Crown-of-thorns starfish (COTS) are a leading cause of coral decline on the Great Barrier Reef (GBR), with the majority of their impact occurring during outbreaks. These outbreaks involve rapid increases in populations followed by abrupt declines, and spread between reefs via larval dispersal—a key process in COTS reproduction. Given the difficulty in quantifying dispersal empirically, predictions are instead formed using coupled models of ocean currents and larval biology. Previous efforts have linked dispersal models to COTS population dynamics, however do so indirectly, or at spatiotemporally limited scales. Using an improved set of dispersal estimates and expanded COTS monitoring data, we assess the role of dispersal in determining a reef’s susceptibility to outbreaks. Our results indicate that while there is minimal evidence that dispersal patterns alone drive outbreaks, once combined with COTS population data it becomes clear that dispersal still plays a major role. By predicting COTS populations on undersampled reefs, we estimate that, on average, reefs that have experienced an outbreak receive 50–100

Conservation prioritisation allocates limited resources to benefit objectives such as biodiversity conservation or ecosystem services. Decisions are often determined on the basis of costs and benefits, but for logistically intensive actions such as pest control, the relative feasibility of working at different locations and times should also inform decisions. In this paper, we develop a spatiotemporal feasibility layer for crown-of-thorns starfish control on Australia's Great Barrier Reef Marine Park and show how it can improve both the efficiency and effectiveness of this adaptive management program. Our approach uses a statistical model to predict monthly probabilities that sea conditions will be suitable to allow safe crown-of-thorns starfish surveillance and culling operations. The model is calibrated using historical data from on-water control programs and then extrapolated spatially across the full extent of the Great Barrier Reef and temporally for each month of the year. The resulting predictions reveal clear spatial and seasonal patterns in the feasibility of crown-of-thorns starfish control operations: some reefs remain reliably accessible year-round; others exhibit high variability, making operations during particular months inefficient. Our work shows that, rather than treating poor conditions as unavoidable inefficiencies, calibrated estimates of feasibility should influence the prioritisation phase. It also highlights the advantages of adaptive decision-making processes, which allow feasibility models to iterate and improve alongside feedback from ongoing management actions.

The re-establishment of seagrass meadows following dieback events depends on the availability of viable propagules, particularly vegetative fragments that facilitate recovery beyond the local meadow through long-distance dispersal. The dispersal of vegetative fragments by ocean currents, waves and wind can be predicted by biophysical models. Among the model parameters, the duration of fragment buoyancy is an important determinant of dispersal but remains poorly quantified for tropical seagrass species. Yet, few empirical studies have assessed fragment dispersal traits and only for a small number of seagrass taxa. This limitation is particularly pronounced in tropical ecosystems, including the Great Barrier Reef (GBR), Australia, where tropical species exhibit diverse life histories and form extensive mixed-species meadows. This study aims to improve the accuracy of biophysical dispersal models for tropical seagrass by generating robust, species-specific data. We quantified the buoyancy duration of fragments from three species-Halophila ovalis, Halodule uninervis, and Zostera muelleri-over 48 days, and assessed whether initial morphological traits influenced buoyancy, finding species type was the primary determinant rather than fragment size. We then incorporated these empirical estimates into a biophysical model to evaluate their effects on dispersal. Our results highlight major differences between species. Z. muelleri floated the longest (24.7 ± 3.0 days); H. uninervis sank the fastest; and H. ovalis was intermediate, generating broken fragments available for further dispersal. Integrating these experimental derived buoyancy values into a biophysical model reduced the mean predicted dispersal distances by 44% on average compared to previous models. These findings highlight interspecific dispersal behaviours and provide useable empirical data to refine future modelling studies. Such improvements are essential for predicting seagrass recovery, guiding restoration site selection, and informing management strategies that maintain connectivity and ecosystem resilience.

Current and future coral reef resilience will depend heavily on larval connectivity between reef systems, enabling populations to recover from repeated disturbance. However, climate warming is rapidly reducing larval dispersal, threatening reef recovery potential following mass bleaching. Using a stochastic biophysical Lagrangian particle-tracking model, this study examined large-scale dispersal of coral larvae across the southern Pacific Ocean, focusing on reefs classified using an eco-evolutionary framework ('resistance, recovery, avoidance'). Dispersal was simulated across 850 reefs in the southwestern Pacific (2011-2024) for two coral species representing branching or massive corals under three warming scenarios (+1 degrees C, +2.5 degrees C, +4 degrees C), and analysed for source-sink dynamics. We identified key stepping-stone reefs in the Coral Sea and show that resilient, heat-tolerant reefs have limited source-sink connectivity within this larger region. Lord Howe Island (LHI) may represent a potential refugium in a future of significant larval dispersal limitation under projected climate warming. However, its limited connectivity constrains its natural contribution to regional larval supply, making it simultaneously a conservation priority and a candidate for managed intervention. Synthesis and applications. Our results demonstrate the importance of integrating connectivity into conservation planning by highlighting that the current marine protected area networks across the southwestern Pacific should be managed as an interconnected network rather than as isolated reserves. Additionally, a prioritisation of the enhanced protection of Coral Sea reefs and LHI is warranted given their importance as stepping-stone reefs bridging distant reef systems or isolated dispersal, respectively. Finally, the intentional movement of larvae from resilient, heat-tolerant reefs to other locations could be investigated given their lower relative outward connectivity, with the aim to boost heat tolerance in surrounding reefs. Taken together, these results show that a potential expansion of transboundary management frameworks will be critical to maintain important larval corridors between the southern Great Barrier Reef, New Caledonia and LHI to sustain regional metapopulation resilience under the pressure of a warming world.Read the free Plain Language Summary for this article on the journal's .

