen isotope composition (bottom) by location and through time.

Controls over oxygen isotope fractionation in the waters and bivalves (Arthritica helmsi) of an estuarine lagoon system

Chamberlayne, BK, JJ Tyler, BM Gillanders, 2021. Geochemistry, Geophysics, Geosystems

Oxygen isotope ratios in bivalve shells have long been used as a proxy for environmental change, reflecting both temperature and the oxygen isotope composition of host water. In estuarine systems, the oxygen isotope composition of water is complicated by variable mixing between river and seawater, as well as evaporative enrichment. In addition, due to species-specific variation in temperature-dependent fractionation into bivalve carbonate, modern calibrations are necessary prior to applications in paleoenvironmental studies. In this study, live specimens of the micromollusc Arthritica helmsi were collected from five sites in the Coorong Lagoon, an estuarine system at the mouth of the River Murray, Australia, on six occasions from November 2016 to May 2018. Whole shell oxygen and carbon isotope compositions (n = 131) were measured alongside monthly temperature and oxygen and hydrogen isotope analyses of waters from the Coorong and neighboring Lake Alexandrina (n = 137). Oxygen and hydrogen isotope ratios in water were mostly controlled by evaporation of source waters, though a period of high river water discharge was reflected in the isotopic values of the Coorong North Lagoon. A species-specific temperature-dependent oxygen isotope fractionation equation was calibrated for A. helmsi: T(°C) = (21.39 ± 0.45) − (4.43 ± 0.38) × (δ18Oshell − δ18O water). This equation is similar to other published paleotemperature equations for biogenic carbonates. These contemporary observations of the isotope hydrology of the Coorong, coupled with our contemporary calibration of oxygen isotope fractionation, lay the foundation for paleoenvironmental studies using bivalves collected from the sediments of the Coorong.

 

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Graphical abstract from paper

Environmental risk assessment and bioaccumulation of pharmaceuticals in a large urbanized estuary

Fonseca, VF, IA Duarte, B Duarte, A Freitas, ASV Pouca, J Barbosa, BM Gillanders, P Reis-Santos. 2021. Science of the Total Environment

We screened for the presence of 66 different pharmaceutical residues in surface waters and in multiple invertebrate and fish species of the Tejo estuary to produce an environmental risk assessment of individual pharmaceuticals and their mixtures, as well as evaluate the bioaccumulation of pharmaceuticals in one of Europe's largest estuarine systems. Sixteen pharmaceutical residues, from seven therapeutic classes, were detected in estuarine waters, with environmental mixture concentrations ranging from 42 to 1762 ng/L. Environmental risk assessment via the determination of risk quotients, demonstrated high ecological risk for the antibiotic amoxicillin and angiotensin II receptor blockers irbesartan and losartan. Moderate risk was estimated for antidepressants, antiepileptics, anxiolytics and beta-blockers, but the risk quotient of the accumulated mixture of compounds was over 380-fold higher than the no risk threshold, driven by antibiotics and angiotensin II receptor blockers. In biota, higher risk therapeutic groups were found in higher concentrations, with nine pharmaceutical residues detected, including six antibiotics and two neuroactive compounds, and maximum tissue concentrations up to 250 μg/kg. Bioaccumulation was species- and compound-specific, with only two compounds found simultaneously in water and biota, likely a result of the complex dynamics and fate of pharmaceuticals in estuarine waters. Nonetheless, higher detection frequencies were observed in species living directly on or just above the substrate (i.e. benthic and demersal species), underpinning the importance of habitat use, as well the potential role of sediment and diet based routes for pharmaceutical uptake. Ultimately, results support urgent action on managing the impact of pharmaceuticals in coastal environments, striving for improved monitoring schemes tailored to the dynamic nature and ecological diversity of estuaries and coastal ecosystems.

