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Context Species classification disputes can be resolved using integrative taxonomy, which involves the use of both phenotypic and genetic information to determine species boundaries. Aims Our aim was to clarify species boundaries of two commercially important cryptic species of halfbeak (Hemiramphidae), whose distributions overlap in south-eastern Australia, and assist fisheries management. Methods We applied an integrative taxonomic approach to clarify species boundaries and assist fisheries management. Key results Mitochondrial DNA and morphological data exhibited significant differences between the two species. The low level of mitochondrial DNA divergence, coupled with the lack of difference in the nuclear DNA, suggests that these species diverged relatively recently (c. 500 000 years ago) when compared with other species within the Hyporhamphus genus (>2.4 million years ago). Genetic differences between the species were accompanied by differences in modal gill raker counts, mean upper-jaw and preorbital length, and otolith shape. Conclusions On the basis of these genetic and morphological differences, as well as the lack of morphological intergradation between species along the overlapping boundaries of their geographical distributions, we propose that Hyporhamphus australis and Hyporhamphus melanochir remain valid species. Implications This study has illustrated the need for an integrative taxonomic approach when assessing species boundaries and has provided a methodological framework for studying other cryptic fish species in a management context.

A new species of deep-water epinephelid fish is described from the west coast of Australia based on 14 specimens, 99-595 mm standard length. Hyporthodus griseofasciatus sp. nov. is endemic to Western Australia from Barrow Island to Two Peoples Bay in depths of 76-470 m. It has a series of eight grey bands alternating with eight brown bands along the body and the soft dorsal, soft anal and caudal fin margins are pale cream to white. It is distinguished from its nearest congener, H. ergastularius, by the presence of a star-like pattern of radiating lines on the head versus an overall brownish colour in the latter as well as significant differences in the quantitative analyses of 25 morphological characters. The two species have allopatric distributions on either side of the Australian continent. H. griseofasciatus is distinguished from H. octofasciatus by several grey bands being distinctly narrower than other grey bands (vs. all grey bands subequal in the latter) and the presence of broad white margins on the dorsal, caudal and anal fins (vs. narrow or absent in the latter). Some scale counts appear to also differ. Analyses of mitochondrial cytochrome oxidase subunit 1 sequences revealed reciprocally monophyletic clades with fixed differences and genetic distances typical of recently diverged species of fishes.

Environmental DNA (eDNA) is increasingly being used to assess community composition in marine ecosystems. Applying eDNA approaches across broad spatial scales now provide the potential to inform biogeographic analyses. However, to date, few studies have employed this technique to assess broad biogeographic patterns across multiple taxonomic groups. Here, we compare eDNA‐derived communities of bony fishes and invertebrates, including corals and sponges, from 15 locations spanning the entire length of the Omani coast. This survey includes a variety of habitats, including coral and rocky reefs, and covers three distinct marine ecoregions. Our data support a known biogeographic break in fish communities between the north and the south of Oman; however, the eDNA data highlight that this faunal break is mostly reflected in schooling baitfish species (e.g., sardines and anchovies), whereas reef‐associated fish communities appear more homogeneous along this coastline. Furthermore, our data provide indications that these biogeographic breaks also affect invertebrate communities, which includes corals, sponges, and broader eukaryotic groups. The observed community shifts were correlated with local environmental and anthropogenic differences characteristic of this coastline, particularly for the eDNA‐derived bony fish communities. Overall, this study provides compelling support that eDNA sequencing and associated analyses may serve as powerful tools to detect community differences across biogeographic breaks and ecoregions, particularly in places where there is significant variation in oceanographic conditions or anthropogenic impacts.

