The biogeography of tropical reef fishes: endemism and provinciality through time

The largest marine biodiversity hotspot straddles the Indian and Pacific Oceans, driven by taxa associated with tropical coral reefs. Centred on the Indo‐Australian Archipelago (IAA), this biodiversity hotspot forms the ‘bullseye’ of a steep gradient in species richness from this centre to the periphery of the vast Indo‐Pacific region. Complex patterns of endemism, wide‐ranging species and assemblage differences have obscured our understanding of the genesis of this biodiversity pattern and its maintenance across two‐thirds of the world's oceans. But time‐calibrated molecular phylogenies coupled with ancestral biogeographic estimates have provided a valuable framework in which to examine the origins of coral reef fish biodiversity across the tropics. Herein, we examine phylogenetic and biogeographic data for coral reef fishes to highlight temporal patterns of marine endemism and tropical provinciality. The ages and distribution of endemic lineages have often been used to identify areas of species creation and demise in the marine tropics and discriminate among multiple hypotheses regarding the origins of biodiversity in the IAA. Despite a general under‐sampling of endemic fishes in phylogenetic studies, the majority of locations today contain a mixture of potential paleo‐ and neo‐endemic fishes, pointing to multiple historical processes involved in the origin and maintenance of the IAA biodiversity hotspot. Increased precision and sampling of geographic ranges for reef fishes has permitted the division of discrete realms, regions and provinces across the tropics. Yet, such metrics are only beginning to integrate phylogenetic relatedness and ancestral biogeography. Here, we integrate phylogenetic diversity with ancestral biogeographic estimation of lineages to show how assemblage structure and tropical provinciality has changed through time.     

Ancient origins of Indo-Pacific coral reef fish biodiversity: a case study of the leopard wrasses (Labridae: Macropharyngodon)

Temporal origins of reef fishes in the Indo-Australian Archipelago were examined using wrasses in the genus Macropharyngodon. The genus was selected as it is morphologically and ecologically distinct, with strongly reef-associated species exhibiting discrete distributions across the Indo-Pacific. Phylogenetic relationships were explored using COI, 16S, and 12S rRNA mitochondrial sequences. Monophyly of the genus was supported by congruent Bayesian, maximum likelihood, and maximum parsimony trees. Estimates of lineage ages based on fossil-calibrated reef fish divergences suggest that Macropharyngodon had an extensive evolutionary history starting in the early Miocene. Repeated divergences of Indian Ocean-Pacific Ocean lineages appear to have occurred over at least 19 million years. Regional endemics represent both old and young clades. Our estimates of early Miocene origins, and mid-Miocene to Pliocene diversifications of Macropharyngodon are supported by recent studies of other reef fish genera, and emphasise the importance of pre-Pleistocene events in generating Indo-Pacific coral reef fish biodiversity.     

Species-level phylogeography and evolutionary history of the hyperdiverse marine gastropod genus Conus

Phylogenetic and paleontological analyses are combined to reveal patterns of species origination and divergence and to define the significance of potential and actual barriers to dispersal in Conus, a species-rich genus of predatory gastropods distributed throughout the world's tropical oceans. Species-level phylogenetic hypotheses are based on nucleotide sequences from the nuclear calmodulin and mitochondrial 16S rRNA genes of 138 Conus species from the Indo-Pacific, eastern Pacific, and Atlantic Ocean regions. Results indicate that extant species descend from two major lineages that diverged at least 33 mya. Their geographic distributions suggest that one clade originated in the Indo-Pacific and the other in the eastern Pacific + western Atlantic. Impediments to dispersal between the western Atlantic and Indian Oceans and the central and eastern Pacific Ocean may have promoted this early separation of Indo-Pacific and eastern Pacific + western Atlantic lineages of Conus. However, because both clades contain both Indo-Pacific and eastern Pacific + western Atlantic species, migrations must have occurred between these regions; at least four migration events took place between regions at different times. In at least three cases, incursions between regions appear to have crossed the East Pacific Barrier. The paleontological record illustrates that distinct sets of Conus species inhabited the Indo-Pacific, eastern Pacific + western Atlantic, and eastern Atlantic + former Tethys Realm in the Tertiary, as is the case today. The ranges of <1% of fossil species (N=841) spanned more than one of these regions throughout the evolutionary history of this group.     

