Xenograpsus Testudinatus Research Articles

Activity of the shallow-water hydrothermal vent crab Xenograpsus testudinatus is affected by tides, water temperature, and light intensity

Activity of the shallow-water hydrothermal vent crab Xenograpsus testudinatus is affected by tides, water temperature, and light intensity

Bacterial community responses of the hydrothermal vent crab Xenograpsus testudinatus fed on microplastics

Microplastics (MPs) provide persistent contaminants in freshwaters and the oceans from anthropogenic sources worldwide. MP contamination in ecosystems has emerged as a global environmental issue. While increasing research focused on the ecological consequences of plastic pollution, health-related implications of plastic pollution have been somewhat overlooked. In this study, we evaluated the effects of polyethylene MP contamination on microbial, physical, and biochemical characteristics of the hydrothermal vent crab Xenograpsus testudinatus over a 7-day food exposure. Different concentrations (0%, 0.3%, 0.6%, and 1.0%) of polyethylene MPs were used for feed intake experiments. Oxford Nanopore Technologies’ full-length sequencing of the 16S rDNA gene was used to explore the changes of the microbial composition in vent crab tissues. At the phylum level, the content of Firmicutes significantly decreased in the digestive gland tissue. Furthermore, the predicted functions of genes in the microbial community were significantly influenced by MPs. In contrast, there were eight functions in gill and 11 functions in digestive gland tissues identified at low and high intake levels. The dominant functions of methylotrophy, dark thiosulfate oxidation, dark oxidation of sulfur compounds, aromatic hydrocarbon degradation, and aromatic compound degradation were significantly increased at high intake levels in the digestive gland. These findings indicate that MP ingestion causes not only a short-term decrease in energy intake for crustaceans but also a change in microbial communities and their functions. This study provided a first account on the toxicity of MPs in a hydrothermal vent crab to aid in the assessment of health risks provided by polyethylene MP to marine invertebrates.

Differential feeding habits of the shallow-water hydrothermal vent crab Xenograpsus testudinatus correlate with their resident vent types at a scale of meters

Abstract. The shallow-water hydrothermal vents (SVs) located off Kueishan (KS) Island, Taiwan, are one of the world's most intensively studied vent systems. It has long been known that white vents (WVs) and yellow vents (YVs) differ in the color and composition of the vent plumes. The endemic vent crabs (Xenograpsus testudinatus) are abundant in both vent types, and ovigerous females migrate to the vent periphery with a distance of 100–200 m to release their offspring. However, most research on the vent crabs was associated with WV or unspecified vent areas. To increase our knowledge of the crabs dwelling in other vent types, we compared the feeding habits of the vent crabs living in WV and YV with 2 sampling months. Specifically, we examined the benthic community of WV and YV, the isotopic niche width, and protein expression patterns of the crabs from the two vents at a distance of 100 m and sampled in July and August 2010. The coverage of sessile organisms and low-mobility fauna in WV was more abundant than in YV, based on the survey in August 2010. The δ13C and δ15N values of crabs differed spatially and temporally (multivariate analysis of variance test; p<0.05). The niche width of the vent crabs from YV-August (0.88 ‰2) narrowed substantially compared to the rest, i.e., YV-July (2.94 ‰2), WV-July (2.88 ‰2), and WV-August (3.62 ‰2; p<0.05), respectively. Based on the protein expression patterns, the vent crabs exhibited three groups, i.e., WV-July and YV-July, WV-August, and YV-August, respectively. Our results indicated that the dwelling crabs were associated with their living vent, and within-vent variability was more noticeable in YV compared to WV. We suggested that vent crabs inhabit their resident vent. Even at a scale of meters, trans-vent movement is probably rare as an adaptation to minimize predation risk.

