Twenty‐first‐century climate change impacts on marine animal biomass and ecosystem structure across ocean basins

Climate change effects on marine ecosystems include impacts on primary production, ocean temperature, species distributions, and abundance at local to global scales. These changes will significantly alter marine ecosystem structure and function with associated socio‐economic impacts on ecosystem services, marine fisheries, and fishery‐dependent societies. Yet how these changes may play out among ocean basins over the 21st century remains unclear, with most projections coming from single ecosystem models that do not adequately capture the range of model uncertainty. We address this by using six marine ecosystem models within the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish‐MIP) to analyze responses of marine animal biomass in all major ocean basins to contrasting climate change scenarios. Under a high emissions scenario (RCP8.5), total marine animal biomass declined by an ensemble mean of 15%–30% (±12%–17%) in the North and South Atlantic and Pacific, and the Indian Ocean by 2100, whereas polar ocean basins experienced a 20%–80% (±35%–200%) increase. Uncertainty and model disagreement were greatest in the Arctic and smallest in the South Pacific Ocean. Projected changes were reduced under a low (RCP2.6) emissions scenario. Under RCP2.6 and RCP8.5, biomass projections were highly correlated with changes in net primary production and negatively correlated with projected sea surface temperature increases across all ocean basins except the polar oceans. Ecosystem structure was projected to shift as animal biomass concentrated in different size‐classes across ocean basins and emissions scenarios. We highlight that climate change mitigation measures could moderate the impacts on marine animal biomass by reducing biomass declines in the Pacific, Atlantic, and Indian Ocean basins. The range of individual model projections emphasizes the importance of using an ensemble approach in assessing uncertainty of future change.     

Historical faunal exchange between the Pontocaspian Basin and North America

Ecrobia is a genus of small brackish‐water mud snails with an amphi‐Atlantic distribution. Interestingly, the species occurring in the northwestern Atlantic, Ecrobia truncata, is more closely related to the Pontocaspian taxa, Ecrobia grimmi and Ecrobia maritima, than to the species occurring in the northeastern Atlantic and Mediterranean Sea. At least three colonization scenarios may account for this peculiar biogeographical pattern: (1) a recent human‐mediated dispersal, (2) a historical transatlantic interchange, and (3) a historical transpolar interchange. To test these three scenarios, we used five operational criteria—time of species divergence, first appearance in the fossil record, dispersal limitation as well as environmental filtering and biotic interactions along the potential migration routes. Specifically, we inferred a time‐calibrated molecular phylogeny for Ecrobia and reconstructed a paleogeographical map of the Arctic Ocean at 2.5 million years ago (Mya). Based on the five operational criteria, scenarios 1 and 2 can likely be rejected. In contrast, all criteria support scenario 3 (historical transpolar interchange). It is therefore suggested that a bird‐mediated and/or ocean current‐mediated faunal interchange via the Arctic Ocean occurred during the Late Pliocene or Early Pleistocene. This dispersal was likely facilitated by reduced distances between the Eurasian and North American/Greenland landmasses, marine introgressions, and/or a stepping‐stone system of brackish‐water habitats in northern Siberia, as well as a lack of competition along the migration route. As for the direction of dispersal, the scientific data presented are not conclusive. However, there is clearly more support for the scenario of dispersal from the Pontocaspian Basin to North America than vice versa. This is the first study providing evidence for a natural faunal exchange between the Pontocaspian Basin and North America via the Arctic Ocean.     

Cycles of trans‐Arctic dispersal and vicariance,and diversification of the amphi‐boreal marine fauna