 

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Graphic drawn by @terngirl during 2019 ASFB conference

Identifying physiological and environmental influences on otolith chemistry in a coastal fishery species

Martino, JC, JA Doubleday, AJ Fowler, BM Gillanders. 2021. Marine and Freshwater Research

Otolith (ear stone) chemistry provides powerful insights into the lives of fish. Although frequently used to reconstruct past environments, the influence of physiology remains unsettled. As such, we investigated the relationships between otolith chemistry, physiological factors and environmental factors in an iconic fishery species, snapper (Chrysophrys auratus). Lifetime otolith profiles were analysed of carbon (δ13C) and oxygen (δ18O) isotopes, and elemental concentrations of lithium (Li : Ca), magnesium (Mg : Ca), manganese (Mn : Ca), strontium (Sr : Ca), and barium (Ba : Ca). Mixed-effects modelling alongside a detailed literature review was used to investigate physiological (age, otolith growth rate, fish size, sex) and environmental influences (sea-surface temperature and chlorophyll-a) on otolith chemistry. Carbon isotopes and magnesium related to physiological factors, suggesting their potential as physiological proxies. Physiology also weakly related to strontium and lithium. By contrast, oxygen isotopes, barium, and manganese (except for natal signatures) were suggested to provide insights into past environments. Our study stresses the importance of consistency in biological characteristics for study designs, and highlights the potential of physiological proxies for distinguishing between populations in uniform water bodies. This study has not only reinforced our confidence in field applications of otolith chemistry, but has furthered our understanding of the influence of physiology.

 

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Image: A School Shark, Galeorhinus galeus, at The North Sea Oceanarium. Source: Jens Christian Schou / Biopix (via EOL). License: CC BY Attribution-Noncommercial

Grow or go? Energetic constraints on shark pup dispersal from pupping areas

McMillan, MN, JM Semmens, C Huveneers, DW Sims, KM Stehfest, BM Gillanders. 2021. Conservation Physiology

Many sharks and other marine taxa use natal areas to maximize survival of young, meaning such areas are often attributed conservation value. The use of natal areas is often linked to predator avoidance or food resources. However, energetic constraints that may influence dispersal of young and their use of natal areas are poorly understood. We combined swim-tunnel respirometry, calorimetry, lipid class analysis and a bioenergetics model to investigate how energy demands influence dispersal of young in a globally distributed shark. The school shark (a.k.a. soupfin, tope), Galeorhinus galeus, is Critically Endangered due to overfishing and is one of many sharks that use protected natal areas in Australia. Energy storage in neonate pups was limited by small livers, low overall lipid content and low levels of energy storage lipids (e.g. triacylglycerols) relative to adults, with energy stores sufficient to sustain routine demands for 1.3–4 days (mean ± SD: 2.4 ± 0.8 days). High levels of growth-associated structural lipids (e.g. phospholipids) and high energetic cost of growth suggested large investment in growth during residency in natal areas. Rapid growth (~40% in length) between birth in summer and dispersal in late autumn–winter likely increased survival by reducing predation and improving foraging ability. Delaying dispersal may allow prioritization of growth and may also provide energy savings through improved swimming efficiency and cooler ambient temperatures (daily ration was predicted to fall by around a third in winter). Neonate school sharks are therefore ill-equipped for large-scale dispersal and neonates recorded in the northwest of their Australian distribution are likely born locally, not at known south-eastern pupping areas. This suggests the existence of previously unrecorded school shark pupping areas. Integrated bioenergetic approaches as applied here may help to understand dispersal from natal areas in other taxa, such as teleost fishes, elasmobranchs and invertebrates.

 

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Image: An idyllic vision of Sydney’s future? Adriana Verges, UNSW, Sydney

https://theconversation.com/sydneys-waters-could-be-tropical-in-decades-heres-the-bad-news-31523

Natural and anthropogenic climate variability shape assemblages of range-extending coral-reef fishes

Monaco, CJ, DJ Booth, WF Figueira, BM Gillanders, DS Shoeman, CJA Bradshaw, I Nagelkerken. 2021. Journal of Biogeography

Aim: Climate change is redistributing species globally, resulting in altered community structures and ecosystem functioning. The current paradigm is that species should track temperature isoclines along latitudinal and depth gradients to remain within their thermal niches. However, the many exceptions to this rule point to complex ecological and environmental processes often overlooked in statistical models predicting species redistributions. We tested the contributions of natural versus anthropogenic climate change to the long-term spatio-temporal dynamics of assemblages of range-shifting tropical fishes at the leading edge of redistribution fronts.

Location: East coast of Australia. Taxon: Tropical coral-reef fishes.

Methods: We analysed 16 years (2003–2018) of tropical species occurrences at two temperate locations using traditional diversity metrics (richness, accumulation curves and β-diversity). We also quantified the role of primary environmental covariates and estimated species associations using joint species distribution models.

