Northwestern Australia Research Articles

Seismically constrained gravity inversions reveal magmatic and metamorphic processes at a major lithospheric boundary in northwestern Australia

Magmatic and metamorphic processes modifying the lower crust and uppermost mantle are key to understanding continental growth and evolution. However, our ability to identify and quantify such processes is challenged by inaccessibility, data sparsity, and uncertainties in defining properties at depth. As a result, knowledge of composition, metamorphic grade, and the nature of the continental crust-mantle transition is often limited. Here, we model the structure and properties of the crust and uppermost mantle between the West and North Australian Cratons to infer tectonic processes at this major lithospheric boundary. Seismically constrained 3D gravity inversions were used to estimate crustal and mantle densities and Moho depths. The application of isostatic principles and the joint interpretation of gravity, active and passive seismic models, well data, and outcrop data are used to identify and characterize anomalous masses that are otherwise unresolvable using supracrustal datasets. The results suggest a thick, dense crust with a mafic bulk composition, a high-density, reflective lower crust, and a low-density uppermost mantle beneath the southern Canning Basin. We interpret these crustal and mantle features as reflecting mafic mantle-derived magmatism and crustal anatexis related to Proterozoic-Cambrian Large Igneous Provinces. In contrast, the Proterozoic Paterson Orogen exhibits a thick, dense, high-grade metamorphic bulk crust with a felsic to intermediate composition, a high-density, low-reflectivity lower crust, and low-density uppermost mantle, inferred to result from convergent tectonics. The northern Canning Basin displays a thinner, less dense crust with an intermediate to mafic composition, and mafic, high-density, reflective lower crust, associated with mafic magma emplacement during rifting and passive margin formation. These variations in crustal structure reveal a complex interplay of Proterozoic terrane amalgamation to the cratonic margin, repeated intraplate high-volume mafic magmatic events, and rifting of the offshore basin, which have collectively shaped the deep crust and uppermost mantle in this region.

Ontogenetic changes in green turtle (Chelonia mydas) diet and home range in a tropical lagoon

Ontogenetic changes in habitat and diet are widespread among marine species. Most species of sea turtles are characterized by extreme ontogenetic changes in habitat use and diet, with large changes occurring in early developmental stages (e.g., neonates to juveniles). Changes can continue even after recruitment to shallow coastal habitats. In places where substantial transitions in habitat occur across short distances, it is possible that the distances of developmental movements from one habitat to another could be short. We investigated ontogenetic changes in home range size, home range location and diet of Chelonia mydas in a tropical coastal lagoon in north-western Australia by combining acoustic telemetry with stable isotope analysis. There was a substantial (but nonlinear) increase in home-range size (kernel utilization distribution: KUD) with length, and an increase in the average distance of the center of home ranges from shore with length: larger turtles tended to occupy larger areas further from the shore. These patterns were accompanied by complex nonlinear changes in δ13C, δ15N and δ34S of red blood cells and nails; changes were rapid from 36 cm (the length of the smallest individual captured) to 50 cm, before reversing more gradually with increasing size. δ15N and δ34S (but not δ13C) of red blood cells and nails increased monotonically with KUD and distance from shore. Seagrass was likely an important food for all sizes, macroalgae was potentially important for small (< 60 cm CCL) individuals, and the proportion of scyphozoan jellyfish in diet increased monotonically with size. The combination of acoustic telemetry and stable isotope analysis revealed ontogenetic shifts in use of space and diet across short distances in a tropical coastal lagoon.

