Have we so far only seen the tip of the iceberg? Exploring species diversity and distribution of the giant amphipod Eurythenes

Additional material of the iconic giant amphipod Eurythenes was investigated. Recently, the species E. gryllus has been separated into 12 distinct species-level lineages of which several have been described as distinct species, based on both morphology and genetics. This study revealed three additional species-level lineages from unique sampling localities, showing that with minimal sampling effort, species diversity within Eurythenes can still increase. One species-level lineage was found in the Indian Ocean and another one in the Pacific, which was subsequently identified as E. thurstoni. In addition to the three species already reported from the Southern Ocean (E. maldoror, E. gryllus s.s. and E. andhakarae), a supplementary bathyal species was found in the Weddell Sea. E. gryllus was confirmed to be amphitropical including newly sampled localities around the Kerguelen Islands and additional samples from the Svalbard Archipelago. Building on new and earlier data, geographic and bathymetric distributions of the different species that have been discovered so far are presented here and several factors are evaluated for their likelihood of having triggered past speciation events in this scavenger. Topographic and hydrographical features are discussed but rejected as sufficient reasons for the distributional patterns observed. Bathymetric segregation is interpreted with regard to what is known about the ecology of the species. The previously reported genetic break around 3000 m persists in this new data-set for all species but one. This study underlines the need of processing all individuals sampled, since two or more sympatric species are found in different proportions, and that conclusions regarding diversity and distribution may drastically change when increasing sampling intensity and coverage. Finally, I suggest here that only a mere fraction of all Eurythenes species has yet been discovered and that a more complete knowledge of the ecology of the species is of paramount importance for interpreting their evolution

Bottom-up and top-down triggers of diversification: A new look at the evolutionary ecology of scavenging amphipods in the deep sea

The initial, anthropocentric view of the deep ocean was that of a hostile environment inhabited by organisms rendered lethargic by constant high pressure, low temperature and sparse food supply, hence evolving slowly. This conceptual framework of a spatially and temporally homogeneous, connected, strongly bottom-up controlled habitat implied a strong constraint on, or poor incentive for, speciation. Hence, the discovery in the late 1960s of high species diversity of abyssal benthic invertebrates came as a surprise. Since then, the slow-motion view of deep-sea ecology and evolution has speeded up and diversified in the light of increasing evidence accumulating from in situ visual observations complemented by molecular and other tools. The emerging picture is that of a much livelier, highly diversified and more complex deep-sea fauna than previously assumed. In this review we examine the consequences of the incoming information for developing a broader view of evolutionary ecology in the deep sea, and for scavenging amphipods in particular. We revisit the food supply to the deep-sea floor and hypothesize that the dead bodies of animals, ranging from zooplankton to large fish are likely to be a more important source of food than their friable faeces. Camera observations of baited traps indicate that amphipod carrion-feeders arrive within hours at the bait which continues to draw new individuals for days to months later, presumably by scent trails in tidal currents. We explore the different stages of food acquisition upon which natural selection may have acted, from detection to ingestion, and discuss the possibility of a broader range of food acquisition strategies, including predation and specializations. Although currently neglected in deep-sea ecology, top-down factors are likely to play a more important role in the evolution of deep-sea organisms. Predation on amphipods at baits by bathyal and abyssal fishes, and large predatory crustaceans in the hadal zone, is often observed. Finally, we develop hypotheses regarding the effects of past, present and imminent anthropogenic activities on scavenger biomass and how these can be tested with the most modern tools

Environmental DNA in an ocean of change: Status, challenges and prospects

Environmental DNA (eDNA) studies have burgeoned over the last two decades and the application of eDNA has increased exponentially since 2010, albeit at a slower pace in the marine system. We provide a literature overview on marine metazoan eDNA studies and assess recent achievements in answering questions related to species distributions, biodiversity and biomass. We investigate which are the better studied taxonomic groups, geographic regions and the genetic markers used. We evaluate the use of eDNA for addressing ecological and environmental issues through food web, ecotoxicological, surveillance and management studies. Based on this state of the art, we highlight exciting prospects of eDNA for marine time series, population genetic studies, the use of natural sampler DNA, and eDNA data for building trophic networks and ecosystem models. We discuss the current limitations, in terms of marker choice and incompleteness of reference databases. We also present recent advances using experiments and modeling to better understand persistence, decay and dispersal of eDNA in coastal and oceanic systems. Finally, we explore promising avenues for marine eDNA research, including autonomous or passive eDNA sampling, as well as the combined applications of eDNA with different surveillance methods and further molecular advances

