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-Evolution of the Southern Ocean. 1A. Reconstruction of the southern continents at 130Ma. Based on Lawver et al., 1992, Fig. 4. Key: AP-Antarctic Peninsula block ; MB-Mozambique Basin ; MBL-Marie Byrd Land block ; SB-Somali Basin ; TIThurston Island block ; WS-proto-Weddell Sea ; ?-uncertain or oceanic crustal material. 1B. Reconstruction of the southern continents at 70Ma. Based on Lawver et al., 1992, Fig. 10. Key: CPCampbell Plateau ; LHR-Lord Howe Rise; STR-South Tasman Rise. In both A and B the circles represent the 30° and 60°S palaeolatitudes, respectively. Continental margins and shelves in stipple.
Source publication
The origins of present day benthic marine faunas from both the Magellan and Antarctic provinces may lie as far back as the Early Cretaceous (approx. 130 Ma). This was the time of the first significant marine incursion across the Gondwana supercontinent and isolation of a high-latitude group of continents. It was also the probable time of formation...
Citations
... Antarctic marine life is characterized by high levels of endemism (Griffiths, 2010) as a result of the long climatic, geodynamic and oceanographic histories of the Southern Ocean (Aronson et al., 2007;Clarke & Crame, 2010;Crame, 1999;Pfuhl & McCave, 2005). ...
... Both the Polar Front and the Antarctic Circumpolar Current form physical barriers preventing Antarctic surface water exchanges between the Southern Ocean and northern ocean areas (Aronson et al., 2007;Griffiths, 2010;Sanches et al., 2016), hence blocking the dispersal of most marine organisms (Convey & Peck, 2019;Peck et al., 2014). As a result of the prevalence of such important marine fronts, combined with strong currents and the remoteness from other landmasses, a unique Southern Ocean marine diversity has been shaped (Barnes & Clarke, 2011;Clarke et al., 2005;Crame, 1999;Lawver et al., 1992). ...
Aim
The Western Antarctic Peninsula is challenged by climate change and increasing maritime traffic that together facilitate the introduction of marine non‐native species from warmer regions neighbouring the Southern Ocean. Ballast water exchange has been frequently reported as an introduction vector. This study uses a Lagrangian approach to model the passive drift of virtual propagules departing from Ballast water hypothetic exchange zones, at contrasting distances from the coasts.
Location
Western Antarctic Peninsula.
Methods
Virtual propagules were released over the 2008–2016 period and at three distances from the nearest coasts: 200 (convention for the management of Ballast Water, 2004), 50 or 11 nautical miles (NM).
Results
Results show that exchanging Ballast water at 200 NM considerably reduces the arrival of propagules in proposed marine protected areas of the western side of the Antarctic Peninsula. On the eastern side, propagules can reach north‐eastern marine protected areas within a few days due to strong currents for all tested scenarios. Seasonal and yearly variations indicate that exceptional climate events could influence the trajectory of particles in the region. Ballast water should be exchanged at least 200 NM offshore on the western side of the Antarctic Peninsula and avoided on the eastern side to limit particle arrival in proposed marine protected areas. Focusing on Deception Island, our results suggested that the Patagonian crab (Halicarcinus planatus) observed in 2010 could have been introduced in case of Ballast water exchange at 50 NM or less from the coast.
Main conclusions
This study highlights the importance of respecting Ballast water exchange convention to limit the risk of non‐native species introduction. Ballast water exchange should be operated at least at 200 NM from the coasts, which further limits particle arrival in shallow water areas. This is especially important in the context of a more visited and warmer Southern Ocean.
... The several phases of tectonic uplift controlled and altered the contours of the land and, thereby, river courses and watershed limits (Lundberg et al., 1998). It is important to note that the southern portion of South America formed a continuous landmass with Australia and New Zealand through Antarctica (Crame, 1999;Scotese, 1991;White, Gibson, & Lister, 2013). ...