The amphi‐boreal faunal element comprises closely related species and conspecific populations with vicarious distributions in the North Atlantic and North Pacific basins. It originated from an initial trans‐Arctic dispersal in the Pliocene after the first opening of the Bering Strait, and subsequent inter‐oceanic vicariance through the Pleistocene when the passage through the Arctic was severed by glaciations and low sea levels. Opportunities for further trans‐Arctic dispersal have risen at times, however, and molecular data now expose more complex patterns of inter‐oceanic affinities and dispersal histories. For a general view on the trans‐Arctic dynamics and of the roles of potential dispersal–vicariance cycles in generating systematic diversity, we produced new phylogeographic data sets for amphi‐boreal taxa in 21 genera of invertebrates and vertebrates, and combined them with similar published data sets of mitochondrial coding gene variation, adding up to 89 inter‐oceanic comparisons involving molluscs, crustaceans, echinoderms, polychaetes, fishes and mammals. Only 39% of the cases correspond to a simple history of Pliocene divergence; in most taxonomical groups, the range of divergence estimates implies connections through the entire Pliocene–Pleistocene–Holocene time frame. Repeated inter‐oceanic exchange was inferred for 23 taxa, and the latest connection was usually post‐glacial. Such repeated invasions have usually led to secondary contacts and occasionally to widespread hybridization between the different invasion waves. Late‐ or post‐glacial exchange was inferred in 46% of the taxa, stressing the importance of the relatively recent invasions to the current diversity in the North Atlantic. Individual taxa also showed complex idiosyncratic patterns and histories, and several instances of cryptic speciation were recognized. In contrast to a simple inter‐oceanic vicariance scenario underlying amphi‐boreal speciation, the data expose complex patterns of reinvasion and reticulation that complicate the interpretation of taxon boundaries in the region.     

Influences of past climatic changes on historical population structure and demography of a cosmopolitan marine predator,the common dolphin (genus Delphinus)

Climatic oscillations during the Pleistocene have greatly influenced the distribution and connectivity of many organisms, leading to extinctions but also generating biodiversity. While the effects of such changes have been extensively studied in the terrestrial environment, studies focusing on the marine realm are still scarce. Here we used sequence data from one mitochondrial and five nuclear loci to assess the potential influence of Pleistocene climatic changes on the phylogeography and demographic history of a cosmopolitan marine predator, the common dolphin (genus Delphinus). Population samples representing the three major morphotypes of Delphinus were obtained from 10 oceanic regions. Our results suggest that short‐beaked common dolphins are likely to have originated in the eastern Indo‐Pacific Ocean during the Pleistocene and expanded into the Atlantic Ocean through the Indian Ocean. On the other hand, long‐beaked common dolphins appear to have evolved more recently and independently in several oceans. Our results also suggest that short‐beaked common dolphins had recurrent demographic expansions concomitant with changes in sea surface temperature during the Pleistocene and its associated increases in resource availability, which differed between the North Atlantic and Pacific Ocean basins. By proposing how past environmental changes had an effect on the demography and speciation of a widely distributed marine mammal, we highlight the impacts that climate change may have on the distribution and abundance of marine predators and its ecological consequences for marine ecosystems.     

DNA barcodes for globally threatened marine turtles: a registry approach to documenting biodiversity

DNA barcoding is a global initiative that provides a standardized and efficient tool to catalogue and inventory biodiversity, with significant conservation applications. Despite progress across taxonomic realms, globally threatened marine turtles remain underrepresented in this effort. To obtain DNA barcodes of marine turtles, we sequenced a segment of the cytochrome c oxidase subunit I (COI) gene from all seven species in the Atlantic and Pacific Ocean basins (815 bp; n = 80). To further investigate intraspecific variation, we sequenced green turtles (Chelonia mydas) from nine additional Atlantic/Mediterranean nesting areas (n = 164) and from the Eastern Pacific (n = 5). We established character-based DNA barcodes for each species using unique combinations of character states at 76 nucleotide positions. We found that no haplotypes were shared among species and the mean of interspecific variation ranged from 1.68% to 13.0%, and the mean of intraspecific variability was relatively low (0–0.90%). The Eastern Pacific green turtle sequence was identical to an Australian haplotype, suggesting that this marker is not appropriate for identifying these phenotypically distinguishable populations. Analysis of COI revealed a north–south gradient in green turtles of Western Atlantic/Mediterranean nesting areas, supporting a hypothesis of recent dispersal from near equatorial glacial refugia. DNA barcoding of marine turtles is a powerful tool for species identification and wildlife forensics, which also provides complementary data for conservation genetic research.     