Monitoring plans using environmental DNA have the potential to offer a standardized and cost‐efficient method to survey biodiversity in aquatic ecosystems. Among these ecosystems, coastal wetlands are key elements that serve as transition zones between marine and freshwater ecosystems and are today the target of many conservation and restoration efforts. In this sense, eDNA monitoring could provide a rapid and efficient tool for studying and generating baseline biodiversity information to guide coastal wetland management programs. Here, we test an eDNA metabarcoding assay as a tool to characterize vertebrate biodiversity in one of the largest coastal wetlands of Chile, the Rio Cruces Wetland, a Ramsar designated site since 1981. We sampled surface water from 49 sites along the entire wetland. Our eDNA approach detected 91genera of vertebrates including amphibians, fishes, mammals, and birds, as well as identified several cryptic, exotic, and endangered species. Our results also indicated that the spatial distribution of eDNA from different species is spatially structured despite the complex hydrodynamics inherent in this wetland due to the influence of daily tidal regimes. For amphibians and fishes, the number of taxa detected with eDNA was higher in the periphery of the wetland, and increased with proximity to the ocean, a pattern consistent with small‐scale spatial sensitivity for some species and eDNA accumulation downstream for others. Birds and mammals showed somewhat more idiosyncratic distributions. Taken together, our results add to the growing body of evidence showing eDNA can serve as a rapid cost‐effective tool to characterize vertebrate communities in protected coastal wetlands, where visual surveys are difficult and animal collections are often prohibited. The use of multiple primer sets is also recommended as it facilitates the detection of ephemeral terrestrial organisms and resident aquatic organisms that make use of these wetlands.

Rising temperatures and extreme climate events are propelling tropical species into temperate marine ecosystems, but not all species can persist. Here, we used the heatwave-driven expatriation of tropical Black Rabbitfish (Siganus fuscescens) to the temperate environments of Western Australia to assess the ecological and evolutionary mechanisms that may entail their persistence. Population genomic assays for this rabbitfish indicated little genetic differentiation between tropical residents and vagrants to temperate environments due to high migration rates, which were likely enhanced by the marine heatwave. DNA metabarcoding revealed a diverse diet for this species based on phytoplankton and algae, as well as an ability to feed on regional resources, including kelp. Irrespective of future climate scenarios, these macroalgae-consuming vagrants may self-recruit in temperate environments and further expand their geographic range by the year 2100. This expansion may compromise the health of the kelp forests that form Australia’s Great Southern Reef. Overall, our study demonstrates that projected favourable climate conditions, continued large-scale genetic connectivity between populations, and diet versatility are key for tropical range-shifting fish to establish in temperate ecosystems., Laura Gajdzik et al. used population genomics, dietary DNA metabarcoding, and climate models to understand the influence of the 2010/2011 marine heatwave on the migration of rabbitfish from tropical environments into temperate environments in Western Australia. Their results reveal (i) little genetic differentiation and high migration rates between tropical residents and temperate vagrants, (ii) an overall diverse diet (including phytoplankton, local and widespread algae, and kelp), and (iii) projected suitable climate conditions for vagrants to establish in temperate marine waters.

Determining how growth rates and body size vary spatially and among reef fish species is important to understanding functional traits and demographic trade-offs. Variability in reef fish growth trajectories may be influenced by intrinsic (e.g., biological, phylogenetic) and extrinsic factors (e.g., environmental), as well as their interaction via ecological processes. To assess interspecific variation in these traits, we estimated age and growth for a guild of butterflyfishes sampled from reefs spanning ~ 10˚ degrees of latitude in the Red Sea to the adjacent Gulf of Aden. This study region was chosen because it spans environmental gradients known to influence fish life history traits and allowed for comparisons between regional versus more widespread butterflyfish species. Across the 10 study species, we found significant interspecific differences in growth. This finding contrasted with almost no intraspecific differences between populations across the study region. Moreover, we found that maximum body size was significantly correlated with the phylogenetic placement of the butterflyfish species. These patterns suggest that intrinsic factors and a high degree of ecological specialization may elicit spatially conservative demographic profiles, even when faced with considerable environmental variation across a region.