Duplicated paralog of sulfide: quinone oxidoreductase contributes to the adaptation to hydrogen sulfide-rich environment in the hydrothermal vent crab, Xenograpsus testudinatus

The hydrothermal crab, Xenograpsus testudinatus (xtcrab) inhabits shallow-water, hydrogen sulfide (H2S)-rich hydrothermal vent regions. Until now, the adaptative strategy of xtcrab to this toxic environment was unknown. Herein, we investigated the sulfide tolerance and detoxification mechanisms of xtcrabs collected in their high-sulfide hydrothermal vent habitat. Experimental immersion of xtcrab in various sulfide concentrations in the field or in aquaria assessed its high sulfide tolerance. HPLC measurement of hemolymph sulfur compounds highlighted xtcrab detoxification capacity via catabolism of sulfide into much less toxic thiosulfate. We focused on a key enzyme for H2S detoxification, sulfide: quinone oxidoreductase (SQR). Cloning and phylogenetic analysis revealed two SQR paralogs in xtcrab, that we named xtSQR1 and xtSQR2. As shown by qPCR, xtSQR2 and xtSQR1 were expressed in the digestive gland, suggesting the involvement of both paralogs in the detoxification of food-related H2S. In contrast, xtSQR1 transcript was highly expressed in the gill, while xtSQR2 was not detectable, suggesting a specific role of SQR1 in gill detoxification of H2S of environmental origin. Comparison between xtcrabs in their hydrogen sulfide-rich hydrothermal habitat, and xtcrabs maintained for one month in sulfide-free seawater aquarium, showed higher transcript levels of gill xtSQR1 in sulfide-rich habitat, further supporting the specific role of xtSQR1 paralog in environmental H2S detoxification in the gill. Gill SQR protein level as measured by Western blot, and gill SQR enzyme activity were also higher in sulfide-rich habitat. Immunohistochemical staining further showed that SQR expression was co-localized with Na+/K+-ATPase-positive epithelial and pillar cells of the gill filament. This is the first evidence of duplicate SQR genes in crustaceans. Overall, our study suggests that the subfunctionalization of duplicate xtSQR genes may play an important role in sulfide detoxification to maintain the sulfide homeostasis in X. testudinatus, providing an ecophysiological basis for its adaptation to the high-sulfide hydrothermal vent environment.

Foraging under extreme events: Contrasting adaptations by benthic macrofauna to drastic biogeochemical disturbance

Abstract Hydrothermal vent systems are important biodiversity hotspots that host a vast array of unique species and provide information on life's evolutionary adaptations to extreme environments. However, these habitats are threatened by both human exploitation and extreme natural events, both of which can rapidly disrupt the delicate balance of the food webs found in these systems. This is particularly true for shallow vent endemic animals due to their limited dietary niche and specialized adaptations to specific biogeochemical conditions. In this study, we used the shallow hydrothermal vents of Kueishantao off the coast of Taiwan as a natural laboratory to examine the response of a benthic food web to a M5.8 earthquake and a C5 typhoon that led to a two‐year “near shutdown” of the vents. These perturbations drastically altered the local biogeochemical cycle and the dietary availability of chemosynthetic versus photosynthetic food resources. Our analysis of multiple stable isotopes, including those of sulphur, carbon, and nitrogen (δ34S, δ13C, and δ15N), from different benthic macrofauna reveals that endemic and non‐endemic consumers exhibited different responses to sudden disruption in habitat and biogeochemical cycling. The endemic vent crab, Xenograpsus testudinatus, continued to partially rely on chemosynthetic sulphur bacteria despite photosynthetic sources being the most dominant food source after the disruption. We posit that X. testudinatus has an obligate nutritional dependence on chemoautotrophic sources because the decrease in chemoautotrophic production was accompanied by a dramatic decrease in the abundance of X. testudinatus. The population decline rate was ~19 individuals per m2 per year before the perturbation, but the decline rate increased to 40 individuals per m2 per year after the perturbation. In contrast, the non‐endemic gastropods exhibited much greater dietary plasticity that tracked the overall abundance of photo‐ and chemo‐synthetic dietary sources. The catastrophic events in shallow hydrothermal vent ecosystem presented a novel opportunity to examine dietary adaptations among endemic and non‐endemic benthic macrofauna in response to altered biogeochemical cycling. Our findings highlight the vulnerability of benthic specialists to the growing environmental pressures exerted by human activities worldwide. Read the free Plain Language Summary for this article on the Journal blog.

Cellular mechanisms underlying extraordinary sulfide tolerance in a crustacean holobiont from hydrothermal vents.

