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Environmental gradients can influence morpho-physiological and life-history differences in natural populations. It is unclear, however, to what extent such gradients can also modulate phenotypic differences in other organismal characteristics such as the structure and function of host-associated microbial communities. In this work, we addressed this question by assessing intra-specific variation in the diversity, structure and function of environmental-associated (sediment and water) and animal-associated (skin and gut) microbiota along an environmental gradient of pollution in one of the most urbanized coastal areas in the world. Using the tropical sea cucumber Holothuria leucospilota, we tested the interplay between deterministic (e.g., environmental/host filtering) and stochastic (e.g., random microbial dispersal) processes underpinning host-microbiome interactions and microbial assemblages. Overall, our results indicate that microbial communities are complex and vary in structure and function between the environment and the animal hosts. However, these differences are modulated by the level of pollution across the gradient with marked clines in alpha and beta diversity. Yet, such clines and overall differences showed opposite directions when comparing environmental- and animal-associated microbial communities. In the sea cucumbers, intrinsic characteristics (e.g., body compartments, biochemistry composition, immune systems), may underpin the observed intra-individual differences in the associated microbiomes, and their divergence from the environmental source. Such regulation favours specific microbial functional pathways that may play an important role in the survival and physiology of the animal host, particularly in high polluted areas. These findings suggest that the interplay between both, environmental and host filtering underpins microbial community assembly in H. leucospilota along the pollution gradient in Hong Kong. [ABSTRACT FROM AUTHOR]

Abstract Environmental gradients can influence morpho-physiological and life-history differences in natural populations. It is unclear, however, to what extent such gradients can also modulate phenotypic differences in other organismal characteristics such as the structure and function of host-associated microbial communities. In this work, we addressed this question by assessing intra-specific variation in the diversity, structure and function of environmental-associated (sediment and water) and animal-associated (skin and gut) microbiota along an environmental gradient of pollution in one of the most urbanized coastal areas in the world. Using the tropical sea cucumber Holothuria leucospilota, we tested the interplay between deterministic (e.g., environmental/host filtering) and stochastic (e.g., random microbial dispersal) processes underpinning host-microbiome interactions and microbial assemblages. Overall, our results indicate that microbial communities are complex and vary in structure and function between the environment and the animal hosts. However, these differences are modulated by the level of pollution across the gradient with marked clines in alpha and beta diversity. Yet, such clines and overall differences showed opposite directions when comparing environmental- and animal-associated microbial communities. In the sea cucumbers, intrinsic characteristics (e.g., body compartments, biochemistry composition, immune systems), may underpin the observed intra-individual differences in the associated microbiomes, and their divergence from the environmental source. Such regulation favours specific microbial functional pathways that may play an important role in the survival and physiology of the animal host, particularly in high polluted areas. These findings suggest that the interplay between both, environmental and host filtering underpins microbial community assembly in H. leucospilota along the pollution gradient in Hong Kong.

The present study explores rare but taxonomically and geographically widespread cases of anterior body axial bifurcation in adult sea cucumbers (Echinodermata: Holothuroidea). One individual of Holothuria (Halodeima) grisea, a common intertidal species along the Atlantic coast of Brazil, was studied externally and internally. Individuals of Apostichopus californicus from the northeastern Pacific coast of Washington (USA), H. (Mertensiothuria) leucospilota in the Indian Ocean off La Réunion, H. (Panningothuria) forskali from the Atlantic coast of Spain, and Parastichopus tremulus from the northeastern Atlantic off Norway were also reported to display similar anterior body axial bifurcation. In each of these species, the anterior body presented two mouths with their respective crown of tentacles. In vivo observations of H. (Halodeima) grisea showed that the two tentacle crowns and mouths were independently functional. Micro‐computed tomography (μCT) revealed that the anterior region of the body (up to the pharynx) was duplicated. Internally, two aquapharyngeal bulbs were found, each with their own calcareous ring (one with two plates missing), madreporite, and Polian vesicles. The body presented a normal set of five longitudinal muscle bands, some of which bifurcated orally to support more than one calcareous ring plate. This is the first report of such abnormalities in Holothuroidea and hypotheses that may explain such phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Sea cucumbers are considered a traditional food delicacy in Asian countries. In last decades high market demand, uncontrolled exploitation and inadequate management have led to stock overexploitation, driving commercial interest in new target species and new areas. In recent years, Mediterranean and North-East Atlantic sea cucumbers have become fishing targets, and, due to overfishing, a significant decline of wild populations have been observed, with detrimental effects on benthic communities and ecosystems. Indeed, in addition to being an important economic resource, sea cucumbers play a key ecological role in benthic dynamics where they are involved as ecosystem engineers in the processing of organic matter in the detrital food web pathway. In this context, aquaculture can play a crucial role in supporting the conservation of natural stocks by reducing harvesting pressure on wild populations and enabling restoration programmes for depleted stocks. Commercial sea cucumber farming is already an established reality in the Indo-Pacific region, where it has become one of the most profitable sectors of aquaculture production. In Europe, on the other hand, sea cucumber aquaculture is still an emerging sector, whose development is hampered by poor and fragmented information on the farming requirements of native species. In this context, this systematic review was carried out with the aim of providing a comprehensive summary of the state of the art of farming practices of the European sea cucumbers considered as a target of commercial fisheries. A total of 34 original articles were included in this review, after title, abstract and full-text screening. The results highlighted a sharp increase in the number of studies over the last six years. Portugal, Turkey and Italy are the countries where most research has been carried out. Among the selected species, Holothuria tubulosa was the most studied, while only one article was found on Parastichopus regalis. The main aims of this review were i) to gather all available literature on the farming practices of North-East Atlantic and Mediterranean sea cucumber species, ii) to outline the most common farming practices, iii) to identify gaps and future directions in this emerging aquaculture sector. [ABSTRACT FROM AUTHOR]

Fishery stock assessments are often based on morphometric data from underwater diver surveys and landing surveys. Measurements of body length are usually converted to estimates of body weight, yet length–weight equations might differ among localities. We evaluated morphometric models for the sea cucumber, Pearsonothuria graeffei, collected at Lizard Island on the northern Great Barrier Reef, Australia, and explored differences in relative condition factor (Kn) across animal sizes. The estimation of body weight was compared among relationships with four different body size metrics: observed body length, SLW (square root of the body length–width product), recalculated body length (Le) from SLW, and body basal area. The basal area of the animals, the SLW index and Le provided more reliable estimations for body weight than using body length alone yet accounted for half of the variation in body weight. The length–weight relationship from animals at Lizard Island differed considerably from relationships published for the same species in New Caledonia and Philippines. Body condition was variable, and our model predicted a peak at 35 cm body length. Body metrics such as basal area, SLW index, and Le could offer more precise models for estimating the body weight of sea cucumbers for fishery purposes. Equations for estimating body weight from length and width of the sea cucumbers should be based on locality-specific data because morphometric relationships are spatially variable. [ABSTRACT FROM AUTHOR]

The natural distribution of the Japanese sea cucumber (Apostichopus japonicus Selenka, 1867), a sea cucumber species, is characterized by the Northwest Pacific. Long-term monitoring studies from 2020 to 2024 document a significant deviation from the known natural distribution of A. japonicus and its ability to extensively colonize the Gulf of Izmit, the easternmost part of the Sea of Marmara. This record is also the first documentation of the species from the Mediterranean Sea. Population data extracted from 67 samples allowed the determination of size and weight distribution, length-weight relationship, and condition factor. The study delves into the implications for fisheries management by evaluating the species' dispersion beyond its natural range and its adaptation, shedding light on potential threats from illegal hookah diving fisheries. While its presence offers potential economic benefits through fishing income, its emergence as an invasive species can pose critical ecological risks to the receiving ecosystem. [ABSTRACT FROM AUTHOR]