Fishes represent an important natural resource and yet their diversity and function in dynamic estuaries with relatively high levels of human pressure such as Sydney Harbour have rarely been quantified. Further, Eastern Australia supports the survival and persistence of an increasing number of tropical species found within temperate estuaries owing to increasing average ocean temperatures. A re-valuation of the number of fish species known from Sydney Harbour is therefore needed. In this study, we generated an up-to-date and annotated checklist of fishes recorded from Sydney Harbour based on verified natural history records as well as newly available citizen science records based on opportunistic observations and structured surveys. We explored the spatial and temporal distribution of these records. In addition, we quantified the function, conservation status, and commercial importance of the identified fishes. The number of fish species recorded from Sydney Harbour now stands at 675, an increase of 89 species (15 %) when compared to the most recent evaluation in 2013. We attribute this increase in fish diversity over a relatively short time to the contribution of newer citizen science programs as well as the influx and survival of fishes in the Harbour with preferences for warmer waters. Some fish families were also overrepresented in the more urbanized and polluted sections of the Harbour. In forecasting further environmental impacts on the fishes of Sydney Harbour, we recommend increased integration of collaborative citizen science programs and natural history collections as a means to track these changes.

Analysis of environmental (e)DNA can facilitate an understanding of the presence and distribution of aquatic species. However, eDNA detection using quantitative PCR requires validated and standardized species-specific assay designs. This study presents two eDNA assays to detect Murray cod, Maccullochella peelii, and mulloway, Argyrosomus japonicus (two ecologically vulnerable Australian species), based on small fragments of the mitochondrial 12S ribosomal RNA gene. A comprehensive description of species-specific assay development, from assay design to testing in silico, in vitro and in situ, has been included to guide effective assay design and validation in future studies. The results indicate that the assay was species specific for M. peelii within its natural distribution. However, the assay also amplified genomic DNA from two allopatric and endangered congeners (Maccullochella ikei and Maccullochella mariensis), thus potentially facilitating their eDNA detection elsewhere. In contrast, the A. japonicus assay was highly species specific with no amplification among close relatives. Both target-species assays are highly sensitive to as few as four and 10 copies per PCR reaction, respectively. This study has demonstrated that the assays assessed are effective tools for detecting the targeted species in situ from environmental DNA samples, which will assist efforts to conserve and manage their stocks.

Environmental DNA (eDNA) has revolutionized our ability to identify the presence and distributions of terrestrial and aquatic organisms. Recent evidence suggests the concentration of eDNA could also provide a rapid, cost‐effective indicator of abundance and/or biomass for fisheries stock assessments. Globally, fisheries resources are under immense pressure, and their sustainable harvest requires accurate information on the sizes of fished stocks. However, in many cases the required information remains elusive because of a reliance on imprecise or costly fishery‐dependent and independent data. Here, we review the literature describing relationships between eDNA concentrations and fish abundance and/or biomass, as well as key influencing factors, as a precursor to determining the broader utility of eDNA for monitoring fish populations. We reviewed 63 studies published between 2012 and 2020 and found 90% identified positive relationships between eDNA concentrations and the abundance and/or biomass of focal species. Key influencing biotic factors included the taxon examined as well as their body size, distribution, reproduction, and migration. Key abiotic factors mostly comprised hydrological processes affecting the dispersal and persistence of eDNA, especially water flow and temperature, although eDNA collection methods were also influential. The cumulative influence of these different factors likely explains the substantial variability observed in eDNA concentrations, both within and among studies. Nevertheless, there is considerable evidence to support using eDNA as an ancillary tool for assessing fish population abundance and/or biomass across discrete spatio‐temporal scales, following preliminary investigations to determine species‐ and context‐specific factors influencing the eDNA abundance/biomass relationship. Advantages of eDNA monitoring relative to other approaches include reduced costs, increased efficiencies, and nonlethal sampling.