Results: We reveal that tropical species richness has increased in this temperate ecosystem over time. Furthermore, we show that the richness of tropical vagrant species increased with the sea-surface temperature experienced by both local vagrants and their putative source populations at the southern Great Barrier Reef, which accounted for 23.1% and 22.1% of the explained variance, respectively. We also detected a signal from El Niño-Southern Oscillation, as species turnover and richness peaked during the strong La Niña event of 2010–2011.

Main conclusions: While the increases in ocean temperature and strength of the surface ocean current due to anthropogenic climate change are gradually favouring the poleward redistribution of tropical species, natural climatic oscillations can have a strong additive effect by rapidly modifying the pool of incoming species and potentially disrupting local communities.

 

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Graphical abstract: Cristian Monaco

Opposing life stage-specific effects of ocean warming at source and sink populations of range-shifting coral reef fishes

Monaco, CJ, I Nagelkerken, DJ Booth, WF Figueira, BM Gillanders, DS Shoeman, CJA Bradshaw. 2021. Journal of Animal Ecology

Climate change is altering the latitudinal distributions of species, with their capacity to keep pace with a shifting climate depending on the stochastic expression of population growth rates, and the influence of compensatory density feedback on age-specific survival rates. We use population-abundance time series at the leading edge of an expanding species’ range to quantify the contribution of stochastic environmental drivers and density feedbacks to the dynamics of life stage-specific population growth. Using a tropical, range-shifting Indo-Pacific damselfish (Abudefduf vaigiensis) as a model organism, we applied variants of the phenomenological Gompertz-logistic model to a 14-year dataset to quantify the relative importance of density feedback and stochastic environmental drivers on the separate and aggregated population growth rates of settler and juvenile life stages. The top-ranked models indicated that density feedback negatively affected the growth of tropical settlers and juveniles. Rates of settlement were negatively linked to temperatures experienced by parents at potential source populations in the tropics, but their subsequent survival and that of juveniles increased with the temperatures experienced at the temperate sink. Including these stochastic effects doubled the deviance explained by the models, corroborating an important role of temperature. By incorporating sea-surface temperature projections for the remainder of this century into these models, we anticipate improved conditions for the population growth of juvenile coral-reef fishes, but not for settlers in temperate ecosystems. Previous research has highlighted the association between temperature and the redistribution of species. Our analyses reveal the contrasting roles of different life stages in the dynamics of range-shifting species responding to climate change, as they transition from vagrancy to residency in their novel ranges.

 

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Developing indicators for adaptive capacity for multiple use coastal regions: Insights from the Spencer Gulf, South Australia

Nursey-Bray, M, BM Gillanders, JA Maher. 2021. Ocean and Coastal Management

Spatially large and multiple use coastal regions face unprecedented pressures. Decision makers need to build policy that links social, economic and ecological dimensions in ways that build the adaptive capacity of these systems while not compromising individual values. This paper reports on an inter-disciplinary project that used a Capitals approach to build socio-economic indicators robust enough to use in integrated community assessments of adaptive capacity. Using the Spencer Gulf, South Australia as a case study, we demonstrate the utility of these indicators to derive quantitative assessments of socio-economic adaptive capacity. We argue that such assessments used at regular periods, in conjunction with scientific indicators, have the potential to be powerful management tools and provide ongoing ability to measure community adaptive capacity over time.

 

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El Nino-Southern Oscillation drives variations in growth and otolith chemistry in a top predatory fish

Reis-Santos, P, MV Condini, CQ Albuquerque, TD Saint’Pierre, AM Garcia, BM Gillanders, SE Tanner. 2021. Ecological Indicators

