Sea Cucumber Populations Research Articles

Development of Reliable Male-Specific Molecular Markers for Genetic Sex Identification in Sea Cucumber Apostichopus japonicus.

Apostichopus japonicus is an important marine aquaculture species in China, with high nutritional and economic value. In A. japonicus, there is no obvious sexual dimorphism in external appearance, and sex differentiation primarily relies on the observation of mature gonads after dissection, which leads to difficulties in sex identification. The confusion in sex identification greatly reduces breeding efficiency in the sea cucumber industry. Therefore, developing a reliable sex-specific marker is crucial. In this study, we identified 586 male-specific sequences through whole-genome assembly and sequence alignment, but did not identify any female-specific sequences, inferring an XY-type sex determination system in sea cucumbers. We developed a set of male-specific molecular markers to establish an accurate, stable, and widely adaptable genetic sex identification technique for A. japonicus. The male-specific molecular markers were validated with 100% accuracy in sea cucumber populations from six different geographical regions in China. In conclusion, this study provides further evidence for the XY-type sex determination system in A. japonicus and establishes an effective genetic sex identification method for multi-geographic populations, which benefits future study on reproductive biology and has significant implications in sea cucumber aquaculture industry.

Searching for drivers of the patchy distribution of sympatric deposit‐feeding sea cucumbers: A multi‐scale monitoring study

AbstractThree sea cucumber species, Holothuria atra, Holothuria leucospilota, and Stichopus chloronotus, are patchily distributed within the coral reefs of Reunion Island, exhibiting locally high densities (> 1 ind m−2). Previous studies stated that these sympatric species have thrived for almost four decades; however, factors involved in their distribution and spatiotemporal dynamics are not well understood yet. The aims of this study are to analyze the fine‐scale spatiotemporal dynamics of these sympatric species and identify the key sedimentary factors (substrate composition and cover) involved in their distribution. Sea cucumber populations and sedimentary factors were monitored along back‐reef and shore‐to‐ocean gradients during four consecutive seasons. Meanwhile, feeding behavior was assessed by measuring motility and excretion rates. Each species presents its own dynamic between the beginning and the end of the monitoring: increase of density for H. leucospilota, stability for H. atra, and decrease for S. chloronotus. Distribution of H. atra was closely related to substrate organic features (high organic matter, chlorophyll a, and ∂13C), H. leucospilota with the occurrence of seagrass and S. chloronotus with none. Results on feeding behavior showed that S. chloronotus emerges as a specialist while the two others appear to be generalists. Conspecific attraction or recruitment pattern may drive the high‐density patchy distribution of both Holothuria species, while the drastic decrease of S. chloronotus could be linked to unstudied factors related to predation or climate change. Water flow regime could also have a significant effect on the patchy distribution of these species, therefore, further studies should pay particular attention to this factor.

Development and application of molecular markers in fisheries, aquaculture, and industry of representative temperate and tropical sea cucumbers: a review

Sea cucumber has emerged as a crucial economic species in aquaculture in China because of its remarkable nutritional and medicinal value. However, wild sea cucumber populations have experienced a decline due to overfishing and environmental factors, underscoring the urgent need for genetic resource conservation and biotechnology innovation within the sea cucumber aquaculture and breeding industry. The development of the sea cucumber industry is still impeded by challenges and difficulties. Nevertheless, significant progress has been made through the utilization of molecular markers, which have effectively addressed a number of fisheries and aquaculture issues. In recent years, diverse types of molecular markers including mitochondrial DNA, microsatellites, and SNP markers have been developed and extensively applied in various aspects of sea cucumber research. These markers play vital roles in genetic sex identification, germplasm resource evaluation, population structure assessment, as well as marker-assisted breeding in marine ranching and sea cucumber aquaculture and breeding industry. This review provides an overview of the fundamental principles, functions, and characteristics associated with various markers employed across various sea cucumber species while also discussing their applications within different aspects of the sea cucumber fisheries, aquaculture, and breeding industry.

Sea cucumber significance: Drying techniques and India's comprehensive status.

