Search Results (133)

We adapt previously developed conceptual and numerical models of ciguateric food chains on the Great Barrier Reef, Australia, to model the bioaccumulation of ciguatoxins (CTXs) in parrotfish, the simplest food chain with only two trophic levels. Our model indicates that relatively low (1 cell/cm²) densities of Gambierdiscus/Fukuyoa species (hereafter collectively referred to as Gambierdiscus) producing known concentrations of CTX are unlikely to be a risk of producing ciguateric fishes on the Great Barrier Reef unless CTX can accumulate and be retained in parrotfish over many months. Cell densities on turf algae equivalent to 10 Gambierdiscus/cm² producing known maximum concentrations of Pacific-CTX-4 (0.6 pg P-CTX-4/cell) are more difficult to assess but could be a risk. This cell density may be a higher risk for parrotfish than we previously suggested for production of ciguateric groupers (third-trophic-level predators) since second-trophic-level fishes can accumulate CTX loads without the subsequent losses that occur between trophic levels. Our analysis suggests that the ratios of parrotfish length-to-area grazed and weight-to-area grazed scale differently (allometrically), where the area grazed is a proxy for the number of Gambierdiscus consumed and hence proportional to toxin accumulation. Such scaling can help explain fish size–toxicity relationships within and between trophic levels for ciguateric fishes. Our modelling reveals that CTX bioaccumulates but does not necessarily biomagnify in food chains, with the relative enrichment and depletion rates of CTX varying with fish size and/or trophic level through an interplay of local and regional food chain influences. Our numerical model for the bioaccumulation and transfer of CTX across food chains helps conceptualize the development of ciguateric fishes by comparing scenarios that reveal limiting steps in producing ciguateric fish and focuses attention on the relative contributions from each part of the food chain rather than only on single components, such as CTX production. Full article

Deliberative approaches to governance systems analysis and improvement are rare. Australia’s Great Barrier Reef (GBR) provides the context to describe an innovative approach that combines reflexive and interactive engagement processes to (a) develop and design a framework to assess the GBR’s complex governance system health; and (b) undertake a benchmark assessment of governance system health. We drew upon appreciative inquiry and used multiple lines of evidence, including an extensive literature review, governance system mapping, focus group discussions and personal interviews. Together, these approaches allowed us to effectively engage key actors in value judgements about twenty key characteristic attributes of the governance system. These attributes were organised into four clusters which enabled us to broadly describe and benchmark the system. These included the following: (i) system coherence; (ii) connectivity and capacity; (iii) knowledge application; (iv) operational aspects of governance. This process facilitated deliberative discussion and consensus-building around attribute health and priorities for transformative action. This was achieved through the inclusion of diverse perspectives from across the governance system, analysis of rich datasets, and the provision of guidance from the project’s Steering Committee and Technical Working Group. Our inclusive, collaborative and deliberative approach, its analytical depth, and the framework’s repeatability enable continuous monitoring and adaptive improvement of the GBR governance system and can be readily applied to complex governance systems elsewhere. Full article

The hypothesis that disturbance to coral reefs creates new surfaces that increase the risk of ciguatera is premised upon the increased algal substrates that develop on these surfaces being colonised by high ciguatoxin (CTX)-producing Gambierdiscus species that proliferate and enter the ciguatera food chain. Current evidence indicates that new algal substrates are indeed rapidly colonised by Gambierdiscus. However, the requirement that these Gambierdiscus species include at least one that is a significant (high) CTX-producer is more likely a limiting step. While ambient environmental conditions impact the capacity of Gambierdiscus to bloom, factors that limit the growth of the bloom could influence (typically increase) the flux of CTX entering marine food chains. Additionally, new algal substrates on damaged reefs can be preferentially grazed to funnel ciguatoxins from Gambierdiscus to herbivores in disturbed reef areas. In societies consuming second trophic level species (herbivores, grazers, and detritivores), such funnelling of CTX would increase the risk of ciguatera, although such risk would be partially offset over time by growth (toxin-dilution) and depuration. Here, we review evidence for six potential mechanisms to increase ciguatera risk from disturbance to coral reefs and suggest a hypothesis where ecosystem changes could increase the flux of CTX to groupers through a shift in predation from predominately feeding on planktonic-feeding prey to mostly feeding on benthic-feeding prey, increasing the potential for CTX to accumulate. Evidence for this hypothesis is stronger for the Pacific and Indian Oceans, and it may not apply to the Caribbean Sea/Atlantic Ocean. Full article

