Barrier Reef World Heritage Area Research Articles

Toxoplasmosis epidemic in a population of urbanised allied rock-wallabies (Petrogale assimilis) on Magnetic Island (Yunbenun), North Queensland.

A mortality event involving 23 allied rock-wallabies (Petrogale assimilis) displaying neurological signs and sudden death occurred in late April to May 2021 in a suburban residential area directly adjacent to Magnetic Island National Park, on Magnetic Island (Yunbenun), North Queensland, Australia. Three allied rock-wallabies were submitted for necropsy, and in all three cases, the cause of death was disseminated toxoplasmosis. This mortality event was unusual because only a small, localised population of native wallabies inhabiting a periurban area on a tropical island in the Great Barrier Reef World Heritage Area were affected. A disease investigation determined the outbreak was likely linked to the presence of free-ranging feral and domesticated cats inhabiting the area. There were no significant deaths of other wallabies or wildlife in the same or other parts of Magnetic Island (Yunbenun) at the time of the outbreak. This is the first reported case of toxoplasmosis in allied rock-wallabies (Petrogale assimilis), and this investigation highlights the importance of protecting native wildlife species from an infectious and potentially fatal parasitic disease.

Marine heatwaves in the Great Barrier Reef and Coral Sea: their mechanisms and impacts on shallow and mesophotic coral ecosystems

The Great Barrier Reef (GBR) World Heritage Area and adjacent Coral Sea Marine Park are under serious threat from global climate change. This study used Daily Optimally Interpolated Sea Surface Temperature (DOISST) data to identify major marine heatwaves (MHWs) that have occurred in this region over the last three decades (1992–2022). We then used Himawari-8 (H-8) SST data to map significant MHW events that occurred between 2015 and 2022. We investigated the mechanisms underlying the MHWs, assessed thier impact on shallow and mesophotic coral reef ecosystems and identified potential coral refugia. MHWs in this region have increased in frequency, intensity and spatial extent. El Niño, especially when it is in phase with positive Indian Ocean Dipole, was the key remote driver leading to intense MHWs. However, the more recent strong MHWs (e.g., 2017 and 2022) occurred in the abscence of these climatic events, signifying the impacts of long-term climate change and local drivers. We also found that reduced wind speed and shoaling mixed layer depth, often together with reduced cloudiness, were the main local drivers pre-conditioning these MHWs. Anomalous air-sea heat flux into the ocean, mainly controlled by shortwave solar radiation (cloudiness) and latent heat flux (wind), was the most constant contributor to the 2015–16 and 2019–20 MHW events. However, local oceanographic dynamics, especially horizontal advection and turbulent mixing, played important roles in MHW heat budgets. This study confirmed that shallow-water coral bleaching severity was positively related to the cumulative MHW intensity in the 2015–16 and 2019–20 MHW events. We identified shallow reefs along the path of the North Queensland Current as potential coral refugia from bleaching because of the cooler waters upwelled from the ocean current. We also found that, except during weather events such as tropical cyclones, mesophotic reefs in the Coral Sea Marine Park may be less susceptible to severe bleaching as the MHWs were more confined within the shallow mixed layer.

Vegetative fragment production as a means of propagule dispersal for tropical seagrass meadows

Background and aimsLong distance dispersal (LDD) contributes to the replenishment and recovery of tropical seagrass habitats exposed to disturbance, such as cyclones and infrastructure development. However, our current knowledge regarding the physical attributes of seagrass fragments that influence LDD predominantly stems from temperate species and regions. The goal of this paper is to measure seagrass fragment density and viability in two tropical species, assessing various factors influencing their distribution. MethodsWe measured the density and viability of floating seagrass fragments for two tropical seagrass species (Zostera muelleri and Halodule uninervis) in two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. We assessed the effect of wind speed, wind direction, seagrass growing/senescent season, seagrass meadow density, meadow location and dugong foraging intensity on fragment density. We also measured seagrass fragment structure and fragment viability; i.e., potential to establish into a new plant. Key resultsWe found that seagrass meadow density, season, wind direction and wind speed influenced total fragment density, while season and wind speed influenced the density of viable fragments. Dugong foraging intensity did not influence fragment density. Our results indicate that wave action from winds combined with high seagrass meadow density increases seagrass fragment creation, and that more fragments are produced during the growing than the senescent season. Seagrass fragments classified as viable for Z. muelleri and H. uninervis had significantly more shoots and leaves than non-viable fragments. We collected 0.63 (±0.08 SE) floating viable fragments 100 m−2 in the growing season, and 0.13 (±0.03 SE) viable fragments 100 m−2 in the senescent season. Over a third (38%) of all fragments collected were viable. ConclusionThere is likely to be a large number of viable seagrass fragments available for long distance dispersal. This study's outputs can inform dispersal and connectivity models that are used to direct seagrass ecosystem management and conservation strategies.

