Ningaloo Research Articles

Ectoparasites of the Critically Endangered Giant Shovelnose Ray Glaucostegus typus in the Eastern Indian Ocean, with a Summary of the Known Metazoan Parasites.

This study examined the metazoan ectoparasites of the Critically Endangered giant shovelnose ray, Glaucostegus typus, in the eastern Indian Ocean. We screened 186 G. typus for ectoparasites in four coastal regions of Western Australia between 2020 and 2022: the Pilbara Region, Exmouth Gulf, Ningaloo Coast and Shark Bay. Five parasite taxa were encountered on 186 G. typus: Caligus furcisetifer (Copepoda: Caligidae), Dermopristis cairae (Monopisthocotyla: Microbothriidae), Branchellion plicobranchus and Stibarobdella macrothela (Hirudinida: Piscicolidae), and praniza larvae of unidentified gnathiid isopod/s (Isopoda: Gnathiidae). Two of these species, B. plicobranchus and S. macrothela, are reported for the first time on G. typus. Only C. furcisetifer and S. macrothela were relatively common, encountered on 31% and 40% of G. typus, respectively. Gnathiids were observed infrequently, encounteredon 13% of G. typus, and D. cairae and B. plicobranchus were scarce, encountered on 1% and 2% of G. typus, respectively. Intensity of infection for C. furcisetifer and gnathiids increased with host length. Likelihood of infection varied seasonally for C. furcisetifer, being considerably lower in summer, and regionally for gnathiids, being greatest at Shark Bay. Intensity and likelihood of infection for S. macrothela increased with host length and varied regionally, being greatest at Shark Bay. These findings improve our understanding of the downstream impacts for dependent parasites that might arise should populations of G. typus continue to decline.

Whale shark (Rhincodon typus) observed gulping on the seafloor at Ningaloo reef aggregation site

Whale shark (Rhincodon typus) observed gulping on the seafloor at Ningaloo reef aggregation site

Can juvenile supply predict future abundance of large-bodied reef fishes?

The extent to which juvenile abundance can predict future populations of lethrinids at Ningaloo Reef was assessed using size frequency data collected over 13 consecutive years. Annual abundance of juvenile lethrinids (<5 cm TL) was highest in northern Ningaloo during La Niña years, when seawater is warmer and oceanic currents stronger. Juvenile lethrinid abundance explained 35% of the variance in 1–2 year-old Lethrinus nebulosus abundance the following year, a steeper relationship in the north suggesting greater survival of juveniles. Juvenile lethrinid abundance was also positively correlated to abundance of 1–2 year-old L. atkinsoni in the southern region of Ningaloo. Abundance of juvenile lethrinids were however poor predictors of L. nebulosus and L. atkinsoni older than 2 years of age. Post settlement processes likely weaken the link between juvenile supply and abundance of lethrinids >2 years old making it difficult to accurately quantify the overall size of future lethrinid populations.

Biogeographical diet variation within and between the rabbitfishes Siganus corallinus, Siganus doliatus, Siganus trispilos and Siganus virgatus.

Feeding habits of herbivorous fishes play an important role in shaping the form and function of coastal marine ecosystems. Rabbitfishes (Siganidae) are important consumers of macroalgae on Indo-West Pacific coral reefs. However, it is unclear how their diet varies among and within species at biogeographical scales, casting doubt on their precise functional roles across different regions. The present study assessed the inter- and intra-specific diet variation of four rabbitfishes (Siganus trispilos, Siganus corallinus, Siganus virgatus and Siganus doliatus) factored by morphological relatedness among populations from Ningaloo Reef (western Australia), the Great Barrier Reef (GBR, eastern Australia) and the Yaeyama Islands (Okinawa Prefecture, Japan). Results showed that the region had a strong effect on diet, effectively reducing the expected effect of morphologic similitude. While intra-specific differences were only significant when populations inhabited different regions; interspecific differences were not as predicted, with different morphotypes having similar diets when populations inhabited the same regions. Rabbitfishes consumed more corticated and filamentous macroalgae on the GBR, more foliose and membranous macroalgae at the Yaeyama Islands, and more leathery macroalgae at Ningaloo Reef. The findings indicate that rabbitfishes have high diet plasticity, and hence their functional role as mediators of competition between macroalgae and corals can change across biogeographic regions. Local context is therefore important when assessing the diet and functional role of herbivorous fishes. As climate change unfolds, shifts in the distribution, trophic behaviour and function of species are expected, making the study of trophic plasticity more important.

