Mapped coral mortality and refugia in an archipelago-scale marine heat wave.

Corals are a major habitat-building life-form on tropical reefs that support a quarter of all species in the ocean and provide ecosystem services to millions of people. Marine heat waves continue to threaten and shape reef ecosystems by killing individual coral colonies and reducing their diversity. However, marine heat waves are spatially and temporally heterogeneous, and so too are the environmental and biological factors mediating coral resilience during and following thermal events. This combination results in highly variable outcomes at both the coral bleaching and mortality stages of every event. This, in turn, impedes the assessment of changing reef-scale patterns of thermal tolerance or places of resistance known as reef refugia. We developed a large-scale, high-resolution coral mortality monitoring capability based on airborne imaging spectroscopy and applied it to a major marine heat wave in the Hawaiian Islands. While water depth and thermal stress strongly mediated coral mortality, relative coral loss was also inversely correlated with preheat-wave coral cover, suggesting the existence of coral refugia. Subsequent mapping analyses indicated that potential reef refugia underwent up to 40% lower coral mortality compared with neighboring reefs, despite similar thermal stress. A combination of human and environmental factors, particularly coastal development and sedimentation levels, differentiated resilient reefs from other more vulnerable reefs. Our findings highlight the role that coral mortality mapping, rather than bleaching monitoring, can play for targeted conservation that protects more surviving corals in our changing climate.

Lineage diversification and rampant hybridization among subspecies explain taxonomic confusion in the endemic Hawaiian fern Polypodium pellucidum.

PREMISE: Polypodium pellucidum, a fern endemic to the Hawaiian Islands, encompasses five ecologically and morphologically variable subspecies, suggesting a complex history involving both rapid divergence and rampant hybridization. METHODS: We employed a large target-capture data set to investigate the evolution of genetic, morphological, and ecological variation in P. pellucidum. With a broad sampling across five Hawaiian Islands, we deciphered the evolutionary history of P. pellucidum, identified nonhybrid lineages and intraspecific hybrids, and inferred the relative influence of geography and ecology on their distributions. RESULTS: Polypodium pellucidum is monophyletic, dispersing to the Hawaiian archipelago 11.53-7.77 Ma and diversifying into extant clades between 5.66 and 4.73 Ma. We identified four nonhybrid clades with unique morphologies, ecological niches, and distributions. Additionally, we elucidated several intraspecific hybrid combinations and evidence for undiscovered or extinct "ghost" lineages contributing to extant hybrid populations. CONCLUSIONS: We provide a foundation for revising the taxonomy of P. pellucidum to account for cryptic lineages and intraspecific hybrids. Geologic succession of the Hawaiian Islands through cycles of volcanism, vegetative succession, and erosion has determined the available habitats and distribution of ecologically specific, divergent clades within P. pellucidum. Intraspecific hybrids have likely arisen due to ecological and or geological transitions, often persisting after the local extinction of their progenitors. This research contributes to our understanding of the evolution of Hawai'i's diverse fern flora and illuminated cryptic taxa to allow better-informed conservation efforts.

Large-scale mapping of live corals to guide reef conservation.

Coral is the life-form that underpins the habitat of most tropical reef ecosystems, thereby supporting biological diversity throughout the marine realm. Coral reefs are undergoing rapid change from ocean warming and nearshore human activities, compromising a myriad of services provided to societies including coastal protection, fishing, and cultural practices. In the face of these challenges, large-scale operational mapping of live coral cover within and across reef ecosystems could provide more opportunities to address reef protection, resilience, and restoration at broad management- and policy-relevant scales. We developed an airborne mapping approach combining laser-guided imaging spectroscopy and deep learning models to quantify, at a large archipelago scale, the geographic distribution of live corals to 16-m water depth throughout the main Hawaiian islands. Airborne estimates of live coral cover were highly correlated with field-based estimates of live coral cover (R2 = 0.94). Our maps were used to assess the relative condition of reefs based on live coral, and to identify potential coral refugia in the face of human-driven stressors, including marine heat waves. Geospatial modeling revealed that water depth, wave power, and nearshore development accounted for the majority (>60%) of live coral cover variation, but other human-driven factors were also important. Mapped interisland and intraisland variation in live coral location improves our understanding of reef geography and its human impacts, thereby guiding environmental management for reef resiliency.

A Near Four-Decade Time Series Shows the Hawaiian Islands Have Been Browning Since the 1980s.