The shallow-water hydrothermal vent system of Kueishan Island has been described as one of the world's most acidic and sulfide-rich marine habitats. The only recorded metazoan species living in the direct vicinity of the vents is Xenograpsus testudinatus, a brachyuran crab endemic to marine sulfide-rich vent systems. Despite the toxicity of hydrogen sulfide, X. testudinatus occupies an ecological niche in a sulfide-rich habitat, with the underlying detoxification mechanism remaining unknown. Using laboratory and field-based experiments, we characterized the gills of X. testudinatus that are the major site of sulfide detoxification. Here sulfide is oxidized to thiosulfate or bound to hypotaurine to generate the less toxic thiotaurine. Biochemical and molecular analyses demonstrated that the accumulation of thiosulfate and hypotaurine is mediated by the sodium-independent sulfate anion transporter (SLC26A11) and taurine transporter (Taut), which are expressed in gill epithelia. Histological and metagenomic analyses of gill tissues demonstrated a distinct bacterial signature dominated by Epsilonproteobacteria. Our results suggest that thiotaurine synthesized in gills is used by sulfide-oxidizing endo-symbiotic bacteria, creating an effective sulfide-buffering system. This work identified physiological mechanisms involving host-microbe interactions that support life of a metazoan in one of the most extreme environments on our planet.

Comparison of polycyclic aromatic hydrocarbon accumulation in crab tissues with the ambient marine particles from shallow hydrothermal vents, northeast Taiwan

This study investigated and compared polycyclic aromatic hydrocarbons (PAHs) in crab (Xenograpsus testudinatus), suspended particulate matter, and surface sediment sampled from Kuei-shan-tao (KST) shallow water vents just offshore northeast Taiwan. The total concentrations of PAHs (t-PAHs) in suspended particles near the vents (533–685 ng g−1 dw) were two orders of magnitude higher than the overlying sediment (3.42–6.06 ng g−1 dw). The t-PAHs in sediment were significantly lower than those found in suspended particulate matter and all crab tissues tested, including hepatopancreas (192–1154 ng g−1 dw), gill (221–748 ng g−1 dw), muscle (30–174 ng g−1 dw), and exoskeleton (22–96 ng g−1 dw). Principal component analysis (PCA) indicated tissue-specific bioaccumulation of PAHs in crabs. The compositions of PAHs in gill, muscle, and exoskeleton were mainly low molecular weight, while the composition in the hepatopancreas included both high and low molecular weight PAHs. Highly variable but characteristic PAH congeners and concentrations in crab tissues and ambient aquatic particles reflect bioaccumulation.

Shallow-water hydrothermal vent system as an extreme proxy for discovery of microbiome significance in a crustacean holobiont

The shallow-water hydrothermal vent (HV) system off Kueishan Island lies at the end of the Okinawa Trough to the northeast of Taiwan. Near its submarine vent openings, aperiodic vent discharges generate a dynamic acidic (pH 5.5-8.1) and sulfidic (9-3000 μM) ecosystem. The dominant metazoan in this unique environment is the brachyuran vent crab, Xenograpsus testudinatus, which has developed robust metabolic strategies and highly adaptive acid-base regulatory mechanisms to maintain its physiological homeostasis. X. testudinatus is considered a holobiont, but the symbiotic mechanisms underlying acid and sulfur tolerance in the host-microbe system remain largely unclear. In this study, we used LoopSeq long-read sequencing of the full-length 16S rRNA gene to identify the bacterial communities present in the gills and carapace surface of X. testudinatus. The alpha diversity analysis, Venn diagram, and principal coordinate analysis (PCoA) indicated that the gills and carapace surface exhibit different bacterial constituents. Further measurements of relative abundance, coupled with functional predictions and fluorescence in situ hybridization (FISH), revealed a predominance of Sulfurovum sp. NBC37-1, a key bacterium that can perform sulfur and hydrogen oxidation to support denitrification processes. Consequently, our findings suggest that the symbiotic bacteria may play a critical role in conferring the extraordinary acid and sulfur tolerances of X. testudinatus, allowing the crustacean holobiont to thrive in its ecological niche within one of the most extreme marine habitats on Earth.