High rates of erosion on a wave‐exposed fringing coral reef

AbstractErosion is a key process in shaping the physical structure of coral reefs, yet due to erosion being semi‐cryptic and difficult to quantify, information remains limited. Here, we investigate erosional processes along Ningaloo Reef, an extensive fringing coral reef in Western Australia. We employed both direct and indirect methods to measure erosion in wave‐exposed reef slopes and protected lagoonal habitats. Direct measurements of erosion on coral blocks were among the highest found globally, with total erosion of 3.07 kg m−2 yr−1 (4% from micro, 0.6% from macro, and 94% from external), whilst indirect rates were estimated at 2.4 ± 0.20 kg m−2 yr−1 (78% from parrotfish, 22% from urchins). Indirect erosion rates were influenced by the species and size of parrotfish, with Chlorurus microrhinos removing 0.44 ± 0.19 kg m−2 yr−1 (22% of parrotfish erosion). Scanning electron microscopy and computed tomography show that micro and macroborer erosion contributions to direct erosion were low, most likely due to heavy grazing by parrotfish and the short deployment period of experimental substrates. A substantial portion of external erosion on blocks (0.53 ± 0.23 kg m−2 yr−1) could not be attributed to bioeroders and was poorly correlated with wave exposure, suggesting processes not quantified contribute to this unaccounted aspect of erosion. Our results confirm that bioerosion by parrotfish is especially significant at Ningaloo Reef, and large‐bodied individuals of C. microrhinos are key in conserving this key ecological process.

Deoxygenation following coral spawning and low-level thermal stress trigger mass coral mortality at Coral Bay, Ningaloo Reef

Oxygen depletion is well recognized for its role in the degradation of tropical coral reefs. Extreme acute hypoxic events that lead to localized mass mortality and the formation of ‘dead zones’ (a region where few or no organisms can survive due to a lack of oxygen) are particularly concerning as they can result in wide-ranging losses of biodiversity, ecosystem productivity and functioning, economic prosperity, and wellbeing. In March of 2022, the annual coral spawning event at Bills Bay (Coral Bay, Ningaloo Reef, Western Australia) coincided with elevated seawater temperature, calm weather conditions and a flood tide resulting in coral spawn becoming trapped in Bills Bay. Immediately after, there was a mass fish kill, which is believed to have been caused by local eutrophication resulting in severe oxygen depletion. The impact the deoxygenation and thermal stress event had on benthic communities has not yet been quantified; hence, the principal aim of this study is to document the extent of change that occurred in the benthic communities before and after the 2022 coral spawning event over a spatial gradient from the nearshore to mid-reef. Percent coral cover in the Bay decreased from 55.62 ± 2.26% in 2016–2018 and 70.44 ± 5.24% in 2021 to 1.16 ± 0.51% in 2022. Over the same period, the percent cover of turf algae increased from 27.40 ± 2.00% in 2016–2018 and 24.66 ± 6.67% in 2021 to 78.80 ± 3.06% in 2022, indicating a dramatic phase shift occurred at Bills Bay. The abundance of healthy coral colonies recorded on replicated belt transects at nine sites declined from 3452 healthy individuals in 2018 to 153 individuals in 2022 and coral generic richness decreased by 84.61%, dropping from 26 genera in 2018 to 4 genera in 2022. Previously dominant genera such as Acropora,Montipora and Echinopora, were extirpated from survey sites. Isolated colonies of massive Porites spp. and encrusting Cyphastrea sp. survived the event and understanding the mechanisms underpinning their greater survivorship is an important area of future research. Long-term monitoring is recommended to track the community recovery process and improve our understanding of the longer-term implications of this acute mortality event on the ecological, socio-economic and cultural values of Ningaloo Reef.