Aim
South America is considered a biologically hybrid continent. To the south, the Patagonian region harbours a unique biota strongly related to other southern continents. To the northern portion, tropical and subtropical areas from the Neotropical region show a more complex taxocoenosis related to the Nearctic and Afro‐Oriental regions. The South American Transition Zone (STZ) has been proposed to belong simultaneously to both regions. This work aimed to test the validity of STZ in the light of the distributions of an ancient freshwater taxon.
Location
South America.
Taxon
Ephemeroptera.
Methods
We compiled a dataset including all mayfly species having at least one record in South America (8,268 records for 661 species). By using the Network Analysis Method (NAM), we analysed the validity and delimitation of the STZ.
Results
The distributions of Ephemeroptera give rise to groups of cohesively sympatric species with a clear distinction between Patagonian and Neotropical regions. Although some degree of overlap occurs between them, the overlapping area does not match the STZ to a significant extent. The units of co‐occurring species recovered show that Neotropical groups mainly occupy the STZ.
Main conclusions
Almost the entire provinces of Puna, Desert and Paramo are not supported as part of the STZ by mayfly distribution. The transition zone between Patagonian and Neotropical mayfly fauna involves Southern Puna and high Andes (south to 17° S latitude), Monte province, and a narrow portion of Patagonian steppe with Chubut River being the southern limit.
... The presence of SACW is related to the presence of a fully operating cold Malvinas (Falkland) Current (MC), which in its turn is related to the opening of the Drake Passage. Despite superficial water circulation that may have started 36-28 Ma, the opening between South America and Antarctica became effective for deep waters not earlier than the middle Miocene (Crame, 1999). Martínez and del Río (2002), however, showed that mollusks from latitudes as south as 42°S were inhabitants of warm waters by the late Miocene (Tortonian, up to 7.25 Ma), suggesting that the MC still had a very low activity in the area during that time. ...
Aim:
We evaluated traditional biogeographic boundaries of coastal marine regions in Southwestern Atlantic using DNA sequence data from common, rocky-shore inhabiting, marine mites of the genera Agauopsis and Rhombognathus, family Halacaridae.
Methods:
We investigated geographic population genetic structure using CO1 gene sequences, estimated divergence times using a multigene dataset and absolute time-calibrated molecular clock analyses, and performed environmental niche modeling (ENM) of common marine mite species.
Results:
Agauopsis legionium has a shallow history (2.01 Ma) with four geographically differentiated groups. Two of them corresponded to the traditional Amazonian and Northeastern ecoregions, but the boundary between the two other groups was inferred at the Abrolhos Plateau, not Cabo Frio. Rhombognathus levigatoides s. lat. was represented by two cryptic species that diverged 7.22 (multilocus data) or 10.01 Ma (CO1-only analyses), with their boundary, again at the Abrolhos Plateau. ENM showed that A. legionium has suitable habitats scattered along the coast, while the two R. levigatoides cryptic species differ considerably in their niches, especially in parameters related to upwelling. This indicates that genetic isolation associated with the Abrolhos Plateau occurred in both lineages, but for the R. levigatoides species complex, ecological niche specialization was also an important factor.
Main conclusions:
Our study suggests that the major biogeographic boundary in the Southwestern Atlantic lies not at Cabo Frio but at the Abrolhos Plateau. There two biogeographically relevant factors meet (a) changes in current directions (which limit dispersal) and (b) abrupt changes in environmental parameters associated with the South Atlantic Central Waters (SACW) upwelling (offering distinct ecological niches). We suggest that our result represents a general biogeographic pattern because a barrier at the Abrolhos Plateau was found previously for the fish genus Macrodon (phylogeographic data), prosobranch mollusks, ascidians, and reef fishes (community-level data).