Sclerochronological approaches using fish otoliths provide a powerful and cost-effective means to evaluate fish responses to environmental variations in regions where there is a paucity of long-term data. We hypothesised that the dynamism in the environmental conditions associated with El Niño Southern Oscillation (ENSO) events in the Southern Atlantic Ocean would likely influence growth patterns and chemical records in fish otoliths. Hence, we developed a 46-year otolith increment-based growth chronology, and otolith chemical chronologies of Sr:Ca and Ba:Ca for an iconic top predatory fish, the dusky grouper Epinephelus marginatus collected off the southern coast of Brazil. Using a set of increasingly complex mixed-effects linear models, our biochronological approach revealed the influence of intrinsic and large-scale environmental drivers on growth and otolith chemical composition of dusky grouper. In particular, the intensity of the Multivariate ENSO index (a measure of the status of ENSO and El Niño or La Niña conditions) was negatively associated with growth, with rapid drops in average growth evident in very strong El Niño events (1992–93, 1997–98, or 2015–16). Similar negative relationships between ENSO and Ba:Ca composition reflected variations in environmental histories of dusky groupers, a species that is mostly sedentary in coastal reefs, whilst no environmental effects were detected for Sr:Ca. Overall, identifying the drivers that underlie variations in fish growth is a crucial challenge for any conservation or fisheries interest species as population dynamics, persistence and sustainable harvesting are tightly linked to individual growth. The development of chemical chronologies provided insight towards relating otolith elemental variation to environmental conditions at multidecadal scales, encouraging further evaluations of individual and population-level fluctuations of otolith chemistry and environmental reconstructions.

 

Image: Figure 3 from paper showing sliding window analysis on the best climatic environmental variable model identifying the optimal weather windows of the effect of the Multivariate ENSO Index (MEI) on otolith growth of dusky grouper (top) and Ba:Ca otolith element composition of dusky grouper (below)

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Image: Within-season shift in the demographic relationships between spawning grounds and nursery areas for King George whiting in South Australia’s gulf systems. (A) From March to early May, thermohaline fronts at the entrance to Spencer Gulf and Investigator Strait inhibit larval transport between the two gulfs, and population processes are localised. (B) After the frontal systems breakdown in May, a density-driven current flows out the eastern side of Spencer Gulf and transports larvae into Investigator Strait. These larvae then contribute to settlement in Gulf St. Vincent and on Kangaroo Island. Red – larvae spawned in Southern Spencer Gulf; Blue – larvae spawned in Investigator Strait. From Rogers PhD thesis.

Using a biophysical model to investigate connectivity between spawning grounds and nursery areas of King George whiting (Sillaginodes punctatus) in South Australia’s gulfs

Rogers, TA, A Redondo-Rodriguez, AJ Fowler, MJ Doubell, MJ Drew, MA Steer, D Matthews, C James, BM Gillanders. 2021. Fisheries Oceanography

Many demersal marine fish species depend on a dispersive larval stage that connects geographically discrete sub populations. Understanding connectivity between these sub-populations is necessary to determine stock structure, which identifies the appropriate spatial scale for fishery management. Such connectivity is poorly understood for King George whiting (Sillaginodes punctatus; Perciformes) in South Australia's gulf system, even though spawning grounds and nursery areas are adequately defined. In response to declines in commercial catches and estimated biomass, this study aimed to determine the most important spawning grounds and nursery areas to recruitment, and the connectivity between them. A biophysical model was seeded with particles according to the distribution and density of eggs throughout the spawning area in 2017 and 2018. Despite inter-annual differences in the origins of particles, dispersal pathways and predicted settlement areas remained consistent between years. Predicted settlement was generally highest to nursery areas only short distances from regional spawning grounds, consistent with previous hydrodynamic models. However, the model also predicted that spawning in one region could contribute to recruitment in an adjacent region later in the spawning season, which aligned with the breakdown of thermohaline fronts at the entrance of each gulf. The connectivity between spawning grounds and nursery areas predicted by the model is supported by spatio-temporal patterns in the otolith chemistry of pre-flexion larvae and settled juveniles. Consequently, the most parsimonious explanation is that the populations of King George whiting in South Australia's gulf system constitute a single, panmictic stock, which has implications for fishery management.

 

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Image: Clarence River - Clarence River in Grafton, New South Wales, Australia, 2021

CC-By-SA-4.0 by Kgbo

Inter-estuarine variation in otolith chemistry in a large coastal predator: a viable tool for identifying coastal nurseries?