Swimming with humans: biotelemetry reveals effects of “gold standard” regulated tourism on whale sharks

Wildlife tourism can benefit conservation of target species, however, it can have detrimental effects on animal behaviour and physiology. Whale shark Rhincodon typus tourism has seen recent rapid growth globally, but methods and regulations vary widely. Ningaloo Reef, Australia is considered “gold standard” whale shark tourism management due to legal regulation, strict enforcement, and high compliance. Rather than relying on observational data, we used biotelemetry to collect high-resolution data (20 Hz) on whale sharks’ movement behaviour in the presence or absence of tourists. Tourism encounters lasted an average of 62 min and swimming with tourists increased the activity levels of larger (> 7 m) but not smaller sharks. Given that activity levels positively correlate with energetic costs, it is likely the 18% increase seen in activity of large sharks would have incurred additional energetic costs. However, when considered as a proportion of daily energy requirements, these additional costs were only incurred for an average of 4% of a whale shark’s day. The tourism-induced impacts we found on the endangered whale sharks at this highly regulated tourism site would not have been apparent from purely observational studies, highlighting the utility of biotelemetry to quantify tourism-related impacts on wildlife.

Links between the three-dimensional movements of whale sharks (Rhincodon typus) and the bio-physical environment off a coral reef

BackgroundMeasuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks (Rhincodon typus) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis.MethodsHere, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km.ResultsWe identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers.ConclusionsOur work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.

Collaborative methods identify a remote global diversity hotspot of threatened, large‐bodied rhino rays

Abstract North‐western Australia is considered a refuge to several highly threatened elasmobranch species, but there has been little research effort targeting lesser known, large‐bodied rhino rays. This study identified 2,343 records of globally threatened rays of the order Rhinopristiformes from the Pilbara region of Western Australia, with a focus on the Ningaloo Coast World Heritage Area and adjacent Exmouth Gulf. Occurrence data were compiled from various sources including commercial fishing reports (35%), citizen science records (34%), targeted scientific surveys (30%) and published literature (1%). The region was inhabited by all of Australia's Pristidae (four sawfish species), all of Australia's Rhinidae (three wedgefish species) and the sole Australian representative of the Glaucostegidae (giant shovelnose ray). Of the 2,343 records, ~49% were sawfishes, while giant guitarfish and wedgefishes contributed to ~33% and 18% of records, respectively. The Exmouth Gulf appears to be a globally important refuge and pupping area for green sawfish (Pristis zijsron) which was the most commonly encountered pristid. Bottlenose wedgefish (Rhynchobatus australiae) were the most commonly identified rhinid, with less frequent encounters of shark rays (Rhina ancylostoma) and eyebrow wedgefish (Rhynchobatus palpebratus). The Ningaloo Coast World Heritage Area and adjacent Exmouth Gulf host all life stages of giant shovelnose ray (Glaucostegus typus). The combined use of several data sources has highlighted the study region as a ‘lifeboat’ for these globally threatened large‐bodied rays. These data are essential in creating effective conservation and management plans in this globally important refuge, and are highly relevant to global conservation initiatives.