Population persistence and recovery in marine systems is driven by larval dispersal in the water column, generating ecological connectivity between the natal and settlement locations. Connectivity modelling is commonly utilised for the spatial planning of marine protected areas and, more recently, for the prioritisation of restoration interventions. Here, we conducted field experiments to validate the spatial patterns and rates of larval arrival as simulated by a high-resolution connectivity model (similar to 300 m resolution), using complementary spatial and temporal sampling of coral larvae and newly settled recruits around a cluster of offshore coral reefs. At the within-reef scale, Lagrangian dispersal modelling demonstrated only a fair performance at predicting observed spatial patterns of larval arrival and settlement, at best. However, at the reef cluster level, hydrodynamicallydriven interannual variations in larval supply were well correlated with observed interannual variations. Combined, the model results resolve empirical observations for the temporal (inter-annual) and spatial scales relevant to meta-population dynamics (1-10s of km's). At the finer spatial scales of resolution (>1/10 ha to <10 ha), relevant to current restoration interventions, skill at predicting larval density is poor whilst skill at predicting larval settlement is fair. Overall, our findings identify the need for a model validation framework that considers the scales of physical processes resolved by the hydrodynamic modelling, spatial-temporal variability in the propagule populations being measured, the error tolerance for how the outputs of model simulations are being utilised (theoretical versus operational), and the complementary use of modelling and field sampling for different scales of application.

Marine reserves deliver impressive increases in the abundance and size of exploited species on protected reefs, but larval dispersal makes it difficult to estimate their wider benefits. Australia's Great Barrier Reef (GBR) contains an extensive network of marine reserves. By combining GBR-wide fish surveys, larval dispersal models, and commercial fishery catch data, we calculate the system-wide ecological and economic contributions of these reserves for coral groupers (Plectropomus spp.), the region's most important line fishery. Despite covering only 30% of reef habitat, the GBR's marine reserve network contains half of the species' biomass and generates most of its reproductive output (55%), half of the system's larval settlement (50%), and almost half of the total fishery yield (47%).

The resilience of seagrass meadows strongly depends on the dispersal of their propagules, which fosters recovery and replenishment after disturbances. However, predicting dispersal patterns across dynamic coastal environments and large spatial and temporal scales remains challenging due to the lack of empirical observations. Biophysical models, integrating oceanic and atmospheric drivers with species-specific traits such as buoyancy and lifespan, are commonly used to simulate propagule transport. Yet, few studies account for the interspecific and interannual variability inherent in tropical seagrass ecosystems. Here we present a high-resolution seagrass biophysical dispersal model applied to 11 tropical seagrass species across the entire Great Barrier Reef World Heritage Area (GBRWHA), Australia, and run this model over a 6-year period (2011-2016). We use this model to assess how the interspecific variability in the buoyancy and windage of seagrass propagules affect their dispersal patterns and how these patterns further vary both seasonally and interannually. Our results reveal that species-specific factors such as their windage and buoyancy, as well as the season and region in which they disperse had the largest influence on dispersal distance. H. spinulosa and S. isoetifolium showed the greatest dispersal in the Whitsunday region, while the wet season promoted higher local retention due to lower wind speeds. From a management perspective, this highlights the need to account for species-specific information when devising seagrass management strategies. The outcomes of this research reveal the inherent complexities of predicting multi-species dispersal over large spatial and temporal scales, with broader implications for predicting dispersal in complex coastal ecosystems.