Sea cucumbers are considered a traditional food delicacy in Asian countries. In last decades high market demand, uncontrolled exploitation and inadequate management have led to stock overexploitation, driving commercial interest in new target species and new areas. In recent years, Mediterranean and North-East Atlantic sea cucumbers have become fishing targets, and, due to overfishing, a significant decline of wild populations have been observed, with detrimental effects on benthic communities and ecosystems. Indeed, in addition to being an important economic resource, sea cucumbers play a key ecological role in benthic dynamics where they are involved as ecosystem engineers in the processing of organic matter in the detrital food web pathway. In this context, aquaculture can play a crucial role in supporting the conservation of natural stocks by reducing harvesting pressure on wild populations and enabling restoration programmes for depleted stocks. Commercial sea cucumber farming is already an established reality in the Indo-Pacific region, where it has become one of the most profitable sectors of aquaculture production. In Europe, on the other hand, sea cucumber aquaculture is still an emerging sector, whose development is hampered by poor and fragmented information on the farming requirements of native species. In this context, this systematic review was carried out with the aim of providing a comprehensive summary of the state of the art of farming practices of the European sea cucumbers considered as a target of commercial fisheries. A total of 34 original articles were included in this review, after title, abstract and full-text screening. The results highlighted a sharp increase in the number of studies over the last six years. Portugal, Turkey and Italy are the countries where most research has been carried out. Among the selected species, Holothuria tubulosa was the most studied, while only one article was found on Parastichopus regalis. The main aims of this review were i) to gather all available literature on the farming practices of North-East Atlantic and Mediterranean sea cucumber species, ii) to outline the most common farming practices, iii) to identify gaps and future directions in this emerging aquaculture sector.

For large-scale artificial breeding of sea cucumber (Holothuria leucospilota), it is necessary to understand how environmental parameters affect larval rearing. In this study, the effects of salinity changes on survival, growth, and development of the mid- and late-auricularia of H. leucospilota were estimated within a 7-day culture period. Salinity shock is usually accompanied by water replacement during hatching. To replicate the occurrence of salinity changes in actual larval production, 1/2 of the larval rearing water (initial salinity ∼31.6 ppt) was replaced daily by the experimental waters at different salinity levels (18, 22, 26, 30, 34, 38, and 42 ppt). On day 7, larval survival rates varied with salinity, while the highest survival rates (44.37–46.63% for mid-auricularia; 50.71–53.98% for late-auricularia) were observed in normal salinities (30 and 34 ppt) and the lowest survival rates (15.71–23.96% for mid-auricularia; 24.11–29.57% for late-auricularia) were observed in extreme salinities (18, 22, and 42 ppt). For any sampling event, the body length of mid-auricularia in normal salinities (30 and 34 ppt) were continued to increase during the 7-day culture period. The highest length of late-auricularia was reached on day 3 (880.01 ± 84.38 and 889.06 ± 112.11 µm, respectively), then decreased to 745.31 ± 127.64 and 742.94 ± 98.43 µm on day 7 due to metamorphosis. On day 7, the proportion of mid-auricularia larvae without development potential was the lowest (36.67%) at a salinity level of 34 ppt, and the proportions were increased with both decreasing/increasing salinities. However, this proportion was much lower for the late-auricularia at the same salinity. The decrease in salinity could promote metamorphosis of the late-auricularia, and the highest proportion of doliolaria (24.32%) was observed at salinity level of 26 ppt on day 7. In extreme salinities (18, 22, and 42 ppt), the hyaline spheres (indication of larval competence) in late-auricularia were less obvious than those in other salinities. The ability in resisting salinity shock was increased with larval development, where late-auricularia had better tolerance to salinity shock than mid-auricularia, whereas larvae at both stages were more tolerant to hypertonic than hypotonic conditions. Based on our results, we propose to rear the mid- and late-auricularia at a comparatively high level of salinity (e.g., ∼31 ppt) to promote their survival and performance, while to decrease the salinity (e.g., ∼26 ppt) in the last period of late-auricularia to increase their competence to metamorphose into doliolaria.

Fishery stock assessments are often based on morphometric data from underwater diver surveys and landing surveys. Measurements of body length are usually converted to estimates of body weight, yet length–weight equations might differ among localities. We evaluated morphometric models for the sea cucumber, Pearsonothuria graeffei, collected at Lizard Island on the northern Great Barrier Reef, Australia, and explored differences in relative condition factor (Kn) across animal sizes. The estimation of body weight was compared among relationships with four different body size metrics: observed body length, SLW (square root of the body length–width product), recalculated body length (Le) from SLW, and body basal area. The basal area of the animals, the SLW index and Le provided more reliable estimations for body weight than using body length alone yet accounted for half of the variation in body weight. The length–weight relationship from animals at Lizard Island differed considerably from relationships published for the same species in New Caledonia and Philippines. Body condition was variable, and our model predicted a peak at 35 cm body length. Body metrics such as basal area, SLW index, and Le could offer more precise models for estimating the body weight of sea cucumbers for fishery purposes. Equations for estimating body weight from length and width of the sea cucumbers should be based on locality-specific data because morphometric relationships are spatially variable.

Sea cucumbers are economical and ecologically important species, playing a crucial role in nutrient recycling in the ocean and providing valuable bioactive compounds for nutrition. Previous research has demonstrated that microplastic fibers, which are widely recognized as emerging contaminants, are transferred to the perivisceral coelomic fluid during respiration in sea cucumbers; however, their fate in sea cucumbers is still not well understood. We tracked the status of sea cucumbers (Apostichopus japonicus) with polyester microplastic fibers in their coelomic fluid in clean water. The results showed that after transferring sea cucumbers to clean water, the number of microplastic fibers transferred significantly decreased in the coelomic fluid, but at least one microplastic fiber was found up to 60 days. In addition, sea cucumbers recovered from the effect of microplastic fiber transfer, as indicated by enzyme levels and histological observations. Furthermore, single microplastic fiber transfer over a 60‐day farmed period did not significantly affect the growth of sea cucumbers. However, repetitive microplastic fiber transfer (i.e., twice and thrice a week over 60 days) significantly decreased the growth rate (p < 0.05). Accordingly, increasing microplastic fibers in sea cucumber habitats pose a threat to sea cucumbers because they can disrupt development. Thus, farmers are advised to select locations for farming sea cucumbers where low microplastic fiber concentrations are expected. Environ Toxicol Chem 2023;42:205–212. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Aiming at the common problems, such as noise pollution, low contrast, and color distortion in underwater images, and the characteristics of holothurian recognition, such as morphological ambiguity, high similarity with the background, and coexistence of special ecological scenes, this paper proposes an underwater holothurian target-detection algorithm (FA-CenterNet), based on improved CenterNet and scene feature fusion. First, to reduce the model's occupancy of embedded device resources, we use EfficientNet-B3 as the backbone network to reduce the model's Params and FLOPs. At the same time, EfficientNet-B3 increases the depth and width of the model, which improves the accuracy of the model. Then, we design an effective FPT (feature pyramid transformer) combination module to fully focus and mine the information on holothurian ecological scenarios of different scales and spaces (e.g., holothurian spines, reefs, and waterweeds are often present in the same scenario as holothurians). The co-existing scene information can be used as auxiliary features to detect holothurians, which can improve the detection ability of fuzzy and small-sized holothurians. Finally, we add the AFF module to realize the deep fusion of the shallow-detail and high-level semantic features of holothurians. The results show that the method presented in this paper yields better results on the 2020 CURPC underwater target-detection image dataset with an AP50 of 83.43%, Params of 15.90 M, and FLOPs of 25.12 G compared to other methods. In the underwater holothurian-detection task, this method improves the accuracy of detecting holothurians with fuzzy features, a small size, and dense scene. It also achieves a good balance between detection accuracy, Params, and FLOPs, and is suitable for underwater holothurian detection in most situations. [ABSTRACT FROM AUTHOR]

