Deep-sea Isopod Research Articles

A deep-sea isopod that consumes Sargassum sinking from the ocean's surface.

Most deep-ocean life relies on organic carbon from the surface ocean. While settling primary production rapidly attenuates in the water column, pulses of organic material can be quickly transported to depth in the form of food falls. One example of fresh material that can reach great depths across the tropical Atlantic Ocean and Caribbean Sea is the pelagic macroalgae Sargassum. However, little is known about the deep-ocean organisms able to use this food source. Here, we encountered the isopod Bathyopsurus nybelini at depths 5002-6288 m in the Puerto Rico Trench and Mid-Cayman Spreading Center using the Deep Submergence Vehicle Alvin. In most of the 32 observations, the isopods carried fronds of Sargassum. Through an integrative suite of morphological, DNA sequencing, and microbiological approaches, we show that this species is adapted to feed on Sargassum by using a specialized swimming stroke, having serrated and grinding mouthparts, and containing a gut microbiome that provides a dietary contribution through the degradation of macroalgal polysaccharides and fixing nitrogen. The isopod's physiological, morphological, and ecological adaptations demonstrate that vertical deposition of Sargassum is a direct trophic link between the surface and deep ocean and that some deep-sea organisms are poised to use this material.

A new family of Asellota (Crustacea, Isopoda) from the deep sea of Zealandia

A new family-level taxon of deep-sea isopods, Basoniscus hikurangi gen. et sp. nov., was recovered from the Hikurangi Plateau in the deep sea off eastern New Zealand. The broad-bodied, eyeless, seemingly unremarkable isopod was unusual in its possession of features that characterize two different families: the shallow water Joeropsididae Nordenstam, 1933 and the deep-sea Haploniscidae Hansen, 1916. An analysis of superfamily Janiroidea G.O. Sars, 1897 was conducted to establish the affinities of the species. Multiple analyses were done using unweighted and implied weighted characters. Existing families were well supported, with B. hikurangi intermediate between Joeropsididae and Haploniscidae. The new species, however, cannot be placed in either family owing to its lack of important defining synapomorphies of each family. As a result, Basoniscidae fam. nov. was created to contain this new species. That rocky hard substrates are undersampled is another implication. Our understanding of deep-sea species richness will not be accurate until more efforts are made to survey these habitats, especially more sites in the southern hemisphere. These gaps in our knowledge of the deep sea impairs any general claims about the distribution of biodiversity on a global scale. This find demonstrates that museums hold underused but valuable resources for understanding and describing the biodiversity of the deep sea.

Diexanthema hakuhomaruae sp. nov. (Copepoda: Siphonostomatoida: Nicothoidae) from the Hadal Zone in the Northwestern Pacific, with an 18S Molecular Phylogeny.

Diexanthema copepods are ectoparasites on deep-sea isopods. This genus currently contains six species, all reported from the North Atlantic. Our study describes a new species of Diexanthema found on isopods from 7184 to 7186m depth in the Kuril-Kamchatka Trench, northwestern Pacific. We observed the copepod's morphology, made camera-lucida drawings, and compared our species with congeners. We determined partial sequences for its 16S rRNA and 18S rRNA genes and constructed an 18S-based maximum-likelihood copepod tree to place it phylogenetically. We identified the host isopod species through morphology and cytochrome c oxidase subunit I (COI, cox1) and 18S sequences. We described the copepod as Diexanthema hakuhomaruae sp. nov. and identified its host as Eugerdella cf. kurabyssalis Golovan, 2015 (Desmosomatidae). This is the first Diexanthema copepod from the Pacific and also from hadal depths. Diexanthema hakuhomaruae most closely resembles D. bathydiaita Richie, 1975, parasitic on Nannoniscus sp. (Nannoniscidae) in the Atlantic, but differs from the latter in having a smooth body surface and leg 5 in the ventrolateral region of the urosome. In the 18S tree, D. hakuhomaruae was the sister group to the Rhizorhina clade, which is consistent with the morphology-based hypothesis that they are closely related.