The fairy wrasses (genus Cirrhilabrus) are among the most successful of the extant wrasse lineages (Teleostei: Labridae), with their 61 species accounting for nearly 10$\%$ of the family. Although species complexes within the genus have been diagnosed on the basis of coloration patterns and synapomorphies, attempts to resolve evolutionary relationships among these groups using molecular and morphological data have largely been unsuccessful. Here, we use a phylogenomic approach with a data set comprising 991 ultraconserved elements (UCEs) and mitochondrial COI to uncover the evolutionary history and patterns of temporal and spatial diversification of the fairy wrasses. Our analyses of phylogenetic signal suggest that most gene-tree incongruence is caused by estimation error, leading to poor resolution in a summary-coalescent analysis of the data. In contrast, analyses of concatenated sequences are able to resolve the major relationships of Cirrhilabrus. We determine the placements of species that were previously regarded as incertae sedis and find evidence for the nesting of Conniella, an unusual, monotypic genus, within Cirrhilabrus. Our relaxed-clock dating analysis indicates that the major divergences within the genus occurred around the Miocene–Pliocene boundary, followed by extensive cladogenesis of species complexes in the Pliocene–Pleistocene. Biogeographic reconstruction suggests that the fairy wrasses emerged within the Coral Triangle, with episodic fluctuations of sea levels during glacial cycles coinciding with shallow divergence events but providing few opportunities for more widespread dispersal. Our study demonstrates both the resolving power and limitations of UCEs across shallow timescales where there is substantial estimation error in individual gene trees.[Biogeography; concatenation; gene genealogy interrogation; gene trees; molecular dating; summary coalescent; UCEs.]

Non‐sex‐linked color polymorphism is common in animals and can be maintained in populations via balancing selection or, when under diversifying selection, can promote divergence. Despite their potential importance in ecological interactions and the evolution of biodiversity, their function and the mechanisms by which these polymorphisms are maintained are still poorly understood. Here, we combine field observations with life history and molecular data to compare four sympatric color morphs of the coral reef fish Paracirrhites forsteri (family Cirrhitidae) in the central Red Sea. Our findings verify that the color morphs are not sex‐limited, inhabit the same reefs, and do not show clear signs of avoidance or aggression among them. A barcoding approach based on 1,276 bp of mitochondrial DNA could not differentiate the color morphs. However, when 36,769 SNPs were considered, we found low but significant population structure. Focusing on 1,121 F ST outliers, we recovered distinct population clusters that corresponded to shifts in allele frequencies with each color morph harboring unique alleles. Genetic divergence at these outlier loci is accompanied by differences in growth and marginal variation in microhabitat preference. Together, life history and molecular analysis suggest subtle divergence between the color morphs in this population, the causes for which remain elusive., Despite their potential importance in ecological interactions and the evolution of biodiversity, non‐sex‐linked color polymorphism is poorly understood. Here, we investigated four sympatric color morphs of the coral reef fish Paracirrhites forsteri (family Cirrhitidae) in the central Red Sea and show that the color morphs inhabit the same reefs. While we could not differentiate between them using mtDNA, when we considered 36,769 SNPs, we found low but significant population structure that corresponded to color morphology with accompanying differences in growth and marginal variation in microhabitat preference.

Environmental DNA (eDNA) metabarcoding methods have demonstrated their potential as noninvasive techniques for the monitoring and conservation of marine fishes, including rare and endangered taxa. However, the majority of these investigations have focused on large‐bodied taxa such as sharks and sturgeons. In contrast, eDNA studies on small‐bodied cryptic taxa are much less common. As a case in point, seahorses (members of the Syngnathidae family) have never been detected by eDNA, despite the fact that globally there are 14 species classified as “Threatened” by the IUCN. Here, we critically evaluate the ability of two existing broad‐spectrum fish metabarcoding assays (MiFish and 16S Fish) and explore the efficacy of two newly designed fish metabarcoding assays (16S_FishSyn_Short and 16S_FishSyn_Long) to detect Syngnathidae amidst a wide spectrum of fish species. Furthermore, a custom Western Australian 16S rRNA fish database was created to increase the likelihood of correct taxonomic assignments. With the newly designed assays, we detected four Syngnathidae species in a targeted eDNA survey of the Perth metropolitan area (Western Australia). These detections include the seahorse species Hippocampus subelongatus and Hippocampus breviceps, which represents the first time seahorse species have been detected using eDNA. The existing MiFish and 16S Fish assays did not detect any Syngnathidae. This evaluation of all four fish metabarcoding assays reinforces the view that every PCR assay has “blind spots”. In the context of complex environmental samples, no assay is universal and false negatives will occur due to a combination of PCR efficacy, primer binding, assay sensitivity, degeneracies in the primers, template competition, and amplicon length. Taken together, these data indicate that eDNA methodologies, with ongoing optimizations, will become an integral part of monitoring small‐bodied cryptic taxa such as seahorses, gobies, and blennies and can assist in mapping species’ distributions and prioritizing conservation areas.