Sea cucumbers, members of the echinoderm class Holothuroidea, are marine invertebrates with ecological significance and substantial commercial value. With approximately 1700 species, these organisms contribute to marine ecosystems through nutrient cycling and face various threats, including overfishing and habitat loss. Despite their importance, they are extensively exploited for diverse applications, from seafood to pharmaceuticals. This study investigates sea cucumbers' nutritional profile and bioactive elements, emphasizing their role as sources of essential compounds with potential health benefits. The demand for sea cucumbers, especially in dried form, is significant, prompting exploration into various drying techniques. Examining the global trade in sea cucumbers highlights their economic importance and the conservation challenges they face. Conservation efforts, such as awareness campaigns and international collaboration, are evaluated as essential steps in combating illicit trade and promoting the sustainable stewardship of sea cucumber populations. PRACTICAL APPLICATION: Around 1700 species of sea cucumbers were identified as vital ecological scavengers in the Holothuroidea class. High commercial value due to their health benefits, particularly their demonstrated inhibitory effect against various types of cancer. "Beche-de-mer" holds a 90% market share and is regarded as a luxury food item in Southeast Asian countries. Due to overexploitation, the species isclassified as Schedule I under the Wildlife Protection Act (WPA) in India, prompting the implementation of a blanket ban on their harvesting to ensure its conservation.

Boom and no bust for a teatfish in Torres Strait, Australia from combined forms of western and Indigenous management

AbstractBlack teatfish (Holothuria whitmaei) is a high value sea cucumber that has been listed under the Convention on International Trade of Endangered Species (CITES) Appendix II. The Black teatfish fishery in Torres Strait, Australia, is fished solely by Indigenous Torres Strait Islanders. Black teatfish were closed to fishing in 2003, based on the results of stock surveys and concerns of overexploitation. A stock survey in 2009 found the Black teatfish population had recovered substantially but the fishery was again closed after trial openings exceeded catch limits. In line with a new harvest strategy adopted for the fishery in 2019, we conducted a stock survey in 2019–2020 that suggested the stock had recovered sufficiently to support a sustainable catch limit of 20 t. Empowering Indigenous Torres Strait Islanders to use Island custom alongside western management strategies, contributed to the success of a trial opening in 2021. The combination of a harvest strategy developed in consultation with traditional owners, a rigorous scientific survey and trial opening protocols informed by Island custom, supported the CITES positive Non‐Detriment Finding for the Torres Strait Bêche‐de‐mer Fishery. This is a significant example of the successful recovery and ongoing sustainable management of a depleted sea cucumber population.

Movement dynamics, sediment turnover and sheltering behaviours of the nocturnal coral reef sea cucumber, Stichopus cf. monotuberculatus

Animal movement and feeding studies shed light on ecological roles and can inform management strategies for fished species. However, the feeding and movement of nocturnal sea cucumbers have been rarely studied. We determined the movement dynamics, feeding ecology and sheltering behaviour of the nocturnal Stichopus cf. monotuberculatus (dragonfish) at One Tree Reef and Heron Island Reef on the southern Great Barrier Reef. The short-term movement of individual sea cucumbers were tracked, and sediment defecation rates were measured. Displacement rates averaged 3–33 cm h−1 across the four sites, with the sea cucumbers moving more slowly approaching sunrise and within patches of organically rich sediment. The movement paths were moderately tortuous, with larger sea cucumbers moving along straighter paths. Rates of sediment turnover averaged 7.8 g h−1 and were greatest for larger individuals. The faecal casts were organically richer and composed of finer grains than the ambient surface sediments, implying that S. cf. monotuberculatus avoids consuming coarse sediments and feeds on nutritionally rich particles. The sea cucumbers sheltered under hard reef substrata and moved non-directionally on the seascape, with a few individuals homing back to their original refuges. The affinity to reef substrata and short nightly net displacements of S. cf. monotuberculatus have implications for the spatial management of this and other similar species. Larger individuals occupied deeper refuges, implying that projected declines in substratum rugosity on coral reefs due to climate change could impact the size structure of sea cucumber populations, with implications for fisheries.

