Correction: Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef.

[This corrects the article DOI: 10.1371/journal.pone.0269806.].

Green Turtle (Chelonia mydas) Blood and Scute Trace Element Concentrations in the Northern Great Barrier Reef.

Marine turtles face numerous anthropogenic threats, including that of chemical contaminant exposure. The ecotoxicological impact of toxic metals is a global issue facing Chelonia mydas in coastal sites. Local investigation of C. mydas short-term blood metal profiles is an emerging field, while little research has been conducted on scute metal loads as potential indicators of long-term exposure. The aim of the present study was to investigate and describe C. mydas blood and scute metal profiles in coastal and offshore populations of the Great Barrier Reef. This was achieved by analyzing blood and scute material sampled from local C. mydas populations in five field sites, for a suite of ecologically relevant metals. By applying principal component analysis and comparing coastal sample data with those of reference intervals derived from the control site, insight was gleaned on local metal profiles of each population. Blood metal concentrations in turtles from coastal sites were typically elevated when compared with levels recorded in the offshore control population (Howick Island Group). Scute metal profiles were similar in Cockle Bay, Upstart Bay, and Edgecumbe Bay, all of which were distinct from that of Toolakea. Some elements were reported at similar concentrations in blood and scutes, but most were higher in scute samples, indicative of temporal accumulation. Coastal C. mydas populations may be at risk of toxic effects from metals such as Co, which was consistently found to be at concentrations magnitudes above region-specific reference intervals. Environ Toxicol Chem 2023;42:2375-2388. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef.

Toxic metal exposure is a threat to green sea turtles (Chelonia mydas) inhabiting and foraging in coastal seagrass meadows and are of particular concern in local bays of the Great Barrier Reef (GBR), as numerous sources of metal contaminants are located within the region. Seagrass species tend to bioaccumulate metals at concentrations greater than that detected in the surrounding environment. Little is known regarding ecotoxicological impacts of environmental metal loads on seagrass or Chelonia mydas (C. mydas), and thus this study aimed to investigate and describe seagrass metal loads in three central GBR coastal sites and one offshore site located in the northern GBR. Primary seagrass forage of C. mydas was identified, and samples collected from foraging sites before and after the 2018/2019 wet season, and multivariate differences in metal profiles investigated between sites and sampling events. Most metals investigated were higher at one or more coastal sites, relative to data obtained from the offshore site, and cadmium (Cd), cobalt (Co), iron (Fe) and manganese (Mn) were found to be higher at all coastal sites. Principle Component Analysis (PCA) found that metal profiles in the coastal sites were similar, but all were distinctly different from that of the offshore data. Coastal foraging sites are influenced by land-based contaminants that can enter the coastal zone via river discharge during periods of heavy rainfall, and impact sites closest to sources. Bioavailability of metal elements are determined by complex interactions and processes that are largely unknown, but association between elevated metal loads and turtle disease warrants further investigation to better understand the impact of environmental contaminants on ecologically important seagrass and associated macrograzers.

The bioavailability of nitrogen associated with sediment in riverine plumes of the Great Barrier Reef.

This study quantified the bioavailable nitrogen contribution from riverine plumes to Great Barrier Reef (GBR) coastal environments. The potential bioavailable nitrogen from two Dry Tropics riverine plumes was considerable [9 - 30% added to the end-of-catchment dissolved inorganic nitrogen (DIN) load]. Particulate inorganic nitrogen conversion to DIN was an important process in short timeframes (25% to 100% of the generated load). The remaining load was contributed by microbial mineralisation of organic nitrogen. Flood plume sediment has potential to generate nitrogen once deposited and/or resuspended. Nitrogen generation was insignificant in a few plumes where immobilisation of nitrogen in bacteria biomass occurred. The source of organic matter in the plumes and availability of nitrogen relative to organic matter were important determinants of mineralisation/immobilisation. This research demonstrates that riverine plumes have potential to be considerable sources of bioavailable nitrogen to coastal environments of the GBR and that organic matter is a key bioavailability driver.

Criteria for effective regional scale catchment to reef management: A case study of Australia's Great Barrier Reef.