Metabolic responses to food and temperature in deep-sea isopods, Bathynomus doederleini

Metabolic rate, the amount of energy consumed per unit of time, for an organism to sustain life, is influenced by both intrinsic and extrinsic factors. Despite similarities among living organisms across the various domains of life, those adapted to deep-sea environments exhibit notable differences from those in shallower waters, even when accounting for size and temperature. However, as deep-sea organisms are infrequently kept in captivity for prolonged periods, investigations into their potential metabolic responses to food and temperature have not been conducted. In this study, we demonstrate the impact of food (specific dynamic action: SDA) and temperature (Q10) on the metabolic rate of the deep-sea isopod, Bathynomus doederleini. There were positive correlations between SDA parameters (peak rate, time to peak, duration, and factorial scope) and meal size in deep-sea organisms. The postprandial metabolic rate, at a meal constituting 45% of wet body weight, increased by approximately 6.5-fold, and the duration was 20 days. Within the temperature range of their natural habitat (15–6 °C), the overall Q10 was 2.36, indicating that a 10 °C increase would lead to a 2.4-fold increase in resting metabolic rate. This species could survive for a year on a few grams of whale blubber at a water temperature of 10.5 °C. This information is crucial to understand the metabolic strategies and consequences of adaptation to deep-sea environments.

Quick Hits: The beginnings of agriculture in Turkey, the bitter origins of watermelon, a giant deep-sea isopod found in Mexico and more in this month's Quick Hits.

Quick Hits: The beginnings of agriculture in Turkey, the bitter origins of watermelon, a giant deep-sea isopod found in Mexico and more in this month's Quick Hits.

Correct Species Identification and Its Implications for Conservation Using Haploniscidae (Crustacea, Isopoda) in Icelandic Waters as a Proxy

Correct identification of species is required to assess and understand the biodiversity of an ecosystem. In the deep sea, however, this is only possible to a limited extent, as a large part of the fauna is undescribed and the identification keys for most taxa are inadequate or missing. With the progressive impact of climate change and anthropogenic activities on deep-sea ecosystems, it is imperative to define reliable methods for robust species identification. In this study, different techniques for the identification of deep-sea species are tested, including a combination of morphological, molecular (DNA barcoding, and proteomic fingerprinting), biogeographical and ecological modeling approaches. These are applied to a family of isopods, the Haploniscidae, from deep waters around Iceland. The construction of interactive identification keys based on the DELTA format (DEscription Language for TAxonomy) were a major pillar of this study, the evaluation of which was underpinned by the application of the supplementary methods. Overall, interactive keys have been very reliable in identifying species within the Haploniscidae. Especially in a deep-sea context, these types of keys could become established because they are easy to adapt and flexible enough to accommodate newly described species. Remarkably, in this study, the interactive key enabled identification of a supposedly new species within the Haploniscidae that was later verified using both molecular genetic – and proteomic methods. However, these keys are limited given that they are based on purely morphological characteristics, including where species with strong ontogenetic or sexual dimorphism occur as both genders are not always described. In this case, integrative taxonomy is the method of choice and the combination presented here has been shown to be very promising for correct identification of deep-sea isopods.

Recent speciation and hybridization in Icelandic deep-sea isopods: An integrative approach using genomics and proteomics.

The crustacean marine isopod species Haploniscusbicuspis (Sars, 1877) shows circum-Icelandic distribution in a wide range of environmental conditions and along well-known geographic barriers, such as the Greenland-Iceland-Faroe (GIF) Ridge. We wanted to explore population genetics, phylogeography and cryptic speciation as well as investigate whether previously described, but unaccepted subspecies have any merit. Using the same set of specimens, we combined mitochondrial COI sequences, thousands of nuclear loci (ddRAD), and proteomic profiles, plus selected morphological characters using confocal laser scanning microscopy (CLSM). Five divergent genetic lineages were identified by COI and ddRAD, two south and three north of the GIF Ridge. Assignment of populations to the three northern lineages varied and detailed analyses revealed hybridization and gene flow between them, suggesting a single northern species with a complex phylogeographic history. No apparent hybridization was observed among lineages south of the GIF Ridge, inferring the existence of two more species. Differences in proteomic profiles between the three putative species were minimal, implying an ongoing or recent speciation process. Population differentiation was high, even among closely associated populations, and higher in mitochondrial COI than nuclear ddRAD loci. Gene flow is apparently male-biased, leading to hybrid zones and instances of complete exchange of the local nuclear genome through immigrating males. This study did not confirm the existence of subspecies defined by male characters, which probably instead refer to different male developmental stages.