Coral disease outbreaks have increased in frequency and extent worldwide since the 1970s, coinciding with the rapid increase in ocean warming. Summer and winter temperature-based metrics have proven effective in predicting coral disease outbreaks in seasonal coral reef regions. However, their utility is unknown in non-seasonal coral reef areas. Here, a new methodology, independent of seasonal patterns, is developed for application in both seasonal and non-seasonal coral reef regions. Percentile-based metric thresholds were defined from seasonal equivalents in the Great Barrier Reef (GBR) and tested in seasonal and non-seasonal coral reef regions of the tropical Pacific Ocean. Between new and existing methodologies, median differences of 0.00 °C (thresholds) and 0.00 °C-weeks (metrics) for Hot Snap and Cold Snap; and 0.01 °C (threshold) and −0.17 °C-weeks (metric) for Winter Condition were observed among reef pixels of the GBR. The new methodology shows strong consistency with the existing tools used for seasonal regions (e.g., R² = 0.811–0.903; GBR case studies). Comparisons of the new metrics with disease observations were constrained by the limited availability of disease data; however, the comparisons undertaken suggest predictive capability in non-seasonal regions. To establish robust correlations, further direct comparisons of the new metrics with disease data across various non-seasonal regions and timeframes are essential. With ocean warming projected to persist in the coming decades, improving the predictive tools used to assess ecological impacts is necessary to support effective coral reef management. Full article

Biological data, such as length–weight relationships, are essential for the management and stewardship of harvested individuals. Sea cucumbers are a lucrative industry globally but many of the associated fisheries lack species-level biological data, which reduces the effectiveness of any management strategy. The Queensland Sea Cucumber Fishery (QSCF) on the Great Barrier Reef is managed through various controls: primarily catch limits, effort limits, zoning, and size restrictions. Over 20 species may be harvested but there is a lack of comprehensive biological data for many of these species, particularly important life history characteristics. This study addresses this knowledge gap by assessing 2621 individual length–weight relationships of key-target sea cucumber species associated with the fishery across the range of the distribution of the species and covering a variety of habitats, depths, sampling times, and management zones. Linear models with log transformations were used to analyse the relationships between length and weight. Results revealed significant positive relationships for all assessed species, with Holothuria atra having the clearest relationship between length and weight (R² = 0.45). Only negative allometric relationships were observed, as is the case for many species of holothurians. Despite challenges associated with measuring and weighing these soft and elastic animals, results will be useful for understanding length–weight dynamics across species. This research underscores the importance of robust biological data for the effective management of sea cucumber fisheries and ultimately reef health. Full article

Citizen or community science (CS) projects in the marine environment rarely consider carbon footprint and sustainability. In this case study, we assessed the effectiveness of ten CS methods used by tourists in the Great Barrier Reef Marine Park (GBRMP) and Coral Sea Marine Park (CSMP) who participated in the 2023 Citizen Science of the Great Barrier Reef expedition and the carbon footprint associated with these field methods. We also assessed the baseline coral reef knowledge of the tourists, observations of marine species, and the communication of our results to the public. Specifically, the tourists utilised up to ten methods: iNaturalist, CoralWatch, Great Barrier Reef Census, Eye on the Reef (EoR), environmental DNA (eDNA) testing kits, photogrammetry, social surveys, and Red Map, as well as marine debris and marine vegetation collections. A total of 10,421 data points were collected across 14 days, including 5390 records (52% of the total) uploaded to iNaturalist, comprising 640 plant and animal species. Public awareness of the CS expedition reached over 700,000 people based on estimates from advertising, media, social media, family and friends, and conference presentations. We estimated the total carbon footprint for the expedition as 268.7 tonnes of CO₂ or 4.47 tonnes of CO₂ per person, equivalent to AUD 112 needed to offset this input. Based on these results, our recommendations to leverage CS methods include governmental review strategies, temporal replication to allow for the measurement of changes through time, integrating sustainability into CS ecotourism platforms, and encouraging broad participation. Full article