Influence of the geography of speciation on current patterns of coral reef fish biodiversity across the Indo‐Pacific

The role of speciation processes in shaping current biodiversity patterns represents a major scientific question for ecologists and biogeographers. Hence, numerous methods have been developed to determine the geography of speciation based on co‐occurrence between sister‐species. Most of these methods rely on the correlation between divergence time and several metrics based on the geographic ranges of sister‐taxa (i.e. overlap, asymmetry). The relationship between divergence time and these metrics has scarcely been examined in a spatial context beyond regression curves. Mapping this relationship across spatial grids, however, may unravel how speciation processes have shaped current biodiversity patterns through space and time. This can be particularly relevant for coral reef fishes of the Indo‐Pacific since the origin of the exceptional concentration of biodiversity in the Indo‐Australian Archipelago (IAA) has been actively debated, with several alternative hypotheses involving species diversification and dispersal. We reconstructed the phylogenetic relationships between three species‐rich families of coral reef fish (Chaetodontidae, Labridae, Pomacentridae) and calculated co‐occurrence metrics between closely related lineages of those families. We demonstrated that repeated biogeographic processes can be identified in present‐day species distribution by projecting co‐occurrence metrics between related lineages in a geographical context. Our study also evidence that sister‐species do not co‐occur randomly across the Indo‐Pacific, but tend to overlap their range within the IAA. We identified the imprint of two important biogeographic processes that caused this pattern in 48% of the sister‐taxa considered: speciation events within the IAA and repeated divergence between the Indian and Pacific Ocean, with subsequent secondary contact in the IAA.     

Molecular evidence for co-occurring cryptic lineages within the Sepioteuthis cf. lessoniana species complex in the Indian and Indo-West Pacific Oceans

The big-fin reef squid, Sepioteuthis cf. lessoniana (Lesson 1930), is an important commodity species within artisanal and near-shore fisheries in the Indian and Indo-Pacific regions. While there has been some genetic and physical evidence that supports the existence of a species complex within S. cf. lessoniana, these studies have been extremely limited in scope geographically. To clarify the extent of cryptic diversity within S. cf. lessoniana, this study examines phylogenetic relationships using mitochondrial genes (cytochrome oxidase c, 16s ribosomal RNA) and nuclear genes (rhodopsin, octopine dehydrogenase) from nearly 400 individuals sampled from throughout the Indian, Indo-Pacific, and Pacific Ocean portions of the range of this species. Phylogenetic analyses using maximum likelihood methods and Bayesian inference identified three distinct lineages with no clear geographic delineations or morphological discriminations. Phylogeographic structure analysis showed high levels of genetic connectivity in the most widespread lineage, lineage C and low levels of connectivity in lineage B. This study provides significant phylogenetic evidence for cryptic lineages within this complex and confirms that cryptic lineages of S. cf. lessoniana occur in sympatry at both small and large spatial scales. Furthermore, it suggests that two closely related co-occurring cryptic lineages have pronounced differences in population structure, implying that underlying differences in ecology and/or life history may facilitate co-occurrence. Further studies are needed to assess the range and extent of cryptic speciation throughout the distribution of this complex. This information is extremely useful as a starting point for future studies exploring the evolution of diversity within Sepioteuthis and can be used to guide fisheries management efforts.     