Deep sea isopods from the western Mediterranean: Distribution and habitat

Isopods are a highly diversified group of deep-sea fauna, with a wide variety of shapes which must reflect a similar great variety of adaptations to the deep environments. The deep Mediterranean, however, has a low diversity of isopods related to its oligotrophy, the thermal stability of deep-water masses (~12.8 °C below 150–200 m) and rather homogeneous geomorphology. The main factor defining isopod habitats in the Balearic Basin is insularity vs mainland influence. Desmosomatidae and Ischnomesidae, examples of epibenthic species (with lack of paddle-shaped legs and non/low-natatory capacity) are mainly linked to mainland areas with higher % organic matter (OM) and labile C, indicating food availability. By contrast, suprabenthic species like Munnopsidae (with some paddle-shaped, natatory, legs) are more dominant in insular areas. Compared with the Atlantic, the degree of impoverishment in diversity (number of species, S) of deep-Mediterranean asellotes is higher among epibenthos (with a lot of families/genera absent in the deep Mediterranean) than for suprabenthic species, with potential natatory capacity (natatory legs). This suggests that the high diversity of deep sea asellotes may depend on the trophic niches (sediment richness and diversity of habitats) available. In the 20 yrs period (1991–2011) of our (non-continuous) sampling series we identified some climatic influence (higher ENSO index) on the high densities reported in 1991–1992 samples, related to species taken at submarine canyons in mainland areas. Higher food availability (by advection) in canyons during 1991 and 1992 related with an increase of rainfall regime may enhance recruitment (e.g. in March 1992 inside canyons) and abundance/diversity of asellotes, especially for epibenthic species (Desmosomatidae).

Changes in species composition of Haploniscidae (Crustacea: Isopoda) across potential barriers to dispersal in the Northwest Pacific

Speciation processes as drivers of biodiversity in the deep sea are still not fully understood. One potential driver for species diversification might be allopatry caused by geographical barriers, such as ridges or trenches, or physiological barriers associated with depth. We analyzed biodiversity and biogeography of 21 morphospecies of the deep-sea isopod family Haploniscidae to investigate barrier effects to species dispersal in the Kuril-Kamchatka Trench (KKT) area in the Northwest (NW) Pacific. Our study is based on 2652 specimens from three genera, which were collected during the German-Russian KuramBio I (2012) and II (2016) expeditions as well as the Russian-German SokhoBio (2015) campaign. The sampling area covered two potential geographical barriers (the Kuril Island archipelago and the Kuril-Kamchatka Trench), as well as three depth zones (bathyal, abyssal, hadal). We found significant differences in relative species abundance between abyssal and hadal depths. Haploniscus belyaevi Birstein, 1963 was the dominant species at abyssal stations while H. hydroniscoides Birstein, 1963 was prevalent in the hadal. Species composition also differed significantly across geographical barriers. While H. hydroniscoides was the most abundant species in the open NW Pacific, not a single specimen of this species was found in the Sea of Okhotsk, which is separated from the Pacific basin by the Kuril Islands. Furthermore, H. belyaevi and two morphologically highly similar morphospecies were the only species found in samples from the Sea of Okhotsk, meaning that the other 18 species, which we identified from our samples, did not occur west of the Kuril Islands. In this study, haploniscid species show very diverse patterns in geographic distribution between geographic areas and with depth. Therefore, the KKT might have an isolating effect on both the bathymetric as well as geographic distribution of some haploniscid species from the NW Pacific into the Sea of Okhotsk and from the western to the eastern abyssal margin of the KKT.