Russell, AL, BM Gillanders, TC Barnes, DD Johnson, MD Taylor. 2021. Estuaries and Coasts

Coastal estuaries provide essential juvenile habitat for many commercially and recreationally important fish, which may move between estuarine and coastal environments throughout their life. Identifying the most important estuarine nurseries that contribute to the broader stock can support targeted management of juvenile and spawning populations. The objective of this study was to (1) compare chemical fingerprints within sagittal otoliths of juvenile Mulloway (Argyrosomus japonicus) sampled from putative south-eastern Australian nurseries, (2) assess their potential as natural tags to distinguish nursery grounds for the broader coastal Mulloway stock and (3) assess the viability of otolith chemistry as a fisheries management tool when limited to opportunistic, fisheries-dependant, otolith sample collection from by-catch. Otoliths from juvenile Mulloway (0 to 3 years, 4 to 44.8 cm total length) were obtained from 8 major estuaries and 2 inshore ocean locations along coastal south-eastern New South Wales, Australia, from April 2015 to July 2018. Concentrations of Sr, Ba, Mg, Mn and Li in the otolith region corresponding to the juvenile nursery stage were determined using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The element to Ca ratios of fish from coastal estuaries differed significantly among collection areas, based upon multivariate elemental fingerprints, with some exceptions. When the otoliths of fish were analysed in a multinomial logistic regression (MLR) classifier, there was an overall mean allocation success of 59% to the estuary of capture. This study highlights the use of otolith ‘fingerprints’ as natural tags in Mulloway, and contributes to progressive research in environmental reconstruction applications of otolith chemistry.

 

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Image: Figure 3 from paper showing mulloway otolith for fish aged 16 years

Potential linkages between juvenile nurseries and exploited populations of mulloway (Argyrosomus japonicus), explored using otolith chemistry

Russell, AL, MD Taylor, TC Barnes, DD Johnson, BM Gillanders. 2021. Fisheries Research

Many exploited coastal species rely on estuarine nurseries, however, the importance of different estuaries and their contribution to exploited populations can vary. Identification of connectivity between source nurseries and exploited populations is important for effective habitat and fishery management. We present a case study which employs otolith chemistry to investigate source-sink population dynamics across broad spatial scales for an exploited migratory sciaenid, Mulloway (Argyrosomus japonicus). Specifically, we compared the otolith chemical fingerprints of juveniles in putative estuarine nurseries across south-eastern Australia with the sub-yearling chemical fingerprints of post-recruited fish in the exploited component of the stock. Multinomial Logistic Regression (MLR) suggested that two of the eight estuarine nurseries sampled were particularly important sources of Mulloway recruits, and there was strong evidence of stock mixing which exceeded that expected from historic tag-recapture studies. However, there was some uncertainty in the patterns resolved. Variation in otolith signatures between the known-source juveniles and post-recruit fish may be explained by inter-annual variability in these systems, caused by extensive flooding on the central and northern-NSW coast during the study period. These events contributed considerable extrinsic variation to the chemical composition, influencing the lack of overlap between otolith chemistry of putative nurseries and sub-yearling otolith chemistry of exploited fish. The approach presented highlights the importance of considering inter-annual variability when examining source-sink relationships in long-lived species, but the use of otolith fingerprints shows promise for evaluating these questions for both Mulloway and other exploited fish species.

 

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Image: The four strontium isotope species. The ratio 87Sr/86Sr is commonly used in geochemical studies but our study used 88Sr/86Sr. From Isobar.

Impact of salinity and carbonate saturation on stable Sr isotopes (d88/86Sr) in a lagoon-estuarine system

Shao, Y, J Farkas, L Mosley, J Tyler, H Wong, B Chamberlayne, M Raven, M Samanta, C Holmden, BM Gillanders, A Kolevica, A Eisenhauer.  2021. Geochimica et Cosmochimica Acta