Regional seismic stratigraphic framework and depositional history of the post-Valanginian passive margin sequences in the Northern Carnarvon Basin, North West Shelf of Australia

The post-rift succession of the Northern Carnarvon Basin (north-western Australia) has commonly been interpreted as a relatively simple and uniform sequence that records a transition from siliciclastic to carbonate sedimentation deposited on a passive margin. However, given the significant vertical and lateral variation in seismic facies visible on seismic data, this interpretation likely oversimplifies the depositional history of the margin. Regional composite seismic lines that cross most of the basin, integrated with lithological and biostratigraphic information from exploration wells, provide the context for a better understanding of the depositional processes and environments that characterize the post-rift continental margin succession. We show that the sedimentary sequences deposited above the Valanginian breakup unconformity contain a wide variety of seismic facies that can be linked to a number of different marine depositional environments, with the greatest lateral variation occurring in the Turonian – Rupelian and in the Tortonian – Present. The former interval consists of three dominant seismic facies, namely polygonally faulted, incised, and parallel bedded, which we interpret to indicate a lateral transition from an environment primarily dominated by fine-grained pelagic/hemipelagic deposition to one dominated by energetic bottom currents that created both depositional and erosional features, such as contourite drifts and associated moats. The latter interval is expressed by sigmoidal and continuous reflections which pass laterally into more chaotic reflection packages, which we interpret as clinoforms and mass-transport complexes (MTCs). The development of bottom currents may be connected to changes in circulation associated with the opening of oceans adjacent to the northwest margin of Australia, while the MTCs may indicate increased regional seismic activity and slope instability resulting from the development of collisional plate boundaries. Definition of these sequences highlights the significant changes that have occurred in the sedimentary processes that operated on the margin, and their potential link to its tectonic evolution.

Species in Disguise: A New Species of Hornshark from Northern Australia (Heterodontiformes: Heterodontidae)

A new species of hornshark is described from northwestern Australia based on six whole specimens and a single egg case. Heterodontus marshallae n. sp. was previously considered to be conspecific with H. zebra from the Western Pacific. The new species differs from H. zebra in the sequence of its NADH2 gene, several morphological characters, egg case morphology and key coloration features. Despite the coloration being similar between H. marshallae n. sp. and H. zebra, i.e., pale background with 22 dark brown bands and saddles, they differ consistently in two key aspects. Firstly, the snout of H. marshallae n. sp. has a dark semicircular bar, usually bifurcated for most of its length vs. a pointed, triangular shaped dark marking in H. zebra. Secondly, H. zebra has a dark bar originating below the posterior gill slits and extending onto anterior pectoral fin, which is absent in H. marshallae n. sp. The Heterodontus marshallae n. sp. is endemic to northwestern Australia and occurs in deeper waters (125–229 m) than H. zebra (0–143 m).

Acting locally, thinking nationally: layering Indigenous ontology within wellbeing frameworks.

There are hundreds of sovereign nations covering the modern nation-state of Australia.1 Noting the inadequacy of many contemporary terms to encompass Indigenous ontology, Indigenous nations have long practised what is now being expressed as 'wellbeing frameworks' in many nation-states. Unlike the sentiment expressed in contemporary wellbeing frameworks, Country - the complex web of relationships between the human and other-than-human that underpins everything2 - and relationality are fundamental to Indigenous 'wellbeing'. The philosophy of mabu liyan (good feeling), intrinsic to the Yawuru nation of North Western Australia, is only one example of Indigenous governance where Country-centred planning and relational wellbeing are 'business as usual'. Layering elements that are critical to Indigenous expressions of wellbeing, specifically Country and relationality, when developing wellbeing frameworks would broaden and deepen contemporary approaches to wellbeing while accommodating differences at the local scale.

Life-history characteristics and mortality of the protogynous hermaphroditic frostback rockcod (Epinephelus bilobatus) from the eastern Indian Ocean