Bathynomus giganteus (Isopoda: Cirolanidae) and the canyon: a population genetics assessment of De Soto Canyon as a glacial refugium for the giant deep-sea isopod

Population genetics has gained popularity as a method to discover glacial refugia in terrestrial species, but has only recently been applied to the marine realm. The last glacial maxima occurred 20,000 years ago, decreasing sea levels by 120 m and exposing much of the continental shelf in the northern Gulf of Mexico, with the exception of De Soto Canyon (2100 m depth). The goal of this study was to determine whether population dynamics of the giant deep-sea isopod, Bathynomus giganteus, were better explained by habitat diversity or by the past presence of a marine glacial refugium in De Soto Canyon. To accomplish this we (1) measured genetic diversity in De Soto Canyon and adjacent regions, (2) characterized gene flow and connectivity between these regions, and (3) investigated historical changes to population size. We sequenced three mitochondrial loci (12S, 16S, and COI) from 212 individuals and also performed a next-generation sequencing pilot study using double digest Restriction site-Associated DNA sequencing. We found high genetic diversity and connectivity throughout the study regions, migration between all three regions, low population differentiation, and evidence of population expansion. This study suggests that habitat heterogeneity, rather than the presence of a glacial refugium, has had an historical effect on the population dynamics of B. giganteus.

Molecular Characterization of a Novel N-Acetylneuraminate Lyase from a Deep-Sea Symbiotic Mycoplasma.

N-acetylneuraminic acid (Neu5Ac) based novel pharmaceutical agents and diagnostic reagents are highly required in medical fields. However, N-acetylneuraminate lyase（NAL）for Neu5Ac synthesis is not applicable for industry due to its low catalytic efficiency. In this study, we biochemically characterized a deep-sea NAL enzyme (abbreviated form: MyNal) from a symbiotic Mycoplasma inhabiting the stomach of a deep-sea isopod, Bathynomus jamesi. Enzyme kinetic studies of MyNal showed that it exhibited a very low Km for both cleavage and synthesis activities compared to previously described NALs. Though it favors the cleavage process, MyNal out-competes the known NALs with respect to the efficiency of Neu5Ac synthesis and exhibits the highest kcat/Km values. High expression levels of recombinant MyNal could be achieved (9.56 mol L−1 culture) with a stable activity in a wide pH (5.0–9.0) and temperature (40–60 °C) range. All these features indicated that the deep-sea NAL has potential in the industrial production of Neu5Ac. Furthermore, we found that the amino acid 189 of MyNal (equivalent to Phe190 in Escherichia coli NAL), located in the sugar-binding domain, GX189DE, was also involved in conferring its enzymatic features. Therefore, the results of this study improved our understanding of the NALs from different environments and provided a model for protein engineering of NAL for biosynthesis of Neu5Ac.

Correction to: An organ of equilibrium in deep-sea isopods revealed: the statocyst of Macrostylidae (Crustacea, Peracarida, Janiroidea)

Unfortunately, Table 1 was incorrectly published in the original version and the same is corrected here in this erratum. The original article was corrected.

An organ of equilibrium in deep-sea isopods revealed: the statocyst of Macrostylidae (Crustacea, Peracarida, Janiroidea)

Isopoda (Crustacea, Peracarida) from the deep sea are relatively well studied but little is known about their lifestyles or the functional morphology and anatomy. The isopod family Macrostylidae, for example, is rather small in size, usually less than 1 cm in body length, and occurs mainly in the deep sea between 3000–6000 m. This family features a paired subepidermal structure on the posterior end of the pleotelson. It has been reported only in this family and was first mentioned by Hansen in 1916, who hypothesised that it represents a pair of statocysts. Nevertheless, neither the structure nor the function has been investigated until now. The shape of some related features, however, has already been used for species differentiation thus indicating that phylogenetically as well as systematically valuable information may be inherent in this feature. Here, the anatomy of this structure was studied based on four species of Macrostylidae from the North Pacific and Atlantic Oceans. It was digitally reconstructed from histological sections. The paired structure comprised two tergal invaginations, each with distinct muscular attachments and a modified seta that distally held a statocyst on the shaft. This resembles equilibrium organs reported from other organisms and thus the statocysts hypothesis seems reliable. Using energy-dispersive X-ray spectroscopy, the substance of the statolith could be determined as silicon dioxide. Based on these findings, the function of this organ and its potential phylogenetic and ecological implications are discussed.

New species of the giant deep-sea isopod genus Bathynomus (Crustacea, Isopoda, Cirolanidae) from Hainan Island, South China Sea.