The Omura’s whale (Balaenoptera omurai) is one of the most recently described species of baleen whale. Initially known only from stranding and whaling specimens, it has now been identified in all ocean basins excluding the central and eastern Pacific. Unlike most baleen whales that migrate between the poles and the equator seasonally, the Omura’s whale is known to inhabit tropical to sub-tropical waters year-round. In Australian waters, there remain fewer than 30 confirmed visual sightings over the past decade. However, based on acoustic records, the Omura’s whale has been detected off areas of the northwest coast of Australia year-round. This study utilises passive acoustic recordings from 41 locations around Australia from 2005 to 2023 to assess the distribution and seasonality of the Omura’s whale. The seasonal presence of Omura’s whale vocalisations varied by location, with higher presence at lower latitudes. Vocalisations were detected year-round in the Joseph Bonaparte Gulf in the Timor Sea, and near Browse Island and Scott Reef, in the Kimberley region. In the Pilbara region, acoustic presence mostly peaked from February to April and no acoustic presence was consistently observed from July to September across all sites. The most southerly occurrence of Omura’s whale vocalisations was recorded off the North West Cape in the Gascoyne region. Vocalisations similar but not identical to those of the Omura’s whale were detected in the Great Barrier Reef. The identified seasonal distribution provides valuable information to assess environmental and anthropogenic pressures on the Omura’s whale and to aid in creating management and conservation policies for the species in Australia. Full article

Coral bleaching is occurring more frequently as the climate changes, with multiple mass mortality events recently recorded on the Great Barrier Reef. Thermal stress coupled with high irradiance have previously been shown to be primary causes for coral bleaching. Therefore, a reduction in either of these pressures could reduce coral stress and eventual bleaching. Herein, we report the early development of a novel technology capable of reducing the amount of light entering a water body by ~20% in open ocean conditions. This mono-particle “sun shield” consists of an ultra-thin monolayer material and reflective calcium carbonate particles. The monolayer enables spreading of the particles into a thin film across the water surface, with only small amounts of material needed: 7.1 g/m². A numerical modelling case study of residence times and the build-up of reactive oxygen stress in corals showed that the successful application of a stable film over the Lizard Island reef flat could reduce the reactive oxygen stress to below bleaching levels across approximately 1.5 km² of reef area. With further development, mono-particle films such as this have the potential to be deployed over at-risk coral reefs at relatively small scales during predicted heatwave conditions, potentially reducing the severity of bleaching on coral reefs. Full article

Despite the ecological importance of giant clams (Tridacninae), their effective management and conservation is challenging due to their widespread distribution and labour-intensive monitoring methods. In this study, we present an alternative approach to detecting and mapping clam density at Pioneer Bay on Goolboddi (Orpheus) Island on the Great Barrier Reef using drone data with a combination of deep learning tools and a geographic information system (GIS). We trained and evaluated 11 models using YOLOv5 (You Only Look Once, version 5) with varying numbers of input image tiles and augmentations (mean average precision—mAP: 63–83%). We incorporated the Slicing Aided Hyper Inference (SAHI) library to detect clams across orthomosaics, eliminating duplicate counts of clams straddling multiple tiles, and further, applied our models in three other geographic locations on the Great Barrier Reef, demonstrating transferability. Finally, by linking detections with their original geographic coordinates, we illustrate the workflow required to quantify animal densities, mapping up to seven clams per square meter in Pioneer Bay. Our workflow brings together several otherwise disparate steps to create an end-to-end approach for detecting and mapping animals with aerial drones. This provides ecologists and conservationists with actionable and clear quantitative and visual insights from drone mapping data. Full article