Species richness of motile cryptofauna across a gradient of reef framework erosion

Coral reef ecosystems contain exceptionally high concentrations of marine biodiversity, potentially encompassing millions of species. Similar to tropical rainforests and their insects, the majority of reef animal species are small and cryptic, living in the cracks and crevices of structural taxa (trees and corals). Although the cryptofauna make up the majority of a reef??s metazoan biodiversity, we know little about their basic ecology. We sampled motile cryptofaunal communities from both live corals and dead carbonate reef framework across a gradient of increasing erosion on a reef in Pacific Panamá. A total of 289 Operational Taxonomic Units (OTUs) from six phyla were identified. We used species-accumulation models fitted to individual- and sample-based rarefaction curves, as well as seven nonparametric richness estimators to estimate species richness among the different framework types. All procedures predicted the same trends in species richness across the differing framework types. Estimated species richness was higher in dead framework (261?C370 OTUs) than in live coral substrates (112?C219 OTUs). Surprisingly, richness increased as framework structure was eroded: coral rubble contained the greatest number of species (227?C320 OTUs) and the lowest estimated richness of 47?C115 OTUs was found in the zone where the reef framework had the greatest vertical relief. This contradicts the paradigm that abundant live coral indicates the apex of reef diversity.     

Phylogeography of Padina boryana (Dictyotales,Phaeophyceae) around the Thai-Malay Peninsula

The Indo-Pacific Ocean is a biodiversity hotspot for marine organisms. In this area, most of the research has focused on marine animals, such as reef fish, molluscs and other associated coral fauna, but very little has been done on macroalgae. The Thai-Malay Peninsula is an important north–south barrier in this area, which faces two different oceans – the Indian Ocean and the Pacific Ocean. This study aims to investigate genetic distribution patterns of Padina boryana Thivy around the Thai-Malay Peninsula, where it is common. Three DNA marker regions, the mitochondrion-encoded cytochrome c oxidase subunit 3 gene (cox3); the plastid rbcL, and the nuclear internal transcribed spacer 2 (ITS2) were used to evaluate genetic diversity and the relationships within and between populations. Samples were collected from both the Andaman Sea and Gulf of Thailand sides of the peninsula. Parsimony networks and maximum likelihood and Bayesian analyses showed clearly that there are two separated P. boryana lineages, one restricted to the Gulf of Thailand and the other to the Andaman Sea and other areas of the Indo-Pacific. The effect of different ocean currents along the Andaman Sea and Gulf of Thailand may have shaped these populations of P. boryana. This phylogeographic separation, based on persistent currents in the area, may affect other marine organisms along the Thai peninsula.     

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km²). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.     

Phylogeography of <Emphasis Type="Italic">Eleotris fusca</Emphasis> (Teleostei: Gobioidei: Eleotridae) in the Indo-Pacific area reveals a cryptic species in the Indian Ocean

Indo-Pacific insular freshwater systems are mainly dominated by amphidromous species. Eleotris fusca is a widespread one, its life cycle is characterised by a marine pelagic larval phase allowing the species to disperse in the ocean and then to recruit to remote island rivers. In the present study, the population structure of E. fusca over its Indo-Pacific distribution range (Western Indian Ocean to French Polynesia, Pacific Ocean) was evaluated. We analysed a section of mitochondrial COI of 557 individuals sampled from 28 islands to visualise the population structure. Haplotypes diversity (Hd) was between 0.458 and 1 and, nucleotide diversity (π) was between 0.001 and 0.02. Two distinct genetic groups appeared, one in the Indian Ocean and the other in the Pacific Ocean (F_ST mean?=?0.901; 5.2% average divergence). Given these results, complete mitogenomes (mtDNA) were sequenced and combined with the nuclear Rhodopsin (Rh) gene for a subset of individuals. The two phylogenetic trees based on each analysis showed the same genetic pattern: two different groups belonging to the Indian and the Pacific oceans (6.6 and 1.6% of divergence for mtDNA and Rh gene respectively), which supported species level differentiation. These analyses revealed the presence of two sister species confounded until present under the name of Eleotris fusca. One of them is cryptic and endemic of the Indian Ocean and the other one is the true E. fusca, which keeps, nevertheless, its status of widespread species.     

Will increased storm disturbance affect the biodiversity of intertidal,nonscleractinian sessile fauna on coral reefs?