Several specimens of the giant deep-sea isopod genus Bathynomus were collected by a deep-sea lander at a depth of 898 m near Hainan Island in the northern South China Sea. After careful examination, this material and the specimens collected from the Gulf of Aden, north-western Indian Ocean, previously reported as Bathynomus sp., were identified to be the same as a new species to the genus. Bathynomus jamesi sp. nov. can be distinguished from the congeners by: the distal margin of pleotelson with 11 or 13 short straight spines and central spine not bifid; uropodal endopod and exopod with distolateral corner slightly pronounced; clypeus with lateral margins concave; and antennal flagellum extending when extended posteriorly reaches the pereonite 3. In addition, Bathynomus jamesi sp. nov. is also supported by molecular analyses based on mitochondrial COI and 16S rRNA gene sequences. The distribution range of the new species includes the western Pacific and north-western Indian Ocean.

First record of the deep-sea isopod family Dendrotionidae (Isopoda: Asellota) from the Northwest Pacific with description of two new species of Dendromunna

Two new abyssal species of Dendrotionidae are described: Dendromunna kurilensis sp. nov. from the Northwest Pacific Basin to the east of the Kuril–Kamchatka Trench and D. okhotensis sp. nov. from the Kuril Basin of the Sea of Okhotsk. The new species represent the first records of the family for the Northwest Pacific and the first records of the genus for the North Pacific. The new species differ from the remaining species of Dendromunna by the extremely long antennae and pereopods (antenna I is about 0.7–0.8 body length, article 4 of antenna II is about 0.6–0.7 body length, bases of pereopods are about 0.2–0.3 body length), the male pereopod I with concave lateral margins, short pereonite 1 (<0.03 body length), and the lack of mandibular palp. D. okhotensis sp. nov. differs from D. kurilensis sp. nov. by the more slender body, presence of stout setae on the pereonites 1–4 ventral surface, by different number of maxilliped retinaculae, and by number of spines of the mandibular spine row. The key to the species of Dendromunna is presented.

Activity syndromes and metabolism in giant deep-sea isopods

Despite growing interest, the behavioural ecology of deep-sea organisms is largely unknown. Much of this scarcity in knowledge can be attributed to deepwater animals being secretive or comparatively ‘rare’, as well as technical difficulties associated with accessing such remote habitats. Here we tested whether two species of giant marine isopod (Bathynomus giganteus, Booralana tricarinata) captured from 653 to 875m in the Caribbean Sea near Eleuthera, The Bahamas, exhibited an activity behavioural syndrome across two environmental contexts (presence/absence of food stimulus) and further whether this syndrome carried over consistently between sexes. We also measured routine metabolic rate and oxygen consumption in response to a food stimulus in B. giganteus to assess whether these variables are related to individual differences in personality. We found that both species show an activity syndrome across environmental contexts, but the underlying mechanistic basis of this syndrome, particularly in B. giganteus, is unclear. Contrary to our initial predictions, neither B. giganteus nor B. tricarinata showed any differences between mean expression of behavioural traits between sexes. Both sexes of B. tricarinata showed strong evidence of an activity syndrome underlying movement and foraging ecology, whereas only male B. giganteus showed evidence of an activity syndrome. Generally, individuals that were more active and bolder, in a standard open arena test were also more active when a food stimulus was present. Interestingly, individual differences in metabolism were not related to individual differences in behaviour based on present data. Our study provides the first measurements of behavioural syndromes and metabolism in giant deep-sea isopods.

Genomic characterization of symbiotic mycoplasmas from the stomach of deep-sea isopod bathynomus sp.

Deep-sea isopod scavengers such as Bathynomus sp. are able to live in nutrient-poor environments, which is likely attributable to the presence of symbiotic microbes in their stomach. In this study we recovered two draft genomes of mycoplasmas, Bg1 and Bg2, from the metagenomes of the stomach contents and stomach sac of a Bathynomus sp. sample from the South China Sea (depth of 898 m). Phylogenetic trees revealed a considerable genetic distance to other mycoplasma species for Bg1 and Bg2. Compared with terrestrial symbiotic mycoplasmas, the Bg1 and Bg2 genomes were enriched with genes encoding phosphoenolpyruvate-dependent phosphotransferase systems (PTSs) and sodium-driven symporters responsible for the uptake of sugars, amino acids and other carbohydrates. The genome of mycoplasma Bg1 contained sialic acid lyase and transporter genes, potentially enabling the bacteria to attach to the stomach sac and obtain organic carbons from various cell walls. Both of the mycoplasma genomes contained multiple copies of genes related to proteolysis and oligosaccharide degradation, which may help the host survive in low-nutrient conditions. The discovery of the different types of mycoplasma bacteria in the stomach of this deep-sea isopod affords insights into symbiotic model of deep-sea animals and genomic plasticity of mycoplasma bacteria.