Many coastal and marine ecosystems around the world are under increasing threat from a range of anthropogenic influences. The management of these threats continues to present ongoing challenges, with many ecosystems increasingly requiring active restoration to support or re-establish the ecosystem's biological, cultural, social and economic values. The current condition of Australia's Great Barrier Reef (GBR) and its threats, including water quality, climate change and the loss of wetlands, causing the continuing decline in the GBR's ecological condition and function, has received global attention. Activities aimed at halting these declines and system restoration have been underway for over forty years. These activities are challenging to implement, and much has been learnt from their various outcomes. This paper considers the GBR and the associated management activities as a case study for regional scale catchment to reef management. It summarises the management approaches to date, describing the key role that science, policy and community have played in underpinning various investments. Four criteria for success are proposed: the lead role of the community, the need for a systems approach, the need for targeted, cost-effective and sustainable long-term investment, and importantly, building knowledge and maintaining consensus and political commitment.

A transdisciplinary approach supports community-led water quality monitoring in river basins adjacent to the Great Barrier Reef, Australia.

Water quality monitoring programs (WQMPs) are crucial for assessment of water quality in river basins where agricultural intensification and development raise concerns in freshwater and marine environments. WQMPs if supported by scientists and local communities, and if based on the knowledge needs of all stakeholders, can provide vital information supporting resource management actions. Our paper focuses on the transdisciplinary development and implementation of a community-led pilot WQMP for the Tully River basin, adjacent to the Great Barrier Reef (GBR). The community-led pilot WQMP was established to fill some knowledge gaps identified during development of the Tully Water Quality Improvement Plan (WQIP) and to provide opportunities for active stakeholder participation in the monitoring. Results indicated some water quality parameters (i.e. nitrates and total phosphorus) had higher than expected values and exceeded state water quality guidelines. Hence, the results provided an evidence base for freshwater quality objective development to conserve, protect and improve water quality conditions in this basin and GBR. Leadership of Indigenous people in the pilot WQMP recognizes their deep desire to improve water resources outcomes and to care for country and people.

Catchment to sea connection: Impacts of terrestrial run-off on benthic ecosystems in American Samoa.

Variation in water quality can directly affect the composition of benthic assemblages on coral reefs. Yet, few studies have directly quantified nutrient and suspended particulate matter (SPM) to examine their potential impacts on benthic community structure, especially around high oceanic islands. We assessed the spatio-temporal variation of nutrients and SPM across six sites in American Samoa over a 12-month period and used exploratory path analysis to relate dissolved inorganic nutrients, land use, and natural and anthropogenic drivers to benthic assemblages on adjacent shallow reefs. Multivariate analyses showed clear gradients in nutrient concentrations, sediment accumulation and composition, and benthic structure across watersheds. Instream nutrients and land uses positively influenced reef flat nutrient concentrations, while benthic assemblages were best predicted by wave exposure, runoff, stream phosphate and dissolved inorganic nitrogen loads. Identifying locality-specific drivers of water quality and benthic condition can support targeted management in American Samoa and in other high islands.

Connecting targets for catchment sediment loads to ecological outcomes for seagrass using multiple lines of evidence.

Catchment impacts on downstream ecosystems are difficult to quantify, but important for setting management targets. Here we compared 12 years of monitoring data of seagrass area and biomass in Cleveland Bay, northeast Australia, with discharge and associated sediment loads from nearby rivers. Seagrass biomass and area exhibited different trajectories in response to river inputs. River discharge was a slightly better predictor of seagrass indicators than total suspended solid (TSS) loads, indicating that catchment effects on seagrass are not restricted to sediment. Linear relationships between Burdekin River TSS loads delivered over 1-4 years and seagrass condition in Cleveland Bay generated Ecologically Relevant Targets (ERT) for catchment sediment inputs. Our predicted ERTs were comparable to those previously estimated using mechanistic models. This study highlights the challenges of linking catchment inputs to condition of downstream ecosystems, and the importance of integrating a variety of metrics and approaches to increase confidence in ERTs.

Impacts of coastal land use change in the wet tropics on nearshore coral reefs: Case studies from Papua New Guinea.