Application of Sargassum sp extract on juvenile sandfish nursery

Sea cucumbers are a high-value fauna that can be found on Kei Island’s coastal area. Because of overexploitation and poor management, the sea cucumber population on Kei Island has declined dramatically. To solve this problem, the cultivation activities (breeding, nursery and growth out) of sea cucumbers need to be developed immediately. The aim of this study was to utilize the brown algae Sargassum sp to support the production of sandfish seeds in Household-Scale Hatchery. This study took place from April - May 2022 at Tual Teripang Center, Tual. Juveniles of sandfish are used as research objects with measuring between 3 - 15 mm in size and have a stocking density of 800 juveniles per tub. The feed used as treatment was included Sargassum sp extract 300 gr/tub (Treatment A), 400 gr/tub (Treatment B), and 500 gr/tub (Treatment C). Feeding has given every day and water changes was 50 - 60% per day. The calculation of growth and survival rate is the variable that observed in this study. As supporting data, water quality test measures were carried out. Three treatments have different effects on juvenile growth. The best result was obtained in Treatment C. For survival, showed all treatments had same effect on the survival rate of juvenile sandfish. It was concluded that Treatment C was better for the growth of juvenile sandfish than Treatment A and Treatment B.

EFISIENSI KINERJA SASI TERIPANG PASIR (Holothuria scabra) DESA TUNGU KEPULAUAN ARU

The sandfish sea cucumber, Holothuria scabra, has economic value and is considered expensive, making it a target for utilization. The sandfish sea cucumber is found in the village of Tungu, but with the implementation of sasi (a traditional system of resource management), it is expected to ensure the sustainability of the sandfish sea cucumber resources. In reality, every time the sasi period is lifted, sandfish sea cucumbers are harvested without any size limitations and there are illegal captures by fishermen from outside the Aru Islands using complete diving equipment. Given these conditions, it is suspected that the sandfish sea cucumber population may decline. Therefore, this research was conducted in August-September 2018, with the aim of assessing the performance efficiency of the sasi system for sandfish sea cucumbers in Tungu Village. Data collection was done through observation and interviews with intentionally selected respondents and analyzed descriptively using several indicators. The research results showed that the catch of sandfish sea cucumbers amounted to 2,240 kg of dried weight, with varying selling prices according to size. The analysis of performance efficiency indicated that the sasi system for sandfish sea cucumbers in Tungu Village falls into the moderate category.

Genome-wide SNP analyses reveal a substantial gene flow and isolated-genetic structure of sea cucumber Holothuria leucospilota populations in Western Central Pacific

The black sea cucumber Holothuria leucospilota is a commercially exploited species in the Western and Central Pacific region including Australia and Vietnam, where it has been overfished. There is interest to develop captive breeding, sea ranching and restocking programs for H. leucospilota. However, the wide distribution of this species could lead to genetic structure among site, which needs to be considered for responsible genetic management for example, restocking. This is the first study to investigate population genetics in H. leucospilota, between Australia and Vietnam, using single nucleotide polymorphisms (SNPs). The results indicated that there was high gene flow (Nm > 4) and genetic similarities among three Vietnamese populations, which inferred a high panmictic stock structure in Vietnam. Less gene flow (Nm > 1) was indicated between Vietnam and Mooloolaba (Eastern Australia) populations, and there was a significant genetic differentiation among any Vietnamese populations and Mooloolaba population (FST from 0.034 to 0.043; P < 0.05). Surprisingly, there was a major genetic difference (FST > 0.2) and a restricted gene flow (Nm <1) between Darwin (Northern Australia) population and other sea cucumber populations studied (Vietnam and Eastern Australia), which revealed a genetic break/divergence in Darwin. Based on these findings, we can propose that the Vietnamese sea cucumber stocks be considered as a single genetic stock with concordant implications for genetic management. We consider whether the genetic differences in the Darwin stock arise from bottlenecking and are not reflective of adaptive differences. In summary, the results from this study provide basic genetic information on H. leucospilota populations, that would help to design restocking management plans, genetic conservation initiatives and sea ranching programs for H. leucospilota.