A report card approach to describe temporal and spatial trends in parameters for coastal seagrass habitats

Report cards that are designed to monitor environmental trends have the potential to provide a powerful communication tool because they are easy to understand and accessible to the general public, scientists, managers and policy makers. Given this functionality, they are increasingly popular in marine ecosystem reporting. We describe a report card method for seagrass that incorporates spatial and temporal variability in three metrics—meadow area, species and biomass—developed using long-term (greater than 10 years) monitoring data. This framework summarises large amounts of spatially and temporally complex data to give a numeric score that provides reliable comparisons of seagrass condition in both persistent and naturally variable meadows. We provide an example of how this is applied to seagrass meadows in an industrial port in the Great Barrier Reef World Heritage Area of north-eastern Australia.

Reactive persistence, spatial management, and conservation of metapopulations: An application to seagrass restoration.

Assessing the conditions for persistence of spatially structured populations, especially those that are exploited by humans or threatened by global change, is of critical importance to inform management and conservation efforts. Observations for entire metapopulations are usually incomplete and rarely, if ever, sufficiently long to deduce population persistence from spatial patterns of abundance. Instead, insights based on metapopulation theory are often used for interpreting the demographic trajectories of real populations and for informing management decisions. The classical theoretical tool used to assess conditions for metapopulation persistence is the "invasibility criterion," which characterizes the asymptotic, or long-term, stability of a small colonizing population. Essentially, when the linear operator governing the metapopulation dynamics of an invasion event has a positive eigenvalue, recovery and resistance to extinction (resilience) are implied. The converse, however, is not necessarily the case-an invasion may grow over multiple generations, even when the eigenvalues indicate that extinction will eventually occur, a situation referred to here as "reactive persistence." For the management, restoration, and conservation of real metapopulations subject to continual disturbance, this transient behavior is often more relevant than the asymptotic behavior over long time scales. We develop the theoretical tools for assessing reactive persistence, demonstrating how the conditions for asymptotic and reactive persistence differ in both the patch-occupancy models suited to many terrestrial populations and those where local patch extinctions can be disregarded in the dynamics, often suited to marine species. After presenting the mathematical basis for generalizing the invasibility criterion to include reactive persistence, we illustrate how these concepts and tools can be applied in practice, using as a case study the population ecology and restoration of the seagrass Zostera muelleri (Irmisch ex Ascherson, 1867) in the Port of Gladstone in the Great Barrier Reef World Heritage Area Australia. It is shown how the analysis of the transient dynamics of the Z. muelleri metapopulation can be used to guide restoration efforts. Moreover, it is demonstrated that these reactive persistence concepts provide a more appropriate basis for site prioritization for restoration interventions than traditional stability analysis.

Spatio-temporal analysis of the environmental ranges and phenotypic traits of Zostera muelleri subpopulations in Central Queensland

