2022 Dugong Aerial Survey: Mission Beach to Moreton Bay

Project objectives: • Dugongs are of significant biodiversity value as the only extant species in the Family Dugongidae and one of only four species in the Order Sirenia, all of which are listed as vulnerable to extinction by the IUCN. • Australia has international responsibilities for dugong conservation, particularly in the Great Barrier Reef (GBR) region, where the dugong feeding grounds are listed as one of the World Heritage values of the region. • Dugongs have been monitored along the Queensland coast since the 1980s using a series of standardised aerial surveys. These surveys have provided long-term information on the distribution and abundance of dugongs, which has informed management and are a requirement of the Reef 2050 Long-Term Sustainability Plan (Reef 2050 Plan). The surveys have been loosely coordinated across jurisdictions and largely conducted at the same time of year at approximately five-year intervals. The areas adjacent to the Great Barrier Reef have been included to account for temporary migrations of dugongs across jurisdictional boundaries. • This report presents the result of an aerial survey for dugongs and large juvenile and adult marine turtles that was conducted in November-December 2022 in the coastal waters of Queensland from Mission Beach to the Queensland-New South Wales border. The survey is the latest in the time series of surveys conducted by James Cook University-TropWATER researchers since the 1980s. • The objectives of our study were to: 1. continue the time series of surveys for dugongs and large marine turtles. 2. to use the latest programming, modelling, and statistical advances to enhance our dugong distribution and abundance analysis. 3. engage with First Nations people across the surveyed area to: (1) raise awareness about dugong and sea turtle ecology and conservation issues, (2) seek interest from the communities in becoming involved in dugong survey work at different spatial scales, particularly aerial imagery surveys. 4. discuss new avenues for reducing uncertainty in the results for the surveys and the potential of new research tools for dugong monitoring in the future 5. provide advice to relevant management partners (GBRMPA, DCCEEW, and the Queensland Government) and Traditional Owners about the implications of the findings for the conservation, management, and monitoring of dugongs and large marine turtles1 in the southern GBR, Hervey Bay-GSS and Moreton Bay

Large-scale, multidirectional larval connectivity among coral reef fish populations in the Great Barrier Reef Marine Park

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 similar to 250 km among regions. Dispersal strength declined significantly with distance, with best-fit dispersal kernels estimating median dispersal distances of similar to 110 km for P. maculatus and similar to 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

Island building and overfishing in the Spratly Islands archipelago are predicted to decrease larval flow and impact the whole system

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 the reefs downstream. This diminishes the resilience of the whole Spratly Islands archipelago reef ecosystem

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

Resilient reefs may exist, but can larval dispersal models find them?

<p>Resilient reefs may exist, but can larval dispersal models find them?</p

Depth stratified light trap sampling reveals variation in the depth distribution of late-stage cryptobenthic reef fish larvae

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.</p

Estuarine crocodiles ride surface currents to facilitate long-distance travel

1. The estuarine crocodile ('Crocodylus porosus') is the world's largest living reptile. It predominately inhabits freshwater and estuarine habitats, but widespread geographic distribution throughout oceanic islands of the South-east Pacific suggests that individuals undertake sizeable ocean voyages. 2. Here we show that adult 'C. porosus' adopt behavioural strategies to utilise surface water currents during long-distance travel, enabling them to move quickly and efficiently over considerable distances. 3. We used acoustic telemetry to monitor crocodile movement throughout 63 km of river, and found that when individuals engaged in a long-distance, constant direction journey (&gt;10 km day)-¹), they would only travel when current flow direction was favourable. Depth and temperature measurements from implanted transmitters showed that they remained at the water surface during travel but would dive to the river substratum or climb out on the river bank if current flow direction became unfavourable. 4. Satellite positional fixes from tagged crocodiles engaged in ocean travel were overlaid with residual surface current (RSC) estimates. The data showed a strong correlation existed between the bearing of the RSC and that of the travelling crocodile (r² = 0.92,P 10 km day)-¹), they would only travel when current flow direction was favourable. Depth and temperature measurements from implanted transmitters showed that they remained at the water surface during travel but would dive to the river substratum or climb out on the river bank if current flow direction became unfavourable. 4. Satellite positional fixes from tagged crocodiles engaged in ocean travel were overlaid with residual surface current (RSC) estimates. The data showed a strong correlation existed between the bearing of the RSC and that of the travelling crocodile (r² = 0.92,

A buoyant tethered sphere for marine current estimation

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

Seeking resistance in coral reef ecosystems: the interplay of biophysical factors and bleaching resistance under a changing climate: the interplay of a reef's biophysical factors can mitigate the coral bleaching response

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

Marine plant dispersal and connectivity measures differ in their sensitivity to biophysical model parameters

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