The Hawaiian Islands have been identified as a global biodiversity hotspot. We examine the Normalized Difference Vegetation Index (NDVI) using Climate Data Records products (0.05 × 0.05°) to identify significant differences in NDVI between neutral El Niño-Southern Oscillation years (1984, 2019) and significant long-term changes over the entire time series (1982-2019) for the Hawaiian Islands and six land cover classes. Overall, there has been a significant decline in NDVI (i.e., browning) across the Hawaiian Islands from 1982 to 2019 with the islands of Lana'i and Hawai'i experiencing the greatest decreases in NDVI (≥44%). All land cover classes significantly decreased in NDVI for most months, especially during the wet season month of March. Native vegetation cover across all islands also experienced significant declines in NDVI, with the leeward, southwestern side of the island of Hawai'i experiencing the greatest declines. The long-term trends in the annual total precipitation and annual mean Palmer Drought Severity Index (PDSI) for 1982-2019 on the Hawaiian Islands show significant concurrent declines. Primarily positive correlations between the native ecosystem NDVI and precipitation imply that significant decreases in precipitation may exacerbate the decrease in NDVI of native ecosystems. NDVI-PDSI correlations were primarily negative on the windward side of the islands and positive on the leeward sides, suggesting a higher sensitivity to drought for leeward native ecosystems. Multi-decadal time series and spatially explicit data for native landscapes provide natural resource managers with long-term trends and monthly changes associated with vegetation health and stability.

A holobiont view of island biogeography: Unravelling patterns driving the nascent diversification of a Hawaiian spider and its microbial associates.

The diversification of a host lineage can be influenced by both the external environment and its assemblage of microbes. Here, we use a young lineage of spiders, distributed along a chronologically arranged series of volcanic mountains, to investigate how their associated microbial communities have changed as the spiders colonized new locations. Using the stick spider Ariamnes waikula (Araneae, Theridiidae) on the island of Hawai'i, and outgroup taxa on older islands, we tested whether each component of the "holobiont" (spider hosts, intracellular endosymbionts and gut microbial communities) showed correlated signatures of diversity due to sequential colonization from older to younger volcanoes. To investigate this, we generated ddRAD data for the host spiders and 16S rRNA gene amplicon data from their microbiota. We expected sequential colonizations to result in a (phylo)genetic structuring of the host spiders and in a diversity gradient in microbial communities. The results showed that the host A. waikula is indeed structured by geographical isolation, suggesting sequential colonization from older to younger volcanoes. Similarly, the endosymbiont communities were markedly different between Ariamnes species on different islands, but more homogeneous among A. waikula populations on the island of Hawai'i. Conversely, the gut microbiota, which we suspect is generally environmentally derived, was largely conserved across all populations and species. Our results show that different components of the holobiont respond in distinct ways to the dynamic environment of the volcanic archipelago. This highlights the necessity of understanding the interplay between different components of the holobiont, to properly characterize its evolution.

Hawaiian Fungal Amplicon Sequence Variants Reveal Otherwise Hidden Biogeography.

To study biogeography and other ecological patterns of microorganisms, including fungi, scientists have been using operational taxonomic units (OTUs) as representations of species or species hypotheses. However, when defined by 97% sequence similarity cutoff at an accepted barcode locus such as 16S in bacteria or ITS in fungi, these OTUs can obscure biogeographic patterns, mask taxonomic diversity, and hinder meta-analyses. Amplicon sequence variants (ASVs) have been proposed to alleviate all of these issues and have been shown to do so in bacteria. Analyzing ASVs is just emerging as a common practice among fungal studies, and it is unclear whether the benefits found in bacterial studies of using such an approach carryover to fungi. Here, we conducted a meta-analysis of Hawaiian fungi by analyzing ITS1 amplicon sequencing data as ASVs and exploring ecological patterns. These surveys spanned three island groups and five ecosystems combined into the first comprehensive Hawaiian Mycobiome ASV Database. Our results show that ASVs can be used to combine fungal ITS surveys, increase reproducibility, and maintain the broad ecological patterns observed with OTUs, including diversity orderings. Additionally, the ASVs that comprise some of the most common OTUs in our database reveals some island specialists, indicating that traditional OTU clustering can obscure important biogeographic patterns. We recommend that future fungal studies, especially those aimed at assessing biogeography, analyze ASVs rather than OTUs. We conclude that similar to bacterial studies, ASVs improve reproducibility and data sharing for fungal studies.

Molecular signatures of long-distance oceanic dispersal and the colonization of Pacific islands in Lycium carolinianum.