Livestock grazing is a major land use in the Great Barrier Reef Catchment Area (GBRCA). Heightened grazing density coupled with inadequate land management leads to accelerated soil erosion and increased sediment loads being transported downstream. Ultimately, these increased sediment loads impact the water quality of the Great Barrier Reef (GBR) lagoon. Ground cover mapping has been adopted to monitor and assess the land condition in the GBRCA. However, accurate prediction of ground cover remains a vital knowledge gap to inform proactive approaches for improving land conditions. Herein, we explored two deep learning-based spatio-temporal prediction models, including convolutional LSTM (ConvLSTM) and Predictive Recurrent Neural Network (PredRNN), to predict future ground cover. The two models were evaluated on different spatial scales, ranging from a small site (i.e., <5 km²) to the entire GBRCA, with different quantities of training data. Following comparisons against 25% withheld testing data, we found the following: (1) both ConvLSTM and PredRNN accurately predicted the next-season ground cover for not only a single site but also the entire GBRCA. They achieved this with a Mean Absolute Error (MAE) under 5% and a Structural Similarity Index Measure (SSIM) exceeding 0.65; (2) PredRNN superseded ConvLSTM by providing more accurate next-season predictions with better training efficiency; (3) The accuracy of PredRNN varies seasonally and spatially, with lower accuracy observed for low ground cover, which is underestimated. The models assessed in this study can serve as an early-alert tool to produce high-accuracy and high-resolution ground cover prediction one season earlier than observation for the entire GBRCA, which enables local authorities and grazing property owners to take preventive measures to improve land conditions. This study also offers a new perspective on the future utilization of predictive spatio-temporal models, particularly over large spatial scales and across varying environmental sites. Full article

Marine aerosol particles can act as cloud condensation nuclei and influence the atmospheric boundary layer by scattering solar radiation. The interaction of ocean waves and coral reefs may affect the distribution and size of marine aerosol particles. Measuring this effect has proven challenging. Here, we tested the hypothesis that the distribution and size of marine aerosol particles would vary over three distinct zones (i.e., coral lagoon, surf break, and open water) near One Tree Island in the Great Barrier Reef, which is approximately 85 km off the east coast of Australia. We used a modified DJI Agras T30 drone fitted with a miniaturised scanning electrical mobility sizer and advanced mixing condensation particle counter to collect data on aerosol size distribution between 30 and 300 nm at 20 m above the water surface. We conducted 30 flights over ten days during the Austral summer/autumn of 2023. The fitted bimodal lognormal curves indicate that the number concentrations for aerosols below 85 nm diameter are more than 16% higher over the lagoon than over open water. The average mean mode diameters remained constant across the different zones, indicating no significant influence of breaking waves on the detected aerosol size modes. The most influential explanatory variable for aerosol size distribution was the difference between air temperature and the underlying sea surface, explaining around 40% of the variability. Salinity also exhibited a significant influence, explaining around 12% of the measured variability in the number concentration of aerosols throughout the campaign. A calculated wind stress magnitude did not reveal significant variation in the measured marine aerosol concentrations. Overall, our drone-based aerosol measurements near the water surface effectively characterise the dynamics of background marine aerosols around One Tree Island Reef, illustrating the value of drone-based systems for providing size-dependent aerosol information in difficult-to-access and environmentally sensitive areas. Full article

The Great Barrier Reef lagoon is a large, relatively shallow area of the Australian continental shelf, isolated from the open ocean by a dense matrix of coral reefs. As the lagoon is generally vertically well mixed by strong tidal currents and wind, it is perhaps not surprising there is no mention in the open literature of the occurrence of internal waves there. Nevertheless, high-resolution satellite imagery is shown in this article to reveal the characteristic surface expressions of nonlinear internal waves in the lagoon. The waves are confined to periods of low winds in austral spring and summer, making them a potentially important mechanism for the dispersal of algae and planktonic larvae. The imagery suggests a link between the waves and tidally forced submesoscale jets and vortices, but the actual mechanism generating the internal waves is unclear and requires investigation. Full article