Population Genetic Differentiation on the Hydrothermal Vent Crabs Xenograpsus testudinatus along Depth and Geographical Gradients in the Western Pacific

Connectivity in deep-sea organisms must be considered across both depth gradient and horizontal geographical scales. The depth-differentiation hypothesis suggests that strong environmental gradients (e.g., light, temperature, pressure) and habitat heterogeneity in the deep-sea can create selection pressure, and this can result in genetic population divergence. The hydrothermal vent crab Xenograpsus testudinatus (Xenograpsidae) is common in vents at Kueishan Island, Taiwan, ranging from 10 to about 300 m depths. Xenograpsus testudinatus has also been found in shallow water vents (3–20 m) at Kagoshima and the Izu archipelago of Japan. We examine the sequence divergences in the mitochondrial COI, 16S rRNA and D-loop genes, to test the hypothesis that there is significant genetic differentiation among populations of X. testudinatus along the depth gradient at Kueishan Island (30, 200, 209–224 and 250–275 m), and among different geographical regions (Kueishan, Kagoshima and the Izu archipelago) in the West Pacific. There is neither significant population differentiation among shallow or deep-sea vents, nor between geographical locations. Vertical migration of zoea, upwelling on the eastern coast of Taiwan and the strong effect of the Kuroshio Currents has probably resulted in a high level of planktonic larval dispersal of X. testudinatus along the depth and geographical gradients in the Western Pacific.

Shallow Hydrothermal Vent Bacteria and Their Secondary Metabolites with a Particular Focus on Bacillus.

Extreme environments are hostile for most organisms, but such habitats represent suitable settings to be inhabited by specialized microorganisms. A marine shallow-water hydrothermal vent field is located offshore in northeast Taiwan, near the shallow shore of the southeast of Kueishantao Island (121°55′ E, 24°50′ N). Research on extremophilic microorganisms makes use of the biotechnological potential associated with such microorganisms and their cellular products. With the notion that extremophiles are capable of surviving in extreme environments, it is assumed that their metabolites are adapted to function optimally under such conditions. As extremophiles, they need specific culture conditions, and only a fraction of species from the original samples are recovered in culture. We used different non-selective and selective media to isolate bacterial species associated with the hydrothermal vent crab Xenograpsus testudinatus and the sediments of its habitat. The highest number of colonies was obtained from Zobell marine agar plates with an overall number of 29 genetically distinct isolates. 16S RNA gene sequencing using the Sanger sequencing method revealed that most of the bacterial species belonged to the phylum Firmicutes and the class Bacilli. The present study indicates that hydrothermal vent bacteria and their secondary metabolites may play an important role for the reconstruction of the evolutionary history of the phylum Procaryota.

Culturable fungi associated with the marine shallow-water hydrothermal vent crab Xenograpsus testudinatus at Kueishan Island, Taiwan

Abstract Reports on fungi occurring on marine crabs have been mostly related to those causing infections/diseases. To better understand the potential role(s) of fungi associated with marine crabs, this study investigated the culturable diversity of fungi on carapace of the marine shallow-water hydrothermal vent crab Xenograpsus testudinatus collected at Kueishan Island, Taiwan. By sequencing the internal transcribed spacer regions (ITS), 18S and 28S of the rDNA for identification, 12 species of fungi were isolated from 46 individuals of X. testudinatus: Aspergillus penicillioides, Aspergillus versicolor, Candida parapsilosis, Cladosporium cladosporioides, Mycosphaerella sp., Parengyodontium album, Penicillium citrinum, Penicillium paxili, Stachylidium bicolor, Zasmidium sp. (Ascomycota), Cystobasidium calyptogenae and Earliella scabrosa (Basidiomycota). With additional data from other published reports, a total of 26 species of fungi (23 Ascomycota, three Basidiomycota) have been recorded from X. testudinatus. Aspergillus is the most speciose genus on the crab, followed by Penicillium and Candida. All but one species (Xylaria arbuscula) had been previously isolated from substrates in the marine environment, although many are typical terrestrial taxa. None of the recorded fungi on X. testudinatus are reported pathogens of crabs, but some have caused diseases of other marine animals. Whether the crab X. testudinatus is a vehicle of marine fungal diseases requires further study.

Specialized adaptations allow vent-endemic crabs (Xenograpsus testudinatus) to thrive under extreme environmental hypercapnia