Simple Summary: Many species of sea cucumber in Echinodermata may eviscerate most of or even all internal organs when encountering predators or adverse environments, and can achieve regeneration within a certain time. Although regeneration time varies, the mechanism is common. This paper reviewed the intestinal regeneration process of sea cucumbers from the perspectives of histocytology and molecular mechanism. Echinodermata has a special evolutionary position between achordate and chordate, so we hope to explore the common regeneration conserved signals between invertebrates and vertebrates by recording the intestinal regeneration of sea cucumbers. Most species of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process, which is a unique mechanism that allows sea cucumbers to survive in adverse environments. In this review, we compare autotomy among different type of sea cucumber and summarize the histocytological events that occur during the five stages of intestinal regeneration. Multiple cytological activities, such as apoptosis and dedifferentiation, take place during wound healing and anlage formation. Many studies have focused on the molecular regulation mechanisms that underlie regeneration, and herein we describe the techniques that have been used as well as the development-related signaling pathways and key genes that are significantly expressed during intestinal regeneration. Future analyses of the underlying mechanisms responsible for intestinal regeneration should include mapping at the single-cell level. Studies of visceral regeneration in echinoderms provide a unique perspective for understanding whole-body regeneration or appendage regeneration. [ABSTRACT FROM AUTHOR]

Actinopyga echinites are among the commercially exploited sea cucumbers; however, limited studies hinder the management interventions for the sustainability of the resource. This study investigates the density and size distribution of A. echinites populations in Cabgan Island, Barobo, Surigao del Sur from March-August 2021 with two stations (shallow seagrass beds as Station 1 and algal flats as Station 2) having three plots (100 m²) laid as monitoring stations. The results revealed the population density of A. echinites ranged from 567-2,567 ind/ha with a mean of 1,572 ± 225 ind/ha in Station 1 and 733-2,400 ind/ha and a mean of 1,389 ± 178 ind/ha in Station 2. Significant differences were only observed across months in each station (P = 0.00) and their interaction between months and stations (P = 0.01). A. echinites had a mean length of 7.58 ± 0.26 cm and weight of 31.39 ± 1.62 g for Station 1 and 7.84 ± 0.47 cm and 39.01 ± 3.91 g for Station 2. Specimens in Station 2 had a greater length and significantly heavier weight than in Station 1 (P = 0.00). Across months, significant differences were recorded for the specimen's length in Station 1 and weight for both stations. The length of A. echinites ranged from 4-12 cm and 4-13.5 cm in Stations 1 and 2, respectively, and weight of 5-129 g in both stations. The highest frequencies were recorded at 7 cm in both stations and shifted to 9 cm. Weight distributions showed the highest frequencies in 35 g in the two stations. The present study shows that the population is still abundant and is more influenced by the sampling months than the stations. The species are smaller compared to other studies and might exhibit habitat preferences. Weight size distribution varied across months and could be related to their reproduction. The study provides significant insights needed for this species' conservation and fishery management. [ABSTRACT FROM AUTHOR]

The presence of the sea cucumber Synaptula hydriformis (Lesueur, 1824) is documented. This is the first record for the species in Santa María key, Sabana-Camagüey archipelago. This record extends the distribution of this species in Cuba, documented in the available scientific literature to date. The presence of this species in several localities of the Caribbean region suggests a wider distribution in the island [ABSTRACT FROM AUTHOR]

While larval ecology is central to the population dynamics of marine benthic species with multiphasic life histories, the adaptations of larvae to environmental variability remain incompletely understood in many species. Using the holothuroid echinoderm (sea cucumber) Isostichopus fuscus, we examined how a planktotrophic species can use pre-competency plasticity to withstand suboptimal conditions of temperature over extended periods. Five cohorts of propagules (embryos/larvae) were exposed to temperature treatments (28–29, 24–25 and 20–22°C) in standardized culture settings. Under the coldest temperatures (typical of offshore upwelling areas), development mirrored that obtained under warmer temperatures until the early auricularia stage, where development was arrested for ~5 months in a manner consistent with quiescence. When temperature was increased again, larvae quickly resumed development and settled; no lasting negative impact was noted. The findings suggest that the larvae can use a form of dormancy to withstand suboptimal oceanic conditions for indefinite periods of time until successful delivery to appropriate inshore locations, the habitat were I. fuscus is exclusively found. [ABSTRACT FROM AUTHOR]

With global climate changing, hypo-salinity events are increasing in frequency and duration because of continuous rainfall and freshwater inflow, which causes reduced cytosolic osmolarity and cellular stress responses in aquatic animals. Sea cucumbers are considered stenohaline because they lack osmoregulatory organs and are vulnerable to salinity fluctuations. In this study, we performed multiple biochemical assays, de novo transcriptomics, and widely targeted metabolomics to comprehensively explore the osmoregulatory mechanisms and physiological responses of sea cucumber Holothuria moebii to hypo-osmotic stress, which is a representative specie that is frequently exposed to hypo-saline intertidal zones. Our results found that H. moebii contracted their ambulacral feet and oral tentacles, and the coelomic fluid ion concentrations were reduced to be consistent with the environment. The microvilli of intestines and respiratory trees underwent degeneration, and the cytoplasm exhibited swelling and vacuolation. Moreover, the Na+, K+, and Cl− concentrations and Na+/K+-ATPase activity were significantly reduced under hypo-osmotic stress. The decrease in protein kinase A activity and increase in 5′-AMP level indicated a significant inhibition of the cAMP signaling pathway to regulate ion concentrations. And small intracellular organic molecules (amino acids, nucleotides and their derivatives) also play crucial roles in osmoregulation through oxidative deamination of glutamate, nucleotide catabolism, and nucleic acid synthesis. Moreover, lysosomes and peroxisomes removed oxidative damage, whereas antioxidant metabolites, such as N-acetyl amino acids and glutathione, were increased to resist oxidative stress. With prolonged hypo-osmotic stress, glycerophospholipid metabolism was enhanced to maintain membrane stability. Furthermore, acyl-CoA-binding protein activity was significantly inhibited, and only a small amount of acylcarnitine was significantly accumulated, which indicated a disruption in energy metabolism. PPAR signaling pathway and choline content were up-regulated to promote fatty acid metabolism under hypo-osmotic stress. Overall, our results provide new insights into the osmoregulatory mechanisms and physiological responses of sea cucumbers to hypo-osmotic stress. [Display omitted] • Transcriptomics and metabolomics reveal hypo-osmotic stress effects on sea cucumber. • Coelomic fluid ion concentrations were highly correlated with environment. • Inorganic ions, amino acids, nucleotides, and their derivatives play crucial osmoregulatory roles. • ROS scavenging and glycerophospholipid metabolism were activated to resist oxidative stress. • Acyl-CoA-binding protein activity was inhibited, resulting in blocked energy metabolism. [ABSTRACT FROM AUTHOR]

The respiratory trees present only in the class Holothuroidea and the rest of the echinoderms lack it. Only some holothurian species have the ability to regenerate their respiratory trees after autotomy. Therefore, respiratory trees could be considered as a suitable model to assess the regeneration mechanisms in animals. In the present study, the respiratory tree regeneration after posterior evisceration were examined in Holothuria parva during 75 days. Since autotomy reduces antioxidant defense in the organisms, in the present study alterations of antioxidant enzymes were also evaluated during the experiment. H. parva is the dominant intertidal species distributed in the north of the Persian Gulf. In the present study, H. parva ejected the left respiratory tree, the digestive tract and supportive mesenteries from the anus, about 1–2 min after potassium chloride injection. The closure of the opening at the posterior ends of the body was the first reaction to the injury. Seven days after evisceration, the small bud formed on the dorsal side of the cloaca which was covered with the coelomic epithelium of cloaca. The coelomic epithelium started to proliferate to undifferentiated cells on the apex of the buds. The primary respiratory tree consisted of the luminal cuboidal epithelium and thin connective tissue surrounded by the slender coelomic epithelium. This preliminary organ was observed at the apex of the buds, 13 days after evisceration. Gradually, myoepithelial cells arranged around a longitudinal axis and formed a circular muscle. The primitive branches of primary respiratory tree started to form 18 days after evisceration. Forty days after evisceration, the luminal epithelium of the respiratory tree had the same appearance as the intact luminal epithelium. The regenerated respiratory tree was histomorphologically very similar to an intact respiratory tree 56 days postevisceration, but unlike that, it was not yet wrapped around the intestine and was completely separate from it. Despite the development of the regenerating respiratory tree, no wrapping around the intestine was observed until the end of the experiment. According to the results, the activity of the catalase (CAT) and superoxide dismutase (SOD) in the muscle homogenate was significantly higher than the control 5 days after evisceration. The CAT and SOD levels gradually decreased in eviscerated animals. The lipid peroxidation level followed a decreasing trend in the eviscerated animals during the experiment. However, its value reduced to the control level at the end of the experiment. HIGHLIGHTS: Holothuria parva is posterior‐eviscerating sea cucumber.Only the left respiratory tree of Holothuria parva was eviscereted.The respiratory tree of Holothuria parva was only regenerated from cloacal end.56 dpe, the tissue structure of regenerated respiratory tree was similar to intact digestive tract.75 dpe, regenerated respiratory tree was not yet wrapped around the intestine.CAT and SOD in the regenerated respiratory tree was significantly higher than the control [ABSTRACT FROM AUTHOR]