Towards a panbiogeography of the seas

A contrast is drawn between the concept of speciation favoured in the Darwin–Wallace biogeographic paradigm (founder dispersal from a centre of origin) and in panbiogeography (vicariance or allopatry). Ordinary ecological dispersal is distinguished from founder dispersal. A survey of recent literature indicates that ideas on many aspects of marine biology are converging on a panbiogeographic view. Panbiogeographic conclusions supported in recent work include the following observations: fossils give minimum ages for groups and most taxa are considerably older than their earliest known fossil; Pacific/Atlantic divergence calibrations based on the rise of the Isthmus of Panama at 3 Ma are flawed; for these two reasons most molecular clock calibrations for marine groups are also flawed; the means of dispersal of taxa do not correlate with their actual distributions; populations of marine species may be closed systems because of self‐recruitment; most marine taxa show at least some degree of vicariant differentiation and vicariance is surprisingly common among what were previously assumed to be uniform, widespread taxa; mangrove and seagrass biogeography and migration patterns in marine taxa are best explained by vicariance; the Indian Ocean and the Pacific Ocean represent major biogeographic regions and diversity in the Indo‐Australian Archipelago is related to Indian Ocean/Pacific Ocean vicariance; distribution in the Pacific is not the result of founder dispersal; distribution in the south‐west Pacific is accounted for by accretion tectonics which bring about distribution by accumulation and juxtaposition of communities; tectonic uplift and subsidence can directly affect vertical distribution of marine communities; substantial parallels exist between the biogeography of terrestrial and marine taxa; biogeographically and geologically composite areas are tractable using panbiogeographic analysis; metapopulation models are more realistic than the mainland/island dispersal models used in the equilibrium theory of island biogeography; and regional biogeography is a major determinant of local community composition. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84 , 675–723.     

Flying shells: historical dispersal of marine snails across Central America

The geological rise of the Central American Isthmus separated the Pacific and the Atlantic oceans about 3 Ma, creating a formidable barrier to dispersal for marine species. However, similar to Simpson's proposal that terrestrial species can 'win sweepstakes routes'-whereby highly improbable dispersal events result in colonization across geographical barriers-marine species may also breach land barriers given enough time. To test this hypothesis, we asked whether intertidal marine snails have crossed Central America to successfully establish in new ocean basins. We used a mitochondrial DNA genetic comparison of sister snails (Cerithideopsis spp.) separated by the rise of the Isthmus. Genetic variation in these snails revealed evidence of at least two successful dispersal events between the Pacific and the Atlantic after the final closure of the Isthmus. A combination of ancestral area analyses and molecular dating techniques indicated that dispersal from the Pacific to the Atlantic occurred about 750 000 years ago and that dispersal in the opposite direction occurred about 72 000 years ago. The geographical distribution of haplotypes and published field evidence further suggest that migratory shorebirds transported the snails across Central America at the Isthmus of Tehuantepec in southern Mexico. Migratory birds could disperse other intertidal invertebrates this way, suggesting the Central American Isthmus may not be as impassable for marine species as previously assumed.     

DNA evidence for a Paleocene origin of the Alcidae (Aves: Charadriiformes) in the Pacific and multiple dispersals across northern oceans

The Alcidae is a group of marine, wing-propelled diving birds known as auks that are distributed along the coasts of the northern oceans. It has been suggested that auks originated in the Pacific coastal shores as early as the Miocene, and dispersed to the Atlantic either through the Arctic coasts of Eurasia and North America (northern dispersal route), or through upwelling zones in the coastal areas of California to Florida (southern dispersal route), before the closure of the Isthmus of Panama in the Pliocene. These hypotheses have not been tested formally because proposed phylogenies failed to recover fully bifurcating, well-supported phylogenetic relationships among and within genera. We therefore constructed a large data set of mitochondrial and nuclear DNA sequences for 21 of the 23 species of extant auks. We also included sequences from two other extant and one extinct species retrieved from GenBank. Our analyses recovered a well-supported phylogenetic hypothesis among and within genera. Aethia is the only genus for which we could not obtain strong support for species relationships, probably due to incomplete lineage sorting. By applying a Bayesian method of molecular dating that allows for rate variation across lineages and genes, we showed that auks became an independent lineage in the Early Paleocene and radiated gradually from the Early Eocene to the Quaternary. Reconstruction of ancestral areas strongly suggests that auks originated in the Pacific during the Paleocene. The southern dispersal route seems to have favored the subsequent colonization of the northern Atlantic Ocean during the Eocene and Oligocene. The northern route across the Arctic Ocean was probably only used more recently after the opening of the Norwegian Sea in the Middle Miocene and the opening of the Bering Strait in the Late Miocene. We postulate that the ancestors of auks lived in a warmer world than that currently occupied by auks, and became gradually adapted to feeding in cool marine currents with high biomass productivity. Hence, warmer tropical waters are now a barrier for the dispersal of auks into the Southern Hemisphere, as it is for penguins in the opposite direction.     