Exposure of marine megafauna to cumulative anthropogenic threats in north-west Australia

As the use of coastal and offshore environments expands, there is a need to better understand the exposure of marine megafauna to anthropogenic activities that potentially threaten their populations. Individual satellite telemetry studies are often hampered by small sample sizes, providing limited information on spatiotemporal distributions of migratory animals and their relationships to anthropogenic threats. We addressed this issue by synthesising satellite tracking data from 484 individuals of three taxonomic groups and six species; three marine turtle, two whale and one shark. The spatial overlap between taxa distributions and multiple anthropogenic activities was assessed as a proxy for the cumulative exposure of these taxa to anthropogenic threats (coastal modification, vessel strike, underwater noise, oil spill, bycatch, entanglement, and artificial light) across an area totalling 2,205,740 km2 off north-western Australia. Core exposure areas (top 50% of the distribution) encompassed ecologically important sites for all taxa, such as the Ningaloo and Pilbara regions, migratory routes for whales and sharks in offshore waters beyond Ningaloo Reef, and marine turtle nesting beaches at Barrow Island and Cape Lambert. Although areas of high exposure represented &amp;lt;14% of taxa distributions, we showed that no taxa occurred in the absence of threats and that even areas with existing spatial protections are experiencing high levels of exposure. Importantly, we developed a robust approach for documenting the potential exposure of marine species to a range of human activities at appropriate spatial scales to inform conservation management.

Stable isotopes reveal sargassum rafts provide a trophic subsidy to juvenile pelagic fishes

Floating macroalgal rafts can form extensive habitat in coastal waters and support abundant and diverse communities of juvenile fishes. Rafts comprised predominantly of Sargassum spp. are common within the Ningaloo Coast World Heritage Area, Western Australia, and may be an important transitional habitat for pre-settlement coastal fishes. We had three aims: 1) to quantify the diversity and abundance of fishes associated with Sargassum rafts; 2) to use stable isotopes to determine whether fishes associating with rafts preyed on nearby plankton or on prey associated with Sargassum; and 3) to determine whether the food web fishes relied upon was ultimately supported by primary production of Sargassum or planktonic phytoplankton (measured as seston). Fishes and macroinvertebrates associating with Sargassum rafts, zooplankton, and seston were collected at six sites in the Ningaloo Marine Park and analysed for δ15N and δ13C, and the diets of the most common fishes were analysed using MixSIAR. Fishes were more abundant around macroalgal rafts than in open water. Eleven species of juvenile fishes associated with Sargassum rafts, with one species (Histrio histrio (Antennariidae)) represented by juveniles and adults. Four of the five fishes most sampled around Sargassum spp. rafts, (Abudefduf vaigiensis (Pomacentridae), Helotes sexlineatus (Terapontidae), Colurodontis paxmani (Monacanthidae) and Petroscirtes breviceps (Blenniidae)) had generalist diets whose food webs were ultimately supported by greater contributions of primary production from Sargassum spp. (55–72%) than planktonic seston. H. histrio was predominantly piscivorous but still derived most (64%) of its organic matter indirectly from Sargassum spp. Our results reveal the importance of Sargassum rafts as habitat that provides shelter and food for juvenile fishes and adult H. histrio. Moreover, the prevalence of juvenile fishes associating with Sargassum rafts highlights a bidirectional form of benthic-pelagic coupling whereby macroalgae that detach from the benthos provide habitat and a trophic subsidy for pelagic juvenile fishes before they the transition into benthic coastal habitats.

Stomach eversion and retraction by a tagged tiger shark at Ningaloo Reef, Western Australia

Stomach eversion is common in sharks captured during fishing activities, however, records of subsequent retraction of the stomach once animals are released are rare and limited by the logistics of recording post-release behaviors in the wild. Here, we report stomach eversion and retraction by a tiger shark captured and tagged at Ningaloo Reef, Western Australia. Initial eversion occurred during capture, and retraction was recorded by video and tri-axial acceleration sensors approximately five minutes after release. The ability to retract the stomach without apparent ill effect is consistent with the documented resilience of tiger sharks to stressful capture events, but remains to be confirmed for other species.