Genetic structure within marine species may be driven by local adaptation to their environment, or alternatively by historical processes, such as geographic isolation. The gulfs and seas bordering the Arabian Peninsula offer an ideal setting to examine connectivity patterns in coral reef fishes with respect to environmental gradients and vicariance. The Red Sea is characterized by a unique marine fauna, historical periods of desiccation and isolation, as well as environmental gradients in salinity, temperature, and primary productivity that vary both by latitude and by season. The adjacent Arabian Sea is characterized by a sharper environmental gradient, ranging from extensive coral cover and warm temperatures in the southwest, to sparse coral cover, cooler temperatures, and seasonal upwelling in the northeast. Reef fish, however, are not confined to these seas, with some Red Sea fishes extending varying distances into the northern Arabian Sea, while their pelagic larvae are presumably capable of much greater dispersal. These species must therefore cope with a diversity of conditions that invoke the possibility of steep clines in natural selection. Here, we test for genetic structure in two widespread reef fish species (a butterflyfish and surgeonfish) and eight range‐restricted butterflyfishes across the Red Sea and Arabian Sea using genome‐wide single nucleotide polymorphisms. We performed multiple matrix regression with randomization analyses on genetic distances for all species, as well as reconstructed scenarios for population subdivision in the species with signatures of isolation. We found that (a) widespread species displayed more genetic subdivision than regional endemics and (b) this genetic structure was not correlated with contemporary environmental parameters but instead may reflect historical events. We propose that the endemic species may be adapted to a diversity of local conditions, but the widespread species are instead subject to ecological filtering where different combinations of genotypes persist under divergent ecological regimes., We test for genetic structure in two widespread species (a butterflyfish and surgeonfish) and eight range‐restricted butterflyfishes across the Red Sea and Arabian Sea using genome‐wide single nucleotide polymorphisms, multiple matrix regression with randomization analyses, and demographic reconstruction. We found that (a) widespread species displayed more genetic subdivision than regional endemics and (b) this genetic structure was not correlated with contemporary environmental parameters but instead may reflect historical events.

Environmental DNA (eDNA) metabarcoding, a technique for retrieving multispecies DNA from environmental samples, can detect a diverse array of marine species from filtered seawater samples. There is a growing potential to integrate eDNA alongside existing monitoring methods in order to establish or improve the assessment of species diversity. Remote island reefs are increasingly vulnerable to climate-related threats and as such there is a pressing need for cost-effective whole-ecosystem surveying to baseline biodiversity, study assemblage changes and ultimately develop sustainable management plans. We investigated the utility of eDNA metabarcoding as a high-resolution, multitrophic biomonitoring tool at the Cocos (Keeling) Islands, Australia (CKI)-a remote tropical coral reef atoll situated within the eastern Indian Ocean. Metabarcoding assays targeting the mitochondrial 16S rRNA and CO1 genes, as well as the 18S rRNA nuclear gene, were applied to 252 surface seawater samples collected from 42 sites within a 140 km2 area. Our assays successfully detected a wide range of bony fish and elasmobranchs (244 taxa), crustaceans (88), molluscs (37) and echinoderms (7). Assemblage composition varied significantly between sites, reflecting habitat partitioning across the island ecosystem and demonstrating the localisation of eDNA signals, despite extensive tidal and oceanic movements. In addition, we document putative new occurrence records for 46 taxa and compare the efficiency of our eDNA approach to visual survey techniques at CKI. Our study demonstrates the utility of a multimarker metabarcoding approach in capturing multitrophic biodiversity across an entire coral reef atoll and sets an important baseline for ongoing monitoring and management.