PHYLOGEOGRAPHY OF THE TRUMPETFISHES (AULOSTOMUS): RING SPECIES COMPLEX ON A GLOBAL SCALE

Abstract.— The distribution of circumtropical marine species is limited by continental boundaries, cold temperate conditions, and oceanic expanses, but some of these barriers are permeable over evolutionary time scales. Sister taxa that evolved in separate ocean basins can come back into contact, and the consequences of this renewed sympatry may be a key to understanding evolutionary processes in marine organisms. The circumtropical trumpetfishes (Aulostomus) include a West Atlantic species (A. maculatus), an Indian‐Pacific species (A. chinensis), and an East Atlantic species (A. strigosus) that may be the product of a recent invasion from the Indian Ocean. To resolve patterns of divergence and speciation, we surveyed 480 bp of mitochondrial DNA cytochrome b in 196 individuals from 16 locations. Based on a conventional molecular clock of 2% sequence divergence per million years, the deepest partitions in a neighbor‐joining tree (d= 0.063‐0.082) are consistent with separation of West Atlantic and Indian‐Pacific species by the Isthmus of Panama, 3–4 million years ago. By the same criteria, trumpetfish in the East Atlantic were isolated from the Indian Ocean about 2.5 million years ago (d= 0.044‐0.054), coincident with the advent of glacial cycles and cold‐water upwelling around South Africa. Continental barriers between tropical oceans have only rarely been surmounted by trumpetfishes, but oceanic barriers do not appear to be substantial, as indicated by weak population partitioning (ø_ST= 0.093) in A. chinensis across the Indian and Pacific Oceans. Finally, morphological and mitochondrial DNA data indicate hybridization of A. strigosus and A. maculatus in Brazil. After 3–4 million years and a globe‐spanning series of vicariant and dispersal events, trumpetfish lineages have come back into contact in the southwest Atlantic and appear to be merging. This ring species phenomenon may occur in a broad array of marine organisms, with clear implications for the production and maintenance of biodiversity in marine ecosystems.     

Marine shelf habitat: biogeography and evolution

We synthesize the evolutionary implications of recent advances in the fields of phylogeography, biogeography and palaeogeography for shallow‐water marine species, focusing on marine speciation and the relationships among the biogeographic regions and provinces of the world. A recent revision of biogeographic provinces has resulted in the recognition of several new provinces and a re‐evaluation of provincial relationships. These changes, and the information that led to them, make possible a clarification of distributional dynamics and evolutionary consequences. Most of the new conclusions pertain to biodiversity hotspots in the tropical Atlantic, tropical Indo‐West Pacific, cold‐temperate North Pacific, and the cold Southern Ocean. The emphasis is on the fish fauna, although comparative information on invertebrates is utilized when possible. Although marine biogeographic provinces are characterized by endemism and thus demonstrate evolutionary innovation, dominant species appear to arise within smaller centres of high species diversity and maximum interspecies competition. Species continually disperse from such centres of origin and are readily accommodated in less diverse areas. Thus, the diversity centres increase or maintain species diversity within their areas of influence, and are part of a global system responsible for the maintenance of biodiversity over much of the marine world.     

Diversity of diazotrophic unicellular cyanobacteria in the tropical North Atlantic Ocean

We present data on the genetic diversity and phylogenetic affinities of N2-fixing unicellular cyanobacteria in the plankton of the tropical North Atlantic Ocean. Our dinitrogenase gene (nifH) sequences grouped together with a group of cyanobacteria from the subtropical North Pacific; another subtropical North Pacific group was only distantly related. Most of the 16S ribosomal DNA sequences from our tropical North Atlantic samples were closely allied with sequences from a symbiont of the diatom Climacodium frauenfeldianum. These findings suggest a complex pattern of evolutionary and ecological divergence among unicellular cyanobacteria within and between ocean basins.     