Local carbonate cycling in lagoon-estuarine systems, involving processes such as inorganic and biogenic carbonate precipitation/dissolution, represents an important but poorly constrained component of the coastal carbon budget. This study investigates the sensitivity of stable Sr isotope tracer (δ88/86Sr) with respect to carbonate saturation and salinity of local waters in the Coorong, Lower Lakes and Murray Mouth (CLLMM) estuary in South Australia. The CLLMM has an extensive range of salinity from fresh to hypersaline (from ∼0 to over 100 PSU), with corresponding variations in water chemistry and major ion composition that in turn controls mineral saturation states, and thus CaCO3 precipitation/dissolution in local waters. Here we use the novel δ88/86Sr tracer in tandem with the more established radiogenic Sr isotope ratio (87Sr/86Sr), where the latter is a robust proxy for Sr sources and thus water provenance. We also produced a geochemical (PHREEQC) model of calcium carbonate (CaCO3) saturation changes across this unique lagoon-estuarine system. The results indicate a systematically increasing trend of δ88/86Sr (from ∼0.25‰ to ∼0.45‰) with increasing salinity and CaCO3 (aragonite, calcite) saturation indices of the coastal waters, which in turn suggest an overall control of carbonate dissolution/precipitation processes on the stable Sr isotope composition in the CLLMM system. This was further corroborated by Ca isotope data (δ44/40Ca) published previously on the same samples from the Coorong, as well as a quantitative simulation of local carbonate removal in the lagoon based on Rayleigh modelling and Sr isotope data. Overall, our results confirm that a coupled Sr isotope approach (combining 87Sr/86Sr and δ88/86Sr) can be used to constrain not only the main water sources (continental versus marine Sr) but also local CaCO3 dissolution/precipitation processes, and thus inorganic carbon and coastal carbonate cycling in the CLLMM system. Finally, this coupled δ88/86Sr and 87Sr/86Sr approach can be potentially applied to fossil carbonate archives to reconstruct paleo-hydrology and salinity changes in the CLLMM and/or other carbonate-producing coastal systems.

 

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Image: Coorong Lagoon, from MDBA

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Graphical abstract: Jackson Stockbridge

Evaluation of a popular spatial cumulative impact assessment method for marine systems: A seagrass case study

Stockbridge, J, AR Jones, SG Gaylard, MJ Nelson, BM Gillanders. 2021. Science of the Total Environment

Human activities put stress on our oceans and with a growing global population, the impact is increasing. Stressors rarely act in isolation, with the majority of marine areas being impacted by multiple, concurrent stressors. Marine spatial cumulative impact assessments attempt to estimate the collective impact of multiple stressors on marine environments. However, this is difficult given how stressors interact with one another, and the variable response of ecosystems. As a result, assumptions and generalisations are required when attempting to model cumulative impacts. One fundamental assumption of the most commonly applied, semi-quantitative cumulative impact assessment method is that a change in modelled cumulative impact is correlated with a change in ecosystem condition. However, this assumption has rarely been validated with empirical data. We tested this assumption using a case study of seagrass in a large, inverse estuary in South Australia (Spencer Gulf). We compared three different seagrass condition indices, based on survey data collected in the field, to scores from a spatial cumulative impact model for the study area. One condition index showed no relationship with cumulative impact, whilst the other two indices had very small, negative relationships with cumulative impact. These results suggest that one of the most commonly used methods for assessing cumulative impacts on marine systems is not robust enough to accurately reflect the effect of multiple stressors on seagrasses; possibly due to the number and generality of assumptions involved in the approach. Future methods should acknowledge the complex relationships between stressors, and the impact these relationships can have on ecosystems. This outcome highlights the need for greater evaluation of cumulative impact assessment outputs and the need for data-driven approaches. Our results are a caution for marine scientists and resource managers who may rely on spatial cumulative impact assessment outputs for informing policy and decision-making.

 

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Graphical abstract from paper

Migration histories and perfluoroalkyl acid (PFAA) loads in an estuarine fish: A novel union of analyses to understand variation in contaminant concentrations

Taylor, MD, BM Gillanders, S Nilsson, J Braunig, TC Barnes, JF Mueller. 2021. Environmental Pollution

Previous studies have shown that accumulation of perfluoroalkyl acids (PFAAs) in the tissues of aquatic species is highly variable. Movement and migration patterns in these species represent an important consideration when evaluating contaminant accumulation in exposed biota, and may have a large influence on the risk profiles for migratory seafood species. In this study, relationships between PFAA concentrations in muscle and liver tissue, and recent fish migration history (inferred from metals profiles in fish otoliths, otherwise known as otolith chemistry) were evaluated in Sea Mullet (Mugil cephalus). A greater number of PFAAs, and higher concentrations, were found in liver compared to muscle tissue. Perfluorooctane sulfonate (PFOS) was present in highest concentrations in both muscle and liver tissues, and there was strong correlation in concentrations between these two tissues. PFOS was found to decrease and increase alongside recent strontium and barium concentrations (respectively) in the otolith, suggesting higher concentrations of PFAAs in fish recently exposed to comparatively lower salinity environments. This study highlights how otolith chemistry can be employed to examine links between contaminant concentrations in fish, and their recent migration history. This approach shows promise for studying contaminant residues in mobile seafood species within the natural environment.