Direct assessment of giant red sea cucumber (Apostichopus californicus) sustainability through experimental fisheries

The giant red sea cucumber ( Apostichopus californicus) fishery in BC, Canada, is considered sustainable by managers but not by many harvesters. In 1997, the Kitasoo/Xai'xais First Nation began experimental fishing areas (EFAs) at Tolmie Channel and Laredo Inlet to test the effects of different exploitation rates on sea cucumber populations and determine what harvest levels are sustainable. These EFAs were annually surveyed by dive transects and subsequently harvested from 1998 to 2018. Bayesian surplus production models developed in 2011 indicated that the fishery was sustainable, after which the fishery changed from annual to 3-year rotational harvests. Here, we develop updated models to estimate the sustainability of the fishery using all currently available EFA data, including direct estimates of unfished biomass. Our models suggest that the fishery is likely to persist for 175 years at the current harvest rate annually or rotationally, though such long-term projections are likely inaccurate. We present methodology to generate scientific advice for the process of determining a maximum sustainable exploitation rate in the form of crash rate analysis.

Shallow epifaunal sea cucumber densities and their relationship with the benthic community in the Okinawa Islands.

Sea cucumbers are important ecological engineers in marine ecosystems. However, the fishery demand of some species, especially large-epifaunal and commercially used (LEC) sea cucumbers, has risen drastically, resulting in serious depletion of local populations for many species. Despite this problem, basic ecological data on sea cucumbers, such as population densities and preferred habitats, are often still insufficient. Here, we report on the population densities of multiple LEC sea cucumber species, and their ambient benthic communities at eight sites around Okinawa Islands. Further, we discuss the correspondence between sea cucumber densities and the surrounding coral communities. Our results show two sites within national or quasi-national parks, Aka and Manza, where stricter rules have been placed on fisheries and land reclamation compared to other areas, had the highest and third highest sea cucumber population densities among sites, respectively. Holothuria atra was observed at all survey sites and made up the majority of sea cucumber populations at all sites except for Chatan and Sesoko, where Holothuria leucospilota and Stichopus chloronotus were most abundant, respectively. Regarding the relationships between benthic composition and LEC sea cucumber species, S. chloronotus was significantly correlated with dead corals, scleractinian corals, and coralline algae. As well, H. leucospilota had significant correlations with rubble. Although there were no significant correlations between any specific scleractinian coral genus and sea cucumber densities, S. chloronotus was marginally insignificant with Platygyra and Psammocora. Notably, medium- to highly valued species were sparse in our surveys, and most of them appeared at only one site. Additionally, at one site (Odo), only three LEC sea cucumber individuals were observed. Combining these facts with relatively low population densities around the Okinawa Islands compared to densities reported in previous research from the Indo-West Pacific Ocean region, we conclude that Okinawan LEC sea cucumber populations have been and are being impacted by high levels of direct (e.g., overexploitation, as well as coastal development) and indirect anthropogenic pressure (e.g., decreasing water quality). To address the current situation, repeated monitoring and more detailed investigations to reveal the drivers that determine LEC sea cucumber species aggregations and population densities are urgently needed, along with more robust management of remaining LEC sea cucumber populations.

Development of a high-throughput SNP array for sea cucumber (Apostichopus japonicus) and its application in genomic selection with MCP regularized deep neural networks