The fourth Global Coral Bleaching Event (GCBE) reached the Great Barrier Reef (GBR) in the Austral summer of 2023/24 and caused substantial coral mortality in the Cooktown-Lizard Island sector of the GBR. Thermal stress in this sector ranged from 5.9 to 8.2 °C-weeks (Degree Heating Weeks—DHW) derived from NOAA Coral Reef Watch products, resulting in a 38.6

Aim: Dispersal and connectivity play important roles in shaping the population structure of giant kelp, Macrocystis pyrifera, across the western coast of South America. Its high potential dispersal capacity suggests the existence of metapopulations, where discrete habitat patches or groups of patches form subpopulations that interact at some level. However, the dispersal patterns of giant kelp in this region have not been quantified. This study assesses the dispersal and settlement of Macrocystis pyrifera in the southeast Pacific, specifically focusing on the impact of environmental variables and ocean currents within the Humboldt Current System. Location: Southeast Pacific (coast of Chile and Peru). Time Period: 1997-2008. Major Taxa Studied: Macrocystis pyrifera (giant kelp). Methods: Using a combination of hydrodynamic and individual-based models, we analysed kelp fragment movements over 12 years, with a particular emphasis on the effects of the El Nino-Southern Oscillation (ENSO) and seasonal changes. Results: Our results highlight a key settlement area in the southern Chilean region. We found that shorter travel distances of kelp fragments increased the likelihood of reaching a suitable habitat, underscoring the importance of local environmental conditions. We delineated intricate northward dispersal paths for kelp fragments, which appear to be governed by the interplay of wind and ocean current dynamics. Seasonal variations, notably in autumn and winter, favour the likelihood of reaching a settlement area due to favourable winds. Furthermore, ENSO events appear to influence dispersal distances, with fragments travelling the longest distances during El Ni & ntilde;o phases. Main Conclusion: These findings are essential for informing kelp conservation strategies in the context of climate change, emphasizing the necessity of considering local and seasonal environmental factors alongside ENSO impacts.

Larval dispersal is a critical ecological process in marine ecosystems, responsible for connecting and replenishing populations in patchy habitat. Because empirical measurements of larval dispersal are very challenging, coupled biological and oceanographic simulations (“biophysical models”) of larval dispersal are commonly used to answer ecological questions and support conservation management decisions. In the process of creating biophysical models, a series of choices must be made that do not have a single correct answer—sometimes because the oceanographic or ecological processes are uncertain; sometimes because trade-offs are required between different goals (e.g. computational time versus spatial resolution). In this paper, we demonstrate that larval dispersal estimates at management scales are strongly affected by these choices. Using three different hydrodynamic models of the Great Barrier Reef, we estimated the dispersal of crown-of-thorns starfish larvae in the spawning seasons between 2018 and 2021. Despite sharing similar physical forcings and using similar models of larval behaviour, we find that the different hydrodynamic models produce divergent predictions of larval dispersal between the reefs. If used to support crown-of-thorns starfish control decisions, these different predictions would recommend different priority reefs. Our results caution against the use of single models of larval dispersal, and suggest that multi-model ensembles may offer a valuable new perspective on dispersal patterns in marine environments.

Cryptobenthic fishes are abundant on coral reefs, and their larvae dominate the ichthyoplankton in near reef waters. However, we have a limited understanding of how pelagic and on-reef processes are linked, especially how late-stage cryptobenthic fish larvae use near reef waters. We therefore used depth-stratified light trap sampling from 2 to 27 m at Lizard Island, Great Barrier Reef. This revealed clear depth variation in late-stage larval fish assemblages. Gobiidae larvae characterised mid-depth (13 m) samples. By contrast, larval Apogonidae were only abundant in shallow samples. Deep samples were typified by (non-target) adult apogonids. Contrary to expectations that poor-swimming cryptobenthic larvae would be flow-sheltering in deeper water, our results suggest that late-stage cryptobenthic larvae use large portions of the water column, although their preferred positions may be taxon-specific.

Biophysical models simulate dispersal and connectivity in marine environments by combining numerical models that represent water circulation with biological parameters that define the attributes of species. The effects of parameters, such as the number of particles released to simulate the trajectories of individual organisms, is potentially large but rarely tested. We present a framework to measure the optimal number of particles required to capture variability in dispersal and connectivity of the marine plants, seagrasses. We found that the number of optimal release particles per element (or grid cell) for dispersal estimates varied with seagrass habitat type, season, and physical parameters of the modelled propagules (i.e., wind drag). Connectivity metrics were comparatively much less sensitive, requiring lower particle numbers to achieve stable results. We provide guidance on important factors to consider when determining the optimal number of particles required to robustly predict dispersal and connectivity in biophysical models of marine plants.

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.

The Spratly Islands archipelago in the South China Sea is a disputed marine area impacted by a destructive free-for-all race to resources. Though physically open, the archipelago is a semi-closed system because the flushing time scales are comparable to the pelagic larval duration of coral and reef fish larvae. Island-building, overfishing and destructive clam harvesting in the archipelago destroy, or at the very least severely damage, the directly impacted reefs. At these reefs, larvae are not produced anymore, or produced in significantly lessened numbers, and thus larval recruitment is decreased in reefs downstream. This diminishes the resilience of the whole Spratly Islands archipelago reef ecosystem.