The frostback rockcod, Epinephelus bilobatus, is a small epinephelid (<50 cm total length) with a limited distribution in the tropical eastern Indian Ocean (i.e., north-western Australia and parts of Indonesia). Although its fishery harvest in Western Australia is low (<6 t year−1), its life history is not well known (i.e., reproductive biology, growth, and natural mortality) preventing assessment of its inherent vulnerability to overfishing. Samples of E. bilobatus were collected from ∼2000 km of the north-western Australian coast, comprising the Kimberley, Pilbara, and Gascoyne regions, between 2012 and 2022 to determine its life-history characteristics. Detailed histological analysis of gonads (n = 1460) identified that E. bilobatus is a monandric protogynous hermaphrodite. The length and age at which females matured was 278 mm LT and 2.5 years in the Pilbara region, and the lengths and ages at which they changed to males was 336 and 342 mm LT and 6.2 and 6.5 years in the Kimberley and Pilbara, respectively (i.e., less than 5% variation between regions). Based on histology, female E. bilobatus were in spawning condition in all months. However, the mean monthly gonadosomatic indices and proportions of developed/spawning females were highest (i.e., >0.95 and 40%, respectively) for 5 months of the year (i.e., January to April and September). Marginal increment analysis confirmed the annual formation of one opaque and one translucent zone in the sagittal otoliths of this species. Epinephelus bilobatus had a moderate longevity (∼20 years) and attained a larger mean length-at-age in the cooler southern Gascoyne region compared to the more northern Kimberley and Pilbara regions. Three values of natural mortality (M) were used to assess the sensitivity of fishing mortality (F) in the Kimberley and Pilbara commercial trap fisheries, with all point estimates of F < M, indicating that at the time of sampling, the harvest of this species over a long period (>20 years) was sustainable for these contemporary fisheries.

A comparison of fast pulse and conventional LA-ICP-MS detrital zircon geochronology: A large n detrital zircon study from the Centralian Superbasin, northwestern Australia

Over ten thousand detrital zircon U–Pb analyses on thirty four samples were undertaken using a fast pulse laser ablation protocol from the Neoprotoerozoic rocks of the largely unexposed Yeneena and northwestern Officer Basins in Western Australia. In addition, conventional laser ablation detrital zircon U–Pb geochronology was carried out on three of the samples. A comparison of the two datasets demonstrated that no statistical significant difference was observed in the detrital zircon spectra between the two techniques.The results of the detrital zircon analyses reveal that after an intial pulse of material dominated by Archean detritus the sediment are dominated by Mesoproterozic sources. This indicates that there is little variation in source materials within and between the identified formations. The major age peaks coincide with magmatic rock ages from within Australia. The results indicate that either the Palaeoproterozoic and Mesoproterozoic terranes remained sources throughout the deposition of the Yeneena and northwestern Officer Basins during the Neoproterozoic, or that recycling of zircons occurred within a quasi-closed system for the duration of sedimentation. The remaining 10 % of grains are difficult to reconcile with magmatic suites of any significant volume within Australia. However, when considering the broader palaeogeographic context at the time the sediments are inferred to have been deposited, rocks from Dronning Maud Land and the Kalahari Craton can supply grains of appropriate ages and are consistent with the known paleocurrent directions.This work demonstrates that there is no significant disadvantage in the application of the fast pulse technique when applied to the collection of U–Pb detrital zircon datasets for the purpose of detrital zircon fingerprinting. However, there is a large upside related to the significant amount of data that can be collected for a given amount of time compared to other more conventional techniques.

Reinstatement of Thysanotus elatior R.Br. (Asparagaceae)

Thysanotus elatior R.Br. (Asparagaceae) is reinstated, described, lectotypified and compared with putatively related species. The species is restricted to the Top End of the Northern Territory and the Kimberley of Western Australia but was previously confused with T. banksii R.Br., a Queensland species. Notes are provided on the distribution, habitat, phenology, conservation status and affinities of Thysanotus elatior. Thysanotus chinensis Benth. also occurs in north-western Australia and a key to distinguish the two is provided. The application of the names Thysanotus elatior and T. tuberosus R.Br. to material there is also discussed.