Logging and plantation agriculture are vital to economies and livelihoods in tropical nations, including Papua New Guinea. To meet global demand, hundreds of thousands of ha of diverse natural habitat have been logged, cleared and replaced with monoculture crops. Resulting hydrological changes have increased sediment, nutrient and pesticide runoff, impacting down-stream habitats. Here, case studies from Kimbe Bay (New Britain) and Mullins Harbour (Milne Bay), examine effects on nearshore coral reefs. In both places, logging and oil palm development had destabilized soils and removed or degraded riparian vegetation. Downstream, nearshore reefs had high silt levels, which, coincident with minor coral bleaching and predation by crown-of-thorns starfish, were correlated with high levels of coral mortality and low coral species richness. Sediment and related impacts can be reduced by effective catchment management, such as avoiding steep slopes, expanding stream and coastal buffer zones, minimizing fertilizer and pesticide use, monitoring and reactive management.

Impact of catchment-derived nutrients and sediments on marine water quality on the Great Barrier Reef: An application of the eReefs marine modelling system.

Water quality of the Great Barrier Reef (GBR) is determined by a range of natural and anthropogenic drivers that are resolved in the eReefs coupled hydrodynamic - biogeochemical marine model forced by a process-based catchment model, GBR Dynamic SedNet. Model simulations presented here quantify the impact of anthropogenic catchment loads of sediments and nutrients on a range of marine water quality variables. Simulations of 2011-2018 show that reduction of anthropogenic catchment loads results in improved water quality, especially within river plumes. Within the 16 resolved river plumes, anthropogenic loads increased chlorophyll concentration by 0.10 (0.02-0.25) mg Chl m-3. Reductions of anthropogenic loads following proposed Reef 2050 Water Quality Improvement Plan targets reduced chlorophyll concentration in the plumes by 0.04 (0.01-0.10) mg Chl m-3. Our simulations demonstrate the impact of anthropogenic loads on GBR water quality and quantify the benefits of improved catchment management.

Fresh waters and estuaries of the Great Barrier Reef catchment: Effects and management of anthropogenic disturbance on biodiversity, ecology and connectivity.

We review the literature on the ecology, connectivity, human impacts and management of freshwater and estuarine systems in the Great Barrier Reef catchment (424,000 km2), on the Australian east coast. The catchment has high biodiversity, with substantial endemicity (e.g., lungfish). Freshwater and estuarine ecosystems are closely linked to the land and are affected by human disturbance, including climate change, flow management, land clearing, habitat damage, weed invasion, and excessive sediments, nutrients and pesticides. They require holistic integrated management of impacts, interactions, and land-sea linkages. This requirement is additional to land management aimed at reducing pollutant delivery to reef waters. Despite advances in research and management over recent decades, there are substantial deficiencies that need addressing, including understanding of physical and biological processes and impacts in ground waters, large rivers and estuaries; ecological effects of pesticides; management and mitigation for invasive species and climate change; and explicit protection of non-marine waters.

Land use change in the river basins of the Great Barrier Reef, 1860 to 2019: A foundation for understanding environmental history across the catchment to reef continuum.

Land use in the catchments draining to the Great Barrier Reef lagoon has changed considerably since the introduction of livestock grazing, various crops, mining and urban development. Together these changes have resulted in increased pollutant loads and impaired coastal water quality. This study compiled records to produce annual time-series since 1860 of human population, livestock numbers and agricultural areas at the scale of surface drainage river basins, natural resource management regions and the whole Great Barrier Reef catchment area. Cattle and several crops have experienced progressive expansion interspersed by declines associated with droughts and diseases. Land uses which have experienced all time maxima since the year 2000 include cattle numbers and the areas of sugar cane, bananas and cotton. A Burdekin Basin case study shows that sediment loads initially increased with the introduction of livestock and mining, remained elevated with agricultural development, and declined slightly with the Burdekin Falls Dam construction.

Validation of an optimised protocol for quantification of microplastics in heterogenous samples: A case study using green turtle chyme.