The relationship between local and regional diversity of indigenous forest fauna in KwaZulu-Natal Province, South Africa

The relationship between local and regional diversity was tested by regressing local community richness against regional species diversity for three taxa, birds, butterflies and mammals, in subtropical forest. The quadratic model best fits the relationship between local and regional diversity for birds. Local bird species richness is theoretically independent of the size of the regional pool of species and may represent saturated communities. A linear model best describes the relationship for mammals and butterflies. For mammals, the slope is shallow (0.264) and regional richness overestimates local species richness, suggesting communities are undersaturated. Extinction filtering may explain this pattern. Past climatic changes have filtered out many mammalian species, these changes have been too recent for autochthanous speciation, and the relatively low vagility of mammals has prevented extensive recolonisation. Differences in the nature of the diversity relationship between taxa are as much due to independent evolutionary histories as to differences in vagility and colonising potential. A pervasive role is suggested for regional biogeographic processes in the development of faunal assemblage structure. Large-scale processes are not considered in current conservation plans. We encourage the shift of conservation emphasis from local ecological processes and species interactions, to whole communities and consideration of regional processes.     

The Bering Strait connection: dispersal and speciation in boreal macroalgae

A large number of boreal seaweeds have either sibling species or conspecific populations of a single species in the North Pacific and North Atlantic Oceans. This pattern is thought to have arisen from the dispersal between the two oceans through the Arctic Ocean after the opening of the Bering Strait in the mid-to-late Miocene or earliest Pliocene and from subsequent vicariant speciation as the Arctic Ocean froze and Bering Strait closed intermittently during glacial periods. Recent molecular studies of species in all three major seaweed phyla reveal patterns of vicariance. However, a number of lines of evidence point to differences in origins of these clades; some appear to be Pacific in origin whereas others appear to be derived from Atlantic stock. Different origins can be explained by recent stratigraphic finds that push the first Cenozoic opening of the Bering Strait back from 3.1–4.1 to 4.8–7.4 Ma (million years ago). Northern hemisphere ocean circulation models suggest that water flow would have been from the North Atlantic–Arctic south through the Bering Strait prior to the closure of the Panamanian Isthmus c. 3.5 Ma in contrast to the northward flow from the Pacific into the Arctic and North Atlantic, which developed after the closing of the Isthmus. Despite these differences in timing of the two invasions, there are no significant differences in levels of relationships among species with a North Atlantic origin compared with species with a North Pacific origin based on currently available data. More work is required to understand vicariance in seaweeds, especially in deciphering when a speciation event has occurred.     

Spatial variation and low diversity in the major histocompatibility complex in walrus (Odobenus rosmarus)

Increased global temperature and associated changes to Arctic habitats will likely result in the northward advance of species, including an influx of pathogens novel to the Arctic. How species respond to these immunological challenges will depend in part on the adaptive potential of their immune response system. We compared levels of genetic diversity at a gene associated with adaptive immune response [Class II major histocompatibility complex (MHC), DQB exon 2] between populations of walrus (Odobenus rosmarus), a sea ice-dependent Arctic species. Walrus was represented by only five MHC DQB alleles, with frequency differences observed between Pacific and Atlantic populations. MHC DQB alleles appear to be under balancing selection, and most (80 %; n = 4/5) of the alleles were observed in walruses from both oceans, suggesting broad scale differences in the frequency of exposure and diversity of pathogens may be influencing levels of heterozygosity at DQB in walruses. Limited genetic diversity at MHC, however, suggests that walrus may have a reduced capacity to respond to novel immunological challenges associated with shifts in ecological communities and environmental stressors predicted for changing climates. This is particularly pertinent for walrus, since reductions in summer sea ice may facilitate both northward expansion of marine species and associated pathogens from more temperate regions, and exchange of marine mammals and associated pathogens through the recently opened Northwest Passage between the Atlantic and Pacific Oceans in the Canadian high Arctic.     

北冰洋海域微食物环研究进展

海洋微食物环在海洋生态系统中起着重要作用.北冰洋因常年为海冰所覆盖,对微食物环的研究较为有限.现有研究表明,微食物环在北冰洋生态系统中的作用与海域和季节相关.近年来环境的快速变化、特别是夏季海冰覆盖面积的迅速减少,会对微食物环的结构和功能产生重大影响,已有研究显示其生态作用有望进一步提高.综合近年来已有的研究成果,对北冰洋微食物环的主要类群:原核生物、真核浮游植物、原生动物和浮游病毒等的基本生态特征进行了概述,讨论了各类群间的相互关系,并对未来的研究重点进行了展望.     