Vocalizations of two conspecific damselfish (Pomacentridae) at two Australian World Heritage sites: The Ningaloo Coast and the Great Barrier Reef

Novel methods to use Ocean Sound to address ecological questions are increasingly being developed but require optimization and validation to ensure their reliability. Source validation, increasing the number of known soniferous species of marine fauna, and characterizing their acoustic repertoires are important components of this effort. Coral reefs are remarkably complex, diverse, and noisy environments, inhabited by many soniferous species, hindering the association of vocalizations with the emitting species. Damselfish (Pomacentridae) are common and conspicuous reef fishes that have been relatively well-studied due to their abundance, territorial behaviors, and sound production. Most fish sound studies support that fish vocalizations are species-specific, often showing niche acoustic partitioning to avoid competition across frequency and time. It is imperative to record fish vocalizations in the field to avoid distortion in their acoustic attributes, which then can be used for further analyses such as automated detections. Here, we characterize the vocalizations of Dascyllus aruanus and Dascyllus reticulatus using field-experimental settings for in situ recordings from the Ningaloo Coast and the Great Barrier Reef. [Work supported by the BHP-AIMS Australian Coral Reef Resilience Initiative. JCAS was supported by Curtin University and BHP-AIMS in the form of a Curtin Strategic Scholarship and Top-up Scholarship.]

Cryptic biodiversity: A portfolio‐approach to coral reef fish surveys

AbstractBiodiversity conservation and management requires surveillance that captures the full spectrum of taxa. Here, we showcase the potential for a portfolio of visual, extractive, and molecular methods for detecting previously hidden components of tropical fish biodiversity in an economically and culturally valuable marine site that spans a tropical‐temperate ecotone—the Ningaloo Coast World Heritage Area. With scale and practicality in mind, we demonstrate how environmental DNA (eDNA) methods deployed in a stratified sampling design can yield a more comprehensive monitoring program for species presence than current alternatives (e.g., extractive sampling via anesthetic). eDNA from filtered water samples detected up to six times as many cryptobenthic fish species per site than samples collected with anesthetic, indicating it is a potentially powerful tool for assessing biodiversity of tropical fishes. However, there were also species that were only found when using anesthetic and the contribution of cryptobenthic species to overall diversity of the fish assemblage was unexpectedly low, suggesting not all cryptobenthic fish species have been detected with eDNA. There were also distinct differences in cryptobenthic assemblages both among sites and sample depths (2–3 m) when using eDNA from filtered water, suggesting this technique may be able to identify fine scale spatial differences in cryptobenthic fish assemblage. eDNA collected from water detects the most cryptobenthic species and is therefore an efficient tool for rapidly assessing biodiversity, but extractive techniques may still be required for biological and monitoring studies, and when combined with eDNA sampling provides the most comprehensive assessment of cryptobenthic fishes.

Parasitic Copepods as Biochemical Tracers of Foraging Patterns and Dietary Shifts in Whale Sharks (Rhincodon typus Smith, 1828)

Understanding the diet of whale sharks (Rhincodon typus) is essential for the development of appropriate conservation strategies for the species. This study evaluated the use of the parasitic copepod (Pandarus rhincodonicus) as a proxy to infer short-term foraging habitats and trophic positions of whale shark hosts. To accomplish this, bulk stable carbon (δ13C) and nitrogen (δ15N) isotope compositions were analysed from 72 paired samples of whale shark skin (dermal) tissues and copepods collected across six years at the Ningaloo Reef aggregation site, Western Australia. This study found that δ15N from parasites and whale shark hosts were strongly correlated. As turn-over times of the parasite and whale shark differ (months vs. years, respectively), the ability of copepods to predict δ15N values indicates that the trophic positions of whale sharks remain consistent across these timeframes. Contrastingly, δ13C in the parasite and host were weakly correlated, likely reflecting differences in the physiology and lifecycle of the copepod parasite compared to the host. Our results suggest δ15N from parasitic copepods provides a reliable proxy of the trophic position of their whale shark hosts, but interpretation of δ13C values as a proxy for the host will require future studies on the lifecycle of P. rhincodonicus.

KANNAPHALLUS RAPHIDIUM N. SP. (MONOGENOIDEA: MAZOCRAEIDEA: HETERAXINIDAE) PARASITIC ON THE GILL LAMELLAE OF THE GOLDEN TREVALLY GNATHANODON SPECIOSUS (CARANGIFORMES: CARANGIDAE) OCCURRING IN THE COASTAL WATERS OF QUEENSLAND AND WESTERN AUSTRALIA.