The holothurian Eupentacta fraudatrix is widely used for studying how regeneration works and as a source of biological active compounds. Data on the lipid content and composition of E. fraudatrix are limited to the description of fatty acid (FA) composition. The storage and structural lipids of E. fraudatrix gut have been analyzed by different chromatographic and mass spectrometry methods. Triacylglycerols, as storage lipids, are characterized by a high concentration of trophic FA markers. Among structural lipids, phosphatidylethanolamines and phosphatidylcholines contain a high concentration of molecular species with a simple ether linkage. Phosphatidylserines (PS) and phosphatidylinositols (PI) differ from other lipids with very-long-chain FA in composition. The FA 23:1n-9, which is characteristic of holothurians, has been detected in PS and PI. The study of marine organisms' lipidome may contribute to understanding the biosynthetic pathways and distribution of trophic markers in lipids. [ABSTRACT FROM AUTHOR]

Holothuria scabra is one of the most intensively studied holothuroids, or sea cucumbers (Echinodermata: Holothuroidea), having been discussed in the literature since the early 19th century. The species is important for several reasons: (1) it is widely distributed and historically abundant in several shallow soft-bottom habitats throughout the Indo-Pacific, (2) it has a high commercial value on the Asian markets, where it is mainly sold as a dried product (beche-de-mer) and (3) it is the only tropical holothuroid species that can currently be mass-produced in hatcheries. Over 20 years have elapsed since the last comprehensive review on H. scabra published in 2001. Research on H. scabra has continued to accumulate, fuelled by intense commercial exploitation, and further declines in wild stocks over the entire distribution range. This review compiles data from over 950 publications pertaining to the biology, ecology, physiology, biochemical composition, aquaculture, fishery, processing and trade of H. scabra, presenting the most complete synthesis to date, including scientific papers and material published by local institutions and/or in foreign languages. The main goal of this project was to summarize and critically discuss the abundant literature on this species, making it more readily accessible to all stakeholders aiming to conduct fundamental and applied research on H. scabra, or wishing to develop aquaculture, stock enhancement and management programs across its geographic range. [ABSTRACT FROM AUTHOR]

There is a demand for proper feed and feeding strategies in the growing sea cucumber aquaculture. The digestive system of holothurians seems to increase nutrient assimilation through the respiratory tree (RT), but digestive functioning in this organ has not been investigated. This study evaluated the enzymatic activity of the cytosolic leucine alanine peptidase (leu‐ala) and acid phosphatase, the membrane‐linked aminopeptidase‐N (APN), the bile salt‐activated lipase, laminarinase (LAM), and β‐glycosidase (BGL), in the RT and segments of the digestive tract (DT; foregut, midgut, and hindgut) of adult Isostichopus badionotus. All enzymes, except LAM and BGL, exhibited comparable activity levels in the RT and the DT segments, but APN and BGL activities were significantly higher in the whole DT compared with those in RT, with high activity of leu‐ala in both organs. These results indicate a relevant role of the RT as an accessory organ in sea cucumber digestive physiology. Consequently, I. badionotus seems to be able to digest feeds from the water column through the RT, maximizing the use of available nutrients by luminal, intracellular, and apical membrane‐linked digestive modes. These findings expand the knowledge of sea cucumber digestive mechanisms, with implications for developing feeding strategies for all life stages in aquaculture. [ABSTRACT FROM AUTHOR]

The demand and high market price for sea cucumber has led to the collapse of wild stocks for many traditional species in Asia and the Indo-Pacific. New species have therefore been introduced to the markets over recent decades, including Cucumaria frondosa. A fishery for C. frondosa emerged in the USA in the 1980s and quickly developed in Iceland, Canada and Russia. Commercial products include frozen and dry body wall (beche-de-mer), frozen muscle bands, dry aquapharyngeal bulb (flower), along with various pharmaceutical and nutraceutical extracts. This species is also a candidate for aquaculture due to its high marketability for food and bioactive products. Despite its naturally high abundance, C. frondosa is a temperate-polar slow-growing species with annual spawning; therefore, a precautionary approach must be taken to develop best practices for management of this resource. The present contribution reviews the biology, ecology, biochemical properties, harvesting and trade, and the potential aquaculture of C. frondosa. This comprehensive synthesis, including 10 theses, 197 scientific papers and 47 reports, aims to provide a framework for future research by highlighting areas of concern for academic studies, fishery management, and aquaculture of cold-water sea cucumber species. [ABSTRACT FROM AUTHOR]

Aiming at the common problems, such as noise pollution, low contrast, and color distortion in underwater images, and the characteristics of holothurian recognition, such as morphological ambiguity, high similarity with the background, and coexistence of special ecological scenes, this paper proposes an underwater holothurian target-detection algorithm (FA-CenterNet), based on improved CenterNet and scene feature fusion. First, to reduce the model’s occupancy of embedded device resources, we use EfficientNet-B3 as the backbone network to reduce the model’s Params and FLOPs. At the same time, EfficientNet-B3 increases the depth and width of the model, which improves the accuracy of the model. Then, we design an effective FPT (feature pyramid transformer) combination module to fully focus and mine the information on holothurian ecological scenarios of different scales and spaces (e.g., holothurian spines, reefs, and waterweeds are often present in the same scenario as holothurians). The co-existing scene information can be used as auxiliary features to detect holothurians, which can improve the detection ability of fuzzy and small-sized holothurians. Finally, we add the AFF module to realize the deep fusion of the shallow-detail and high-level semantic features of holothurians. The results show that the method presented in this paper yields better results on the 2020 CURPC underwater target-detection image dataset with an AP50 of 83.43%, Params of 15.90 M, and FLOPs of 25.12 G compared to other methods. In the underwater holothurian-detection task, this method improves the accuracy of detecting holothurians with fuzzy features, a small size, and dense scene. It also achieves a good balance between detection accuracy, Params, and FLOPs, and is suitable for underwater holothurian detection in most situations.

Information on newly settled juveniles and recruitment processes in sea cucumbers is sparse for most commercial species, impeding protection of nursery habitats, which are key to management. Here, the ecology of early life stages of Holothuria floridana was investigated. In laboratory experiments, females released a small number of oocytes, which underwent abbreviated lecithotrophic development. During broadcast spawning, some of the negatively buoyant and sticky oocytes settled on the adults where they remained anchored up to the pentactula stage (encapsulated). Several wild adults collected in the Placencia Lagoon (Belize) each hosted ~2 propagules (eggs, blastulae, pentactulae, juveniles). The nursery habitat was characterized by high adult density, shallow seagrass beds close to mangroves, and mud dominated substrata. The present work illustrates a unique facultative offspring-adult association in a free-spawning lecithotrophic species of Holothuroidea, possibly representing a hybrid state between broadcasting and external brooding. This uncommon reproductive feature may ensure successful local recruitment in one of the most competitive habitats of the tropical Americas, where predation pressure is likely to be very high. [ABSTRACT FROM AUTHOR]

Most species of the class Holothuroidea are able to regenerate most of their internal organs following a typical evisceration process, which is a unique mechanism that allows sea cucumbers to survive in adverse environments. In this review, we compare autotomy among different type of sea cucumber and summarize the histocytological events that occur during the five stages of intestinal regeneration. Multiple cytological activities, such as apoptosis and dedifferentiation, take place during wound healing and anlage formation. Many studies have focused on the molecular regulation mechanisms that underlie regeneration, and herein we describe the techniques that have been used as well as the development-related signaling pathways and key genes that are significantly expressed during intestinal regeneration. Future analyses of the underlying mechanisms responsible for intestinal regeneration should include mapping at the single-cell level. Studies of visceral regeneration in echinoderms provide a unique perspective for understanding whole-body regeneration or appendage regeneration.