... Biogeographical mechanisms explaining the distribution of southern temperate taxa have been debated for more than a century (Crame, 1999;Darwin, 1845;Dell, 1972;Knox, 1960;Strugnell, Rogers, Prod€ ohl, Collins, & Allcock, 2008). Recently, the literature has been characterized by disagreement over the relative importance of vicariance versus dispersal in the biogeography of the Southern Ocean biota but consensus has emerged about the combined significance of these processes (Clarke, Barnes, & Hodgson, 2005;Fraser, Nikula, Spencer, & Waters, 2009;Gonz alez-Wevar, Nakano, Cañete, & Poulin, 2010;Gonzalez-Wevar et al., 2017;Moon, Chown, & Fraser, 2017;Nikula, Fraser, Spencer, & Waters, 2010;Nikula, Spencer, & Waters, 2012;Poulin, Gonzalez-Wevar, D ıaz, G erard, & H€ une, 2014;Sauc ede, Pierrat, Danis, & David, 2014;Waters, 2008). ...
Aim
We assess biogeographical patterns, population structure and the range of species in the pulmonate genus Siphonaria across the sub‐Antarctic. We hypothesized that locally endemic cryptic species will be found across the distribution of these direct‐developing limpets in the sub‐Antarctic.
Location
The sub‐Antarctic coasts of the Southern Ocean including South America, the Falkland/Malvinas, South Georgia, Kerguelen and Macquarie Islands.
Methods
Multi‐locus phylogenetic reconstructions, mt DNA time‐calibrated divergence time estimations and population‐based analyses of Siphonaria populations were used at the scale of the Southern Ocean.
Results
We resolve two widely distributed lineages of Siphonaria ( S. lateralis and S. fuegiensis ) across the sub‐Antarctic. Mt DNA divergence time estimates suggest that they were separated around 4.0 Ma (3.0 to 8.0 Ma). Subsequently both species followed different evolutionary pathways across their distributions. Low levels of genetic diversity characterize the populations of both species, reflecting the role of Quaternary glacial cycles during their respective demographic histories, suggesting high levels of dispersal among geographically distant localities.
Main conclusions
Siphonaria lateralis and S. fuegiensis constitute sister and broadly co‐distributed species across the sub‐Antarctic. Unexpected transoceanic similarities and low levels of genetic diversity in both these direct‐developing species imply recurrent recolonization processes through long‐distance dispersal to isolated sub‐Antarctic islands. For such groups of Southern Ocean invertebrates, rafting may be more effective for long‐distance dispersal than a free‐living planktotrophic larval stage. This biogeographical model may explain why many marine species lacking a dispersal phase exhibit broad distributions, low genetic diversity and low population structure over thousands of kilometres.
... Previous phylogeographic work has indicated that the Kiwaidae may have radiated into the Southern Ocean from a Pacific origin, probably through the deep-water connection of the Drake Passage some 30 million years ago (Ma) (Roterman et al. 2013). In this scenario, the Kiwaidae would have entered the Southern Ocean prior to the geographic and physiological isolation of this water body (Crame 1999). The process of Antarctic cooling began during the late Eocene, approximately 55 Ma, but the cold-water environment typical of the South-ern Ocean today was likely not characterised until a final cooling step lasting until about 14 Ma (Clarke 1990, Zachos et al. 2001, Shevenell et al. 2004). ...
... The process of Antarctic cooling began during the late Eocene, approximately 55 Ma, but the cold-water environment typical of the South-ern Ocean today was likely not characterised until a final cooling step lasting until about 14 Ma (Clarke 1990, Zachos et al. 2001, Shevenell et al. 2004). These large-scale geo-climatic considerations are important when assessing the evolution and radiation of Southern Ocean fauna and have been subject to debate on many occasions (Clarke 1993, Crame 1999. The origins and antiquity of Southern Ocean biota, in many cases, may pre-date the Antarctic cooling event. ...