Relatively little is known about how the future effects of climatic change, including increases in sea level, temperature and storm severity and frequency, will impact on patterns of biodiversity on coral reefs, with the notable exception of recent work on corals and fish in tropical reef ecosystems. Sessile invertebrates such as ascidians, sponges and bryozoans occupying intertidal rubble habitats on coral reefs contribute significantly to the overall biodiversity and ecosystem function, but there is little or no information available on the likely impacts on these species from climate change. The existing strong physical gradients in these intertidal habitats will be exacerbated under predicted climatic change. By examining the distribution and abundance of nonscleractinian, sessile invertebrate assemblages exposed to different levels of wave action and at different heights on the shore around a coral reef, we show that coral reef intertidal biodiversity is particularly sensitive to physical disturbance. As physical disturbance regimes increase due to more intense storms and wave action associated with global warming, we can expect to see a corresponding decrease in the diversity of these cryptic sessile assemblages. This could impact negatively on the future health and productivity of coral reef ecosystems, given the ecosystem services these organisms provide.     

Estimates of species diversity of free-living marine isopod crustaceans on coral reefs

 A core group of isopod crustacean genera appears to be present at many coral reef sites. Within these genera, however, species show high local endemicity. Based on the estimated percentage of endemism for the Atlantic (19% for individual sites, 90% for the tropical western Atlantic as a unit), the Indian Ocean (50%), the eastern-central Pacific (80%), and the western Pacific (40%), it is estimated that there are some 5,000 to 13,000 isopod species in the world’s coral reefs, and that some 2,000 to 6,000 of these are endemics. (At present, approximately 4,400 species of marine and 560 species of freshwater isopods have been described.) Based on the crudely estimated relative abundances of other peracaridan crustaceans in coral reefs (compared to isopods), the total diversity of reef amphipods, tanaidaceans, cumaceans, and mysidaceans is approximately 54,500 species. Accepted: 29 August 1997     

Origins of species richness in the Indo‐Malay‐Philippine biodiversity hotspot: evidence for the centre of overlap hypothesis

The Indo‐Malay‐Philippine (IMP) biodiversity hotspot, bounded by the Philippines, the Malay Peninsula and New Guinea, is the epicentre of marine biodiversity. Hypotheses to explain the source of the incredible number of species found there include the centre of overlap hypothesis, which proposes that in this region the distinct faunas of the Pacific and Indian Oceans overlap. Here we review the biogeographical evidence in support of this hypothesis. We examined tropical reef fish distributions, paying particular attention to sister species pairs that overlap in the IMP hotspot. We also review phylogeographical studies of wide‐ranging species for evidence of lineage divergence and overlap in the IMP region. Our synthesis shows that a pattern of isolation between the Pacific and the Indian Ocean faunas is evident across a wide range of taxa. The occurrence of sister species, with one member in each ocean, indicates that the mechanism(s) of isolation has been in effect since at least the Miocene, while phylogeographical studies indicate more recent divergences in the Pleistocene. Divergence in isolation followed by population expansion has led to an overlap of closely related taxa or genetic lineages in the hotspot, contributing to diversity and species richness in the region. These findings are consistent with the centre of overlap hypothesis and highlight the importance of this process in generating biodiversity within the IMP.     

Coral growth with thermal stress and ocean acidification: lessons from the eastern tropical Pacific

The rapid growth of scleractinian corals is responsible for the persistence of coral reefs through time. Coral growth rates have declined over the past 30 years in the western Pacific, Indian, and North Atlantic Oceans. The spatial scale of this decline has led researchers to suggest that a global phenomenon like ocean acidification may be responsible. A multi-species inventory of coral growth from Pacific Panamá confirms that declines have occurred in some, but not all species. Linear extension declined significantly in the most important reef builder of the eastern tropical Pacific, Pocillopora damicornis, by nearly one-third from 1974 to 2006. The rate of decline in skeletal extension for P. damicornis from Pacific Panamá (0.9% year⁻¹) was nearly identical to massive Porites in the Indo-Pacific over the past 20–30 years (0.89–1.23% year⁻¹). The branching pocilloporid corals have shown an increased tolerance to recurrent thermal stress events in Panamá, but appear to be susceptible to acidification. In contrast, the massive pavonid corals have shown less tolerance to thermal stress, but may be less sensitive to acidification. These differing sensitivities will be a fundamental determinant of eastern tropical Pacific coral reef community structure with accelerating climate change that has implications for the future of reef communities worldwide.     