Blooms of the harmful dinoflagellate Karenia brevis on the West Florida Shelf (WFS), Gulf of Mexico, are hypothesized to initiate in association with the colonial cyanobacterium Trichodesmium spp. and benefit from dissolved organic nitrogen (DON) release derived from N₂-fixation by the cyanobacteria. Previous studies have detected DON release using direct experimental measurements, but there have been few studies that have followed nutrient release by in situ blooms of Trichodesmium and the associated plankton community. It was determined that long-term Trichodesmium spp. and Karenia brevis abundances on the WFS were related, following a 2-month lag. A separate Eulerian study of a Trichodesmium erythraeum bloom event was conducted over 9 days on the Great Barrier Reef. Concentrations of T. erythraeum increased over the course of the study, with coincident increases in dinoflagellate abundance and decreases in diatom abundance. Inside the bloom, concentrations of NH₄⁺, PO₄³⁻, and DON increased significantly. The copepod grazer Macrosetella gracilis also increased in abundance as T. erythraeum numbers increased, contributing to nutrient release. Copepod grazing rates were measured, and N release rates estimated. Together, these studies show that Trichodesmium blooms have consequences for dinoflagellate abundance at both seasonal and ephemeral scales via direct and indirect N release. Full article

Recent studies have shown that seagrasses could possess potential applications in the treatment of inflammatory disorders. Five seagrass species (Zostera muelleri, Halodule uninervis, Cymodocea rotundata, Syringodium isoetifolium, and Thalassia hemprichii) from the Great Barrier Reef (QLD, Australia) were thus collected, and their preliminary antioxidant and anti-inflammatory activities were evaluated. From the acetone extracts of five seagrass species subjected to 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging antioxidant assay, the extract of Z. muelleri had the highest activity (half minimal concentration of inhibition (IC₅₀) = 138 µg/mL), with the aerial parts (IC₅₀ = 119 µg/mL) possessing significantly higher antioxidant activity than the roots (IC₅₀ ≥ 500 µg/mL). A human peripheral blood mononuclear cells (PBMCs) assay with bacterial lipopolysaccharide (LPS) activation and LEGENDplex cytokine analysis showed that the aerial extract of Z. muelleri significantly reduced the levels of inflammatory cytokines tumour necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 by 29%, 74%, and 90%, respectively, relative to the LPS treatment group. The aerial extract was thus fractionated with methanol (MeOH) and hexane fraction, and purification of the MeOH fraction by HPLC led to the isolation of 4-hydroxybenzoic acid (1), luteolin (2), and apigenin (3) as its major constituents. These compounds have been previously shown to reduce levels of TNF-α, IL-1β, and IL-6 and represent some of the major bioactive components of Z. muelleri aerial parts. This investigation represents the first study of the antioxidant and anti-inflammatory properties of Z. muelleri and the first isolation of small molecules from this species. These results highlight the potential for using seagrasses in treating inflammation and the need for further investigation. Full article

Fishery stock assessments are often based on morphometric data from underwater diver surveys and landing surveys. Measurements of body length are usually converted to estimates of body weight, yet length–weight equations might differ among localities. We evaluated morphometric models for the sea cucumber, Pearsonothuria graeffei, collected at Lizard Island on the northern Great Barrier Reef, Australia, and explored differences in relative condition factor (Kn) across animal sizes. The estimation of body weight was compared among relationships with four different body size metrics: observed body length, SLW (square root of the body length–width product), recalculated body length (Le) from SLW, and body basal area. The basal area of the animals, the SLW index and Le provided more reliable estimations for body weight than using body length alone yet accounted for half of the variation in body weight. The length–weight relationship from animals at Lizard Island differed considerably from relationships published for the same species in New Caledonia and Philippines. Body condition was variable, and our model predicted a peak at 35 cm body length. Body metrics such as basal area, SLW index, and Le could offer more precise models for estimating the body weight of sea cucumbers for fishery purposes. Equations for estimating body weight from length and width of the sea cucumbers should be based on locality-specific data because morphometric relationships are spatially variable. Full article