The trace fossil Lumbricaria Münster is a common constituent of the Upper Jurassic lithographic limestones in southern Germany. Despite having been recognized more than 300 years ago, its nature and producer remain enigmatic. Controversial interpretations of Lumbricaria regard it either as the remains of worms, or as cololites (i.e. faecal material preserved in the gut) or coprolites (i.e. ejected faecal material) of worms, fish, holothurians or cephalopods. A morphological analysis of the type material and numerous specimens reveals two basic morphotypes of Lumbricaria, conformable with the ichnospecies L. intestinum (loosely confined, intertwined to elongate) and L. colon (well confined, densely entangled). Transitions and combinations between both ichnospecies exist and are the result of taphonomic effects. A comparison with modern analogues favours cephalopods (in particular nautiloids or ammonites) as the most likely producers of Lumbricaria, an interpretation that is supported by the finding of an Upper Jurassic nautiloid cast preserving a Lumbricaria‐like faecal string within its body chamber. Ammonites are the likely producers of Lumbricaria from the Upper Jurassic of Germany. [ABSTRACT FROM AUTHOR]

Rhizocorallites articularis Müller, 1955 are string-shaped sediment aggregates with a homogeneous fill and transverse segmentation, known from marginal-marine deposits of the Middle Triassic (Anisian) of the Germanic Basin. They preferably occur as winding and bent strings at the base of thin storm layers (tempestites). Originally interpreted as the dwellings of a tubiculous annelid or a backfilled burrow similar to Taenidium, a reinvestigation of the type and supplementary material reveals characteristics more conformable with an interpretation as the faecal string (i.e., coprolite) or intestine content (i.e., cololite) left by an epibenthic organism. Comparison with modern analogues suggests holothurians as potential producers of R. articularis. This is confirmed by one of the paratype specimens that, in addition to the segmented string-shaped aggregate, preserved other connecting organs interpreted as stomach, intestine, rectum, and cloaca of a decaying holothurian. Different taphonomic pathways of decaying sea cucumbers result in varying styles of preservation, reaching from conservation (obrution) by burial with sediment to reworking by currents and incorporation into event deposits. Comparable specimens from the Upper Jurassic (Tithonian) lithographic limestone of southern Germany are assigned to Rhizocorallites inaequalis isp. nov. and, due to their exceptional preservation partly within the carcasses of holothurians, confirm an origin as cololites. Several records of Rhizocorallites from different parts of the world indicate its wide distribution from the Upper Ordovician to the Upper Cretaceous. [ABSTRACT FROM AUTHOR]

With a focus on building an inventory of subtropical species of epifaunal holothurians and completing an environmental assessment, SCUBA surveys were carried out in the Amami Islands of Kagoshima Prefecture in southern Japan. The following 12 nominal species belonging to seven genera (subgenera), as well as two as yet undescribed species belonging to two genera, were observed: Bohadschia argus Jäger, 1833; B. bivittata Mitsukuri, 1912; B. vitiensis (Semper, 1867); Holothuria (Halodeima) atra Jäger, 1833; H.(H.) edulis Lesson, 1830; Holothuria (Microthele) nobilis (Selenka, 1867); Personothuria graeffei (Semper, 1867); Stichopus chloronotus Brandt, 1835; S. hermanni Semper, 1867; S. naso Semper, 1867; Thelenota anax H.L. Clark, 1921; Euapta sp.; Synapta maculata (Chamisso et Eysenhardt, 1821); and Opheodesoma sp. In the semi-closed waters around the Amami Islands, epifaunal holothurians showed what seemed to be species-specific distribution patterns related to topographical features. Furthermore, ignition loss values of feces and sediments suggested that selective deposit feeding may be predominant in at least several of the species sampled. [ABSTRACT FROM AUTHOR]

In 2011, a tropical holothurian was found off the temperate coast of Kagoshima, Kyushu, Japan. This holothurian was identified as Stichopus naso Semper, 1867, which was first described in the Philippines, and is known to be distributed within the tropical Indo-West Pacific region. Herein, we examined its morphological characteristics and compared it with pre-described examples and discuss its origin from the perspective of climate change and artificial transfer. We considered that both perspectives are plausible because sea water temperature has recently risen around Japan, creating the possibility of eggs and larval transfer from southern regions and the consequent establishment of adult S. naso populations. Accidental introduction via ballast water from vessels and other pathways may not be implausible. In any case, ocean warming caused by global climate change is considered as a key factor in the survival and settlement of adult S. naso populations. [ABSTRACT FROM AUTHOR]

Temperature and dissolved oxygen concentration are important abiotic factors that can limit the growth and survival of sea cucumbers by affecting their immune systems. As global warming intensifies, sea cucumbers are increasingly exposed to adverse environmental conditions, which can cause severe economic losses and limit the sustainable development of sea cucumber aquaculture. It is therefore important to better understand how sea cucumbers respond to environmental stress, especially with regard to its effects on immunity. In the present study, the time series of immunity-related gene expression in sea cucumbers under thermal and hypoxic stresses were analyzed separately. The expression trends of 17 genes related to the nuclear factor κB (NF-κB) pathway, the protease family, the complement system, heat shock proteins (HSPs) and the transferrin family during exposure to two stresses at eight time points were concluded. These genes have interconnected roles in stress defense. The expression levels of genes relating to the NF-κB pathways and HSPs were strongly affected in the sea cucumber thermal stress response, while melanotransferrin (Mtf) , ferritin (Ft) and mannan-binding C-type lectin (MBCL) were affected by hypoxia. In contrast, complement factor B (Bf) , myosin V (Mys) and serine protease inhibitor (SPI) were not that sensitive during the initial period of environmental stress. Similar expression patterns under both thermal and hypoxic stress for certain genes, including an increase in Hsp90 and decreases in lysozyme (Lys) , major yolk protein (MYP) and cathepsin C (CTLC) were observed in sea cucumbers. Conversely, NF-κB and Hsp70 were differentially affected by the two stress treatments. Lysozyme-induced immune defense was inconstant in sea cucumbers coping with stress. A gene ontology (GO) analysis of the selected genes revealed that the most co-involved terms related to immunity and iron ion. Our analysis suggests that sea cucumbers demonstrate complex and varied immune responses to different types of stresses. This dynamic image of the immune responses and stress tolerance of sea cucumbers provides new insights into the adaptive strategies of holothurians in adverse environments. • Expressed trends of 17 immune genes under two stresses at 8 time points were concluded. • Genes related to Nf-κB pathway, protease, complement system, HSP and transferrin family were coefficient to defense stress. • Sea cucumber showed complex and different immune pattern towards different stresses. • These dynamic images provide new insights into adaptive strategies in sea cucumber tolerance to adverse environment. [ABSTRACT FROM AUTHOR]