Quantifying the extent of microplastic (<5 mm) contamination in the marine environment is an emerging field of study. Reliable extraction of microplastics from the gastro-intestinal content of marine organisms is crucial to evaluate microplastic contamination in marine fauna. Extraction protocols and variations thereof have been reported, however, these have mostly focussed on relatively homogenous samples (i.e. water, sediment, etc.). Here, we present a microplastic extraction protocol for examining green turtle (Chelonia mydas) chyme (i.e. ingested material and digestive tract fluid), which is a heterogeneous composite of various organic dietary items (e.g. seagrass, jellyfish) and incidentally-ingested inorganic materials (sediment). Established extraction methods were modified and combined. This protocol consists of acid digestion of organic matter, emulsification of residual fat, density separation from sediment, and chemical identification by Fourier transform-infrared spectroscopy. This protocol enables the extraction of the most common microplastic contaminants>100 µm: polyethylene, high-density polyethylene, (aminoethyl) polystyrene, polypropylene, and polyvinyl chloride, with 100% efficiency. This validated protocol will enable researchers worldwide to quantify microplastic contamination in turtles in a reliable and comparable way. •Optimization of microplastic extraction from multifarious tissues by applying established methods in a sequential manner.•Effective for heterogenous samples comprising organic and inorganic material.

Support for improved quality control but misplaced criticism of GBR science. Reply to viewpoint "The need for a formalised system of Quality Control for environmental policy-science" by P. Larcombe and P. Ridd (Marine Pollution Bulletin 126: 449-461, 2018).

This is a response to the published Viewpoint by Larcombe and Ridd (2018). We agree with Larcombe and Ridd (2018) that scientific merit goes hand in hand with rigorous quality control. However, we are responding here to several points raised by Larcombe and Ridd (2018) which in our view were misrepresented. We describe the formal and effective science review, synthesis and advice processes that are in place for science supporting decision-making in the Great Barrier Reef. We also respond in detail to critiques of selected publications that were used by Larcombe and Ridd (2018) as a case study to illustrate shortcomings in science quality control. We provide evidence that their representation of the published research and arguments to support the statement that "many (…) conclusions are demonstrably incorrect" is based on misinterpretation, selective use of data and over-simplification, and also ignores formal responses to previously published critiques.

Ingestion of microplastic debris by green sea turtles (Chelonia mydas) in the Great Barrier Reef: Validation of a sequential extraction protocol.

Ocean contamination by plastics is a global issue. Although ingestion of plastic debris by sea turtles has been widely documented, contamination by microplastics (<5mm) is poorly known and likely to be under-reported. We developed a microplastic extraction protocol for examining green turtle (Chelonia mydas) chyme, which is multifarious in nature, by modifying and combining pre-established methods used to separate microplastics from organic matter and sediments. This protocol consists of visual inspection, nitric acid digestion, emulsification of residual fat, density separation, and chemical identification by Fourier transform infrared spectroscopy. This protocol enables the extraction of polyethylene, high-density polyethylene, (aminoethyl) polystyrene, polypropylene, and polyvinyl chloride microplastics >100µm. Two macroplastics and seven microplastics (two plastic paint chips and five synthetic fabric particles) were isolated from subsamples of two green turtles. Our results highlight the need for more research towards understanding the impact of microplastics on these threatened marine reptiles.

Avoiding Implementation Failure in Catchment Landscapes: A Case Study in Governance of the Great Barrier Reef.

Water quality outcomes affecting Australia's Great Barrier Reef (GBR) are governed by multi-level and multi-party decision-making that influences forested and agricultural landscapes. With international concern about the GBR's declining ecological health, this paper identifies and focuses on implementation failure (primarily at catchment scale) as a systemic risk within the overall GBR governance system. There has been limited integrated analysis of the full suite of governance subdomains that often envelop defined policies, programs and delivery activities that influence water quality in the GBR. We consider how the implementation of separate purpose-specific policies and programs at catchment scale operate against well-known, robust design concepts for integrated catchment governance. We find design concerns within ten important governance subdomains that operate within GBR catchments. At a whole-of-GBR scale, we find a weak policy focus on strengthening these delivery-oriented subdomains and on effort integration across these subdomains within catchments. These governance problems when combined may contribute to failure in the implementation of major national, state and local government policies focused on improving water quality in the GBR, a lesson relevant to landscapes globally.

Excess seawater nutrients, enlarged algal symbiont densities and bleaching sensitive reef locations: 2. A regional-scale predictive model for the Great Barrier Reef, Australia.

