Great Barrier Reef Region Research Articles

Ecotoxicity threshold values for 4-hydroxychlorothalonil, carbendazim, dimethoate and methoxyfenozide in fresh and marine waters: Part 1. Derivation of threshold values

Pesticide active ingredients are frequently detected in the rivers, creeks, wetlands, estuaries, and marine waters of the Great Barrier Reef (GBR) region and are one of the main contributors to poor water quality. Pesticide concentrations detected in the environment through water quality monitoring programs can be compared against estimates of ecologically “safe” concentrations (i.e., water quality guidelines) to assess the potential hazard and risk posed to aquatic ecosystems. Water quality guidelines are also required to estimate the aquatic risk posed by pesticide mixtures, which is used for the Reef 2050 Water Quality Improvement Plan pesticide target. Seventy-four pesticide active ingredients and their degradates are frequently detected in GBR catchment waterways, however many do not have water quality guidelines in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The current study derives ecotoxicity threshold values (ETVs) as unendorsed guideline values for active ingredients in two fungicides (4-hydroxychlorothalonil (fungicide degradate) and carbendazim) and two insecticides (dimethoate and methoxyfenozide) that are commonly detected in GBR catchment waterways. The proposed ETVs have been derived using species sensitivity distributions, as recommended in the Australian and New Zealand nationally endorsed method for deriving water quality guidelines for aquatic ecosystem protection. Four ETVs were derived for each chemical with values that should theoretically protect 99, 95, 90 and 80 % of species (i.e., PC99, PC95, PC90, PC80, respectively). The PC99 and PC95 values for 4-hydroxychlorothalonil, carbendazim, dimethoate and methoxyfenozide were 0.49 μg/L and 4 μg/L, 0.029 μg/L and 0.45 μg/L, 0.11 μg/L and 5.8 μg/L and 0.19 μg/L and 2 μg/L, respectively. The ETVs will be used in an ecological hazard and risk assessment across GBR waterways in part two of this study. The ETVs can also be used to assess potential risk across Australia and internationally where monitoring data are available.

Environmental DNA highlights the influence of salinity and agricultural run-off on coastal fish assemblages in the Great Barrier Reef region

Agricultural run-off in Australia's Mackay-Whitsunday region is a major source of nutrient and pesticide pollution to coastal and inshore ecosystems of the Great Barrier Reef. While the effects of run-off are well documented for the region's coral and seagrass habitats, the ecological impacts on estuaries, the direct recipients of run-off, are less known. This is particularly true for fish communities, which are shaped by the physico-chemical properties of coastal waterways that vary greatly in tropical regions. To address this knowledge gap, we used environmental DNA (eDNA) metabarcoding to examine fish assemblages at four locations (three estuaries and a harbour) subjected to varying levels of agricultural run-off during a wet and dry season. Pesticide and nutrient concentrations were markedly elevated during the sampled wet season with the influx of freshwater and agricultural run-off. Fish taxa richness significantly decreased in all three estuaries (F = 164.73, P = <0.001), along with pronounced changes in community composition (F = 46.68, P = 0.001) associated with environmental variables (largely salinity: 27.48% contribution to total variance). In contrast, the nearby Mackay Harbour exhibited a far more stable community structure, with no marked changes in fish assemblages observed between the sampled seasons. Among the four sampled locations, variation in fish community composition was more pronounced within the wet season (F = 2.5, P = 0.001). Notably, variation in the wet season was significantly correlated with agricultural contaminants (phosphorus: 6.25%, pesticides: 5.22%) alongside environmental variables (salinity: 5.61%, DOC: 5.57%). Historically contaminated and relatively unimpacted estuaries each demonstrated distinct fish communities, reflecting their associated catchment use. Our findings emphasise that while seasonal effects play a key role in shaping the community structure of fish in this region, agricultural contaminants are also important contributors in estuarine systems.

Finding common ground: Understanding and engaging with science mistrust in the Great barrier reef region.