Reef Fishes in Biodiversity Hotspots Are at Greatest Risk from Loss of Coral Species

Coral reef ecosystems are under a variety of threats from global change and anthropogenic disturbances that are reducing the number and type of coral species on reefs. Coral reefs support upwards of one third of all marine species of fish, so the loss of coral habitat may have substantial consequences to local fish diversity. We posit that the effects of habitat degradation will be most severe in coral regions with highest biodiversity of fishes due to greater specialization by fishes for particular coral habitats. Our novel approach to this important but untested hypothesis was to conduct the same field experiment at three geographic locations across the Indo-Pacific biodiversity gradient (Papua New Guinea; Great Barrier Reef, Australia; French Polynesia). Specifically, we experimentally explored whether the response of local fish communities to identical changes in diversity of habitat-providing corals was independent of the size of the regional species pool of fishes. We found that the proportional reduction (sensitivity) in fish biodiversity to loss of coral diversity was greater for regions with larger background species pools, reflecting variation in the degree of habitat specialization of fishes across the Indo-Pacific diversity gradient. This result implies that habitat-associated fish in diversity hotspots are at greater risk of local extinction to a given loss of habitat diversity compared to regions with lower species richness. This mechanism, related to the positive relationship between habitat specialization and regional biodiversity, and the elevated extinction risk this poses for biodiversity hotspots, may apply to species in other types of ecosystems.     

Extent of Mangrove Nursery Habitats Determines the Geographic Distribution of a Coral Reef Fish in a South-Pacific Archipelago

Understanding the drivers of species'' geographic distribution has fundamental implications for the management of biodiversity. For coral reef fishes, mangroves have long been recognized as important nursery habitats sustaining biodiversity in the Western Atlantic but there is still debate about their role in the Indo-Pacific. Here, we combined LA-ICP-MS otolith microchemistry, underwater visual censuses (UVC) and mangrove cartography to estimate the importance of mangroves for the Indo-Pacific coral reef fish Lutjanus fulviflamma in the archipelago of New Caledonia. Otolith elemental compositions allowed high discrimination of mangroves and reefs with 83.8% and 98.7% correct classification, respectively. Reefs were characterized by higher concentrations of Rb and Sr and mangroves by higher concentrations of Ba, Cr, Mn and Sn. All adult L. fulviflamma collected on reefs presented a mangrove signature during their juvenile stage with 85% inhabiting mangrove for their entire juvenile life (about 1 year). The analysis of 2942 UVC revealed that the species was absent from isolated islands of the New Caledonian archipelago where mangroves were absent. Furthermore, strong positive correlations existed between the abundance of L. fulviflamma and the area of mangrove (r = 0.84 for occurrence, 0.93 for density and 0.89 for biomass). These results indicate that mangrove forest is an obligatory juvenile habitat for L. fulviflamma in New Caledonia and emphasize the potential importance of mangroves for Indo-Pacific coral reef fishes.     

Diverse staghorn corals (Acropora) in high-latitude Eocene assemblages: implications for the evolution of modern diversity patterns of reef corals

Acropora is the most diverse genus of reef-building corals in the world today. It occurs in all three major oceans; it is restricted to latitudes 31 degrees N-31 degrees S, where most coral reefs occur, and reaches greatest diversity in the central Indo-Pacific. As an exemplar genus, the long-term history of Acropora has implications for the evolution and origins of present day biodiversity patterns of reef corals and for predicting their response to future climate change. Diversification of Acropora was thought to have occurred in the central Indo-Pacific within the previous two million years. We examined Eocene fossils from southern England and northern France and found evidence that precursors of up to nine of 20 currently recognized Acropora species groups existed 49-34 Myr, at palaeolatitudes far higher than current limits, to 51 degrees N. We propose that pre-existing diversity contributed to later rapid speciation in this important functional group of corals.     