How isolated is Antarctica?

The traditional view of Antarctica and the surrounding Southern Ocean as an isolated system is now being challenged by the recent discovery at the Antarctic Peninsula of adult spider crabs Hyas areneus from the North Atlantic and of larvae of subpolar marine invertebrates. These observations question whether the well described biogeographical similarities between the benthic fauna of the Antarctic Peninsula and the Magellan region of South America result from history (the two regions were once contiguous), or from a previously unrecognized low level of faunal exchange. Such exchange might be influenced by regional climate change, and also exacerbated by changes in human impact.     

Postglacial Colonization of the North European Seas by Pacific Fishes and Lamprey

A critical analysis of literature data on the distribution, morphology, and phylogeography of the Arctic lamprey (Lethenteron camtschaticum) and five species of marine and anadromous fish such as navaga (Eleginus navaga), pollock (Theragra chalcogramma), rainbow smelt (Osmerus mordax dentex), Pacific herring (Clupea pallasii), and pond smelt (Hypomesus olidus) has been performed. The results show that all these species have colonized Northern European seas, distributing along the Arctic coastline of Eurasia after the glacier retreat. The reasons that the dispersal of these species in the Atlantic Ocean may be impeded (preference for a cold environment, competition, and decrease of the evolutionary potential) are discussed.     

Atlantic reef fish biogeography and evolution

Aim To understand why and when areas of endemism (provinces) of the tropical Atlantic Ocean were formed, how they relate to each other, and what processes have contributed to faunal enrichment. Location Atlantic Ocean. Methods The distributions of 2605 species of reef fishes were compiled for 25 areas of the Atlantic and southern Africa. Maximum‐parsimony and distance analyses were employed to investigate biogeographical relationships among those areas. A collection of 26 phylogenies of various Atlantic reef fish taxa was used to assess patterns of origin and diversification relative to evolutionary scenarios based on spatio‐temporal sequences of species splitting produced by geological and palaeoceanographic events. We present data on faunal (species and genera) richness, endemism patterns, diversity buildup (i.e. speciation processes), and evaluate the operation of the main biogeographical barriers and/or filters. Results Phylogenetic (proportion of sister species) and distributional (number of shared species) patterns are generally concordant with recognized biogeographical provinces in the Atlantic. The highly uneven distribution of species in certain genera appears to be related to their origin, with highest species richness in areas with the greatest phylogenetic depth. Diversity buildup in Atlantic reef fishes involved (1) diversification within each province, (2) isolation as a result of biogeographical barriers, and (3) stochastic accretion by means of dispersal between provinces. The timing of divergence events is not concordant among taxonomic groups. The three soft (non‐terrestrial) inter‐regional barriers (mid‐Atlantic, Amazon, and Benguela) clearly act as ‘filters’ by restricting dispersal but at the same time allowing occasional crossings that apparently lead to the establishment of new populations and species. Fluctuations in the effectiveness of the filters, combined with ecological differences among provinces, apparently provide a mechanism for much of the recent diversification of reef fishes in the Atlantic. Main conclusions Our data set indicates that both historical events (e.g. Tethys closure) and relatively recent dispersal (with or without further speciation) have had a strong influence on Atlantic tropical marine biodiversity and have contributed to the biogeographical patterns we observe today; however, examples of the latter process outnumber those of the former.     

Diversity of Diazotrophic Unicellular Cyanobacteria in the Tropical North Atlantic Ocean

We present data on the genetic diversity and phylogenetic affinities of N₂-fixing unicellular cyanobacteria in the plankton of the tropical North Atlantic Ocean. Our dinitrogenase gene (nifH) sequences grouped together with a group of cyanobacteria from the subtropical North Pacific; another subtropical North Pacific group was only distantly related. Most of the 16S ribosomal DNA sequences from our tropical North Atlantic samples were closely allied with sequences from a symbiont of the diatom Climacodium frauenfeldianum. These findings suggest a complex pattern of evolutionary and ecological divergence among unicellular cyanobacteria within and between ocean basins.     

The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography

Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than previously recognised.