Driving patterns of coral bleaching over reefs are a suite of biophysical interactions where the physical environment modulates organism response through an interplay with intrinsic biological functioning. Flow conditions over reefs can mitigate the physiological impacts of thermal stress across multiple spatial scales. More details can be found in article number 1800226 by Charlotte E. Page et al., Seeking Resistance in Coral Reef Ecosystems: The Interplay of Biophysical Factors and Bleaching Resistance under a Changing Climate, DOI: 10.1002/bies.201800226.

If we are to ensure the persistence of species in an increasingly warm world, of interest is the identification of drivers that affect the ability of an organism to resist thermal stress. Underpinning any organism's capacity for resistance is a complex interplay between biological and physical factors occurring over multiple scales. Tropical coral reefs are a unique system, in that their function is dependent upon the maintenance of a coral-algal symbiosis that is directly disrupted by increases in water temperature. A number of physical factors have been identified as affecting the biological responses of the coral organism under broadscale thermal anomalies. One such factor is water flow, which is capable of modulating both organismal metabolic functioning and thermal environments. Understanding the physiological and hydrodynamic drivers of organism response to thermal stress improves predictive capabilities and informs targeted management responses, thereby increasing the resilience of reefs into the future.

Larval dispersal is a critically important yet enigmatic process in marine ecology, evolution, and conservation. Determining the distance and direction that tiny larvae travel in the open ocean continues to be a challenge. Our current understanding of larval dispersal patterns at management-relevant scales is principally and separately informed by genetic parentage data and biological-oceanographic (biophysical) models. Parentage datasets provide clear evidence of individual larval dispersal events, but their findings are spatially and temporally limited. Biophysical models offer a more complete picture of dispersal patterns at regional scales but are of uncertain accuracy. Here, we develop statistical techniques that integrate these two important sources of information on larval dispersal. We then apply these methods to an extensive genetic parentage dataset to successfully validate a high-resolution biophysical model for the economically important reef fish species Plectropomus maculatus in the southern Great Barrier Reef. Our results demonstrate that biophysical models can provide accurate descriptions of larval dispersal at spatial and temporal scales that are relevant to management. They also show that genetic parentage datasets provide enough statistical power to exclude poor biophysical models. Biophysical models that included species-specific larval behaviour provided markedly better fits to the parentage data than assuming passive behaviour, but incorrect behavioural assumptions led to worse predictions than ignoring behaviour altogether. Our approach capitalises on the complementary strengths of genetic parentage datasets and high-resolution biophysical models to produce an accurate picture of larval dispersal patterns at regional scales. The results provide essential empirical support for the use of accurately parameterised biophysical larval dispersal models in marine spatial planning and management.

Larval dispersal is the key process by which populations of most marine fishes and invertebrates are connected and replenished. Advances in larval tagging and genetics have enhanced our capacity to track larval dispersal, assess scales of population connectivity, and quantify larval exchange among no-take marine reserves and fished areas. Recent studies have found that reserves can be a significant source of recruits for populations up to 40 km away, but the scale and direction of larval connectivity across larger seascapes remain unknown. Here, we apply genetic parentage analysis to investigate larval dispersal patterns for two exploited coral reef groupers (Plectropomus maculatus and Plectropomus leopardus) within and among three clusters of reefs separated by 60-220 km within the Great Barrier Reef Marine Park, Australia. A total of 69 juvenile P. maculatus and 17 juvenile P. leopardus (representing 6% and 9% of the total juveniles sampled, respectively) were genetically assigned to parent individuals on reefs within the study area. We identified both short-distance larval dispersal within regions (200 m to 50 km) and long-distance, multidirectional dispersal of up to ~250 km among regions. Dispersal strength declined significantly with distance, with best-fit dispersal kernels estimating median dispersal distances of ~110 km for P. maculatus and ~190 km for P. leopardus. Larval exchange among reefs demonstrates that established reserves form a highly connected network and contribute larvae for the replenishment of fished reefs at multiple spatial scales. Our findings highlight the potential for long-distance dispersal in an important group of reef fishes, and provide further evidence that effectively protected reserves can yield recruitment and sustainability benefits for exploited fish populations.

The high cost of acoustic Doppler ocean current meters means few are deployed in marine research studies. To address this problem, we have developed a low-cost robust current velocimeter based on the drag-tilt principle. The instrument tilts in response to current flow, for which the angle and direction of tilt are related to the water velocity. Static analytic approximation shows a sigmoid-type tilt response to increasing current speed. We detail a calibration method that models the relationship using a Gompertz curve. Calibration and field tests conducted near Magnetic Island, Australia, show a speed accuracy of 0.05 m/s for current speeds less than 0.6 m/s, and direction accuracy better than 15 ° for current speeds greater than 0.15 m/s. This instrument should be especially useful for research projects where numerous or spatially dense measurements of ocean currents are required.