At a time when ambitious environmental management initiatives are required to protect and restore aquatic ecosystems, public trust in the science that underpins environmental policy and decision-making is waning. This decline in public trust coincides with a rise in misinformation, and threatens to undermine public support for, and participation in, environmental protection. Our study investigates the prevalence and predictors of mistrust in science associated with the protection and management of the Great Barrier Reef (GBR) and its catchments. Using survey data from 1,877 residents of the GBR region, we identify environmental values, perceptions, and attitudes that are associated with science mistrust. Our results include a typology of GBR science trust and scepticism. Science-sceptical respondents, representing 31% of our sample, were likely to perceive waterway management decisions as being unfair, felt less responsible, and were less motivated to contribute to improving waterway health than those with greater trust in science. Science-sceptical respondents also had differing perceptions of some threats to waterways, in particular climate change. However, similarities and 'common ground' between respondents with varying levels of trust in science included a shared recognition of the importance of waterways' ecosystem services, and a shared perception of the relative health and problems within their regions' waterways. Our findings can help to break down assumptions about science-sceptical groups in the GBR region and elsewhere. We offer recommendations to guide more constructive engagement that seeks to restore trust and build consensus on mutual goals and pathways to protect vital ecosystem functions and services.

Basin-scale riverine ecosystem services vary with network geometry

Riverine ecosystems provide a variety of services supporting biodiversity, human livelihoods, and the maintenance of river health. Multiple anthropogenic threats to riverine ecosystem services (RES) have been identified and considered in river management strategies. However, the way in which the river network is spatially arranged across the landscape – river network geometry – may also play a role in the delivery of RES. Here we studied the effect of river network geometry on the delivery of five RES in 14 catchments of the Great Barrier Reef region, Australia. Our investigation has three parts. First, we conducted a sensitivity analysis on modelled RES, holding all non-geometric catchment characteristics, other than catchment size and slope, constant to allow attribution of modelled differences directly to differences in geometry. Second, we analysed the relationships between observed RES and network structural indices. Third we compared observed RES with modelled results. Modelled results suggest that RES are sensitive to the differences in river network geometry. Furthermore, correlation analyses show good agreement between observed RES and network structural indices, and there is good correlation between the modelled and observed RES. These results suggest an important role of river network geometry in the delivery of multiple RES by mediating upstream inputs as they pass through the river network. A one size fits all approach to river management may thus be ineffective and specific management interventions will be needed in catchments of different network geometries.

Cryptic marine barriers to gene flow in a vulnerable coastal species, the dugong (Dugong dugon)

AbstractDespite the lack of obvious physical barriers and their ability to travel significant distances, many marine mammals exhibit substantial population structuring over relatively short geographical distances. The dugong (Dugong dugon), the only extant representative of family Dugongidae, is listed as Vulnerable to Extinction globally. We investigated the genetic population structure of dugongs in the shallow coastal waters along &gt;2,000 km of the eastern Queensland coast, including the Great Barrier Reef region. Microsatellite genotypes for 22 loci in 293 dugongs, SNP genotypes based on 10,690 loci in 43 dugongs, and 410 bp mitochondrial control‐region sequences from 639 dugongs were analyzed. Clustering analysis techniques consistently identified an abrupt genetic break in the Whitsunday Islands region (20.3°S), which interrupts an overall pattern of isolation‐by‐distance. Geographic distance was relatively more important than sea‐surface temperature and seagrass distribution in explaining pairwise microsatellite genetic distances. The cause of reduced dispersal across this region is unknown but might relate to an unusual tidal and current mix, termed the “sticky‐water” effect, and/or a break in the geographical distribution of off‐shore seagrass meadows. The genetic structure suggests distinct breeding units north and south of the Whitsunday Islands region for consideration in further developing management plans for Queensland dugongs.

Assessment of Tropical Cyclone Risk to Coral Reefs: Case Study for Australia

In this study, we attempt to expand tropical cyclone (TC) risk assessment methodology and build an understanding of TC risk to Australia’s natural environment by focusing on coral reefs. TCs are natural hazards known to have the potential to bring destruction due to associated gale-force winds, torrential rain, and storm surge. The focus of TC risk assessment studies has commonly centred around impacts on human livelihoods and infrastructure exposed to TC events. In our earlier study, we created a framework for assessing multi-hazard TC risk to the Australian population and infrastructure at the Local Government Area level. This methodology is used in this study with coral reefs as the focus. TC hazard, exposure, and vulnerability indices were created from selected coral-related datasets to calculate an overall TC risk index for the Ningaloo Reef (NR) and the Great Barrier Reef (GBR) regions. The obtained results demonstrate that the northern NR and the southern GBR had the highest risk values within the study area; however, limitations in data quality have meant that results are estimates at best. The study has shown the potential benefits of such a TC risk assessment framework that can be improved upon, as coral data collection becomes more readily available.