Long-term spatial variations in turbidity and temperature provide new insights into coral-algal states on extreme/marginal reefs

Globally, coral reefs are under threat, with many exhibiting degradation or a shift towards algal-dominated regimes following marine heat waves, and other disturbance events. Marginal coral reefs existing under naturally extreme conditions, such as turbid water reefs, may be more resilient than their clear water counterparts as well as offer some insight into how reefs could look in the future under climate change. Here, we surveyed 27 benthic habitats across an environmental stress gradient in the Exmouth Gulf region of north Western Australia immediately following a marine heatwave event. We used multidecadal remotely sensed turbidity (from an in-situ validated dataset) and temperature, to assess how these environmental drivers influence variability in benthic communities and coral morphology. Long-term turbidity and temperature variability were associated with macroalgal colonisation when exceeding a combined threshold. Coral cover was strongly negatively associated with temperature variability, and positively associated with depth, and wave power, while coral morphology diversity was positively associated with turbidity. While moderate turbidity (long-term average ~ 2 mg/L suspended matter) appeared to raise the threshold for coral bleaching and macroalgal dominance, regions with higher temperature variability (> 3.5 °C) appeared to have already reached this threshold. The region with the least turbidity and temperature variability had the highest amount of coral bleaching from a recent heatwave event and moderate levels of both these variables may confer resilience to coral reefs.

Reconstructing the colonization history of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Northwestern Australia.

Bottlenose dolphins (Tursiops spp.) are found in waters around Australia, with T. truncatus typically occupying deeper, more oceanic habitat, while T. aduncus occur in shallower, coastal waters. Little is known about the colonization history of T. aduncus along the Western Australian coastline; however, it has been hypothesized that extant populations are the result of an expansion along the coastline originating from a source in the north of Australia. To investigate the history of coastal T. aduncus populations in the area, we generated a genomic SNP dataset using a double-digest restriction-site-associated DNA (ddRAD) sequencing approach. The resulting dataset consisted of 103,201 biallelic SNPs for 112 individuals which were sampled from eleven coastal and two offshore sites between Shark Bay and Cygnet Bay, Western Australia. Our population genomic analyses showed a pattern consistent with the proposed source in the north with significant isolation by distance along the coastline, as well as a reduction in genomic diversity measures along the coastline with Shark Bay showing the most pronounced reduction. Our demographic analysis indicated that the expansion of T. aduncus along the coastline began around the last glacial maximum and progressed southwards with the Shark Bay population being founded only 13 kya. Our results are in line with coastal colonization histories inferred for Tursiops globally, highlighting the ability of delphinids to rapidly colonize novel coastal niches as habitat is released during glacial cycle-related global sea level and temperature changes.

What came first, the shark or the egg? Discovery of a new species of deepwater shark by investigation of egg case morphology.

Apristurus ovicorrugatus, a new species of deepwater catshark, is described from northwestern Australia. Unique egg cases belonging to an unknown species of Apristurus prompted a more detailed investigation of Apristurus specimens off northwestern Australia. One specimen previously identified as A. sinensis collected off Dampier Archipelago was found gravid with a single egg case. Removal of this egg case confirmed that this species was responsible for producing the unique egg cases previously recorded. The egg cases of this species have strong T-shaped longitudinal ridges on the dorsal and ventral surfaces which are unique in the genus Apristurus. The ridges most closely resemble those present in Bythaelurus canescens from South America, but are larger and always T-shaped. The holotype is closest morphologically to A. sinensis but differs in having a medium brown buccal cavity (vs. jet black), ridged egg cases (vs. smooth egg cases), fewer intestinal spiral valve turns and larger pectoral fins. The holotype is also similar, and closest on a molecular level, to A. nakayai with which it shares a unique synapomorphic character, the white shiny iris (apomorphic within the genus). A late-term embryo removed from an egg case superficially resembled the holotype except in having two parallel rows of enlarged dermal denticles on the dorsolateral predorsal surface. Recent nomenclatural changes to the genera Apristurus and Pentanchus are discussed and challenged. This study highlights the important contribution that egg case morphology has on oviparous elasmobranch taxonomy.