A spatial risk assessment model is developed for the Great Barrier Reef (GBR, Australia) that helps identify reef locations at higher or lower risk of coral bleaching in summer heat-wave conditions. The model confirms the considerable benefit of discriminating nutrient-enriched areas that contain corals with enlarged (suboptimal) symbiont densities for the purpose of identifying bleaching-sensitive reef locations. The benefit of the new system-level understanding is showcased in terms of: (i) improving early-warning forecasts of summer bleaching risk, (ii) explaining historical bleaching patterns, (iii) testing the bleaching-resistant quality of the current marine protected area (MPA) network (iv) identifying routinely monitored coral health attributes, such as the tissue energy reserves and skeletal growth characteristics (viz. density and extension rates) that correlate with bleaching resistant reef locations, and (v) targeting region-specific water quality improvement strategies that may increase reef-scale coral health and bleaching resistance.

Risk analysis of the governance system affecting outcomes in the Great Barrier Reef.

The state and trend of the Great Barrier Reef's (GBR's) ecological health remains problematic, influencing United Nations Educational, Scientific and Cultural Organization (UNESCO) statements regarding GBR governance. While UNESCO's concerns triggered separate strategic assessments by the Australian and Queensland governments, there has been no independent and integrated review of the key risks within the overall system of governance influencing GBR outcomes. As a case study of international significance, this paper applies Governance Systems Analysis (GSA), a novel analytical framework that identifies the governance themes, domains and subdomains most likely to influence environmental and socio-economic outcomes in complex natural systems. This GBR-focussed application of GSA identifies governance subdomains that present high, medium, or low risk of failure to produce positive outcomes for the Reef. This enabled us to determine that three "whole of system" governance problems could undermine GBR outcomes. First, we stress the integrative importance of the Long Term Sustainability Plan (LTSP) Subdomain. Sponsored by the Australian and Queensland governments, this subdomain concerns the primary institutional arrangements for coordinated GBR planning and delivery, but due to its recent emergence, it faces several internal governance challenges. Second, we find a major risk of implementation failure in the achievement of GBR water quality actions due to a lack of system-wide focus on building strong and stable delivery systems at catchment scale. Finally, we conclude that the LTSP Subdomain currently has too limited a mandate/capacity to influence several high-risk subdomains that have not been, but must be more strongly aligned with Reef management (e.g. the Greenhouse Gas Emission Management Subdomain). Our analysis enables exploration of governance system reforms needed to address environmental trends in the GBR and reflects on the potential application of GSA in other complex land and sea-scapes across the globe.

Historical photographs revisited: A case study for dating and characterizing recent loss of coral cover on the inshore Great Barrier Reef.

Long-term data with high-precision chronology are essential to elucidate past ecological changes on coral reefs beyond the period of modern-day monitoring programs. In 2012 we revisited two inshore reefs within the central Great Barrier Reef, where a series of historical photographs document a loss of hard coral cover between c.1890-1994 AD. Here we use an integrated approach that includes high-precision U-Th dating specifically tailored for determining the age of extremely young corals to provide a robust, objective characterisation of ecological transition. The timing of mortality for most of the dead in situ corals sampled from the historical photograph locations was found to coincide with major flood events in 1990-1991 at Bramston Reef and 1970 and 2008 at Stone Island. Evidence of some recovery was found at Bramston Reef with living coral genera similar to what was described in c.1890 present in 2012. In contrast, very little sign of coral re-establishment was found at Stone Island suggesting delayed recovery. These results provide a valuable reference point for managers to continue monitoring the recovery (or lack thereof) of coral communities at these reefs.

Spatial and Temporal Variability in Pesticide Exposure Downstream of a Heavily Irrigated Cropping Area: Application of Different Monitoring Techniques.

Pesticide exposure threatens many freshwater and estuarine ecosystems around the world. This study examined the temporal and spatial trends of pesticide concentrations in a waterway within an agriculturally developed dry-tropics catchment using a combination of grab and passive sampling methods over a continuous two-year monitoring program. A total of 43 pesticide residues were detected with 7 pesticides exceeding ecologically relevant water quality guidelines/trigger values during the study period and 4 (ametryn, atrazine, diuron, and metolachlor) of these exceeding guidelines for several months. The presence and concentration of the pesticides in the stream coincided with seasonal variability in rainfall, harvest timing/cropping cycle, and management changes. The sampling approach used demonstrates that the application of these complementary sampling techniques (both grab and passive sampling methods) was effective in establishing pesticide usage patterns in upstream locations where application data are unavailable.