Quantifying Catch Rates, Shark Abundance and Depredation Rate at a Spearfishing Competition on the Great Barrier Reef, Australia.

Simple SummaryCatch-per-unit-effort at a spearfishing competition in North Queensland, Australia was 1.25 fish per hour. Citizen scientists reported 358 sharks comprising of 10 species/groups, with 3.11 sharks observed per hour. Twelve percent of all sharks sighted in this study were regarded as potentially dangerous to humans. This is the first scientific study of shark depredation for spearfishing. C. amblyrhynchos were primarily responsible for depredation, with 5.9% of speared fish taken. Sixty percent of interviewees perceived that shark numbers have increased in the past 10 years.We developed and applied a method to quantify spearfisher effort and catch, shark interactions and shark depredation in a boat-based recreational spearfishing competition in the Great Barrier Reef Marine Park in Queensland. Survey questions were designed to collect targeted quantitative data whilst minimising the survey burden of spearfishers. We provide the first known scientific study of shark depredation during a recreational spearfishing competition and the first scientific study of shark depredation in the Great Barrier Reef region. During the two-day spearfishing competition, nine vessels with a total of 33 spearfishers reported a catch of 144 fish for 115 h of effort (1.25 fish per hour). A subset of the catch comprised nine eligible species under competition rules, of which 47 pelagic fish were weighed. The largest fish captured was a 34.4 kg Sailfish (Istiophorus platypterus). The most common species captured and weighed was Spanish Mackerel (Scomberomorus commerson). The total weight of eligible fish was 332 kg and the average weight of each fish was 7.1 kg. During the two-day event, spearfishers functioned as citizen scientists and counted 358 sharks (115 h effort), averaging 3.11 sharks per hour. Grey Reef Sharks (Carcharhinus amblyrhynchos) comprised 64% of sightings. Nine speared fish were fully depredated by sharks as spearfishers attempted to retrieve their catch, which equates to a depredation rate of 5.9%. The depredated fish included four pelagic fish and five reef fish. The shark species responsible were Grey Reef Shark (C. amblyrhynchos) (66%), Bull Shark (Carcharhinus leucas) (11%), Whitetip Reef Shark (Triaenodon obesus) (11%) and Great Hammerhead (Sphyrna mokarran) (11%). There were spatial differences in fish catch, shark sightings and rates of depredation. We developed a report card that compared average catch of fish, sightings of sharks per hour and depredation rate by survey area, which assists recreational fishers and marine park managers to assess spatio-temporal changes. The participating spearfishers can be regarded as experienced (average 18 days a year for average 13.4 years). Sixty percent of interviewees perceived that shark numbers have increased in the past 10 years, 33% indicated no change and 7% indicated shark numbers had decreased. Total fuel use of all vessels was 2819 L and was equivalent to 6.48 tons of greenhouse gas emissions for the competition.

Modelling the influence of coral-reef-derived dimethylsulfide on the atmosphere of the Great Barrier Reef, Australia

Marine dimethylsulfide (DMS) is an important source of natural sulfur to the atmosphere, with potential implications for the Earth’s radiative balance. Coral reefs are important regional sources of DMS, yet their contribution is not accounted for in global DMS climatologies or in model simulations. This study accounts for coral-reef-derived DMS and investigates its influence on the atmosphere of the Great Barrier Reef (GBR), Australia, using the Australian Community Climate and Earth System Simulator Atmospheric Model version 2 (ACCESS-AM2). A climatology of seawater surface DMS (DMSw) concentration in the GBR and an estimate of direct coral-to-air DMS flux during coral exposure to air at low tide are incorporated into the model, increasing DMS emissions from the GBR region by 0.02 Tg yr-1. Inclusion of coral-reef-derived DMS increased annual mean atmospheric DMS concentration over north-eastern Australia by 29%, contributing to an increase in gas-phase sulfate aerosol precursors of up to 18% over the GBR. The findings suggest that the GBR is an important regional source of atmospheric sulfur, with the potential to influence local-scale aerosol-cloud processes. However, no influence on sulfate aerosol mass or number concentration was detected, even with a reduction in anthropogenic sulfur dioxide emissions, indicating that DMS may not significantly influence the regional atmosphere at monthly, annual or large spatial scales. Further research is needed to improve the representation of coral-reef-derived DMS in climate models and determine its influence on local, sub-daily aerosol-cloud processes, for which observational studies suggest that DMS may play a more important role.