PREMISE: Long-distance dispersal has been important in explaining the present distributions of many plant species. Despite being infrequent, such dispersal events have considerable evolutionary consequences, because bottlenecks during colonization can result in reduced genetic diversity. We examined the phylogeographic history of Lycium carolinianum, a widespread taxon that ranges from southeastern North America to several Pacific islands, with intraspecific diversity in sexual and mating systems. METHODS: We used Bayesian, likelihood, and coalescent approaches with nuclear and plastid sequence data and genome-wide single nucleotide polymorphisms to reconstruct the dispersal history of this species. We also compared patterns of genetic variation in mainland and island populations using single nucleotide polymorphisms and allelic diversity at the S-RNase mating system gene. RESULTS: Lycium carolinianum is monophyletic and dispersed once from the North American mainland, colonizing the Pacific islands ca. 40,100 years ago. This dispersal was accompanied by a loss of genetic diversity in SNPs and the S-RNase locus due to a colonization bottleneck and the loss of self-incompatibility. Additionally, we documented at least two independent transitions to gynodioecy: once following the colonization of the Hawaiian Islands and loss of self-incompatibility, and a second time associated with polyploidy in the Yucatán region of Mexico. CONCLUSIONS: Long-distance dispersal via fleshy, bird dispersed fruits best explains the unusually widespread distribution of L. carolinianum. The collapse of diversity at the S-RNase locus in island populations suggests that self-fertilization may have facilitated the subsequent colonization of Pacific islands following a single dispersal from mainland North America.

A molecular phylogeny of the Pacific clade of Cyrtandra (Gesneriaceae) reveals a Fijian origin, recent diversification, and the importance of founder events.

Cyrtandra (Gesneriaceae) is among the largest genera of flowering plants in the remote oceanic islands of the Pacific, with an estimated 175 species distributed across an area that extends from the Solomon Islands, east to the Marquesas Islands, and north to the Hawaiian Islands. The vast majority of species are single-island endemics that inhabit upland rainforests. Although previous molecular phylogenetic studies greatly advanced our understanding of the diversification of Pacific Cyrtandra, a number of uncertainties remain regarding phylogenetic relationships, divergence times, and biogeographic patterns within this large and widely dispersed group. In the present study, five loci (ITS, ETS, Cyrt1, psbA-trnH, and rpl32-trnL) were amplified and sequenced for phylogenetic reconstruction of 121 Cyrtandra taxa. Maximum likelihood and Bayesian inference confirmed that C. taviunensis from Fiji is sister to the remaining members of the Pacific clade. Dating analyses and ancestral area estimation indicates that the Pacific clade of Cyrtandra originated in Fiji during the Miocene ca. 9mya. All major crown lineages within the Pacific clade appeared < 5mya, coincident with the emergence of numerous Pacific islands and a subsequent increase in available habitat. The biogeographic history of Cyrtandra in the Pacific has been shaped by extinction, dispersal distance, and founder events. Biogeographic stochastic mapping analyses suggest that cladogenesis within Pacific Cyrtandra involved a combination of narrow (within-area) sympatry and founder events. A mean of 24 founder events was recovered between Pacific archipelagos, while a mean of 10 founder events was recovered within the Hawaiian archipelago.

Diversification in Hawaiian long-legged flies (Diptera: Dolichopodidae: Campsicnemus): biogeographic isolation and ecological adaptation.

Flies in the genus Campsicnemus have diversified into the second-largest adaptive radiation of Diptera in the Hawaiian Islands, with 179 Hawaiian endemic species currently described. Here we present the first phylogenetic analysis of Campsicnemus, with a focus on the Hawaiian fauna. We analyzed a combination of two nuclear (CAD, EF1α) and five mitochondrial (COI, COII, 12S, 16S, ND2) loci using Bayesian and maximum likelihood approaches to generate a phylogenetic hypothesis for the genus Campsicnemus. Our sampling included a total of 84 species (6 species from Europe, 1 from North America, 7 species from French Polynesia and 70 species from the Hawaiian Islands). The phylogenies were used to estimate divergence times, reconstruct biogeographic history, and infer ancestral ecological associations within this large genus. We found strong support for a South Pacific+Hawaiian clade, as well as for a monophyletic Hawaiian lineage. Divergence time estimates suggest that Hawaiian Islands were colonized approximately 4.6 million years ago, suggesting that most of the diversity within Campsicnemus evolved since the current high islands began forming ∼5 million years ago. We also observe a novel ecotype within the Pacific Campsicnemus; a widespread obligate water-skating form that has arisen multiple times across the Pacific Islands. Together, these analyses suggest that a combination of ecological, biogeographic and temporal factors have led to the impressive diversity of long-legged flies in Hawaii and elsewhere in the Pacific.