An undescribed species of KannaphallusUnnithan, 1957 (Monogenoidea: Heteraxinidae) was collected from the gills of the golden trevally Gnathanodon speciosus (Forsskål) (Carangidae) from Moreton Bay, Queensland, during January 2016 and from Ningaloo Reef, Western Australia, during December 2021 and June 2022. The diagnosis for Kannaphallus was emended and the new species, Kannaphallus raphidium, was described. Kannaphallus virilis of Young, nec Unnithan was placed in synonymy with K. raphidium. The distal components of the male reproductive system and the arrangement of the clamp rows of the haptor occurred as mirror images among specimens of K. raphidium, suggesting that the respective antipodes of K. raphidium may have reproductive implications and function in the site selection of the parasite on the host's gills. A specimen of K. raphidium from Western Australia was sequenced for the cytochrome c oxidase subunit 1 (COI) mtDNA and ITS2 rDNA barcoding markers, and the phylogenetically informative 28S rDNA marker. Maximum likelihood and Bayesian inference analyses based on a partial 28S rDNA alignment, including all comparable heteraxinid sequence data available, resolved the Heteraxininae and Cemocotylinae as reciprocatively paraphyletic and provided evidence that Kannaphallus may be paraphyletic. No taxonomic changes concerning the subfamilies and genera of the Heteraxinidae were proposed. Finally, Kannaphallus univaginalisRamalingam, 1960 and Cemocotylelloides univaginalis (Ramalingam, 1960) Nitta, Kondo, Ohtsuka, Kamarudin, and Ismail, 2022 are considered nomen nuda sensu the International Code of Zoological Nomenclature.

The short spined crown-of-thorns starfish Acanthaster brevispinus is a corallivore too

The short spined crown-of-thorns starfish Acanthaster brevispinus inhabits deeper water soft bottom habitats, in contrast to the more infamous Indo-Pacific Acanthaster species complex of which population outbreaks have been responsible for widespread coral mortality throughout the Indo-West Pacific region. Acanthaster brevispinus has not previously been regarded as a threat to corals or coral reefs. Here, we report A. brevispinus occurring on mesophotic off-reef or inter-reef habitats in 20–70-m depths dominated by solitary corals off both the western and eastern coasts of Australia. On Ningaloo Reef, A. brevispinus were found on mushroom coral (Cycloseris distorta) beds using an underwater towed camera and further exploration using a remotely operated vehicle (ROV) confirmed predation by A. brevispinus on C. distorta. On the southern Great Barrier Reef, A. brevispinus in large numbers were found in habitat dominated by the dendrophylliid Heteropsammia cf. cochlea. Predation on H. cf. cochlea was also directly observed. This is the first confirmed report of predation on hard corals by A. brevispinus, and while there are yet to be any records of population outbreaks of this species, such outbreaks could have a significant effect on mesophotic solitary coral assemblages.

Assessment of Tropical Cyclone Risk to Coral Reefs: Case Study for Australia

In this study, we attempt to expand tropical cyclone (TC) risk assessment methodology and build an understanding of TC risk to Australia’s natural environment by focusing on coral reefs. TCs are natural hazards known to have the potential to bring destruction due to associated gale-force winds, torrential rain, and storm surge. The focus of TC risk assessment studies has commonly centred around impacts on human livelihoods and infrastructure exposed to TC events. In our earlier study, we created a framework for assessing multi-hazard TC risk to the Australian population and infrastructure at the Local Government Area level. This methodology is used in this study with coral reefs as the focus. TC hazard, exposure, and vulnerability indices were created from selected coral-related datasets to calculate an overall TC risk index for the Ningaloo Reef (NR) and the Great Barrier Reef (GBR) regions. The obtained results demonstrate that the northern NR and the southern GBR had the highest risk values within the study area; however, limitations in data quality have meant that results are estimates at best. The study has shown the potential benefits of such a TC risk assessment framework that can be improved upon, as coral data collection becomes more readily available.