Shallow hydrothermal vent environments are typically very warm and acidic due to the mixing of ambient seawater with volcanic gasses (> 92% CO2) released through the seafloor making them potential ‘natural laboratories’ to study long-term adaptations to extreme hypercapnic conditions. Xenograpsus testudinatus, the shallow hydrothermal vent crab, is the sole metazoan inhabitant endemic to vents surrounding Kueishantao Island, Taiwan, where it inhabits waters that are generally pH 6.50 with maximum acidities reported as pH 5.50. This study assessed the acid–base regulatory capacity and the compensatory response of X. testudinatus to investigate its remarkable physiological adaptations. Hemolymph parameters (pH, [HCO3−], {text{P}}_{{{text{CO}}_{2} }}, [NH4+], and major ion compositions) and the whole animal’s rates of oxygen consumption and ammonia excretion were measured throughout a 14-day acclimation to pH 6.5 and 5.5. Data revealed that vent crabs are exceptionally strong acid–base regulators capable of maintaining homeostatic pH against extreme hypercapnia (pH 5.50, 24.6 kPa {text{P}}_{{{text{CO}}_{2} }}) via HCO3−/Cl− exchange, retention and utilization of extracellular ammonia. Intact crabs as well as their isolated perfused gills maintained {text{P}}_{{{text{CO}}_{2} }}tensions below environmental levels suggesting the gills can excrete CO2 against a hemolymph-directed {text{P}}_{{{text{CO}}_{2} }} gradient. These specialized physiological mechanisms may be amongst the adaptations required by vent-endemic animals surviving in extreme conditions.

Growth study under combined effects of temperature, pH and salinity and transcriptome analysis revealed adaptations of Aspergillus terreus NTOU4989 to the extreme conditions at Kueishan Island Hydrothermal Vent Field, Taiwan.

A high diversity of fungi was discovered on various substrates collected at the marine shallow-water Kueishan Island Hydrothermal Vent Field, Taiwan, using culture and metabarcoding methods but whether these fungi can grow and play an active role in such an extreme environment is unknown. We investigated the combined effects of different salinity, temperature and pH on growth of ten fungi (in the genera Aspergillus, Penicillium, Fodinomyces, Microascus, Trichoderma, Verticillium) isolated from the sediment and the vent crab Xenograpsus testudinatus. The growth responses of the tested fungi could be referred to three groups: (1) wide pH, salinity and temperature ranges, (2) salinity-dependent and temperature-sensitive, and (3) temperature-tolerant. Aspergillus terreus NTOU4989 was the only fungus which showed growth at 45 °C, pH 3 and 30 ‰ salinity, and might be active near the vents. We also carried out a transcriptome analysis to understand the molecular adaptations of A. terreus NTOU4989 under these extreme conditions. Data revealed that stress-related genes were differentially expressed at high temperature (45 °C); for instance, mannitol biosynthetic genes were up-regulated while glutathione S-transferase and amino acid oxidase genes down-regulated in response to high temperature. On the other hand, hydrogen ion transmembrane transport genes and phenylalanine ammonia lyase were up-regulated while pH-response transcription factor was down-regulated at pH 3, a relative acidic environment. However, genes related to salt tolerance, such as glycerol lipid metabolism and mitogen-activated protein kinase, were up-regulated in both conditions, possibly related to maintaining water homeostasis. The results of this study revealed the genetic evidence of adaptation in A. terreus NTOU4989 to changes of environmental conditions.

Distribution and sexual dimorphism of the crab Xenograpsus testudinatus from the hydrothermal vent field of Kueishan Island, northeastern Taiwan.

The sulphur-rich and acidic vent waters of a shallow hydrothermal vent field next to Kueishan Island in Taiwan provide a specific and generally toxic environment. Among only a few aquatic organisms able to survive there, the grapsoid crab Xenograpsus testudinatus is the dominant species with a high population density in the vent area. Here we study the gender-specific distribution, morphological traits, and relationship of wet weight vs. carapace width of this crab. A total of 1120 individuals including 831 male and 289 female (included 15 ovigerous) were examined during August and September in 2011 and May and September in 2012. Except in August 2011, there are no significant differences in the distribution of X. testudinatus in the hydrothermal vent area from the vent spout during most months. Among crabs, the weight of male (6.87 ± 2.90 g) was significantly heavier than that of females (4.17 ± 1.25 g) (p < 0.001, Student’s t-test). As for the wet weight of crabs, significant differences were noted in both the length of chela and the width of carapace between males and females. Sexual dimorphism of X. testudinatus is evident in three morphological traits. Pearson’s correlation showed a significant and positive correlation (p < 0.001) of wet weight, width of carapace and length of chela of the two sexes. Ovigerous crabs (shortest carapace width: 1.93 cm) were present in the specimen collected from August 2011 and May 2012. The ovigerous crabs were not found in the samples collected from September in both years 2011 and 2012, indicating that reproduction may have ceased during the period of sampling. The present results suggested that the reproductive period of X. testudinatus was before September. The distribution pattern and sexual dimorphism of X. testudinatus provided a better understanding of the idiobiology of this dominant metazoan in the hydrothermal vent area.