Cruise Report RV Heincke HE560

The primary aim of this expedition was to investigate the spatial and temporal distribution, the ecology and physiology, as well as competition of co-occurring gadoid species (Atlantic cod, Polar cod, haddock) in the communities of Arctic and Atlantic influence around Svalbard. We sampled the benthic and pelagic communities (including plankton) on the shallow shelf regions of Svalbard to estimate the effects of climate change on Arctic ecosystems to obtain a picture of the entire system structure and function for a long-term monitoring program of the ‘Atlantification’ of the Svalbard region. We assessed the potential impact of changes in trophic interaction (predator-prey relations) of Atlantic cod (Gadus morhua), Polar cod (Boreogadus saida), haddock (Melanogrammus aeglefinus) and decapod crabs on the productivity and stability of benthic and pelagic communities in Arctic ecosystems, into which their distribution ranges now extend due to ocean warming. In addition to a stock assessment and distribution analysis of gadoid fish and decapod crabs, we aimed to obtain specimens of these species in the Atlantic and polar waters around Svalbard, which were transported alive back to Germany. Laboratory experiments under scenarios of climate change at the Alfred Wegener Institute then provided (and still provide) further insight into capacities for adaptation, performance and interaction of selected species of the Arctic ecosystem around Svalbard. The results will on the one hand be used in an international Norwegian-German project and the pan-Arctic data management system (Piepenburg et al. 2011), on the other hand they will flow into fisheries modelling at the University of Hamburg, the Thuenen Institute and socio-economic modelling approaches that build on the German ocean acidification project BIOACID (www.bioacid.de)

Using DNA Metabarcoding to Characterize the Prey Spectrum of Two Co-Occurring Themisto Amphipods in the Rapidly Changing Atlantic-Arctic Gateway Fram Strait

The two congeneric hyperiids Themisto libellula and T. abyssorum provide an important trophic link between lower and higher trophic levels in the rapidly changing Arctic marine ecosystem. These amphipods are characterized by distinct hydrographic affinities and are hence anticipated to be impacted differently by environmental changes, with major consequences for the Arctic food web. In this study, we applied DNA metabarcoding to the stomach contents of these Themisto species, to comprehensively reveal their prey spectra at an unprecedented-high-taxonomic-resolution and assess the regional variation in their diet across the Fram Strait. Both species feed on a wide variety of prey but their diet strongly differed in the investigated summer season, showing overlap for only a few prey taxa, such as calanoid copepods. The spatially structured prey field of T. libellula clearly differentiated it from T. abyssorum, of which the diet was mainly dominated by chaetognaths. Our approach also allowed the detection of previously overlooked prey in the diet of T. libellula, such as fish species and gelatinous zooplankton. We discuss the reasons for the differences in prey spectra and which consequences these may have in the light of ongoing environmental changes

DNA metabarcoding reveals a diverse, omnivorous diet of Arctic amphipods during the polar night, with jellyfish and fish as major prey

IntroductionCurrently, Arctic marine ecosystems are witnessing the most rapid physical changes worldwide, leading to shifts in pelagic and benthic communities and food web structure, concomitant with the introduction of boreal species. Gelatinous zooplankton or jellyfish represent one particular group of which several boreal species are prone to undergo significant poleward range expansions and population increases in the Arctic in the course of the ongoing changes. Historically, jellyfish were considered a trophic dead-end, but an increasing number of studies using modern tools have highlighted their role as major prey items in marine food webs. In this study, we aimed to verify the role of jellyfish and other metazoans as food sources in the Arctic polar night food web, when pelagic resources are limited.MethodsWe identified the diet of different bentho-pelagic amphipod species in the Atlantifying Kongsfjorden (West Svalbard) during the polar night. We regularly sampled lysianassoid and gammarid amphipods using baited traps and hand nets over a period of one month during the polar night and identified their diet spectrum by applying DNA metabarcoding (COI) to their stomach contents.ResultsWe demonstrate that all investigated species are omnivorous. Fish species including polar cod and snailfish, likely in the shape of carrion, played an important role in the diet of the scavengers Orchomenella minuta and Anonyx sarsi. Predation and potential scavenging on jellyfish contributed to the diet of all four investigated species, particularly for the species Gammarus setosus and G. oceanicus, as evidenced by high read abundances and high frequencies of occurrence. Besides jellyfish, crustaceans and macroalgae were important components of the diet of the two Gammarus species.DiscussionThe diverse jellyfish community present in Kongsfjorden in the polar night is clearly being utilized as a food source, either through pelagic feeding or feeding on jelly-falls, albeit to a different extent in the local amphipod community. These findings provide novel insights into the Arctic food web during the polar night and represent the first evidence of feeding on natural (non-experimental) jelly-falls

A biodiversity survey of scavenging amphipods in a proposed marine protected area: the Filchner area in the Weddell Sea, Antarctica

An integrative inventory of the amphipod scavenging fauna (Lysianassoidea), combining morphological identifications with DNA barcoding, is provided here for the Filchner area situated in the south-eastern Weddell Sea. Over 4400 lysianassoids were investigated for species richness and relative abundances, covering 20 different stations and using different sampling devices, including the southernmost baited traps deployed so far (76°S). High species richness was observed: 29 morphospecies of which 5 were new to science. Molecular species delimitation methods were carried out with 109 cytochrome c oxidase I gene (COI) sequences obtained during this study as well as sequences from specimens sampled in other Antarctic regions. These distance-based analyses (trees and the Automatic Barcode Gap Discovery method) indicated the presence of 42 lineages; for 4 species, several (cryptic) lineages were found. More than 96% of the lysianassoids collected with baited traps belonged to the species Orchomenella pinguides s. l. The diversity of the amphipod scavenger guild in this ice-bound ecosystem of the Weddell Sea is discussed in the light of bottom–up selective forces. In this southernmost part of the Weddell Sea, harbouring spawning and nursery grounds for silverfish and icefishes, abundant fish and mammalian food falls are likely to represent the major food for scavengers. Finally, the importance of biodiversity surveys in the context of the establishment of a marine protected area in this region (Weddell Sea MPA) is highlighted and how future studies can contribute to a better understanding the ecological role of scavengers in this system is discussed