Remnants of populations provide effective source material for reintroduction of an endangered Hawaiian plant, Schiedea kaalae (Caryophyllaceae).

PREMISE OF THE STUDY: Reintroductions may be essential to prevent extinction of many critically endangered species. Ideally, reintroduction efforts rely on adjacent source populations, but limited source material may necessitate crossing individuals from different and possibly distant populations. To determine the consequences of integrating multiple populations in reintroductions, we investigated levels of inbreeding depression, outbreeding depression, and heterosis for populations of Schiedea kaalae (Caryophyllaceae), an endangered species endemic to the Wai'anae and Ko'olau Mountains of O'ahu, Hawai'i. The possibility of gene flow among plants was explored through pollinator observations. METHODS: Individuals from ex situ living collections of nine populations were hand-pollinated with pollen from the same plant, plants from the same population (for three populations only), or plants from different populations. Progeny were outplanted into two common gardens, one in each mountain range on O'ahu. Cumulative fitness was estimated using several independent life history stages. KEY RESULTS: Inbreeding depression was minimal, and no outbreeding depression was detected. In contrast, strong heterosis was evident in progeny from between-population crosses, which had higher relative fitness than progeny from self-pollinations or within-population crosses. Observations of floral visitors provided the first evidence that biotic pollination may be important for this species. CONCLUSIONS: Results demonstrate the ability to conduct genetic rescue of rare species and suggest that reintroductions may be most successful using heterotic individuals from crosses between populations and at sites where pollinators are present and promote outcrossing.

Cyrtandraobliquifolia (Gesneriaceae), a new species from Kaua'i, Hawaiian Islands.

Cyrtandraobliquifolia K.R. Wood & W.L. Wagner (Gesneriaceae), a new shrub species known only from Kaua'i, Hawaiian Islands, is described and illustrated with notes on its distribution, ecology, and conservation status. The new species is morphologically most similar to Cyrtandrawawrae C.B. Clarke but differs by its unique combination of oblique, non-peltate, auriculate leaf bases, more deeply divided calyx lobes, inflorescence with fewer flowers and lacking profusely umbellate cymes. Cyrtandraobliquifolia is known from only two localities which have undergone severe habitat degradation from landslides and invasive plants and animals and is determined to be Critically Endangered (CR) when evaluated under IUCN criteria.

Schiedeawaiahuluensis (Caryophyllaceae), an enigmatic new species from Kaua'i, Hawaiian Islands and the first species discovered by a drone collection system.

During a survey by the National Tropical Botanical Garden drone team, an enigmatic Schiedea was observed in December 2021on steep, rocky cliff faces of the Waiahulu Valley in the Waimea Canyon of Kaua'i. Subsequently, another survey was conducted in March 2022 and, by use of a remotely controlled cutting device suspended below the drone, the first herbarium specimen was collected, as well as a seed collection of an undescribed cliff-dwelling species of Schiedea. Detailed study of the collections and plants grown at the University of California, Irvine greenhouse showed that it had enlarged, somewhat whitish sepals similar to those of cliff-dwelling S.attenuata (the sole species in sect. Leucocalyx), yet differed significantly from all other species in the genus. It also shares with S.attenuata a woody habit, hermaphroditic flowers, coloured nectar and styles 5 to 7 or 8. We describe it here as S.waiahuluensis given the only known localities are on the cliffs of this valley and place it in an enlarged sect. Leucocalyx. With the discovery of this new species, there are 36 species in this Hawaiian endemic genus.

 Myrsinecirrhosa (Primulaceae), a distinctive new shrub species from Kaua'i, Hawaiian Islands.

Myrsinecirrhosa Lorence & K.R.Wood (Primulaceae), a new single-island endemic shrub species from Kaua'i, Hawaiian Islands, is described and illustrated. Notes on its distribution, ecology and conservation status are included. The new species is known from an area with ca. 45 individuals, where it is restricted to the remote central windward region of Kaua'i in open bogs and along open windy ridges. Suggested IUCN Red List status is CR (Critically Endangered). It differs from its Kaua'i congeners by its longer petals and narrowly elliptic leaves with strongly undulate margins and tendril-like apex. Phylogenetic analysis using RADseq data supports the recognition of this new species.