High-throughput single nucleotide polymorphism (SNP) genotyping assays are powerful tools for genetic studies and genomic breeding applications for many species. Though large numbers of SNPs have been identified in sea cucumber (Apostichopus japonicus), but, as yet, no high-throughput genotyping platform is available for this species. In this study, we designed and developed a high-throughput 24 K SNP genotyping array named HaishenSNP24K for A. japonicus, based on the multi-objective-local optimization (MOLO) algorithm and HD-Marker genotyping method. The SNP array exhibited a relatively high genotyping call rate (> 96%), genotyping accuracy (>95%) and exhibited highly polymorphic in sea cucumber populations. In addition, we also assessed its application in genomic selection (GS). Deep neural networks (DNN) that can capture the complicated interactions of genes have been proposed as a promising tool in GS for SNP-based genomic prediction of complex traits in animal breeding. To overcome the problem of over-fitting when using the HaishenSNP24K array as high-dimensional DNN input, we developed minmax concave penalty (MCP) regularization for sparse deep neural networks (DNN-MCP) that finds an optimal sparse structure of a DNN by minimizing the square error subject to the non-convex penalty MCP on the parameters (weights and biases). Compared to two linear models, namely RR-GBLUP and Bayes B, and the nonlinear model DNN, DNN-MCP has greatly improved the genomic prediction ability for three quantitative traits (e.g., wet weight, dry weight and survival time) in the sea cucumber population. To the best of our knowledge, this is the first work to develop a high-throughput SNP array for A. japonicus and a new model DNN-MCP for genomic prediction of complex traits in GS. The present results provide evidence that supports the HaishenSNP24K array with DNN-MCP will be valuable for genetic studies and molecular breeding in A. japonicus.

Diversity, distribution and temporal variation in abundance and biomass of sea cucumber population in Pozm Bay, north of Oman Sea, Iran

The ecosystem of Pozm Bay, north of Oman Sea, Iran, is one of the unique marine habitats for benthic aquatic species. Therefore, this study investigated the distribution, diversity and temporal variation in abundance and biomass of sea cucumber species in Pozm Bay. Five transects, each of them in four triplicates and perpendicular to the sea were sampled at 3, 6, 9 and 12 m depths and three seasons (winter, spring and autumn). Different spicule patterns were chosen as identification key for each studied species. A total of five species from two families of sea cucumbers were identified in the study area, in which 191 and 41/km 2 were belonged to Holothuridae and Stichopodidae with three and one species, respectively. H. leucospilota, was found to be a dominant species in Pozm Bay and had the biggest body size and biomass in winter. The most density of sea cucumbers was recorded in winter at 48.36 g/m2, while the lowest biomass was calculated at 18.02 g/m2. H. leucospilota, H. arenicola, H. atra and S. variegatus were abundant at transects 3, 1, 3 and 1, respectively. The highest and lowest density of sea cucumbers in winter were observed at transects 1 and 2, respectively. In addition, in spring, the highest and lowest density of sea cucumbers were recorded at transects 3 and 2, respectively. Shannon and Margalof ecological indices showed that all species were common in different seasons and had a contagious dispersion pattern. Moreover, it appeared that the distribution of sea cucumbers was affected by habitat complexity in the study area. Together, findings showed that the study of distribution patterns, diversity and temporal variation of sea cucumbers can deepen our knowledge about the abundance and biomass of these valuable species, which is useful in managing the fisheries resources and protective programs in Pozm Bay.

A Review of Factors Influencing the Seagrass-Sea Cucumber Association in Tropical Seagrass Meadows

In the tropical ecosystem, sea cucumbers are associated with seagrass meadows in various ways, often forming a network of ecological interactions. From this myriad of interactions, the trophic relationship between the seagrasses and sea cucumbers has received recent attention with the advent of analytical techniques. However, little is understood about the exact mechanism by which seagrasses are sustaining the sea cucumber populations in the food chain, considering the high number of refractory components in seagrasses and the lack of digestive enzymes among sea cucumbers. This manuscript aims to review existing concepts in ecology concerning the association between tropical seagrasses and sea cucumbers to provide directions for research and management of this vital resource. We searched literature from electronic databases and identified key concepts concerning sea cucumber and seagrass communities based on geographic distribution, nutrient compositions, seagrass decomposition process, and trophic enrichments in the food chain. A conceptual model was then developed detailing the factors influencing the association between the seagrass meadows and sea cucumbers. Despite the limited published information on the seagrass–sea cucumber association, a synthesis of the current understanding of this topic is provided to address the declining sea cucumber populations in the tropical seagrass meadows. We suggest that the successful restoration of sea cucumber fisheries requires a thorough understanding of the seagrass decomposition process, which is vital to the diet of sea cucumbers.

Trace metal levels in the edible tissues of sea cucumbers (Holothuria tubulosa and Holothuria polii) from Sardinia (Western Mediterranean).