• This is the first report of the characterization of an OSC gene from the deep-sea holothurian Chiridota sp. • OSC catalyzed 2,3-Oxidosqualene to form parkeol. • The OSC of Chiridota sp. had higher stability than that of the shallow-sea holothurian Stichopus horrens under high pressure. Saponins derived from holothurians have high potential medicinal value. However, the de novo synthesis of the derivatization of triterpenes is still unclear. Oxidative squalene cyclase (OSC) can catalyze 2,3-Oxidosqualene into diverse products that serve as important precursors for triterpene synthesis. However, the function of the OSC gene in Chiridota sp. has not been elucidated. In this study, an OSC gene derived from the deep-sea holothurian Chiridota sp. was cloned and characterized functionally in a yeast system. The open reading frame of the OSC gene was 2086 bp, which encoded 695 amino acids. The Chiridota sp. OSC gene has a similarity of 66.89 % to the OSC of other holothurian species and 63.51 % to that of Acanthaster planci. The phylogenetic tree showed that the echinozoan OSCs clustered together, and then they formed a sister group to fungi and plant homologs. Chiridota sp. OSC catalyzed 2,3-Oxidosqualene into parkeol. Under high pressure, the relative enzymatic activity and stability of cyclase in Chiridota sp. was higher than that in the shallow-sea holothurian Stichopus horrens. The newly cloned OSC of Chiridota sp. provides key information for the interpretation of the saponin synthesis pathway in deep-sea holothurians. [ABSTRACT FROM AUTHOR]

Sea cucumbers (Holothuroidea or holothurians) are a valuable fishery and are also crucial nutrient recyclers, bioturbation agents, and hosts for many biotic associates. Their ecological impacts could be substantial given their high abundance in some reef locations and thus monitoring their populations and spatial distribution is of research interest. Traditional in situ surveys are laborious and only cover small areas but drones offer an opportunity to scale observations more broadly, especially if the holothurians can be automatically detected in drone imagery using deep learning algorithms. We adapted the object detection algorithm YOLOv3 to detect holothurians from drone imagery at Hideaway Bay, Queensland, Australia. We successfully detected 11,462 of 12,956 individuals over 2.7ha with an average density of 0.5 individual/m2. We tested a range of hyperparameters to determine the optimal detector performance and achieved 0.855 mAP, 0.82 precision, 0.83 recall, and 0.82 F1 score. We found as few as ten labelled drone images was sufficient to train an acceptable detection model (0.799 mAP). Our results illustrate the potential of using small, affordable drones with direct implementation of open-source object detection models to survey holothurians and other shallow water sessile species.

Abstract An investigation was carried out in the field and in the laboratory in order to evaluate the contribution of sea cucumber Holothuria tubulosa on organic load reduction from fish farming in the Eastern Mediterranean. Five experimental cages and three double systems of seawater aquaria were used for this purpose. The mean reduction of OM and OC was 30.73% and 58.58%, respectively. Moreover, the mean absorption efficiency of OM and OC during transit in the intestine of H. tubulosa was 43.40% and 54.65%, respectively. One-way ANOVA indicated significant differences on OM and OC accumulation rate between holothurians and control (p <.05). The results indicated that the feeding activity of H. tubulosa seemed to reduce the total organic load of the fish farm biodeposits, demonstrating their potential as an important organic-reducing component for the sustainability of aquaculture in the Mediterranean region. Highlights • Sustainability of aquaculture in the Mediterranean • Sea cucumber Holothuria tubulosa as a potential organic-reducing component • Organic load of fish farm biodeposits • Integrated multi-trophic aquaculture (IMTA) systems [ABSTRACT FROM AUTHOR]

Abstract Multiple environmental stressors caused by global warming influence the regulation of proteins involved in various biological processes in aquatic organisms. As an important component of the marine ecosystem, sea cucumber is a suitable echinoderm species for researching stress responses. In this study, we have investigated the proteomic response of respiratory trees in the sea cucumber Apostichopus japonicus , challenged with environmental stresses by using the iTRAQ technique. Results showed that 262, 155 and 433 proteins were differentially regulated in response to heat, hypoxia, and heat plus hypoxia, respectively. Expression of key genes and proteins were measured by real-time PCR and western blot to validate the accuracy of the proteome files. Results showed that the interaction between these two stressors has an additive effect at the proteome level. Proteins involved in amino acid and carbohydrate metabolic processes were largely induced by heat while repressed by hypoxia. Exposure to multiple climate change stressors caused several proteins involved in lipid metabolic progress to be down-regulated and lipid catabolic processes were induced. Additionally, hypoxia and the combined stress induced proteins involved in iron homeostasis. ATP synthesis and gluconeogenesis were induced under heat and the combined stress, while ATP and glycogen synthesis were depressed under hypoxia. Proteins related with immune and defense response were largely induced and protein synthesis ability was depressed under all three stresses. Thus, sea cucumber may adopt different strategies to cope with varied environmental stress, and the situation in heat group is more similar with the combined treatment than hypoxia group. These proteomic changes in response to high-temperature and low-oxygen levels may provide insights into the defense strategies of sea cucumber in response to global climate changes. Significance of the study The study focused on comparative quantitative proteomics on Apostichopus japonicus respiratory tree using iTRAQ in responses to multiple climate change stressors: heat, hypoxia and the combined stress. Data showed that A. japonicus can have an acute reaction in diverse biological pathways to both individual and interacting environmental stress, including substance metabolism, signal transduction, protein synthesis, immune response and energy production. Results indicated that sea cucumber adopted different strategies to cope with varied environmental stress, and the interaction between these two stressors has an additive effect at the proteome level. These results offer insight into the molecular regulation of A. japonicus to multiple environmental stress and reveal possible molecular events in sea cucumber under climate changes. The understanding of adaptive variation under global climate changes in aquatic organisms could be improved. Graphical abstract Unlabelled Image Highlights • Comparative proteomic analysis was used to illustrated proteins responded to varied environmental stress in sea cucumber. • 262, 155 and 433 proteins were differentially regulated in response to heat, hypoxia, and heat plus hypoxia, respectively. • RT-qPCR and western blot confirmed key genes and proteins expressions. • The interaction between these two stressors has an additive effect at the proteome level. • Sea cucumber adopted different strategies to cope with varied environmental stress. [ABSTRACT FROM AUTHOR]

Abstract The present study investigated methods to trigger spawning and artificially induce oocyte maturation in the commercial cold-water suspension-feeding sea cucumber Cucumaria frondosa. Spawning occurred after exposure to live phytoplankton, commercial phytoplankton paste, and conspecific sperm. Live phytoplankton at 1 × 105 cells ml−1 induced the highest proportion of females to spawn (mean of 56%); promoted the greatest oocyte release (mean of 19,200 oocytes female−1), best quality of eggs and highest survival of embryos (65%; 20 d post fertilization). More concentrated live phytoplankton (1 × 106 cells ml−1) triggered 43% of the females to release ~16,100 oocytes female−1 and survival rates 20 d post fertilization were lower (50%). Both phytoplankton paste treatments (1 × 105 and 1 × 106 cells ml−1) yielded intermediate results in terms of percent spawning females (26%), abundance of oocytes released (11,000 and 7300 oocytes female−1, respectively), quality of eggs, and survival of embryos (44 and 50%, respectively). Sperm from conspecific (2 and 10 × 106 spermatozoa ml−1) induced the lowest proportion of females to spawn (16%) with release of 3000 and 1700 oocytes female−1, respectively; furthermore, all embryos died within 10 d post fertilization. Results for males were slightly different: spawning was more frequent (63%) in the sperm treatment at 2 × 106 spermatozoa ml−1 followed by live phytoplankton at 1 × 106 and 1 × 105 cells ml−1 (43%), and phytoplankton paste at 1 × 105 cells ml−1 (46%); the lowest spawning success was observed for phytoplankton paste at 1 × 106 cells ml−1 and conspecific sperm at 10 × 106 spermatozoa ml−1 (26%). Thermal shock, desiccation, potassium chloride (injection or bath), and serotonin (injection) did not induce spawning in C. frondosa. When oocytes isolated from mature ovaries were exposed to three different concentrations of 1-Methyladenine (1-MA), Dithiothreitol (DTT), 2,3-Dimercapto-1-propanol (BAL), and L-cysteine (L-cyst), DTT at 10−1 M induced the highest proportion of oocytes (48%) to shed follicle cells (i.e. ovulate); whereas other treatments induced only 2–6% of ovulation, similar to the control (seawater). All oocytes that shed follicle cells remained unfertilizable. Overall, live phytoplankton emerged as the most suitable spawning trigger for C. frondosa , a Dendrochirotida that produces maternally-provisioned oocytes. In the context of expanding sea cucumber aquaculture, this finding provides a tool to maximize the availability of gametes in this cold-water species, with possible applicability to similar commercial dendrochitotids. Highlights • Live and commercial phytoplankton, and sperm from conspecifics artificially triggered spawning in Cucumaria frondosa. • Live phytoplankton resulted in the highest number of eggs released, and best egg/embryo quality and survival rates. • Thermal shock, desiccation, potassium chloride, and serotonin failed to trigger spawning. • Among 1-MA, DTT, BAL, and L-cyst, only DTT successfully induced ovulation; however, oocytes were not fertilizable. [ABSTRACT FROM AUTHOR]