Population genetics of Sida fallax Walp. (Malvaceae) in the Hawaiian Islands.

Introduction: Sida fallax (Malvaceae) is the most widespread and variable taxon of Malvaceae in the Hawaiian Islands, growing with a diversity of morphological forms in different habitats including Midway Atoll, Nihoa, and all the main islands. Morphological variation exists within and among populations. The study aimed to investigate the genetic variation within and among populations from various habitats and geographic locations throughout the Hawaiian range of S. fallax. Methods: A total of 124 samples, with up to five samples per population where possible, were collected from 26 populations across six of the main Hawaiian Islands (Kaua'i, O'ahu, Maui, Moloka'i, Lana'i, and Hawai'i) and Nihoa in the Northwestern Hawaiian Islands. The sampling strategy encompassed collecting populations from different habitats and geographic locations, including coastal and mountain ecotypes, with many intermediate morphological forms. Multiplexed ISSR genotyping by sequencing (MIG-seq) was used to detect single nucleotide polymorphisms (SNP) and genetic differences among individuals and populations were evaluated using PCO analyses. Results: The relationship of FST with the geographical distance between the populations was assessed using the Mantel test. The results showed that populations on a single island were more closely related to each other and to populations on islands within their respective groups than they were to populations on other islands. Discussion: The overall genetic relationships among islands were, to a large extent, predictive based on island position within the chain and, to a lesser extent, within island topography.

Predation of the endangered Ae'o (Hawaiian Stilt) by a native raptor, the Pueo (Hawaiian Short-eared Owl) on the island of O'ahu, Hawai'i, USA.

While the impact of introduced predators is a widely acknowledged issue and key component of conservation considerations for endemic waterbird populations in the Hawaiian Islands, the impact of native predators on endemic, endangered waterbirds is not as frequently discussed or factored into recovery models. The Pueo (Hawaiian Short-eared Owl; Asio flammeus sandwichensis) is a subspecies of Short-eared Owl endemic to the Hawaiian Islands and is State-listed as Endangered on the island of O'ahu. The Ae'o (Hawaiian Stilt; Himantopus mexicanus knudensi) is a subspecies of the Black-necked Stilt endemic to Hawai'i and is federally listed as Endangered throughout its range. A variety of non-native predators are confirmed to consume Ae'o eggs, chicks, and adults, including invasive mammals (e.g., feral cats), birds (e.g., Barn Owls), and amphibians (e.g., bullfrogs). While predation by native predators was suspected, there are no cases documented in the literature to date describing Pueo preying upon Ae'o. Here, we describe four events that provide evidence of Pueo predating Ae'o during the 2019-2021 breeding seasons in a wetland area on the island of O'ahu: (1) confirmed Pueo predating an Ae'o chick, (2) a suspected predation attempt of a Pueo chasing adult Ae'o, and (3) two suspected predation events based on (a) 10 adult-sized Ae'o carcasses and remains found near an active Pueo nest and (b) game camera photos of Pueo visiting two Ae'o nests. To our knowledge, these novel observations are the first published accounts of predator-prey interactions between these two subspecies.

Seasonal Variability in the Prevalence of DWV Strains in Individual Colonies of European Honeybees in Hawaii.

The most prevalent viral pathogen of honeybees is Deformed Wing Virus (DWV) and its two most widely studied and common master-variants are DWV-A and DWV-B. The prevalence of DWV variants in the UK and in the US is changing, with the prevalence of the DWV-A strain declining and DWV-B increasing over time. In 2012, only DWV-A was detected on the Hawaiian Islands of Oahu. In this study we focused on a colony-level survey of DWV strains in a single apiary and examined the prevalence of DWV variants over the course of two years. In 2018 and 2019, a total of 16 colonies underwent viral testing in January, May, and September. Of those 16 colonies, four were monitored in both 2018 and 2019. Individual colonies showed variability of DWV master variants throughout the sampling period. DWV-A was consistently detected; however, the detection of DWV-B was variable across time in individual colonies. Ultimately, this study demonstrated a seasonal variation in both viral prevalence and load for DWV-B, providing a perspective on the dynamic nature of DWV master variants emerging in Hawaii.

Interannual variability in marine debris accumulation on Hawaiian shores: The role of North Pacific Ocean basin-scale dynamics.