Intraspecific variation in phenotypic traits of seagrasses enables populations to tolerate varying environmental conditions and facilitates population persistence and expansion. Significant variation in seagrass population morphometrics may reflect highly plastic responses to abiotic and biotic factors, allowing populations to acclimate to changing environmental conditions. Alternatively, morphological variation may arise from developmental canalisation or genetically determined fixed traits, which may inhibit future plasticity and adaptive flexibility to changing environmental conditions. Understanding the drivers behind intraspecific variation in phenotypic traits is important for seagrass restoration practitioners when identifying populations that may provide suitable donor propagules with high adaptability to new sites or propagules that may be more resilient to future environmental changes. This study aimed to investigate whether variation in morphological traits of four subpopulations of Zostera muelleri on the Curtis Coast of the Great Barrier Reef World Heritage Area, Queensland, correlated with meadow-specific environmental conditions and whether this varied between seasons. Morphometric analysis was conducted on Z. muelleri apical shoots, sampled during the spring growing/flowering season and autumn senescent season. Meadow-specific environmental conditions were assessed using historical data dating back to 2008 and environmental simulation models developed for predicting wave, and light conditions. Results indicated that Z. muelleri subpopulations exhibited distinct morphologies throughout their seasonal growth cycle that may correlate with meadow-specific differences in sediment composition, hydrodynamic stress, and light availability. However, further investigation is required to understand if expressed morphological traits are reflective of environmentally driven phenotypic plasticity or genetically predetermined fixed traits (local adaptation or developmental canalisation). Knowledge gained from further studies into the drivers behind the observed variations in morphological traits would increase the understanding of the importance of trait-based selection of propagules for seagrass restoration meadows’ resilience and persistence.

‘The public perception of the role, importance, and vulnerability of seagrass. A case study from the Great Barrier Reef’

Seagrass meadows, one of the world′s greatest natural assets, are globally declining due to direct-anthropogenic (e.g., pollution, coastal development, run-off) and climate change (e.g., cyclones, floods, marine heatwaves) threats. One of the primary constraints in seagrass management and restoration is a lack of societal awareness about their role in the marine environment, their importance to human well-being, and their vulnerability. Public perception studies are useful tools to assess communities′ ecological knowledge and attitudes. The Great Barrier Reef World Heritage Area (GBRWHA), famous worldwide for its iconic coral reef, also hosts one of the world′s largest areas of seagrass meadows, which provide many ecosystem services to the associated communities (e.g., nursery habitat, coastal protection, carbon sequestration etc.). However, the perception of seagrasses among coastal communities of the GBRWHA is poorly understood. Through an online survey of marine recreational users, we assessed public awareness of the role seagrasses play, its benefits, and threats to seagrasses in the GBRWHA, in comparison to coral reefs. Our results showed that there is an imbalance in perception of the role and ecosystem services provided by seagrasses and coral reefs among frequent visitors of the GBRWHA. Only 17% of respondents recognized ‘seagrass’ as a habitat of the GBRWHA. Ecosystem services from coral reefs were considered greater than from seagrasses (p < 0.05). Compared to previous studies, a higher percentage of participants believe in climate change (75%). Nevertheless, the general perception is that climate change impact magnitude is higher in coral reefs compared to seagrasses (p < 0.05). Additionally, climate change mitigation, a seagrass-related ecosystem service, was equally attributed to coral reefs and seagrasses (p > 0.05). Willingness-to-pay for coral reef restoration was higher than for seagrass (p < 0.05). For both marine habitats, willingness-to-pay for restoration was higher in younger people and participants with a university degree. Content analysis showed that people believe that marine habitats′ conservation/restoration can be achieved as a collective effort. On the other hand, a lack of trust in government actions was identified as a barrier to willingness-to-pay. These results confirm the need to raise awareness about the importance of seagrasses and of its vulnerability to climate change. To achieve that, we provide two key recommendations: to enhance purposeful experiences through citizen science and to increase effective scientific communication.

Improving Approaches to Mapping Seagrass within the Great Barrier Reef: From Field to Spaceborne Earth Observation

Seagrass meadows are a key ecosystem of the Great Barrier Reef World Heritage Area, providing one of the natural heritage attributes underpinning the reef’s outstanding universal value. We reviewed approaches employed to date to create maps of seagrass meadows in the optically complex waters of the Great Barrier Reef and explored enhanced mapping approaches with a focus on emerging technologies, and key considerations for future mapping. Our review showed that field-based mapping of seagrass has traditionally been the most common approach in the GBRWHA, with few attempts to adopt remote sensing approaches and emerging technologies. Using a series of case studies to harness the power of machine- and deep-learning, we mapped seagrass cover with PlanetScope and UAV-captured imagery in a variety of settings. Using a machine-learning pixel-based classification coupled with a bootstrapping process, we were able to significantly improve maps of seagrass, particularly in low cover, fragmented and complex habitats. We also used deep-learning models to derive enhanced maps from UAV imagery. Combined, these lessons and emerging technologies show that more accurate and efficient seagrass mapping approaches are possible, producing maps of higher confidence for users and enabling the upscaling of seagrass mapping into the future.