Holothurians are marine invertebrates also known as sea cucumbers. They are used in fresh or dried forms in various cuisines around the world and have alleged medicinal properties. Consequently, sea cucumbers, notably the orange-footed sea cucumber (Cucumaria frondosa)are increasingly harvested from the environment or farmed via aquaculture. We report three cases of unusual occupational exposure to C. frondosa resulting in cutaneous, respiratory and ocular irritating symptoms. These symptoms occurred as sea cucumbers were cut on half and eviscerated manually, following a machine breakdown in a sea cucumber processing factory. Given the composition of holothurians, these symptoms probably resulted from the aerosolization of various holothurins, saponins secreted by sea cucumbers as mean of defense. Treatment was solely symptomatic and included decontamination of the skin and the eyes, inhaled glucocorticoids, anticholinergic agents and oral glucocorticoids. As the exposure resulted from a machine breakdown, no specific protective equipment was put in place. Employees were advised not to handle manuallythe sea cucumbers in case such a breakdown was to happen again. • Holothurians (sea cucumbers) are increasingly harvested, processed in factories and consumed. • Sea cucumbers contains holothurins: saponins that exhibited cytostatic properties in vitro • External exposure to sea cucumbers can lead to irritating symptoms. • As there is no antidote, treatment of sea cucumbers' external exposures is symptomatic. [ABSTRACT FROM AUTHOR]

Intestinal bacterial communities are highly relevant to the digestion, nutrition, growth, reproduction, and immunity of animals, but little is known about the composition and function of intestinal microbiota in deep-sea invertebrates. In this study, the intestinal microbiota of six holothurian Molpadia musculus were investigated, showing that their midguts were predominantly occupied by Izemoplasmatales bacteria. Using metagenomic sequencing, a draft genome of 1,822,181 bp was successfully recovered. After comparison with phylogenetically related bacteria, genes involved in saccharide usage and de novo nucleotide biosynthesis were reduced. However, a set of genes responsible for extracellular nucleoside utilization and 14 of 20 amino acid synthesis pathways were completely retained. Under oligotrophic condition, the gut-associated bacterium may make use of extracellular DNA for carbon and energy supplement, and may provide essential amino acids to the host. The clustered regularly interspaced short palindromic repeat (CRISPR) and restriction–modification (RM) systems presented in the genome may provide protection against invading viruses. A linear azol(in)e-containing peptide gene cluster for bacteriocin synthesize was also identified, which may inhibit the colonization and growth of harmful bacteria. Known virulence factors were not found by database searching. On the basis of its phylogenetic position and metabolic characteristics, we proposed that the bacterium represented a novel genus and a novel family within the Izemoplasmatales order and suggested it be named “Candidatus Bathyoplasma sp. NZ”. This was the first time describing host-associated Izemoplasmatales.

Sea cucumbers (Holothuroidea; Echinodermata) are ecologically significant constituents of benthic marine habitats. We surveilled RNA viruses inhabiting eight species (representing four families) of holothurian collected from four geographically distinct locations by viral metagenomics, including a single specimen of Apostichopus californicus affected by a hitherto undocumented wasting disease. The RNA virome comprised genome fragments of both single-stranded positive sense and double stranded RNA viruses, including those assigned to the Picornavirales, Ghabrivirales, and Amarillovirales. We discovered an unconventional flavivirus genome fragment which was most similar to a shark virus. Ghabivirales-like genome fragments were most similar to fungal totiviruses in both genome architecture and homology and had likely infected mycobiome constituents. Picornavirales, which are commonly retrieved in host-associated viral metagenomes, were similar to invertebrate transcriptome-derived picorna-like viruses. The greatest number of viral genome fragments was recovered from the wasting A. californicus library compared to the asymptomatic A. californicus library. However, reads from the asymptomatic library recruited to nearly all recovered wasting genome fragments, suggesting that they were present but not well represented in the grossly normal specimen. These results expand the known host range of flaviviruses and suggest that fungi and their viruses may play a role in holothurian ecology.

Sea cucumbers are bottom dwelling invertebrates, which are mostly found on subtropical and tropical sea grass beds, sandy reef flats, or reef slopes. Although constantly exposed to fouling communities in these habitats, many species are surprisingly free of invertebrate epibionts and microfouling algae such as diatoms. In our study, we investigated the anti-fouling (AF) activities of different crude extracts of tropical Indo-Pacific sea cucumber species against the fouling diatom Cylindrotheca closterium. Nine sea cucumber species from three genera (i.e., Holothuria, Bohadschia, Actinopyga) were selected and extracted to assess their AF activities. To verify whether the sea cucumber characteristic triterpene glycosides were responsible for the observed potent AF activities, we tested purified fractions enriched in saponins isolated from Bohadschia argus, representing one of the most active anti-fouling extracts. Saponins were quantified by vanillin-sulfuric acid colorimetric assays and identified by LC-MS and LC-MS/MS analyses. We were able to demonstrate that AF activities in sea cucumber extracts were species-specific, and growth inhibition as well as attachment of the diatom to surfaces is dependent on the saponin concentration (i.e., Actinopyga contained the highest quantities), as well as on the molecular composition and structure of the present saponins (i.e., Bivittoside D derivative was the most bioactive compound). In conclusion, the here performed AF assay represents a promising and fast method for selecting the most promising bioactive organism as well as for identifying novel compounds with potent AF activities for the discovery of potentially novel pharmacologically active natural products.

Sea cucumbers produce numerous compounds with a wide range of chemical structural diversity. Among these, saponins are the most diverse and include sulfated, non-sulfated, acetylated and methylated congeners with different aglycone and sugar moieties. In this study, MALDI and ESI tandem mass spectrometry, in the positive ion mode, were used to elucidate the structure of new saponins extracted from the viscera of H. lessoni. Fragmentation of the aglycone provided structural information on the presence of the acetyl group. The presence of the O-acetyl group was confirmed by observing the mass transition of 60 u corresponding to the loss of a molecule of acetic acid. Ion fingerprints from the glycosidic cleavage provided information on the mass of the aglycone (core), and the sequence and type of monosaccharides that constitute the sugar moiety. The tandem mass spectra of the saponin precursor ions [M + Na]+ provided a wealth of detailed structural information on the glycosidic bond cleavages. As a result, and in conjunction with existing literature, we characterized the structure of five new acetylated saponins, Lessoniosides A–E, along with two non-acetylated saponins Lessoniosides F and G at m/z 1477.7, which are promising candidates for future drug development. The presented strategy allows a rapid, reliable and complete analysis of native saponins.