The deep-sea squat lobster Kiwa tyleri (also known as yeti crab) is the dominant macroinvertebrate inhabiting hydrothermal vents on the northern and southern segments of the East Scotia Ridge in the Southern Ocean. Here, we describe the first zoeal stage of the species—which is morphologically advanced—and provide evidence for its lecithotrophy in development. This morphologically advanced stage at hatching suggests that dispersal potential during early ontogeny may be limited. Adults of K. tyleri typically inhabit a warm-eurythermal, and spatially defined, temperature envelope of vent chimneys. In contrast, ovigerous females with late embryos are found away from these temperatures, off the vent site. This implies that at least part of embryogenesis takes place away from the chemosynthetic environment. Larvae are released into the cold waters of the Southern Ocean that are known to pose physiological limits on the survival
of reptant decapods. Larval lecithotrophy may aid long developmental periods under these conditions and facilitate development independent of pronounced seasonality in primary production. It remains uncertain, however, how population connectivity between distant vent sites may be achieved.
At opposite ends of our world lie the poles. In the North, the Arctic, an ocean surrounded by coasts; in the South, the Antarctic continent surrounded by an ocean that separates it from the nearest landmasses. At first glance, the poles could not be more dissimilar owing to their contrasting location, geography, and tectonic and evolutionary history. The amplitude and types of ice cover, though differing between the poles, are influenced by the same climatic, atmospheric, and hydrodynamic processes that affect the entire Earth. Freshwater influx into their coastal areas too—beyond the effects of glaciological changes and dynamics such as glacier melt and increasing meltwater discharges—is different: in contrast to the Arctic, the Antarctic continent and sub-Antarctic islands lack major rivers. However, their latitudinal range and low temperatures, ice shelves, icebergs, sea ice, impacts from tidewater and land-based glaciers, significant seasonal variation in light intensity and, hence, primary productivity, offer parallel environments for organisms that have adapted to such conditions. Although we know much about the similarities and differences from an environmental perspective, there are still many unknowns about how benthic communities, especially the meiobenthos, from both regions compare. In this chapter, we provide an overview of the contrasts and parallels between Arctic and Antarctic meiobenthos and place it into context of their extreme habitats. Following a brief account of Arctic and Antarctic evolution and the historical study of their faunas, we (i) compare how extreme polar conditions affect meiofauna across four main habitats: polar coastal areas and fjords, continental shelves and ice shelves, the deep sea, and sea ice, and we (ii) discuss the implications of climate change on meiofauna in these habitats. Reflecting on (i) and (ii) allowed us to identify frontiers for future research of polar meiofauna, which we put forward in the concluding sections of this chapter.
The Antarctic coastal fauna is characterized by high endemism related to the progressive cooling of Antarctic waters and their isolation by the Antarctic Circumpolar Current. The origin of the Antarctic coastal fauna could involve either colonization from adjoining deep-sea areas or migration through the Drake Passage from sub-Antarctic areas. Here, we tested these hypotheses by comparing the morphology and genetics of benthic foraminifera collected from Antarctica, sub-Antarctic coastal settings in South Georgia, the Falkland Islands and Patagonian fjords. We analyzed four genera (Cassidulina, Globocassidulina, Cassidulinoides, Ehrenbergina) of the family Cassidulinidae that are represented by at least nine species in our samples. Focusing on the genera Globocassidulina and Cassidulinoides, our results showed that the first split between sub-Antarctic and Antarctic lineages took place during the mid-Miocene climate reorganization, probably about 20 to 17 million years ago (Ma). It was followed by a divergence between Antarctic species ~ 10 Ma, probably related to the cooling of deep water and vertical structuring of the water-column, as well as broadening and deepening of the continental shelf. The gene flow across the Drake Passage, as well as between South America and South Georgia, seems to have occurred from the Late Miocene to the Early Pliocene. It appears that climate warming during 7–5 Ma and the migration of the Polar Front breached biogeographic barriers and facilitated inter-species hybridization. The latest radiation coincided with glacial intensification (~ 2 Ma), which accelerated geographic fragmentation of populations, demographic changes, and genetic diversification in Antarctic species. Our results show that the evolution of Antarctic and sub-Antarctic coastal benthic foraminifera was linked to the tectonic and climatic history of the area, but their evolutionary response was not uniform and reflected species-specific ecological adaptations that influenced the dispersal patterns and biogeography of each species in different ways.