Insights into fungal diversity of a shallow-water hydrothermal vent field at Kueishan Island, Taiwan by culture-based and metabarcoding analyses.

This paper reports the diversity of fungi associated with substrates collected at a shallow hydrothermal vent field at Kueishan Island, Taiwan, using both culture-based and metabarcoding methods. Culture of fungi from yellow sediment (with visible sulfur granules), black sediment (no visible sulfur granules), the vent crab Xenograpsus testudinatus, seawater and, animal egg samples resulted in a total of 94 isolates. Species identification based on the internal transcribed spacer regions of the rDNA revealed that the yellow sediment samples had the highest species richness with 25 species, followed by the black sediment (23) and the crab (13). The Ascomycota was dominant over the Basidiomycota; the dominant orders were Agaricales, Capnodiales, Eurotiales, Hypocreales, Pleosporales, Polyporales and Xylariales. Hortaea werneckii was the only common fungus isolated from the crab, seawater, yellow and black sediment samples. The metabarcoding analysis amplifying a small fragment of the rDNA (from 18S to 5.8S) recovered 7-27 species from the black sediment and 12-27 species from the yellow sediment samples and all species belonged to the Ascomycota and the Basidiomycota. In the yellow sediments, the dominant order was Pleosporales and this order was also dominant in the black sediment together with Sporidiobolales. Based on the results from both methods, 54 and 49 species were found in the black and yellow sediments, respectively. Overall, a higher proportion of Ascomycota (~70%) over Basidiomycota was recovered in the yellow sediment and the two phyla were equally abundant in the black sediment. The top five dominant fungal orders in descending order based on species richness were Pleosporales>Eurotiales>Polyporales>Hypocreales>Capnodiales in the black sediment samples, and Polyporales>Pleosporales>Eurotiales>Capnodiales>Hypocreales in the yellow sediment samples. This study is the first to observe a high diversity of fungi associated with various substrates at a marine shallow water hydrothermal vent ecosystem. While some fungi found in this study were terrestrial species and their airborne spores might have been deposited into the marine sediment, several pathogenic fungi of animals, including Acremonium spp., Aspergillus spp., Fusarium spp., Malassezia spp., Hortaea werneckii, Parengyodontium album, and Westerdykella dispersa, were recovered suggesting that these fungi may be able to cause diseases of marine animals.

Reproductive adaptations of the hydrothermal vent crab Xenograpus testudinatus: An isotopic approach.

The vent crab Xenograpsus testudinatus was firstly discovered in 2000 at the hydrothermal vent field off the coast of Kueishan Island. The present study attempts to understand the adaptive reproduction of this crab living in an extreme environment by examining its spatial and temporal distribution and isotopic signatures. The seasonal variation of the female-male ratio suggests that ovigerous females may migrate from beneath the vent orifice to the vent-periphery region to release their larvae to avoid the larvae contacting high toxic plumes, and then returns to the vent orifice habitat. We used variation of the isotopic crab signatures as indicators for this unique female migration. Our results showed that this vent crab evolved an adaptive modulation of reproductive behavior to successfully survive and propagate in an oceanic shallow hydrothermal vent field.

First record of a shallow hydrothermal vent crab, Xenograpsus testudinatus, from Shikine-jima Island in the Izu archipelago

First record of a shallow hydrothermal vent crab, Xenograpsus testudinatus, from Shikine-jima Island in the Izu archipelago

Trophic structure and energy flow in a shallow-water hydrothermal vent: Insights from a stable isotope approach.