 

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Image: Figure 8 from paper showing fish moving with and without tidal influence. (a) fish moves between locations, but may have the same elemental signatures as the fish that moves with the tide; (b) fish stays in the same location, but may have different elemental signatures as the tide moves water around the fish. Light blue depicts marine, white depicts brackish and dark blue depicts fresh waters.

Variability in water chemistry in the Lower Mekong Basin: Considerations for fish life history reconstruction

Vu, AV, LJ Baumgartner, GS Doran, M Mallen-Cooper, JD Thiem, JA Howitt, KE Limburg, BM Gillanders, IG Cowx. 2021. Estuarine, Coastal and Shelf Science

Spatial and temporal variation of nine elements (Ba, Ca, Cu, Mg, Mn, Na, Se, Sr, and Zn) and some additional environmental parameters (salinity, water levels, and conductivity) were examined over two 2,000 km along the length of the main Mekong River channel from Luang Prabang in Northern Lao PDR to the Mekong Delta in Vietnam. Longitudinal profiles of some dissolved elemental concentrations varied significantly along the river channel. For example, Sr concentration in marine water was up to 83 times higher than in fresh water. By contrast, Ba concentration was around 4 times higher in fresh water than in marine water, but was significantly influenced by inflows from major tributaries in Cambodia (dilution effects). We found dissolved Ba was elevated in low salinity. Furthermore, Sr concentration was more variable than Ba, especially in the Mekong Delta due to different tidal influences in each of the Delta branches. Selenium was only present along the coast and one river branch in the delta. The variation in water chemistry of the Mekong main channel identified through this study provides information that can be used in the interpretation of regional fish movements using otolith chemistry, including across the freshwater, estuarine and marine interface. Accurate interpretation is essential given the Lower Mekong Basin has a high biodiversity that is under threat from rapid development, and substantial knowledge gaps exist on the life history requirements of numerous fish species.

 

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Graphical abstract: Nina Wootton

A comparison of microplastic in fish from Australia and Fiji

Wootton, N, M Ferreira, P Reis-Santos, BM Gillanders. 2021. Frontiers in Marine Science

Awareness surrounding plastic pollution has increased significantly in the past decade, leading to concerns on potential adverse effects on biota, including the consumption of microplastic by fish. Globally, plastic has been found in many species of fish, but little research has been undertaken in the southern hemisphere. We assessed the abundance and type of plastic in fish captured and sold for human consumption in Australia and Fiji. Fish (goatfish, sea mullet, paddletail, and common coral trout) had their gastrointestinal tracts dissected and microplastic quantified under a microscope. Plastic polymer types were confirmed using μ-FTIR. In Australia, plastic was found in 61.6% of fish gastrointestinal tracts, while in Fiji, 35.3% of fish had plastic. Fish from Australia had almost double the amount of plastic on average than fish caught in Fiji, with 1.58 (± 0.23) pieces per fish in Australia compared to 0.86 (± 0.14) in fish caught in Fiji. The types of plastic differed between countries, with fibers comprising 83.6% of microplastic pieces in fish from Australia whereas 50% of microplastic found in fish from Fiji was film. Polyolefin was the most abundant polymer type in both fibers from Australia and film from Fiji. We hypothesize variations in abundance and plastic type are a reflection of the population density and coastal geomorphology, but may also be a result of legislation and waste management strategies in the two countries. This work adds evidence to the pervasive presence of plastic in fish gastrointestinal tracts, reinforcing the urgent need for efficient plastic waste management, but also a better understanding of the impacts of microplastic on marine biota.

 

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Graphical abstract: Nina Wootton

Low abundance of microplastics in commercially caught fish across southern Australia

Wootton, N, P Reis-Santos, N Dowsett, A Turnbull, BM Gillanders. 2021. Environmental Pollution