Sea cucumbers represent an important part of the diet in Asian and Pacific regions and are also used in traditional medicine. These habits have led to the overexploitation of local sea cucumber populations in these areas, driving the pursuit of new stock regions, such as Mediterranean areas. In Italy, contrarily to that observed for other Mediterranean countries, the exploitation of sea cucumber stocks is not extensive, which opens a new market opportunity. Thus, from a food safety perspective, this work aims at reporting the first assessment of trace metal concentrations (As, Cd, Cr, Cu, Hg, Ni, Pb) in the edible tissues of Holothuria polii and Holoturia tubulosa collected in Sardinia, the second-largest island in the Mediterranean Sea. Metal concentrations found in H. polii were generally higher than in H. tubulosa. However, in both species, they were lower than those reported for other areas of the Western Mediterranean. Cd, Hg, and Pb were below the limits established for seafood in Europe. As concentrations were in the range of those measured in other commercial seafood species in the Mediterranean. Thus, these species may be harvested and traded to fulfil the demands of local and international markets.

Modelling the Distribution of a Commercial NE-Atlantic Sea Cucumber, Holothuria mammata: Demographic and Abundance Spatio-Temporal Patterns

There is an increasing demand for sea cucumbers, for human consumption, mainly from Asian markets and, as a consequence, NE-Atlantic species are now new targets for exploitation and exportation. Holothuria mammata is one of the most valuable species in Europe. However, the lack of historical economic interest in this species in most European countries has also led to a lack of studies concerning biological and ecological aspects on wild populations and this is a major issue for stock management. This study aims to determine the temporal and spatial patterns of distribution of H. mammata, considering its abundance and demographic structure in a NE-Atlantic area, SW Portugal, as a function of environmental conditions. For that, a population from a marine protected area was followed for 1 year at 1.5-month intervals. Throughout the coastal area, six sites were selected and at each sampling campaign three random transects per site and substrate (rock and sand) in which all H. mammata individuals were counted and measured. For each site and survey several environmental parameters of interest, from the water column, the sediment and substrate cover, were also measured. Generalized Linear Models were used to model the spatial and temporal distribution of the species according to environmental conditions, to determine the species’ habitat preferences. The distribution models indicate that abiotic and biotic parameters of the water column are not the main drivers shaping the distribution of H. mammata. The species has a patchy distribution, and its habitat preferences depend on environmental stability, the presence of shelter and habitat complexity, which is more important for smaller, more vulnerable, individuals, while bigger size classes tend to venture more into less stable environments in an opportunistic fashion. The knowledge of these population traits is determinant to develop stock management measures, which are now urgent to prevent the depletion of commercial sea cucumber populations in the NE-Atlantic. Sustainable fisheries policies should be developed and start by considering to delimit fishing areas and periods, considering the species spatial and temporal distribution patterns.

Survival and growth of wild-translocated individuals and released-cultured juveniles of sea cucumber Isostichopus badionotus off the northern Yucatan Peninsula, Mexico

A decade ago, the Four-sided sea cucumber, Isostichopus badionotus, became an important fishery in the Yucatan peninsula, Mexico. However, difficulties in fishery management caused deterioration in its population and fishery. Consequently, at this time it is urgent to identify viable strategies to achieve its population restoration. Survival and growth are key biological factors for restoration programs in overfished sea cucumber populations. This work evaluates the survival and growth of both wild-translocated individuals and released-cultured juveniles off the northern coast of the Yucatan Peninsula. In 2018, 60 wild, sea cucumber individuals were translocated into the sea at high (HD = 1.071 ind·m−2) and low densities (LD = 0.357 ind·m−2), and monitored in nine surveys over 133 days. In 2019, 60 cultured juveniles were released at nearby locations at natural shelters (NS) and artificial shelters (AS). These shelters were monitored over eight surveys in 67 days. Permanence rate (Pe) and disappearance rate (β) of individuals were calculated. Increase in average length and weight, and growth rates in length (cm·day−1) and weight (g·day−1), were estimated. Survival was higher (Pe = 51% and β = −0.005 ind·day−1) in wild-translocated individuals at LD (p < 0.05), with no growth detected. Survival of released juveniles was significantly higher (p < 0.05) in AS (Pe = 59.6%, b = −0.016 ind·day−1), which this latter was attributed to protection against predation, while growth rates were between 0.34 and 0.75 g·day−1. Results indicate wild-translocated individuals and released-cultured juveniles survived in the new habitat and grew after translocation and release, which suggests populations of I. badionotus may have the potential for restoration under guided fishery programs.