Quantifying the environmental impact of a major coal mine project on the adjacent Great Barrier Reef ecosystems

A major coal mine project in Queensland, Australia, is currently under review. It is planned to be located about 10 km away from the Great Barrier Reef World Heritage Area (GBRWHA). Sediment dispersal patterns and their impact on marine ecosystems have not been properly assessed yet. Here, we simulate the dispersal of different sediment types with a high-resolution ocean model, and derive their environmental footprint. We show that sediments finer than 32 μm could reach dense seagrass meadows and a dugong sanctuary within a few weeks. The intense tidal circulation leads to non-isotropic and long-distance sediment dispersal patterns along the coast. Our results suggest that the sediments released by this project will not be quickly mixed but rather be concentrated where the most valuable ecosystems are located. If accepted, this coal mine could therefore have a far-reaching impact on the GBRWHA and its iconic marine species.

Community-specific “desired” states for seagrasses through cycles of loss and recovery

Seagrass habitats provide critical ecosystem services, yet there is ongoing concern over mounting pressures and continuing degradation. Defining a desired state for these habitats is a key step in implementing appropriate management but is often difficult given the challenges of available data and an evaluation of where to set benchmarks. We use more than 20 years of historical seagrass biomass data (1995–2018) for the diverse seagrass communities of Australia's Great Barrier Reef World Heritage Area (GBRWHA) to develop desired state benchmarks. Desired state for seagrass biomass was estimated for 25 of 36 previously defined seagrass communities with the remainder having insufficient data. Desired state varied by more than one order of magnitude between community types and was influenced by the mix of species in the communities and the range of environmental conditions. We identify a historical, decadal-scale cycle of decline with recovery to desired state in coastal intertidal communities. In contrast a number of the estuary and coastal subtidal communities have not recovered to desired state biomass. Understanding a historical context is critically important for setting benchmarks and making informed management decisions on the present state of seagrass in the GBRWHA. The approach we have developed is scalable for monitoring, management and assessment of pressures for other management areas and for other jurisdictions. Our results guide conservation planning through prioritization of the at-risk seagrass communities that are continuing to fall below their desired state.

Gaining public engagement to restore coral reef ecosystems in the face of acute crisis

The twin crisis of biodiversity loss and climate change make it urgent to find ways of restoring natural ecosystems, including coral reefs. Methods for coral reef restoration are rapidly advancing, bringing with them a range of potential risks and opportunities. Attention to public engagement in the governance of such activities therefore becomes critical. This research examines public attitudinal and behavioral engagement in ‘traditional’ coral restoration projects in the Great Barrier Reef World Heritage Area (i.e. coral gardening at relatively small scales). Grounded on dual-process decision-making and trust theories, rational factors (i.e., perceived benefits), emotions (i.e., hope and guilt) and trust are conceptually three main determinants of public engagement in ecological restoration. We used a mixed-method approach, including 63 individual interviews and a follow-up survey with 1585 participants, to clarify the roles of these psychological factors in motivating public engagement in current coral restoration projects. Trust was found to be the most important factor influencing public acceptance (i.e., attitudinal engagement) of coral restoration, while the emotion of guilt was the most influential factor affecting public support (i.e., behavioral engagement). Therefore, when advocating for conservation projects, different campaigns could be implemented with: (1) positive messages of hope and trust to gain public acceptance for government-funded restoration projects and (2) messages highlighting individual responsibility to motivate behavioral support to scale up restoration projects.