Plastic pollution has increased significantly in the past decades and is now a major global environmental issue. Plastic objects enter the ocean and are broken down into smaller pieces, while wastewater and runoff also carry microplastics (plastics <5 mm) into the ocean. Plastic has been found in over 700 different species of marine wildlife but little research has examined fish sold for human consumption. We determined the microplastic abundance in nine commercially important, wild-caught fish species purchased from seafood markets across 4000 km of Australia (Western Australia, South Australia, Victoria, Tasmania, New South Wales). For microplastic quantification, fish gastro-intestinal tracts were chemically digested and the amount and type of microplastic identified under a microscope and Fourier transform infrared spectrometer. Across all states, an average of 35.5% of fish samples had at least one piece of microplastic in their gastro-intestinal tract. South Australia had the highest percentage of fish with plastic (49%) and Tasmania the lowest (20%). The average microplastic load was 0.94 piece per fish but ranged from 0 to 17 pieces, with polyolefin identified as the dominant polymer group. Overall, the ingestion of microplastic was widespread across species, locations, diets and habitat niches of fish species investigated, but the average plastic ingestion was less than other similar global studies. This study provides novel insights on the use of fish species from seafood markets to assess environmental contamination by microplastic, as well as an important perspective of the potential for microplastic contamination to enter the human food chain.

 

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Graphical abstract: Nina Wootton

Microplastic in fish – a global synthesis

Wootton, N, P Reis-Santos, BM Gillanders. 2021. Reviews in Fish Biology and Fisheries

Plastic contamination is ubiquitous, with plastic found in hundreds of species of aquatic wildlife, including fish. Lacking a broad and comprehensive view of this global issue across aquatic environments, we collated and synthesised the literature that focuses on microplastic ingestion in fish from marine, freshwater and estuarine environments. First, we assessed how the approaches used to investigate microplastic in fish have changed through time, comparing studies globally. A greater understanding of this changing landscape is essential for rigorous and coherent comparisons with only 42% of published studies following recommended approaches of chemical digestions and verifying plastic via polymer identification. Then, using this subset of studies, we found that 49% of all fish sampled globally for microplastic ingestion had plastic (average of 3.5 pieces per fish), with fish from North America ingesting more plastic than fish from other regions. We then evaluated the role of environment, habitat, feeding strategy and source (i.e. aquaculture or wild-caught) in the ingestion of microplastic. Research from marine environments dominated (82% of species) but freshwater fish ingested more plastic, as did detritivores, fish in deeper waters and those from aquaculture sources. By collating global microplastic research we identified regional disparities and key knowledge gaps that support research towards freshwater environments and aquaculture sources. Overall, we highlight the need for consistent guidelines in methods used to evaluate microplastic in fish, to ensure data are unambiguous, comparable and can be widely used to support mitigation and management strategies, inform potential policy actions, and evaluations of environmental, food safety, and human health goals.

 

Otolith chemistry delineates the influence of natal origin, dispersal and flow on the population dynamics of golden perch (Macquaria ambigua) in a regulated river

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Image: Golden Perch, Macquaria ambigua. Source: Gunther Schmida / http://www.guntherschmida.com.au via the Atlas of Living Australia. License: CC BY Attribution-Noncommercial-ShareAlike

Zampatti, BP, SJ Leigh, PJ Wilson, DA Crook, BM Gillanders, R Maas, JI Macdonald, J Woodhead. 2021. Marine and Freshwater Research

For riverine fishes threatened by fragmentation and flow modification, effective management requires an understanding of when and where key life history processes (spawning, recruitment and movement) take place. The structural and chemical properties of otoliths provide a unique means to recount a fish’s life in time and space. We investigated the age structure of the migratory, pelagic-spawning golden perch (Macquaria ambigua) in the Murray River, Australia, and used water and otolith 87Sr/86Sr ratios to delineate the natal origin and movement of fish from discrete cohorts. Water 87Sr/86Sr was distinct among the Darling River (a major tributary) and lower and mid-Murray River. Otolith chemistry revealed golden perch collected in the lower Murray River were progeny of spawning in either the Murray or Darling rivers, during years characterised by within-channel rises in flow, or in both rivers in a year of overbank flooding. Movement of juvenile fish from the Darling River substantially influenced population structure in the lower Murray River, whereby post-flood population growth was largely due to the immigration of age-1+ fish. This study demonstrates the potential importance of tributary recruitment sources, dispersal and connectivity on main-stem population dynamics and the utility of otolith chemistry for spatially reconciling population structure and the life histories of freshwater fishes.

 

Near Calperun Station, SA

Near Calperun Station, SA

Giant Australian cuttlefish

Giant Australian cuttlefish

Flinders Chase

Flinders Chase

Tourville Bay

Tourville Bay

Streaky Bay

Streaky Bay

Kangaroo Island

Kangaroo Island

Routeburn Track

Routeburn Track

White Island

White Island