Genomic Relationships of Glycine remota, a Recently Discovered Perennial Relative of Soybean, within Glycine

Abstract— The legume genus, Glycine, which includes the Asian annual cultivated soybean, also includes a group of Australian perennial species comprising the subgenus Glycine. Because the subgenus Glycine represents the tertiary gene pool for one of the world’s most important crops, the group has been the target of collection and study for decades, resulting in a steady growth in the number of formally recognized species, from six in the 1970s to over 20 at present, as well as a number of additional informal taxa. These studies have also produced a system of nuclear diploid “genome groups” corresponding to clades in molecular phylogenies. The aptly named G. remota is known only from a single isolated population in the Kimberley region of northwestern Australia and was named only in 2015. The species is unique within Glycine in having unifoliolate leaves; its discoverers hypothesized that G. remota, if diploid, is related to species of the I-genome that are also native to the Kimberley region. We produced low coverage short-read genome sequencing data from an herbarium specimen of G. remota. Genome size estimates from the sequencing data suggests that G. remota is a diploid, while ploidy estimation is inconclusive likely due to the history of whole genome duplication in Glycine. Phylogenomic analyses of genome-wide SNPs, as well as phylogenetic analyses of the low copy nuclear gene (histone H3D), the entire ribosomal RNA cistron, and the internal transcribed spacer all placed the species unequivocally in the diploid I-genome clade. A complete plastome sequence was also generated and its placement with a plastome phylogeny is also consistent with membership in the I-genome.

Early Permian zircon ages from the P. confluens and P. pseudoreticulata spore-pollen zones in the southern Bonaparte and Canning basins, Northwestern Australia

The Pseudoreticulatispora confluens–P. pseudoreticulata spore-pollen zonal datum typically coincides with the end of widespread Permian glacial deposits in Western Australia. Although previously attributed to the mid-Sakmarian, chemical abrasion isotope dilution thermal ionisation mass spectrometry (TIMS) dating of zircons from volcanic tuffs in the Ditji Formation of the Bonaparte Basin and the Grant Group in the Canning Basin point to an Asselian age of about 295.25 Ma for this datum. All dated zircons from the Ditji Formation came from petroleum well cuttings but the accompanying palynology was mostly from sidewall cores; however, all Grant Group samples were from conventional core. TIMS dates from the Ditji Formation range in age from 295.2 to 292.7 Ma whereas the only productive tuff from the Grant Group yielded a 296.26 Ma date. By comparison, there are no zircon dates to constrain the onset of glacial deposition in Australia. The Bonaparte Basin ages overlap with those for the Edie Tuff (296.1–294.5 Ma) in Queensland’s Galilee Basin, approximately 2000 km to the southeast, which also lies close to the base of the P. pseudoreticulata Zone. To date the only fossil group within the P. confluens Zone in Western Australia to provide independent age control, albeit loosely, are goniatites from the northern Perth Basin (Uraloceras irwinense and Juresanites jacksoni) that have consistently been attributed to the Sakmarian; these require a reassessment of their affinity with Russian faunas and therefore to global stratotypes. The position of the Carboniferous–Permian boundary is elusive in Australia and will remain so until additional volcanic tuffs containing young datable zircons are found; however, spore-pollen and zircon dates from Namibia place this boundary within the P. confluens Zone.

Discovery of Holocene ooid shoals in a siliciclastic delta, De Grey River, North West Shelf, Australia

AbstractOnshore and offshore site investigations along the dryland tide-dominated De Grey River delta (northwestern Australia) led to the unexpected discovery of the largest yet-known marine ooid shoals in the Indo-Pacific region. Ooids exhibit up to 60 tangential aragonitic laminae that were formed around fluvial sediment grains during the late Holocene. Covering an area &amp;gt;1250 km2, their spatial extent rivals in size individual ooid shoals from the Bahamas. Shoals appear to be spatially linked with the De Grey River, suggesting that fluvial outputs, combined with a macrotidal range, facilitated the precipitation of the ooids. Following their formation, ooids were reworked through tidal and wave processes along the delta. As a result, the delta sedimentary features, including beach ridges, mouth bars, and distributary channels, are composed of ooids.This discovery broadens the range of depositional and climatic environments in which ooids can form and demonstrates that fluvial runoff may not inhibit aragonite precipitation. Such a configuration also provides a unique analogue for ancient ooids found in association with siliciclastic grains and further indicates that the interpretation of typical siliciclastic geomorphologies from geophysical data does not preclude the presence of carbonate grains.