Indo-Pacific population structure and evolutionary history of the coconut crab Birgus latro

Mitochondrial DNA variation was used to examine population structure in a widespread, marine-dispersed species, Birgus latro . Crabs were collected from eight locations throughout the species' Indo-Pacific distribution. Purified mtDNA from 160 individuals was cut with five restriction enzymes, revealing high haplotype diversity (0.96) and moderate nucleotide diversity (0.75%). Island populations from the Indian Ocean (Christmas I.) and Pacific Ocean were significantly different ( G _ST= 0.37) and had distinct mtDNA lineages with a net sequence divergence of 1.4%. Pacific island populations had diverged in a manner consistent with isolation by distance, with only the most peripheral populations being significantly different. The results for mtDNA are largely concordant with those from allozymes, although estimates of gene flow between the Indian and Pacific Oceans were much lower when based on mtDNA. The mtDNA phylogeny also permitted a deeper examination of the evolutionary and demographic history of Birgus latro . Long-term separation of populations is evident in the complete phylogenetic subdivision of mtDNA lineages between the Indian and Pacific Ocean populations sampled. The starlike phylogeny of alleles from the Pacific suggests a rapid population expansion in the Pacific during the Pleistocene. Including information about allele phylogeny, as well as distribution and frequency, obscured contemporary population structure, but provided unique insights into the evolutionary history of the species.     

Resurrection of Indian Ocean humbug damselfish,Dascyllus abudafur (Forsskål) from synonymy with its Pacific Ocean sibling,Dascyllus aruanus (L.)

Previous phylogeographic studies of the humbug damselfish, a widespread Indo-West Pacific coral reef fish, have revealed a split of two main mitochondrial lineages distributed on either side of the Indo-Pacific barrier. This has been interpreted as the result of vicariance. It has been hypothesized that reproductive barriers might currently limit gene flow between humbug damselfish populations from the Indian Ocean and the Pacific Ocean. In this study, we review the published phylogeographic information to update the distribution of the two main mitochondrial lineages of humbug damselfish. The Indian lineage was distributed from the Red Sea to the eastern extremity of the Sunda Shelf while the Pacific lineage, which diverged from the former by 0.6% net nucleotide divergence and diagnostic substitutions at three nucleotide sites at the cytochrome b locus, was distributed east and north of the Sunda Shelf. The two forms, which are also genetically distinct at nuclear loci, were also characterized by distinct pigmentation patterns. We argue that the two forms represent geminate species. Epithet aruanus Linnaeus is maintained for the Pacific Ocean humbug damselfish while epithet abudafur (Forsskål) is here resurrected for the Indian Ocean humbug damselfish. Future studies should focus on the population genetic structure of the transition zone between Dascyllus abudafur and D. aruanus.     

Global Biogeography of Reef Fishes: A Hierarchical Quantitative Delineation of Regions

Delineating regions is an important first step in understanding the evolution and biogeography of faunas. However, quantitative approaches are often limited at a global scale, particularly in the marine realm. Reef fishes are the most diversified group of marine fishes, and compared to most other phyla, their taxonomy and geographical distributions are relatively well known. Based on 169 checklists spread across all tropical oceans, the present work aims to quantitatively delineate biogeographical entities for reef fishes at a global scale. Four different classifications were used to account for uncertainty related to species identification and the quality of checklists. The four classifications delivered converging results, with biogeographical entities that can be hierarchically delineated into realms, regions and provinces. All classifications indicated that the Indo-Pacific has a weak internal structure, with a high similarity from east to west. In contrast, the Atlantic and the Eastern Tropical Pacific were more strongly structured, which may be related to the higher levels of endemism in these two realms. The “Coral Triangle”, an area of the Indo-Pacific which contains the highest species diversity for reef fishes, was not clearly delineated by its species composition. Our results show a global concordance with recent works based upon endemism, environmental factors, expert knowledge, or their combination. Our quantitative delineation of biogeographical entities, however, tests the robustness of the results and yields easily replicated patterns. The similarity between our results and those from other phyla, such as corals, suggests that our approach may be of broad utility in describing and understanding global marine biodiversity patterns.