Shallow-water hydrothermal vent ecosystems are distinct from the deep-sea counterparts, because they are in receipt of sustenance from both chemosynthetic and photosynthetic production and have a lack of symbiosis. The trophic linkage and energy flow in these ecosystems, however remain elusive, which allows us poor understanding of the whole spectrum of biological components distributed across such environmental gradients. In this study, a thorough isotopic survey was conducted on various biological specimens and suspended particulates collected along four transects across the venting features of a shallow-water hydrothermal field off Kueishan Island, Taiwan. The isotope data combined with a Bayesian-based mixing model indicate that the vent-associated particulate organic matter (vent POM), as primary contribution of chemoautotrophic populations, has a high δ13C value (−18.2 ± 1.1‰) and a low δ15N value (−1.7 ± 0.4‰). Zooplankton and epibenthic crustaceans, as the fundamental consumers, exhibit δ13C and δ15N values ranging from −21.3 to −19.8‰ and +5.1 to +7.5‰, respectively, and can utilize the vent POM for 38–53% of their diets. The vent-obligate crab Xenograpsus testudinatus shows a large variation in δ13C (from −18.8 to −13.9‰) and δ15N values (from 1.1 to 9.8‰), although an omnivorous trophic level (2.5) is identified for it using δ15N values of amino acids, and it can utilize the vent POM for 6–87% of its diet. The consistently low (< 10.0‰) and overlapping δ15N values for most of the analyzed macroinvertebrates suggest extensive ingestion of chemosynthetic production complementing the photosynthetic production, a weak prey–predator relationship and low trophic complexity possibly imposed by the extreme environmental contexts of shallow-water hydrothermal ecosystems.

The presence of Macromedaeus distinguendus (De Haan, 1835) (Brachyura, Xanthidae) in the shallow hydrothermal vent system off northeastern Taiwan

Abstract The present study investigated the population of the xanthid brachyuran crab, Macromedaeus distinguendus (De Haan, 1835), at a toxic hydrogen sulfide, shallow hydrothermal vent area at Turtle Island, off northeastern Taiwan. This is the first record of this species from this extreme environment, and M. distinguendus is only the second brachyuran discovered in this area. The wet weight of male and female M. distinguendus varied from 0.11 to 1.22 g (mean ± standard deviation: 0.56 ± 0.39 g) and 0.06 to 0.62 g (0.37 ± 0.15 g), respectively. The wet weight: carapace width ratio was significantly correlated in both sexes. The local distribution patterns of M. distinguendus were different from those of the obligate hydrothermal crab Xenograpsus testudinatus N. K. Ng, J.-F. Huang &amp; Ho, 2000 (Xenograpsidae) in this area. An analysis of resource use and habitat partitioning revealed that the two crab species were able to co-exist within the study area.

Are vent crab behavioral preferences adaptations for habitat choice?

Hydrothermal vent organisms are adapted to their extreme and patchily distributed habitats. They are expected to have evolved mechanisms that keep them in their specific habitation. Since little is known about the recruitment or habitat selection of HV organisms such as brachyurans, we examined the properties of several hydrothermal vent-associated cues on the behavior of the hydrothermal vent (HV) crab Xenograpsus testudinatus in the laboratory that were contrasted by the offering of non-vent cues. This crab species is endemic and dominates the vent fauna of Turtle Island off the NE coast of Taiwan. HV crabs were separately and in combination offered the following vent-specific cues: (1) sulfuric sediment, (3) air-bubbling, (4) elevated temperature, (5) dead settled zooplankton, (7) other crabs, and (8) shade. The non-vent-specific cues were: (2) quarz sediment, (6) dead fish, (8) light. These cues were provided on either side of a two-choice chamber. The movement of individual crabs was monitored: as initial and final choices, and as the proportion of time the crabs spent in each compartment (resident time). Cues were offered alone and no such cue as a control in the same set-up. Sulfuric sediments and dead fish were significantly more attractive to females, and other crabs irrespective of gender were significantly more attractive to males. When compared to expected distributions, crabs, irrespective of gender, significantly avoided light and tended to select other crabs, air-bubbling, sulfuric sediment, elevated temperature, dead fish, dead zooplankton, and quarz sediments in the order of decreasing importance. Data do not support the hypothesis that dead settled zooplankton was particularly attractive nor that the other gender was selected. A combination of several vent-associated cues (sulfuric sediment, elevated temperature, air-bubbling) facilitated the strongest attraction to the crabs as reflected by all response variables. The ‘first choice’ responses were always consistent with the side of the choice compartment in which they spent the longest amount of time (resident time), but not with the ‘final choice’ of crabs, suggesting that the ‘resident time’ in addition to their ‘first choice’ is more reliable than just the ‘final choice’. The present results provide the first indication that several vent-associated habitat cues function as attractors for HV crabs. Habitat choice is also reflected by crab larval distribution in the field which tend to stay near the bottom not to be carried away from their specific habitat.