A new species of holothurian of the genus Psolus Oken, 1815 is described. Psolus rufus sp. nov. was found in the central Cantabrian slope (Bay of Biscay) at 1500 m depth. The new species is characterized by having: ovoid body, reddish colour in vivo ; dorsal area enclosed in a complete test composed of imbricating scales; 10 triangular plates of the same size surrounding mouth; 10 oral tentacles; no dorsal papillae; tube feet in two rows in the ventrolateral radii but one single row in the medial third or the body; ossicles are big dorsal plates and small plates in the sole, which are smooth, irregular and perforated. The molecular study of the COI gene supports the morphological results, grouping P. rufus sp. nov. together with other members of the genus. However, the new species is genetically distinct from the two groups (Antarctic and Canadian) of the available sequenced Psolus species. Furthermore, a key to the Psolus species of the north-eastern Atlantic Ocean is provided. [ABSTRACT FROM AUTHOR]

The brown sea cucumber Isostichopus fuscus is the most important commercial holothurian in the eastern Pacific, and its high market value caused overfishing and sharp declines of its populations and catches in several Latin American countries. In Mexico, the fishery has been intense in the northern Gulf of California since the 1990s, and it is currently under strong regulation. To evaluate the current status of the organisms, we measured the size, weight and estimated the relative condition index (Kn) of 702 specimens sampled in 86 rocky reefs of that region in 2016, at depths from 3 to 22 m. Mean length ± SD was 22.32 ± 5.23 cm, lower than average in the northern Gulf, but nevertheless, the average weight was 420.61 ± 192.48 g, among the highest recorded in the eastern Pacific; this is presumably due to the high primary production of the region that favors the presence of well-nourished organisms. The weight (W)-length (L) relationship was W = 3.27 L1.56, and condition index ranged from 0.045 to 2.13 (mean Kn = 0.96 ± 0.29), a figure that did not differ to that reported along the Mexican Pacific. There were differences in the value of Kn among sites, being higher in areas that are subject to the low fishing effort. [ABSTRACT FROM AUTHOR]

The Philippines is known for its high diversity of sea cucumbers; however, there is little done on sea cucumber diversity in the southern Philippines. To augment this paucity of information, a rapid survey of the shallow-water sea cucumbers was carried out in three sites in Sarangani Bay by using the transect method for four months in both the seagrass and coral reef habitats. We recorded 21 species of sea cucumbers - 17 of these species were found in the seagrass beds and 10 species in the coral reef areas. The three most abundant species observed were the Holothuria scabra (29.2%), Bohadschia marmorata (21.2%), and Actinopyga echinites (17.6%) (n=1,969). Aside from some economically important sea cucumbers observed, we also noted rare species such as the Holothuria immobilis and Actinopyga capillata, which only have a few records in the Philippines. We are also the first to document Holothuria isuga in the Philippines, which is previously known only from five localities. The results offer opportunities for sea cucumber studies in the southern Philippines, especially on the biology and ecology of the rare and newly recorded species. [ABSTRACT FROM AUTHOR]

Tropical sea cucumber fisheries are generally traditional, small-scale, multispecies and poorly managed. Many recent studies have improved our knowledge on the biology and ecology of the commercially important species; the main results are analysed and the remaining gaps discussed. The fisheries and the patterns of trade changes during the last decade are presented from the data available and confirm overexploitation in the traditional Indian Ocean and West Pacific countries and territories. Several Latino-American countries now have active fisheries. Despite the management and conservation issues which have recently received more attention at international, regional and national levels, more measures are still needed at all these levels, to ensure sustainable exploitations of these resources. [ABSTRACT FROM AUTHOR]

The surface defense molecules of aquatic invertebrates against infectious microorganisms have remained largely unexplored. In the present study, hemagglutinins were isolated from an extract of body surface layer of Japanese sea cucumber, Apostichopus japonicus , by affinity chromatography with fixed rabbit erythrocyte membranes. The N-terminal sequence of a 15-kDa agglutinin was almost identical with that of SJL-1, a C-type lectin formerly identified in this species. Because cDNA sequence and tissue distribution of SJL-1 have not been reported, we performed cDNA sequencing, gene expression analysis, and western blotting and immunohistochemical evaluation with anti-recombinant SJL-1 (rSJL-1) antibodies. The hemagglutinin gene was transcribed mainly in the integument, tentacles, and respiratory tree. Western blotting revealed that SJL-I is present in a body surface rinse, indicating that SJL-1 is secreted onto the body surface. SJL-1-positive cells scattered beneath the outermost layer of the integument were detected by immunohistochemistry. Furthermore, rSJL-1 agglutinated Gram-positive and Gram-negative bacteria, and yeast. These results indicate that SJL-1 acts as a surface defense molecule in A. japonicus . [ABSTRACT FROM AUTHOR]

This study examines the interaction between two types of phagocytes (P1 and P2) of the holothurian Eupentacta fraudatrix and its in vitro modulation by dexamethasone. Our results indicate that inhibition of apoptosis in P1 phagocytes by P2 phagocytes was accompanied by increased activities of antioxidant enzymes and reduced synthesis of interleukin-1α-like substances. We hypothesize that P1-phagocyte-related effects occurred in response to a high level of hydrogen peroxide produced by P2 phagocytes. The reduced anti-apoptotic effect of P2-phagocyte supernatant during prolonged incubation (24 h) was accompanied by a decline in defense reactions in P1 phagocytes due to depletion of antioxidant enzymes (catalase, glutathione reductase, and glutathione transferase). Inhibition of apoptotis in P1 phagocytes associated with upregulation of antioxidant enzyme defense in response to P2 phagocytes preincubated with dexamethasone (100 µM) indicates that P2 phagocytes affect P1 phagocytes via a ROS-associated mechanism. Thus, our data provide evidence that P1 and P2 phagocytes exhibit their maximum activity at different stages of the immune response, thus causing inhibition of activity in target cells during prolonged exposure. Dexamethasone enhances these effects. [ABSTRACT FROM AUTHOR]

The Japanese sea cucumber Apostichopus japonicus plays important ecological and economic roles in the coastal areas of Japan. Here, we aim to reveal the relation between habitat characteristics and density of juvenile and adult sea cucumbers in Maizuru Bay. Density of adult sea cucumbers was estimated by underwater visual surveys and bottom trawls and that of newly settled individuals by seedling collectors distributed in the bay. The physical environment of the sea bottom was evaluated from median diameter, total organic carbon, total nitrogen, carbon-to-nitrogen ratio, carbon isotope ratio, nitrogen isotope ratio, depth, slope, and distance from the coastline. Adult sea cucumber density was higher in the east side than the west side of Maizuru Bay, the former having a no-take zone for sea cucumbers. Juvenile sea cucumbers were most abundantly collected in the central part of the bay. High organic matter from the sea, short distance from the coastline, and high seabed gradient (steepness) had a positive effect on the density of adult sea cucumbers, and depth had positive effects on their body size. We suggest that sustainable management of sea cucumbers can be achieved by a combination of the establishment of no-take zones and increased protection of nursery habitats. [ABSTRACT FROM AUTHOR]

Tritaeta gibbosa is an epibiotic amphipod that lives in self-constructed invaginations in the tissue of various hosts as diverse as sponges, soft corals, ascidians and echinoderms. Here, some aspects of the relationship of T. gibbosa to different hosts are described. The main focus, however, is the colonisation of the holothurian Ocnus planci. The association between this holothurian species and T. gibbosa was studied by means of histology and scanning electron microscopy. The investigations revealed that T. gibbosa does not damage the host tissue. Only some stretching, thinning, thickening, and displacement of the holothurian cuticle, epidermis and dermis was observed. This suggests that the invagination is formed by pressure caused by a specific behaviour of T. gibbosa . The amphipod takes advantage of the properties of the mutable connective tissue characteristic for echinoderms. The majority of invaginations are situated at the holothurian’s anterior end. Furthermore, most invaginations are perpendicularly oriented to the long axis of the holothurian body. This seems to improve the exploitation of food particles coming from the tentacles of O. planci . The amphipod specimens are subadult to adult and there is a strong bias toward females as is generally the case in benthic T . gibbosa populations. Although some new information about the ecology of T. gibbosa is added by this study, some general questions such as the tissue reactions of the various hosts, the ontogeny and juvenile behaviour, and the type of association to the host still need investigation. [ABSTRACT FROM AUTHOR]