A survival pack for escaping predation in the open ocean: amphipod – pteropod associations in the Southern Ocean

Hyperiidean amphipods are a major prey for fish and seabirds. In the Southern Ocean, they are particularly abundant, with distributions ranging from the Polar Frontal Zone to Antarctic shelf waters. The species Hyperiella dilatata has previously been reported to show a peculiar anti-predatory behaviour: It captures chemically protected, gymnosome pteropods in the water column and carries them on its dorsum, like a backpack. We report this association at four oceanic sampling sites between latitudes 45° and 71° S. Molecular barcodes of both hosts and pteropods are provided and compared with those of other hyperiidean and pteropod specimens. Morphological identifications as well as molecular analyses show a so far undocumented association of Hyperiella antarctica with the pteropod Spongiobranchaea australis in the Polar Frontal Zone (Lazarev Sea). H. dilatata carried Clione limacina antarctica specimens in the Weddell Sea, as recorded previously for the Ross Sea. Lengths of the abducted pteropods varied between 1 and 5 mm, with the biggest pteropod measuring more than half the host’s size. One of the abducting amphipods was a female carrying eggs. The formation of such tandem is known to be very efficient as protection from visually hunting icefish in the crystal-clear coastal waters around the Antarctic continent; however, in the open ocean, this behaviour was so far undocumented. Here, we develop hypotheses on its origin and function

Ancient globetrotters—connectivity and putative native ranges of two cosmopolitan biofouling amphipods

The geographic distributions of some coastal marine species have appeared as cosmopolitan ever since they were first scientifically documented. In particular, for many benthic species that are associated with anthropogenic substrata, there is much speculation as to whether or not their broad distributions can be explained by natural mechanisms of dispersal. Here, we focused on two congeneric coastal crustaceans with cosmopolitan distributions—the tube-dwelling amphipods Jassa marmorata and Jassa slatteryi. Both species are common elements of marine biofouling on nearly all kinds of artificial hard substrata in temperate to warm seas. We hypothesized that the two species’ modern occurrences across the oceans are the result of human shipping activities that started centuries ago. Mitochondrial DNA sequences of the CO1 fragment of specimens from distinct marine regions around the world were analysed, evaluating genetic structure and migration models and making inferences on putative native ranges of the two Jassa species. Populations of both species exhibited considerable genetic diversity with differing levels of geographic structure. For both species, at least two dominant haplotypes were shared among several geographic populations. Rapid demographic expansion and high migration rates between geographically distant regions support a scenario of ongoing dispersal all over the world. Our findings indicate that the likely former native range of J. marmorata is the Northwest Atlantic, whereas the likely former native range of J. slatteryi is the Northern Pacific region. As corroborated by the genetic connectivity between populations, shipping still appears to be the more successful vector of the two species’ dispersal when compared to natural mechanisms. Historical invasion events that likely started centuries ago, along with current ongoing dispersal, confirm these species’ identities as true “neocosmopolitans”

A genetic fingerprint of Amphipoda from Icelandic waters – the baseline for further biodiversity and biogeography studies

Source at https://doi.org/10.3897/zookeys.731.19931.Amphipods constitute an abundant part of Icelandic deep-sea zoobenthos yet knowledge of the diversity of this fauna, particularly at the molecular level, is scarce. The present work aims to use molecular methods to investigate genetic variation of the Amphipoda sampled during two IceAGE collecting expeditions. The mitochondrial cytochrome oxidase subunit 1 (COI) of 167 individuals originally assigned to 75 morphospecies was analysed. These targeted morhospecies were readily identifiable by experts using light microscopy and representative of families where there is current ongoing taxonomic research. The study resulted in 81 Barcode Identity Numbers (BINs) (of which >90% were published for the first time), while Automatic Barcode Gap Discovery revealed the existence of 78 to 83 Molecular Operational Taxonomic Units (MOTUs). Six nominal species (Rhachotropis helleri, Arrhis phyllonyx, Deflexilodes tenuirostratus, Paroediceros propinquus, Metopa boeckii, Astyra abyssi) appeared to have a molecular variation higher than the 0.03 threshold of both p-distance and K2P usually used for amphipod species delineation. Conversely, two Oedicerotidae regarded as separate morphospecies clustered together with divergences in the order of intraspecific variation. The incongruence between the BINs associated with presently identified species and the publicly available data of the same taxa was observed in case of Paramphithoe hystrix and Amphilochus manudens. The findings from this research project highlight the necessity of supporting molecular studies with thorough morphology species analyses