The systematics of Subantarctic and Antarctic near-shore marine benthic invertebrates requires major revision and highlights the necessity to incorporate additional sources of information in the specimen identification chart in the Southern Ocean (SO). In this study, we aim to improve our understanding of the biodiversity of Kidderia (Dall 1876) through molecular and morphological comparisons of Antarctic and Subantarctic taxa. The microbivalves of the genus Kidderia are small brooding organisms that inhabit intertidal and shallow subtidal rocky ecosystems. This genus represents an interesting model to test the vicariance and dispersal hypothesis in the biogeography of the SO. However, the description of Kidderia species relies on a few morphological characters and biogeographic records that raise questions about the true diversity in the group. Here we will define the specimens collected with genetic tools, delimiting their respective boundaries across provinces of the SO, validating the presence of two species of Kidderia. Through the revision of taxonomic issues and species delimitation, it was possible to report that the Antarctic species is Kidderia subquadrata and the species recorded in the Subantarctic islands Diego Ramirez, South Georgia and the Kerguelen Archipelago is Kidderia minuta. The divergence time estimation suggests the origin and diversification of Kidderia lineages are related to historical vicariant processes probably associated with the separation of the continental landmasses close to the late Eocene.
Supplementary information:
The online version contains supplementary material available at 10.1007/s00300-021-02885-6.
In the Southern Ocean, rapid climatic fluctuations during the Quaternary are thought to have induced range contractions and bottlenecks, which drastically impacted marine communities. For photosynthetic macroalgae that are restricted to very shallow waters, survival in deepwater refugia is not possible. Comparing pattern of distribution of genetic diversity using sequences of mitochondrial and chloroplast markers in distinct species of green, brown and red macroalgae, we sought to detect common responses to the effect of these glacial cycles. All the Antarctic macroalgae were characterized by very low genetic diversity, absence of genetic structure and significant signatures of recent population expansion. The eight studied species seem to have barely survived glacial events in situ, in a unique refugium from which they recolonized their current distribution area. We propose that polynyas or areas showing long-term geothermal activity along Antarctic continental margins or peri-Antarctic islands could be good candidate as glacial refugium, but more variable genetic markers will be needed to precisely pinpoint its location. Common haplotypes, scattered over hundreds or even thousands of kilometres of coastline, point out to long-distance dispersal of fronds drifting on the strong oceanic currents in the region as the main mechanism of postglacial expansion.
The Arctic and Antarctic share many oceanographical features but differ greatly in their geological histories. These divergent aspects lead to similarities and differences between the sets of species inhabiting the poles. However, the patterns are not unambiguously homogenous throughout the tree of life. For the first time, Hydrozoa (Leptothecata and Anthoathecata) is used as a model group to study patterns of diversity, distribution, bathymetry and life history strategies between the polar regions. The analyses are based on a comprehensive literature survey of hydrozoan records. Subtle differences in species richness and contrasting values of endemism are found between the Antarctic (252 species and 58% endemics) and Arctic (233 species and 20% endemics) regions. Shared trends include the lack of a medusa stage in most of the representatives, a high percentage of rarity (Arctic: 49%; Antarctic: 63%), and few common species (18% in both regions). A few species (Grammaria abietina, Obelia longissima and Paragotoea bathybia) and genera (Bouillonia and Gymnogonos) might be tentatively considered bipolar, but further molecular investigation is recommended. The bathymetric distribution mirrors the geomorphological characteristics of each region. The highest species richness occurred in the continental shelves of both polar regions. Updated inventories from each polar region are provided as supplementary material. The present work establishes a fundamental step towards an integrated bipolar framework for the study of diversity and ecology of polar regions, laying the foundation for future approaches on a wide array of topics, from origin and diversification, to changes in the distribution of polar biota.