Mineralogy and geochemistry of pattern formation in zebra rock from the East Kimberley, Australia

Rhythmic patterns are widespread in geological materials. A particularly striking, macroscale example is zebra rock from the East Kimberley region of northwestern Australia. The rock is famous for its distinctive, rhythmically ordered, iron-oxide pattern, which transforms an Ediacaran-aged siltstone into an attractive semi-precious gemstone. Several different formation mechanisms of this pattern have been proposed in previous studies, with the two most prominent being redoximorphic banding in acid-sulfate soils and Liesegang banding in an acidic hydrothermal system. Using a combination of mineralogy, geochemistry and geological context, this study attempts to confirm both the occurrence and relative timing of acid-sulfate fluid rock interactions in zebra rock and seeks to determine whether pedogenic processes or hydrothermal alteration can better explain the origin of these patterns. We present the first evidence that the iron-oxide banding developed simultaneously with a period of aluminosilicate dissolution, clay precipitation, and fluid flow, consistent with the infiltration of an acidic fluid. This conclusion was evidenced through the hexagonal-platelet morphology of the hematite pigment, kaolinite-hematite textural relationships, and a paleoflow direction preserved in the asymmetric intensity of the hematite concentration. However, while the mineralogy of zebra rock strongly suggests interactions with acid-sulfates, the origin and temperature of the fluid could not be conclusively determined. Supporting a hydrothermal origin, a thorough analysis of zebra rock mineralogy revealed a mineral assemblage consistent with advanced argillic hydrothermal alteration, wherein pyrophyillite, kaolinite, and dickite indicate minimum palaeotemperatures upwards of 120 °C and the presence of alunite and a svanbergite-woodhouseite solid solution suggests oxidising, acidic (pH <5) conditions. The low Rb/Sr ratio and relative immobility of rare earth elements in most zebra rock deposits are also consistent with an acidic hydrothermal origin. Further support was also observed in the mineralogical trends between examined outcrops, grading from alunite-type to kaolinite/dickite-type facies in a south-west direction. But despite this evidence, the acid-sulfate soil hypothesis could not be refuted and was itself supported by the large number of pyrite dissolution voids both underlying and within the patterned layer. Furthermore, the consistent compaction of reduction spheroids, dissolution voids, and pseudomorphic inclusions within the light banding of zebra rock are in agreement with near-surface supergene weathering, ruling out hypogene hydrothermal alteration. A mechanism of pattern formation is proposed whereby zebra rock banding is formed by the Liesegang phenomenon, driven by the oxidation of Fe2+ ions during the infiltration of an Fe2+-rich, acid-sulfate fluid into oxidising host sediments.

Aerial abundance estimates for two sympatric dolphin species at a regional scale using distance sampling and density surface modeling