A spatial analysis of seagrass habitat and community diversity in the Great Barrier Reef World Heritage Area

The Great Barrier Reef World Heritage Area (GBRWHA) in north eastern Australia spans 2500 km of coastline and covers an area of ~ 350,000 km2. It includes one of the world’s largest seagrass resources. To provide a foundation to monitor, establish trends and manage the protection of seagrass meadows in the GBRWHA we quantified potential seagrass community extent using six random forest models that include environmental data and seagrass sampling history. We identified 88,331 km2 of potential seagrass habitat in intertidal and subtidal areas: 1111 km2 in estuaries, 16,276 km2 in coastal areas, and 70,934 km2 in reef areas. Thirty-six seagrass community types were defined by species assemblages within these habitat types using multivariate regression tree models. We show that the structure, location and distribution of the seagrass communities is the result of complex environmental interactions. These environmental conditions include depth, tidal exposure, latitude, current speed, benthic light, proportion of mud in the sediment, water type, water temperature, salinity, and wind speed. Our analysis will underpin spatial planning, can be used in the design of monitoring programs to represent the diversity of seagrass communities and will facilitate our understanding of environmental risk to these habitats.

Variations in wetland conditions within the Fitzroy Basin, north-eastern Australia: a palaeoecological approach

The North-east Australian Coastal Catchments (NACC) are host to nationally significant wetland complexes, many of which, are ecologically connected to the Great Barrier Reef World Heritage area. However, these wetlands are subject to ongoing and increasing pressure from human activities such as the intensification of land use. Current wetland condition is monitored across the NACC, being assessed against a pre-development static baseline, which includes the use of Regional Ecosystem mapping of remnant and pre-clearing vegetation to provide a broadscale present-day biotic reference. Two sediment cores from wetlands within the Fitzroy Basin were analysed to establish a history of wetland variability and to identify the potential influence of climate and land-use changes over the past ~1000 years. Our results have provided long-term environmental reconstructions, showing wetland histories influenced by natural climate variability (El Niño–Southern Oscillation, the Little Ice Age), and environmental changes associated with European land-use intensification. This study is the first of its kind for wetlands located within the Fitzroy Basin.

Mutualistic relationships in marine angiosperms: Enhanced germination of seeds by mega‐herbivores

AbstractAngiosperms have co‐evolved with animals over thousands of years leading to an array of mutualistic relationships. Passage of plant seeds through animal intestines leads to an important mutualism providing the animal with food and the plant with seed dispersal and enhanced germination. This phenomenon is well studied in terrestrial angiosperms, but there is less research in aquatic environments. We studied the effect of gut passage in marine mega‐herbivores (green sea turtles and dugongs) on seed germination for a common Australian seagrass, Zostera muelleri.We collected fecal samples likely to contain seeds, as well as seagrass seeds from plants at two coastal seagrass meadows in the central Great Barrier Reef World Heritage Area, Australia. Seeds collected from feces and plants were subjected to germination trials across different temperature treatments: low (19°C), medium (26°C), and high (32°C). We found excreted seeds had a significantly greater germination probability (two to four times greater) and germinated significantly faster (18–61% faster) than seeds from the plant. Excreted seeds which had not germinated at the end of the experiment were significantly less likely to be viable compared with seeds taken from the plant. Seeds released from the plant have a slow germination and low germination probability compared with excreted seeds, but retain a high percentage of seed viability. Our study is the first record of marine mega‐herbivores enhancing germination of Z. muelleri seeds. By transporting seeds to new locations and enhancing germination, these animals are important in seagrass resilience and connectivity among metapopulations.

Synthesizing 35 years of seagrass spatial data from the Great Barrier Reef World Heritage Area, Queensland, Australia

AbstractThe Great Barrier Reef World Heritage Area in Queensland, Australia contains globally significant seagrasses supporting key ecosystem services, including habitat and food for threatened populations of dugong and turtle. We compiled 35 years of data in a spatial database, including 81,387 data points with georeferenced seagrass and species presence/absence, depth, dominant sediment type, and collection date. We include data collected under commercial contract that have not been publicly available. Twelve seagrass species were recorded. The deepest seagrass was found at 76 m. Seagrass meadows are at risk from anthropogenic, climate and weather processes. Our database is a valuable resource that provides coastal managers and the global marine community with a long‐term spatial resource describing seagrass populations from the mid‐1980s against which to benchmark change. We address the data issues involved in hindcasting over 30 years to ensure confidence in the accuracy and reliability of data included.