Distinct coral reef habitat communities characterized by environmental DNA metabarcoding

Coral reefs are biodiversity hotspots, places of high endemicity and provide essential services to billions of people globally. With increasing threats to these reefs worldwide, there is a need to implement faster, more efficient ways to monitor spatial and temporal patterns of biodiversity. Environmental DNA (eDNA) metabarcoding offers a promising tool to address this issue, as it has revolutionized our ability to monitor biodiversity from complex environmental samples such as seawater. However, the capacity for eDNA to resolve fine scale shifts in community composition across habitats in seascapes is yet to be fully explored. Here, we applied eDNA metabarcoding using the rRNA 18S Universal eukaryote assay to explore differences in community profiles between samples collected from the lagoon and reef slope habitats across more than 170 km of the Ningaloo Coast World Heritage Area in Western Australia. We recovered 2061 amplicon sequence variants that comprised of 401 taxa spanning 14 different metazoan phyla such as cnidarians, poriferans, molluscs, algae, worms, and echinoderms. Our results revealed strong clustering of samples by habitat type across the length of the reef. Community dissimilarity (beta diversity) between samples collected from the reef slope and lagoon habitats was high and was driven largely by a strong rate of spatial turnover, indicating a distinct set of taxa representing each reef zone community. We also detected a strong pattern of isolation by distance within our slope samples, suggesting that communities are spatially stratified across the length of the reef. Despite high connectivity due to regular flushing of the lagoon environment, our results demonstrate that metabarcoding of seawater eDNA from different habitats can resolve fine scale community structure. By generating multi-trophic biodiversity data, our study also provided baseline data for Ningaloo from which future changes can be assessed.

Spiroisoxazoline Inhibitors of Acetylcholinesterase from Pseudoceratina verrucosa. Quantitative Chiroptical Analysis of Configurational Heterogeneity, and Total Synthesis of (±)-Methyl Purpuroceratate C.

Examination of the MeOH extract of the sponge, Pseudoceratina cf. verrucosa, Berquist 1995 collected near Ningaloo Reef, Western Australia for selective acetylcholinesterase (AChE) inhibitors, yielded five new bromotyrosine alkaloids, methyl purpuroceratates A and B (1b and 2b), purpuroceratic acid C (3a), and ningalamides A and B (4 and 5). The structures of 1-4 share the dibromo-spirocyclohexadienyl-isoxazoline (SIO) ring system found in purealidin-R, while ketoxime 5 is analogous to ianthelline and purpurealidin I. The planar structures of all five compounds were obtained from analysis of MS, 1D and 2D NMR data, and the absolute configuration of the spiroisoxazoline (SIO) unit was assigned by electronic circular dichroism (ECD) and comparison with standards prepared by total synthesis of methyl purpuroceratate C, (±)-3b. Compound 4 is the most complex SIO described, to date. The configuration of the homoserine module (C) in 4 was ascertained, after acid hydrolysis, by derivatization of an l-tryptophanamide derivative based on Marfey's reagent. Chiral-phase HPLC, with comparison to synthetic standards, revealed that most SIOs isolated from P. cf. verrucosa were configurationally heterogeneous; some, essentially racemic. Chiral-phase HPLC, with UV-ECD detection, is demonstrated as a superlative method for configurational assignment and quantitation of the enantiomeric composition of SIOs. Two SIOs─aerophobin-1 and aplysinamisine II─emerged as selective inhibitors of AChE over butyrylcholinesterase (BuChE, IC50 ratio >10), while aplysamine-2 moderately inhibited both cholinesterases (ChEs, IC50, (AChE) 0.46 μM; IC50, (BuChE) 1.03 μM). SIO alkaloids represent a potential new structural manifold for lead-discovery of new therapeutics for treatment of Alzheimer's disease.