Monitoring wildlife populations over scales relevant to management is critical to supporting conservation decision-making in the face of data deficiency, particularly for rare species occurring across large geographic ranges. The Pilbara region of Western Australia is home to two sympatric and morphologically similar species of coastal dolphins—the Indo-pacific bottlenose dolphin (Tursiops aduncus) and Australian humpback dolphin (Sousa sahulensis)—both of which are believed to be declining in numbers and facing increasing pressures from the combined impacts of environmental change and extensive industrial activities. The aim of this study was to develop spatially explicit models of bottlenose and humpback dolphin abundance in Pilbara waters that could inform decisions about coastal development at a regional scale. Aerial line transect surveys were flown from a fixed-wing aircraft in the austral winters of 2015, 2016, and 2017 across a total area of 33,420 km2. Spatio-temporal patterns in dolphin density were quantified using a density surface modeling (DSM) approach, accounting for imperfect detection as well as both perception and availability bias. We estimated the abundance of bottlenose dolphins at 3,713 (95% CI = 2,679–5,146; average density of 0.189 ± 0.046 SD individuals per km2) in 2015, 2,638 (95% CI = 1,670–4,168; 0.159 ± 0.135 individuals per km2) in 2016 and 1,635 (95% CI = 1,031–2,593; 0.101 ± 0.103 individuals per km2) in 2017. Too few humpback dolphins were detected in 2015 to model abundance, but their estimated abundance was 1,546 (95% CI = 942–2,537; 0.097 ± 0.03 individuals per km2) and 2,690 (95% CI = 1,792–4,038; 0.169 ± 0.064 individuals per km2) in 2016 and 2017, respectively. Dolphin densities were greatest in nearshore waters, with hotspots in Exmouth Gulf, the Dampier Archipelago, and Great Sandy Islands. Our results provide a benchmark on which future risk assessments can be based to better understand the overlap between pressures and important dolphin habitats in tropical northwestern Australia.

Low Bioerosion Rates on Inshore Turbid Reefs of Western Australia

Bioerosion on inshore reefs is expected to increase with global climate change reducing reef stability and accretionary potential. Most studies investigating bioerosion have focused on external grazers, such as parrotfish and urchins, whose biomass is more easily measured. Yet, cryptic endolithic bioeroders such as macroboring (worms, sponges and bivalves) and microboring taxa (fungus and algae) have the potential to be the dominant source of reef erosion, especially among inshore reef systems exposed to increased nutrient supply. We measured bioerosion rates of bioeroder functional groups (microborers, macroborers, and grazers), and their response to environmental parameters (temperature, light, turbidity, chlorophyll a), as well as habitat variables (coral cover, turfing algae, macroalgae) across two inshore turbid reefs of north Western Australia. Total bioerosion rates were low (0.163 ± 0.012 kg m−2 year−1) likely due to low light and nutrient levels. Macroborers were the dominant source of bioerosion and were positively correlated with turfing algae cover, highlighting the role of turf-grazing fish on endolithic bioerosion rates. Overall low bioerosion rates suggest that despite the reduced coral cover and carbonate production, these reefs may still maintain positive reef accretion rates, at least under current environmental conditions. However, an improved understanding of relationships between environmental drivers, habitat and grazing pressure with bioeroding communities is needed to improve predictions of reef carbonate loss with future climate change.

A focus on flatback turtles: the social acceptability of conservation interventions in two Australian case studies

Human-induced climate change is a threat to marine species and ecosystems worldwide, including sea turtles. As climate changes are projected to intensify, directed management and intervention is required to safeguard the future of vulnerable species and ecosystems. Prioritisation tools that explore the cost-benefit-risk can help in the choice of interventions. However, an often-overlooked element underpinning the success of directed interventions is the extent to which they are perceived as acceptable by local communities (i.e. social acceptability). We assess the social acceptability for a range of adaptation interventions for flatback turtles Natator depressus (FBTs) in north-western Australia. A survey of residents in Port Hedland and Broome showed that FBTs are important to the identity of both towns and local FBT decline or extinction would have negative local social and economic impacts. In both locations, survey respondents expressed strong support for intervening to protect FBTs and there was broad agreement between respondents from both locations on the most and least acceptable interventions. For example, in both locations the most acceptable intervention was to restrict 4-wheel-drive beach access for locals and visitors and the least acceptable was to intervene genetically in the FBT populations. In the case of FBT conservation in Port Hedland and Broome, (1) interventions that limit human behaviour, as opposed to interfering with the species themselves, are likely to be most socially acceptable, and therefore (2) are also most likely to be implemented successfully and avoid conflicts within the community.