Consumers' preferences and willingness to pay for improved environmental standards: insights from cane sugar in the Great Barrier Reef region*

Reducing nutrient runoff from sugarcane production into the Great Barrier Reef (GBR) has become a major policy focus for the Queensland and Australian Governments. This study explores consumer willingness to pay (WTP) to achieve higher environmental standards for sugar originating from the GBR catchments, through the use of a GBR‐safe ecolabel. A Best‐Worst Scaling (BWS) and a Contingent Valuation (CV) experiment are conducted on a random sample of 1,100 Australian residents. The BWS experiment reveals that personal health considerations are more important than sustainability and environmental factors, including impacts on the GBR. Results of the CV experiment show that respondents are more likely to pay a premium to support Reef‐friendly sugar if they are living in urban areas, plan to visit the GBR in the future, think that the GBR condition has declined, and are generally concerned about keeping a healthy diet. We estimate that the average WTP is $24.5/year/household, which only represents 0.34 per cent of the average weekly grocery bill of Australian households. This small contribution through increased sugar prices could conservatively raise $46.9M/year in support of sugar producers to improve water quality in the GBR. Based on these results, we recommend policy‐makers consider instruments that further involve sugar consumers.

A characterization of clouds over the Great Barrier Reef and the role of local forcing

AbstractA characterization of cloud properties associated with precipitation in the region around the Great Barrier Reef (GBR) is constructed using decade‐long (2007–2017) satellite observations from Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) combined with CloudSat. The spatial and vertical distributions of low‐level cloud properties over the region are also investigated and discussed. In general, different cloud types are observed over different regions and vary by season: high clouds are dominant over the low latitudes in summer, altocumulus are mainly observed over northeast Queensland and low‐level clouds are dominant over the ocean and coast during the winter months at higher latitudes under a trade wind regime. A strong latitudinal dependence of total precipitation across the Greater GBR region is identified with a significant orographic enhancement near Cairns in the wet tropics. MODIS and CloudSat‐CALIPSO cloud observations show good agreement on significant differences in low‐level cloud microphysical properties between the land and the ocean. The largest land–ocean differences in warm cloud microphysical properties are found over the mid‐latitudes near 18°S, which is strongly associated with orographic forcing, with these enhancements extending further east to the coral reef area. However, the frequency of warm cloud is not enhanced upwind of the mountains in the wet tropics. In addition, no significant differences in warm cloud properties between the actual GBR and the open ocean are identified. These results suggest that low‐level clouds over the GBR do not show any significant response to the reef‐related microphysical perturbations.

Jellyfish risk communications: The effect on risk perception, travel intentions and behaviour, and beach tourism destinations

Jellyfish hazards at 3S destinations are underrepresented in tourism research. Using a novel conceptual model based on risk perception and destination image theories, we used an experimental setting to examine whether different types of jellyfish risk messages influenced people's travel intentions and behaviours. In addition, the study tested the influence of worry and culture.We sampled 415 prospective visitors to two of the world's most successful beach tourism destinations, the Costa Brava coastline of Spain and the Great Barrier Reef region of northern Australia, both adversely affected by the presence of jellyfish. At these unique destinations, contact with jellyfish can be painful and deadly. Early in the Covid-19 pandemic, fictitious vignettes were posted on an internet Travel Forum containing two different jellyfish risk messages, one informal and the other official. Participants' responses to these communications were tested.We found that risk messages influenced destination image but not travel intention. People from risk-averse Germanic European countries were more inclined to alter their behaviour by avoiding the water than other cultures. These findings add to the body of knowledge about the relationship between risk communications, risk perceptions and destination image.This study suggests that wildlife-associated risk communications can influence people's risk perceptions, but not sufficiently to change their travel plans. This knowledge is important in policy-making and managing responses to risk at tourism destinations. It is also important in building visitor trust and confidence, whereby tourists know that their safety and enjoyment are valued and are paramount to the destination.