Community-based marine debris removal efforts on the Hawaiian Islands of Kaua'i and Hawai'i, spanning 2013-2022, provided large datasets and documented remarkable variations in annual amounts of debris, mainly from abandoned, lost and derelict fishing gear. To test the hypothesis that the influx of marine debris on Hawaiian shores is determined by the proximity of the North Pacific garbage patch, whose pattern changes under the control of large-scale ocean dynamics, we compared these observational data with the output of an oceanographic drift model. The high correlations between the total mass of debris collected and the model, ranging between r = 0.81 and r = 0.84, validate the attribution of the strong interannual signal to significant migrations of the garbage patch reproduced in the model experiments. Synchronous variations in marine debris fluxes on the two islands, separated by >500 km, confirm the large scale of the interannual changes in the North Pacific marine debris system.

Subsurface temperature estimates from a Regional Ocean Modelling System (ROMS) reanalysis provide accurate coral heat stress indices across the Main Hawaiian Islands.

As ocean temperatures continue to rise, coral bleaching events around the globe are becoming stronger and more frequent. High-resolution temperature data is therefore critical for monitoring reef conditions to identify indicators of heat stress. Satellite and in situ measurements have historically been relied upon to study the thermal tolerances of coral reefs, but these data are quite limited in their spatial and temporal coverage. Ocean circulation models could provide an alternative or complement to these limited data, but a thorough evaluation against in situ measurements has yet to be conducted in any Pacific Islands region. Here we compared subsurface temperature measurements around the nearshore Main Hawaiian Islands (MHI) from 2010 to 2017 with temperature predictions from an operational Regional Ocean Modeling System (ROMS) to evaluate the potential utility of this model as a tool for coral reef management. We found that overall, the ROMS reanalysis presents accurate subsurface temperature predictions across the nearshore MHI region and captures a significant amount of observed temperature variability. The model recreates several temperature metrics used to identify coral heat stress, including predicting the 2014 and 2015 bleaching events around Hawai'i during the summer and fall months of those years. The MHI ROMS simulation proves to be a useful tool for coral reef management in the absence of, or to supplement, subsurface and satellite measurements across Hawai'i and likely for other Pacific Island regions.

Clermontiahanaulaensis (Campanulaceae, Lobelioideae), a new, critically endangered species from Maui, Hawaiian Islands.

Clermontiahanaulaensis H.Oppenheimer, Lorence & W.L.Wagner, sp. nov., a newly discovered, narrowly distributed endemic species, is herein described based on its morphological characteristics and illustrated with field photos and a line drawing. It is currently known only from the slopes of Hana'ula, in Pohakea Gulch, Mauna Kahalawai, west Maui, Hawaiian Islands. It differs from all other species of Clermontia Gaudich. by the combination of its (2)3-4(-5) flowered inflorescence, violet colored perianth often suffused with creamy white streaks or sometimes creamy white with violet-purple irregular veins, (30)35-45(-50) mm long, perianth tube 15-25(-27) mm long, 9-10 mm wide, the lobes 20-26 mm long, (2-)3-3.5 mm wide, with petaloid calyx lobes 1/2-4/5 as long as the petals. A key to the Clermontia species and subspecies occurring on Maui is provided. Its habitat is described. Its conservation status is proposed as critically endangered (CR), and conservation efforts are discussed.

Cryptic Genetic Diversity in the Coastal Isopod Alloniscus oahuensis from the Pacific Ocean.

The isopod sub-order Oniscidea includes over 3,700 species and is known to occur in all terrestrial environments, except those at extreme elevations and polar latitudes. Current estimates of the biodiversity of the Oniscidea may be underestimates, as recent molecular studies have uncovered high levels of cryptic diversity in several taxa in the sub-order. High levels of cryptic diversity have been found in coastal species, species from remote and isolated regions, and species with complex taxonomic histories. Alloniscus oahuensis is a good candidate to harbor cryptic diversity, as it is a coastal isopod species with a geographic range that spans several remote and isolated archipelagos in the Pacific Ocean and has a complex taxonomic history. In this study, we used sequences for three mitochondrial genes and one nuclear gene to determine whether A. oahuensis harbors highly divergent lineages that may represent cryptic species. By characterizing 60+ A. oahuensis individuals from 17 localities from various Pacific Ocean archipelagos, we uncovered two deeply divergent lineages with disjunct distributions. The levels of genetic divergence observed amongst the two lineages match or exceed those reported across other cryptic species in the Oniscidea, suggesting that A. oahuensis may represent a cryptic species complex in need of a taxonomic revision. The extremely low lineage diversities within A. oahuensis indicate that the lineages may have spread across the Pacific Ocean recently, potentially due to anthropogenic activity.