Seagrass seed bank spatial structure and function following a large-scale decline

We examined the spatial structure (distribution, density) and function (viability) of the seagrass sediment seed bank, the storage of viable propagules (e.g. seeds, tubers, diaspores) in the sediment over time,in the northern Great Barrier Reef World Heritage Area in Cairns, Queensland, following a large-scale decline in seagrass area. A spatially explicit seagrass seed bank analysis was paired with a long-term annual assessment of seagrass distribution to assess seed bank spatial patterns and their relationship with the recovery and presence of seagrass, and water depth. Four years post-decline, the seed bank contained Zostera muelleri, Halodule uninervis, Halophila ovalis and Cymodocea serrulata seeds. Seed banks reflected adjacent meadow community composition; however, the density of seeds for all recorded species was significantly lower than analogous seagrass populations, indicating a reduction in the capacity for recovery from the seed bank. A spatial structure existed in both the total (viable + non-viable) and viable seed bank, and distance between seed clusters ranged from 50-550 m depending on species and seed type. Observed patterns in clustering may be explained by variation in water depth and the past distribution of seagrass in these meadows. These results demonstrate that the distribution of seagrass seeds within the seed bank, which directly influences the natural recovery of seagrass communities, is not uniform across species and may result in patchy recovery of the meadows. Therefore, the resilience provided by the seed bank in seagrass communities should not be viewed as a static level of insurance for the entire meadow, but rather as dynamic and species-specific, with variability over both space and time.

Spatial and temporal variability of green turtle and dugong herbivory in seagrass meadows of the southern Great Barrier Reef (GBR)

Megaherbivore grazing (e.g. by turtles, and sirenians) plays a major and well-documented role in structuring seagrass meadows around the world; however, we know little about local-scale (intra- and inter-meadow) variability in megaherbivore grazing. This is surprising given that megaherbivores are highly selective eaters who may feed by targeting certain meadows, or areas within a meadow. We ran an experiment in the Great Barrier Reef to test the question: How does megaherbivory vary on a regional scale? We used megaherbivore exclusion cages in 5 meadows along a 50 km region of coastline around Gladstone in the southern Great Barrier Reef World Heritage Area to understand variability in megaherbivory between meadows. We found differences in the impacts of megaherbivore grazing on seagrass biomass and shoot heights between meadows. There were also interannual differences in grazing impacts at one meadow that had been studied previously. These differences may be due to megaherbivore population and grazing dynamics, as well as the response of seagrass to grazing pressure. Our results show that seagrass meadows grazed by megaherbivores are dynamic systems that vary on regional spatial scales as well as over time. This is important for management measures that seek to consider the seagrass-herbivore system as a whole and understand the implications of monitoring efforts based on seagrass aboveground condition.

Safeguarding our sacred islands: Traditional Owner-led Sea Country governance, planning and management in Australia

This timely collation of case studies, written by and with Traditional Owners of diverse Australian offshore islands, offers direct insights into benefits arising from strategic and participatory action planning for biocultural island conservation and monitoring. We pay respect to the Old People and Elders whose dedicated care of their island homelands means we today can still experience their cultural and natural diversity. We extend greetings to our Pacifika neighbours, and to carers of islands around Earth. Our paper scopes socio-economic benefits arising from planning for islands, for Aboriginal peoples and Torres Strait Islanders, and more generally. Global, national, state and local co-investments support place-specific planning for some islands by Traditional Owners as a starting point toward shared governance and caring for Country. Case studies describe Country planning for Mayala Country in Australia’s northwest, Woppaburra experiences within the Great Barrier Reef World Heritage Area and integrated biocultural health monitoring arising from remote island Indigenous Protected Area planning in Torres Strait. New institutional initiatives are also seeking to create solid foundations for more substantive island research collaborations. Across Australia, novel relationships grounded in culturally assured, holistically integrated approaches to island governance and caring for Country involving Traditional Owners and island resource users/managers are creating equity in livelihoods and stronger wellbeing. Australia’s innovative Sea Country collaborations, with priorities initiated and led by island Traditional Owners, carry real value for sustained island conservation and provide positive inspirations for global humanity in the accelerating Anthropocene.