New constraints on the postglacial shallow-water carbonate accumulation in the Great Barrier Reef

More accurate global volumetric estimations of shallow-water reef deposits are needed to better inform climate and carbon cycle models. Using recently acquired datasets and International Ocean Discovery Program (IODP) Expedition 325 cores, we calculated shallow-water CaCO3 volumetrics and mass for the Great Barrier Reef region and extrapolated these results globally. In our estimates, we include deposits that have been neglected in global carbonate budgets: Holocene Halimeda bioherms located on the shelf, and postglacial pre-Holocene (now) drowned coral reefs located on the shelf edge. Our results show that in the Great Barrier Reef alone, these drowned reef deposits represent ca. 135 Gt CaCO3, comparatively representing 16–20% of the younger Holocene reef deposits. Globally, under plausible assumptions, we estimate the presence of ca. 8100 Gt CaCO3 of Holocene reef deposits, ca. 1500 Gt CaCO3 of drowned reef deposits and ca. 590 Gt CaCO3 of Halimeda shelf bioherms. Significantly, we found that in our scenarios the periods of pronounced reefal mass accumulation broadly encompass the occurrence of the Younger Dryas and periods of CO2 surge (14.9–14.4 ka, 13.0–11.5 ka) observed in Antarctic ice cores. Our estimations are consistent with reef accretion episodes inferred from previous global carbon cycle models and with the chronology from reef cores from the shelf edge of the Great Barrier Reef.

DNA-Based Detection and Patterns of Larval Settlement of the Corallivorous Crown-of-Thorns Sea Star (Acanthaster sp.).

AbstractPopulation irruptions of the western Pacific crown-of-thorns sea star (Acanthaster sp.) are a perennial threat to coral reefs and may be initiated by fluctuations in reproductive or settlement success. However, the processes dictating their early life history, particularly larval settlement, remain poorly understood given limitations in sampling larvae and newly settled juveniles in the field. Here, we introduce an innovative method to measure crown-of-thorns sea star settlement, using artificial settlement collectors and droplet digital polymerase chain reaction based on crown-of-thorns sea star-specific mitochondrial DNA primers. This study demonstrated the utility of this method and explored temporal and spatial patterns of crown-of-thorns sea star settlement on the Great Barrier Reef from 2016 to 2020. Settlement varied considerably between sampling periods at Rib Reef and peaked between October 2016 and January 2017. Our results further suggest that crown-of-thorns sea star larvae readily settle in shallow reef environments, with no preferential settlement detected between depths tested (4-12 m). Substantial variation between Great Barrier Reef regions was revealed in 2019-2020, because collectors deployed on reefs in the central Great Barrier Reef were >10 times as likely to record newly settled crown-of-thorns sea stars as reefs in the northern Great Barrier Reef near Lizard Island. The trends reported here add to our understanding of this critical life-history stage; however, further method validation and larger-scale studies are needed to address pertinent information gaps, such as the stock-recruitment dynamics of this species. Most importantly, fluctuations in crown-of-thorns sea star settlement can now be detected using this sampling protocol, which demonstrates its utility in heralding new and renewed population irruptions of this destructive sea star.

Australian tidal currents – assessment of a barotropic model (COMPAS v1.3.0 rev6631) with an unstructured grid

Abstract. While the variations of tidal range are large and fairly well known across Australia (less than 1 m near Perth but more than 14 m in King Sound), the properties of the tidal currents are not. We describe a new regional model of Australian tides and assess it against a validation dataset comprising tidal height and velocity constituents at 615 tide gauge sites and 95 current meter sites. The model is a barotropic implementation of COMPAS, an unstructured-grid primitive-equation model that is forced at the open boundaries by TPXO9v1. The mean absolute error (MAE) of the modelled M2 height amplitude is 8.8 cm, or 12 % of the 73 cm mean observed amplitude. The MAE of phase (10∘), however, is significant, so the M2 mean magnitude of vector error (MMVE, 18.2 cm) is significantly greater. The root sum square over the eight major constituents is 26 % of the observed amplitude. We conclude that while the model has skill at height in all regions, there is definitely room for improvement (especially at some specific locations). For the M2 major axis velocity amplitude, the MAE across the 95 current meter sites, where the observed amplitude ranges from 0.1 to 156 cm s−1, is 6.9 cm s−1, or 22 % of the 31.7 cm s−1 observed mean. This nationwide average result is encouraging, but it conceals a very large regional variation. Relative errors of the tidal current amplitudes on the narrow shelves of New South Wales (NSW) and Western Australia exceed 100 %, but tidal currents are weak and negligible there compared to non-tidal currents, so the tidal errors are of little practical significance. Looking nationwide, we show that the model has predictive value for much of the 79 % of Australia's shelf seas where tides are a major component of the total velocity variability. In descending order this includes the Bass Strait, the Kimberley to Arnhem Land, and southern Great Barrier Reef regions. There is limited observational evidence to confirm that the model is also valuable for currents in other regions across northern Australia. We plan to commence publishing “unofficial” tidal current predictions for chosen regions in the near future based on both our COMPAS model and the validation dataset we have assembled.