An assessment of post-release mortality for a commonly discarded deep-sea isopod (Bathynomus giganteus) using reflex impairment

AbstractEstimates of post-release mortality (PRM) rates for discarded bycatch are largely unknown across marine fisheries and represent a substantial source of uncertainty when estimating total fishery mortality. One way to predict PRM is through the use of reflex action mortality predictors (RAMP), whereby the presence or absence of target reflexes and known post-release fate are used to create a delayed mortality model. We employed reflex impairment assessments in concert with post-capture caging and video monitoring to predict 5-d PRM rates for the deep-sea giant isopod Bathynomus giganteus, a common bycatch species in numerous deepwater fisheries worldwide, and also considered the factors contributing to mortality. Mortality rates 5 d post-capture ranged from 50 to 100% and both RAMP scores and time at the surface were significant predictors of mortality, although our conclusions regarding the effect of surface time are limited. In-cage video documented little movement within the 24-h monitoring period following capture, and it appeared that surviving individuals often fed within the holding period after cage deployment. Our results suggest that PRM in B. giganteus is common and that this unaccounted source of mortality should be quantified for other deep-sea crustaceans captured as bycatch.

Megafaunal communities along a depth gradient on the tropical Brazilian continental margin

The species composition, abundance and diversity patterns of the epibenthic megafauna and fish community from the tropical Brazilian continental margin were analysed based on 42 bottom trawls from the Campos Basin continental shelf and slope. Trawls were collected aboard R/V Gyre during autumn 2008 from depths of 13 to 2030 m. Overall, 452 species belonging to five main taxa were identified: teleosts (Actinopterygii) were represented by 196 species, crustaceans by 113 species and echinoderms by 108 species. These three groups contributed 92% to the 452 taxa. Several species (289) were recorded only once or twice, and the species accumulation curves showed no signs of being close to reaching asymptotic values. A tendency of increasing diversity and richness with depth was observed. Analysis of the trawls showed the existence of megafaunal assemblages significantly associated with depth and water mass. The shelf group (13–100 m) had subgroups associated with Coastal Water (CW) and South Atlantic Central Water (SACW). The upper-slope group (376–501 m) was found exclusively under the influence of SACW. The mid- and lower-slope group (978–2030 m) had two subgroups associated with the presence of Antarctic Intermediate Water and North Atlantic Deep Water. The 39 typifying species contributed 90% to the global similarity. Teleosts and squids greatly contributed to the within-group similarity over the shelf, while decapods, echinoids and galatheids contributed to the upper-slope assemblage. Deep-sea isopods and decapods mostly contributed to the mid- and lower-slope assemblages.

Field and Laboratory Methods for DNA Studies on Deep-sea Isopod Crustaceans

AbstractField and laboratory protocols that originally led to the success of published studies have previously been only briefly laid out in the methods sections of scientific publications. For the sake of repeatability, we regard the details of the methodology that allowed broad-range DNA studies on deep-sea isopods too valuable to be neglected. Here, a comprehensive summary of protocols for the retrieval of the samples, fixation on board research vessels, PCR amplification and cycle sequencing of altogether six loci (three mitochondrial and three nuclear) is provided. These were adapted from previous protocols and developed especially for asellote Isopoda from deep-sea samples but have been successfully used in some other peracarids as well. In total, about 2300 specimens of isopods, 100 amphipods and 300 tanaids were sequenced mainly for COI and 16S and partly for the other markers. Although we did not set up an experimental design, we were able to analyze amplification and sequencing success of different methods on 16S and compare success rates for COI and 16S. The primer pair 16S SF/SR was generally reliable and led to better results than universal primers in all studied Janiroidea, except Munnopsidae and Dendrotionidae. The widely applied universal primers for the barcoding region of COI are problematic to use in deep-sea isopods with a success rate of 45–79% varying with family. To improve this, we recommend the development of taxon-specific primers.