Environmental DNA (eDNA) metabarcoding is increasingly being used to assess community composition in coastal ecosystems. In this study, we chose to examine temporal and spatial changes in the aquatic community of Manly Lagoon - one of the most heavily developed and polluted estuaries in eastern Australia. Based on metabarcoding of the 16S mitochondrial gene (for fish) and the 18S nuclear gene (for macroinvertebrates), we identified seasonal differences in fish and macroinvertebrate community composition as well as species richness, which correlated, in some cases, with the environmental parameters of sea surface temperature and freshwater input. Moreover, given the greater taxonomic resolution of fish versus macroinvertebrate assignments, we identified several known migratory fish species of management importance that contributed significantly to the overall patterns observed. Overall, our data support the use of eDNA metabarcoding to track fish assemblages shifting in response to environmental drivers in polluted estuaries with increased sampling and consultation with historical data.

Hybridisation has traditionally been considered rare and unimportant in generating biodiversity in the marine environment, particularly in coral reefs ecosystems. Here we review the literature for evidence of hybridisation in coral reef organisms and find that hybridisation is prevalent in well-studied groups, namely fish and hermatypic corals. At least 183 fish and 81 scleractinian coral species are reported to hybridise, with the highest prevalence in angelfishes and psammocorid corals (hybridisation in 46–50% of species in each family). Mapping the geographic location of hybrids revealed that hybridisation was positively associated with proximity to biogeographic borders for fish but not corals, and not linked with areas of low species richness in either group. Molecular studies detected admixture, indicative of past hybridisation, in 30 of 53 cases for fish, and in 22 (possibly 39) out of 47 studies for corals. Patterns of introgression described in the fish studies supported a decrease in lineage diversity in nine cases and the formation of hybrid lineages in seven cases. In the other 14 cases, the two parent species remained genetically distinct despite evidence of introgression. For corals, the evidence of hybrid lineages was rare (5 species), rather there was more support indicating that hybridisation leads to a decrease (36 species), or no change (27 species), in lineage diversity. Collectively, these results show that hybridisation can influence the evolution of fishes and corals in multiple ways and suggests the prevalence of hybridisation is likely to be significantly underestimated for coral reef taxa. The application of new genomic tools will advance our knowledge of the prevalence and evolutionary importance of hybridisation in coral reef organisms. Furthermore, these tools will aid in identifying how natural and assisted hybridisation may help coral reef species adapt to increasing environmental changes.

Many coral reef fishes display remarkable genetic and phenotypic variation across their geographic ranges. Understanding how historical and contemporary processes have shaped these patterns remains a focal question in evolutionary biology since they reveal how diversity is generated and how it may respond to future environmental change. Here, we compare the population genomics and demographic histories of a commercially and ecologically important coral reef fish, the common coral grouper (

M.D. is grateful for support from the Templeton Foundation (grant #60501, “Putting the Extended Evolutionary Synthesis to the Test”) and from a Leverhulme Trust Fellowship. The problem Earth‐based observations of the biosphere are spatially biased in ways that can limit our ability to detect macroecological patterns and changes in biodiversity. To resolve this problem, we need to supplement the ad hoc data currently collected with planned biodiversity monitoring, in order to approximate global stratified random sampling of the planet. We call this all‐encompassing observational system ‘the macroscope’. The solution With a focus on the marine realm, we identify seven main biosphere observation tools that compose the macroscope: satellites, drones, camera traps, passive acoustic samplers, biologgers, environmental DNA and human observations. By deploying a nested array of these tools that fills current gaps in monitoring, we can achieve a macroscope fit for purpose and turn these existing powerful tools into more than the sum of their parts. An appeal Building a macroscope requires commitment from many fields, together with coordinated actions to attract the level of funding required for such a venture. We call on macroecologists to become advocates for the macroscope and to engage with existing global observation networks. Postprint