Toxicity of Herbicide Mixtures to Tropical Freshwater Microalgae Using a Multispecies Test.

Agriculture within the Great Barrier Reef catchment area has contributed to pesticide contamination of adjacent freshwater ecosystems that flow into the Great Barrier Reef World Heritage Area. A novel multispecies toxicity test was used to assess the toxicity of diuron and hexazinone, 2 herbicides commonly detected within the Great Barrier Reef catchment area, to a community of 3 tropical freshwater microalgae: Monoraphidium arcuatum, Nannochloropsis-like sp., and Pediastrum duplex. Diuron was the most toxic herbicide, with 10% inhibition concentration (IC10) values of 4.3, 7.1, and 29 µg/L for P. duplex, M. arcuatum, and Nannochloropsis-like sp., respectively, followed by hexazinone, with IC10 values of 15, 18, and 450 µg/L, respectively Toxicity testing on 2 commercial formulations (Barrage, 13.2% hexazinone and 48.6% diuron; Diurex, 90% diuron) showed that additives in the commercial formulations did not significantly increase the toxicity of diuron. Direct toxicity assessments were carried out on water samples from the herbicide-contaminated Sandy Creek, which discharges to the Great Barrier Reef lagoon, and a clean reference site, Tully Gorge in the Tully River. Toxicity was observed in several Sandy Creek samples. Artificial herbicide mixtures were assessed in synthetic soft water and natural freshwaters, with toxic responses being observed at environmentally relevant concentrations. The present study successfully applied a novel multispecies tropical microalgal toxicity test, indicating that it is an effective tool for the assessment of herbicide toxicity in both natural and synthetic freshwaters. Environ Toxicol Chem 2021;40:473-486. © 2020 SETAC.

The Differential Importance of Deep and Shallow Seagrass to Nekton Assemblages of the Great Barrier Reef

Seagrass meadows are an important habitat for a variety of animals, including ecologically and socioeconomically important species. Seagrass meadows are recognised as providing species with nursery grounds, and as a migratory pathway to adjacent habitats. Despite their recognised importance, little is known about the species assemblages that occupy seagrass meadows of different depths in the coastal zone. Understanding differences in the distribution of species in seagrass at different depths, and differences in species diversity, abundance, biomass, and size spectra, is important to fully appreciate both the ecological significance and economic importance of these seagrass meadows. Here, we assess differences in the assemblage characteristics of fish, crustacea, and cephalopods (collectively, nekton) between deep (&gt;9 m; Halophila spinulosa dominant) and shallow water (&lt;2 m; Halodule uninervis and/or Zostera muelleri dominant) seagrass meadows of the central Great Barrier Reef coast of Queensland, Australia. Nekton assemblage structure differed between deep and shallow seagrass. Deeper meadows were typified by juvenile emperors (e.g., Lethrinus genivittatus), hairfinned leatherjacket (Paramonacanthus japonicus) and rabbitfish (e.g., Siganus fuscescens) in both biomass per unit effort (BPUE) and catch per unit effort (CPUE), whereas shallow meadows were typified by the green tiger prawn (Penaeus semisulcatus) and pugnose ponyfish (Secutor insidiator) in both BPUE and CPUE. Both meadow depths were distinct in their nekton assemblage, particularly for socioeconomically important species, with 11 species unique to both shallow and deep meadows. However, both meadow depths also included juveniles of socioeconomically important species found in adjacent habitats as adults. The total nekton CPUE was not different between deep and shallow seagrass, but the BPUE and body mass of individual animals were greater in deep than shallow seagrass. Size spectra analysis indicated that in both deep and shallow meadows, smaller animals predominated, even more so than theoretically expected for size spectra. Our findings highlight the unique attributes of both shallow and deeper water seagrass meadows, and identify the distinct and critically important role of deep seagrass meadows within the Great Barrier Reef World Heritage Area (GBRWHA) as a habitat for small and juvenile species, including those of local fisheries value.