Assessing the Unintended Consequences of Legitimating Responses to Grand Challenges

Our study shows that legitimating processes involved in responding to grand challenges can have detrimental consequences for how these challenges are addressed. Findings from our in-depth case study reveal the dynamics of a multi-stakeholder partnership established to address water health issues in a critical river basin located in Australia’s Great Barrier Reef region. While organizational actors involved in this partnership successfully legitimated their response to the grand challenge, this response became increasingly disconnected from the worsening conditions the partnership intended to address. This disconnect was driven by an imbalance between outputs produced by the partnership and outcomes with regard to the grand challenge. Our study reveals a cumulative and reinforcing (de)legitimating process whereby organizational actors can become increasingly skilled in legitimating their collective response while simultaneously moving further away from addressing the worsening grand challenge itself. Drawing on our findings, we develop a (de)legitimating process model which enables a better understanding of how legitimating processes shape efforts to address grand challenges.

Limited genetic signal from potential cloning and selfing within wild populations of coral-eating crown-of-thorns seastars (Acanthaster cf. solaris)

Population outbreaks of crown-of-thorns seastars (CoTS; Acanthaster spp.) are contributing to extensive coral loss and reef degradation throughout the Indo-Pacific, but the causes and underlying mechanisms of population maintenance and outbreaks are equivocal. Two recent publications suggest that, in addition to outbreeding sexual reproduction, asexual reproduction through larval fission and selfing may contribute to rapid increases in the local abundance of Acanthaster spp. We re-analysed two large microsatellite datasets (collectively representing 3714 individuals) that investigated connectivity in the Great Barrier Reef and wider Pacific region to investigate if potential cloning or selfing can be evidenced in the population genetic structure. Within this dataset, we identified only a small number (18, < 0.5%) of putative clones (repeated multilocus genotypes). We argue that several of these are due to sampling and processing errors rather than direct evidence of cloning. Analysis of the population genetic structure (i.e. pairwise genetic differences between individuals, deviations from Hardy–Weinberg Equilibrium, and linkage disequilibrium) also yielded no genetic evidence for asexual reproduction. There was a tendency towards slight heterozygote deficits, so we cannot refute that selfing does occur, but observed patterns are most likely attributable to sampling artefacts. Although we cannot exclude that asexual reproduction occurs to some extent in Acanthaster populations, we find no evidence that these processes make a contribution to population structure or directly enhance larval supply.

‘B’ the Change You Want to See: Commensuration Work when Strategizing for a Grand Challenge

This study is motivated by a theoretically interesting observation made while in the field: In the process of strategizing for a grand challenge, members of a cross-sector collaboration produced a report card in which ratings are used to assess the ‘water health’ of a critical river basin in the Australian iconic Great Barrier Reef region. Observations show that the report card was continuously adjusted by groups of actors pushing towards one of the Partnership’s three strategic objectives, namely, to generate tangible impact, to demonstrate legitimacy, or to foster members engagement. Although this ‘commensuration work’ appears to coalesce into an objectified depiction of river health, a close examination brings to light how these attempts ultimately infused the artefact with a multivocal quality. Beneficial at first, multivocality eventually lead the artefact to become ‘over-stretched’ thus creating ambiguity around its role in attaining the Partnership’s strategic goals. This study contributes to the strategizing for grand challenges literature by problematizing further the role commensuration plays in facilitating multivocality while exacerbating strategic ambiguity. It also offers a contribution to the literature on commensuration by empirically documenting the micro-practices used by actors to commensurate a grand challenge.