Aim To determine the impact of ecological and environmental histories on the evolution of coral reef damselfishes at two adjacent marine biogeographic suture zones. Location Indo-West Pacific, notably including two suture zones: Socotra and Christmas and Cocos/Keeling Islands. Taxon Chromis dimidiata, Chromis margaritifer, and Chromis fieldi. Methods We utilized a combination of nuclear and mitochondrial genetic markers in addition to visual abundance survey data of these fishes. Results Despite genetic patterns consistent with incomplete lineage sorting and relatively low genetic differentiation among the three studied Chromis species, there is evidence of hybridization between C. margaritifer and C. fieldi at Christmas Island based on molecular and visual identification. Introgression appears to be spreading westwards to other C. fieldi populations based on COI haplotype comparison. Moreover, the genetic distance between C. margaritifer and C. fieldi suggests that Pleistocene sea-level fluctuations may have contributed to allopatric divergence and secondary contact between these two closely related species. Main conclusions Our study highlights that evolutionary processes in coral reef fishes operate differently between suture zones, possibly due to different ecological and environmental predispositions regulating secondary contact of sister species. While secondary contact likely led to hybridization and introgression at Christmas and Cocos/Keeling Islands, none of those processes seem present at Socotra for the chocolate-dipped damselfish. This difference is likely due to an environmental barrier caused by hydrodynamic regimes in the Gulf of Aden.

We examined genetic diversity and connectivity of two indigenous Mediterranean goatfish species (Mullus barbatus and M. surmuletus), and a Lessepsian migrant species (Upeneus moluccensis), across the Nile Delta outflow using two mitochondrial DNA markers (COI and cyt b). Genetic diversity was high for the two Mediterranean species but relatively lower for the migrant species, suggesting founder effects after invasion from the Red Sea. Confirmation of this hypothesis, however, would require comparison with populations of origin in the Red Sea and the Indo-West Pacific. AMOVA and network analyses revealed no genetic partitioning for all species, indicating the Nile outflow does not currently, and may not have historically, posed a significant barrier to larval dispersal in these goatfish despite a present-day temperature and salinity gradient along the Mediterranean coastline of Egypt.

Increasing fishing effort, including bycatch and discard practices, are impacting marine biodiversity, particularly among slow-to-reproduce taxa such as elasmobranchs, and specifically sharks. While some fisheries involving sharks are sustainably managed, collateral mortalities continue, contributing towards >35% of species being threatened with extinction. To effectively manage shark stocks, life-history information, including resource use/feeding ecologies is pivotal, especially among those species with wide-ranging distributions and habitats. Two cosmopolitan sharks bycaught off eastern Australia are the common blacktip shark (Carcharhinus limbatus; globally classified as Near Threatened) and great hammerhead (Sphyrna mokarran; Critically Endangered). We opportunistically sampled the digestive tracts of these two species and also any whole prey; (termed the ‘Russian-doll’ approach) caught in bather-protection gillnets off northern New South Wales to investigate their regional feeding ecologies and the capacity for DNA metabarcoding to delineate trophic interactions. Sphyrna mokkaran fed predominantly on Myliobatiformes and Rajiformes, but also teleosts, while C. limbatus mostly consumed teleosts, with some inter-specific dietary overlap of prey items. Extensive cross-contamination of predator and prey digestive tracts, likely via the predator’s stomach chyme, was evident from the metabarcoding assays limiting the opportunity to delineate trophic interactions from these data. This Russian-doll effect requires further investigation in DNA metabarcoding studies focused on dietary preferences, but implies any outcomes will need to be interpreted concomitant with traditional visual approaches.

Hybridization events are not uncommon in marine environments where physical barriers are attenuated. Studies of coral reef taxa have suggested that hybridization predominantly occurs between parapatric species distributed along biogeographic suture zones. By contrast, little is known about the extent of sympatric hybridization on coral reefs, despite the large amount of biogeographic overlap shared by many coral reef species. Here, we investigate if the propensity for hybridization along suture zones represents a general phenomenon among coral reef fishes, by focusing on the marine angelfishes (family Pomacanthidae). Although hybridization has been reported for this family, it has not been thoroughly surveyed, with more recent hybridization studies focusing instead on closely related species from a population genetics perspective. We provide a comprehensive survey of hybridization among the Pomacanthidae, characterize the upper limits of genetic divergences between hybridizing species and investigate the occurrence of sympatric hybridization within this group. We report the occurrence of hybridization involving 42 species (48% of the family) from all but one genus of the Pomacanthidae. Our results indicate that the marine angelfishes are among the groups of coral reef fishes with the highest incidences of hybridization, not only between sympatric species, but also between deeply divergent lineages.