Exceptional preservation of organic matter and iron-organic colloidal mineralization in hydrothermal black smoker-type sulfide mineralization from the Paleoarchean seafloor

Fossil organic matter (OM) in Paleoarchean rocks is an invaluable tracer of ancient life, yet it is often contentious due to low preservation potentials of its original organic molecular characteristics under generally high metamorphic grades. This study reports on exceptionally preserved OM within black smoker-type sulfide mineralizations from the 3.24 billion-years-old Sulphur Springs volcanic-hosted massive sulfide deposit, East Pilbara Terrane, northwestern Australia. Fine scale mineralogical and organic molecular variations – documented by SEM and TEM techniques, Raman and FTIR Spectroscopy, as well as ToF-SIMS analysis – trace the formation of millimetre-scale pyritic hydrothermal orifices. Overmature OM (≳200–250 °C) enriched in aromatic hydrocarbons occurs within earliest formed colloform-banded pyrite that could have precipitated at high temperature upon mixing of hot hydrothermal fluids with cold seawater. In contrast, mature OM (within the catagenesis window; ∼100–150 °C) with lower proportions of aromatic hydrocarbons occasionally occurs alongside pyrite within barite near the inner paleofluid conduits of the hydrothermal orifices. A deposition of this OM generation from cooler fluids enriched in sulfate during waning hydrothermal activity is corroborated by its association with original mineralogy, particularly the occurrence of isolated nanoinclusions of OM within hydrothermal barite away from grain boundaries or fissures and cracks, which renders impossible an origin from post-depositional hydrocarbon migration. When compared to the overmature OM within colloform-banded pyrite, the better-preserved inner OM not only contains less abundant, smaller, and less ordered aromatic hydrocarbons, but also higher amounts of aliphatic molecules with longer chain lengths and higher proportions of carbonyl and amide functional groups. Although the latter characteristics are consistent with contributions by microbial biomass, abiotic origins are equally plausible because hydrothermal processes can produce OM with similar organic molecular attributes. Irrespective of these uncertainties on the ultimate sourcing of OM, common intergrowths of the cooler OM with nanoscopic iron oxides – hematite and lesser magnetite – hint at its hydrothermal deposition from colloidal particles that have been stabilized by iron-organic complexation. Further research is required to ascertain the significance of this process for the hydrothermal cycling and release of organic carbons and bound iron into the Paleoarchean oceans. Collectively, our results show that ancient marine hydrothermal systems can preserve OM with differing degrees of thermal degradation, which allows for insights into its sourcing, cycling, and deposition.

A comparison of global mangrove maps: Assessing spatial and bioclimatic discrepancies at poleward range limits

Mangrove distribution maps are used for a variety of applications, ranging from estimates of mangrove extent, deforestation rates, quantify carbon stocks, to modelling response to climate change. There are multiple mangrove distribution datasets, which were derived from different remote sensing data and classification methods, and so there are some discrepancies among these datasets, especially with respect to the locations of their range limits. We investigate the latitudinal discrepancies in poleward mangrove range limits represented by these datasets and how these differences translate climatologically considering factors known to control mangrove distributions. We compare four widely used global mangrove distribution maps - the World Atlas of Mangroves, the World Atlas of Mangroves 2, the Global Distribution of Mangroves, the Global Mangrove Watch. We examine differences in climate among 21 range limit positions by analysing a set of bioclimatic variables that have been commonly related to the distribution of mangroves. Global mangrove maps show important discrepancies in the position of poleward range limits. Latitudinal differences between mangrove range limits in the datasets exceed 5°, 7° and 10° in western North America, western Australia and northern West Africa, respectively. In some range limit areas, such as Japan, discrepancies in the position of mangrove range limits in different datasets correspond to differences exceeding 600 mm in annual precipitation and > 10 °C in the minimum temperature of the coldest month. We conclude that dissimilarities in mapping mangrove range limits in different parts of the world can jeopardise inferences of climatic thresholds. We expect that global mapping efforts should prioritise the position of range limits with greater accuracy, ideally combining data from field-based surveys and very high-resolution remote sensing data. An accurate representation of range limits will contribute to better predicting mangrove range dynamics and shifts in response to climate change.