Vulnerability of threatened Australian humpback dolphins to flooding and port development within the southern Great Barrier Reef coastal region

In this study, we used a 10-year (2007–2016) mark-recapture dataset to investigate the potential effects of flooding and port development on the population dynamics of Australian humpback dolphins (Sousa sahulensis), inhabiting the Fitzroy River and Port Curtis, within the southern Great Barrier Reef region. A Multisite Capture-Recapture model was used to quantify population size and demographic parameters for both sexes and sites. Flood occurrence and intensity (both sites), and port development (Port Curtis) were included as explanatory variables. Abundance estimates indicated that about 77 adult dolphins were present in both sites, of which 69% were females. Most females (69%) were resident with a yearly recruitment close to zero for most years. Most males and unsexed (68%) individuals showed little evidence of long-term residency. The abundances of males and unsexed individuals varied between 15 and 20 dolphins in the Fitzroy River and 19–26 in Port Curtis, but the accuracy was too low to assess changes. Female abundances started at 56 in both sites and declined to about 32 per site in 2011, coinciding with port development construction activities and a concurrent major flood. In Port Curtis, the number of females returned to their original levels once the port development was completed in 2013. In the Fitzroy River, the declining trend continued and reached the lowest estimated abundance of 29 in 2016. As port developments and floods are expected to increase along the Queensland coastal region over coming decades, the results of this study highlight increasing concerns about the vulnerability and long-term sustainability of inshore dolphins in the GBR.

Bund removal to re-establish tidal flow, remove aquatic weeds and restore coastal wetland services-North Queensland, Australia.

The shallow tidal and freshwater coastal wetlands adjacent to the Great Barrier Reef lagoon provide a vital nursery and feeding complex that supports the life cycles of marine and freshwater fish, important native vegetation and vital bird habitat. Urban and agricultural development threaten these wetlands, with many of the coastal wetlands becoming lost or changed due to the construction of artificial barriers (e.g. bunds, roads, culverts and floodgates). Infestation by weeds has become a major issue within many of the wetlands modified (bunded) for ponded pasture growth last century. A range of expensive chemical and mechanical control methods have been used in an attempt to restore some of these coastal wetlands, with limited success. This study describes an alternative approach to those methods, investigating the impact of tidal reinstatement after bund removal on weed infestation, associated changes in water quality, and fish biodiversity, in the Boolgooroo lagoon region of the Mungalla wetlands, East of Ingham in North Queensland. High resolution remote sensing, electrofishing and in-water logging was used to track changes over time– 1 year before and 4 years after removal of an earth bund. With tides only penetrating the wetland a few times yearly, gross changes towards a more natural system occurred within a relatively short timeframe, leading to a major reduction in infestation of olive hymenachne, water hyacinth and salvina, reappearance of native vegetation, improvements in water quality, and a tripling of fish diversity. Weed abundance and water quality does appear to oscillate however, dependent on summer rainfall, as changes in hydraulic pressure stops or allows tidal ingress (fresh/saline cycling). With an estimated 30% of coastal wetlands bunded in the Great Barrier Reef region, a passive remediation method such as reintroduction of tidal flow by removal of an earth bund or levee could provide a more cost effective and sustainable means of controlling freshwater weeds and improving coastal water quality into the future.

Controls on Carbon, Nutrient, and Sediment Cycling in a Large, Semiarid Estuarine System; Princess Charlotte Bay, Australia

AbstractSemiarid estuaries are characterized by pronounced seasonal variability, and a functional understanding of these systems requires constraint of coupled biogeochemical processes and relevant temporal and spatial scales. Here, we integrate 2 years of spatial surveys and time‐series measurements to quantify physical, chemical, and biological drivers in the largest estuarine system in the Great Barrier Reef region. During wet season, freshwater inputs of nutrients and sediment to estuaries were dominated by flood pulses, whereas carbonate input was also influenced by groundwater discharge. This carbonate input counteracted the minimum buffering zone that would otherwise occur at low salinities, thereby decreasing system‐wide air‐water CO2 fluxes. Sediment resuspension was a major control on the transformation and transport of material over tidal and seasonal scales. During wet season, tidal resuspension of benthic algae in nearshore mixing zones acted as an autotrophic filter, removing most bioavailable nutrients from the brackish plume. During dry season, upstream transport combined with hypersaline conditions trapped material in upper estuaries where denitrification and net heterotrophy were high. However, the role of sediment transport varied depending on tidal asymmetry and density‐driven circulation. Estuarine regions with large intertidal areas were dominated by salt flat erosion, which showed a diagenetic signature associated with mid‐Holocene swamp sediments. Tidal resuspension of these organic‐rich sediments appeared to be the dominant control on biogeochemical cycling in coastal waters. This study demonstrates that a holistic understanding of coastal ecosystem connectivity and function requires resolution of both along‐axis and water‐column gradients as well as a range of timescales from tidal to geological cycles.