Ecological study of two sea cucumbers (Holothuria parva and Holothuria arenicola) in the Hormozgan and Bushehr provinces of Persian Gulf

The understanding of the distribution and population structure of the various species in the marine environment is very helpful to effectual resource management and conservation. This study aimed to assess ecological factors relating to sea cucumber populations on the rocky shores of the Persian Gulf. Population of two species of sea cucumber were investigated along 6 intertidal rocky sites, including Deylam, Bushehr, Dayer, Nayband, Bostaneh, and Lengeh in Bushehr and Hormozgan Provinces. During the period of the sampling, no sea cucumbers were observed in Deylam and Lengeh stations. To address this, 500 individuals of sea cucumber were collected and transported from their natural habitat to the laboratory. During the whole study, two species were observed (Holothuria parva and Holothuria arenicola). The Highest abundance were obtained at the stations of Dayer (198 individuals) and Bostaneh (188 individuals). The maximum density (individuals per 200 m2) was estimated for Dayer (49.5 ± 6.13) and Bostaneh (47 ± 8.79). The results of the study revealed a negative allometric growth for both species. The results showed that different ecological indices of sea cucumbers community in the study areas affected by physicochemical parameters such as pH, temperature, salinity and possibly lack of correct management in order to enforce more protective approaches relating to these animals.

Application of asexual reproduction techniques and grow ability of the sandfish Holothuria scabra

Sea cucumber population in nature is reported to have experienced exploitation pressure in various places. Natural sea cucumber reproduction (sexual) takes a long time to produce a new adult individual. This is feared to be the cause of the extinction of sea cucumbers. Sandfish, Holothuria scabra, do not include sea cucumber species which are categorized as capable of asexual reproduction. However, several laboratory-scale studies state that sandfish can be induced for asexual reproduction. This study aims to determine the level of life graduation and the growth of sandfish produced by asexual reproduction. Individual sandfish is tied with rubber bands about 60% from the anterior to the posterior. The result showed that the sandfish were successfully induced to undergo asexual reproduction which is known as “fission”. The time needed for a sandfish to break itself into 2 new individuals takes less than 2 days. The first days after dividing the body seem to be a critical period. Only 13.64% of new individuals survive the critical phase. It concluded that the growth of asexual reproduction sandfish is slow because it takes time to regenerate the scattered internal organs during the process of division.

An annual faecal 16S amplicon sequencing of individual sea cucumber ( Apostichopus japonicus ) demonstrates the feeding behaviours against eukaryotes in natural environments

To fill in the gaps in knowledge as to how individual sea cucumber Apostichopus japonicus behave consuming eukaryotic food sources in natural environments, eukaryotic communities in the faeces of sea cucumbers and sediments were analysed through one whole year based on 16S rRNA gene sequencing of the organelle genomes. A total of 390 eukaryotic features were obtained, and 99.7% of the features were assigned to chloroplasts. The eukaryotic communities in faeces and sediments showed seasonal fluctuations through one whole year based on Bray-Curtis distance and community composition. Comparison of eukaryotic communities between faeces and sediments showed that 12 families including Chaetocerotaceae and Laminariaceae were more abundant in faeces than in sediments, suggesting that sea cucumbers may choose sediment containing these algal taxa more often compared with others in natural environments. All features of Laminariaceae were assigned to Saccharina japonica, which is consistent with the fact that this alga is one of the most suitable diets in the aquaculture of A. japonicus. Assessments of individual 16S amplicon sequences of both faecal and sediment samples could be an alternative tool to help us understand dynamic feeding behaviours of sea cucumber populations in contributing to bioresource conservation and development of a superior approach to aquaculture.