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Modelling the habitat preferences of the NE-Atlantic Sea cucumber Holothuria forskali: Demographics and abundance
... Monitoring such benthic organisms can be challenging, primarily due to their cryptic behaviour, patchy distribution, and high body flexibility, which can be reshaped according to the habitat characteristics. Therefore, the most widely used non-destructive sampling techniques for studying sea cucumbers' ecology are based on snorkelling or self-contained underwater breathing apparatus (SCUBA) visual census (Azevedo e Silva et al., 2023;Félix et al., 2024) and mark/recapture techniques (Purcell et al., 2016b;Siegenthaler et al., 2015). In the last decade, advancements in remote sensing technologies have been integrated into marine research, leading to a notable enhancement in bathymetric data resolution. ...
... Holothuria tubulosa (Gmelin, 1788), Holothuria poli (Delle Chiaje, 1923), and Holothuria mammata (Grube, 1840) are common infralittoral sea cucumber species of the Mediterranean Sea, inhabiting soft bottoms with abundant organic matter and Posidonia oceanica (Linnaeus) Delile, 1813 meadows. The removal due to overfishing can result in diminished ecosystem functionality, often leading to loss of ecosystem services in the affected areas, potentially creating cascading effects in other coastal environments (Félix et al., 2024). Consequently, in 2018, the Italian Ministry of Agriculture, Food and Forestry issued Ministerial Decree 156/2018, which effectively prohibits sea cucumber fishing along the national coastline (Pasquini et al., 2022). ...
... Their habitat preferences were shaped by the availability of shelter, food resources, and the complexity of the habitat. In contrast, larger size classes demonstrated a greater tendency to opportunistically investigate less stable and more open sandy environments (Félix et al., 2024). The observed differential cover percentage of detritus among the censused individuals corroborated that smaller-sized classes are generally tended to be less conspicuous due to the accumulation of organogenic detritus, including shell fragments and their bodies. ...
Sea cucumbers constitute common benthic organisms in the subtidal zones capable of providing key ecosystem services. Due to the recent harvesting and increased commercial interest in Mediterranean species, fundamental ecological knowledge is required to promote adequate management measures. In this regard, a remotely sensed mapping method is proposed for deriving length-frequency distribution and defining habitat preferences of a common sea cucumber species. Image analyses and classification carried out on high spatial resolution carto-graphic products, including orthophoto mosaics and digital surface models derived by 'Structure-from-Motion' photogrammetric processing, allowed accurate estimation of sea cucumber densities over an area of 5500 m 2. The mean length of mapped specimens ranged from 8 to 50 cm, with a peak in abundance recorded in April. A distinct preference for sandy substrates was observed, characterized by low vector ruggedness measure values ranging from 0 to 0.15. A negative correlation was also identified in areas with slopes exceeding 15 • , especially among larger size classes. Spatial patterns investigated with a Log-Gaussian Cox Process showed significant temporal trends with well-defined aggregation patterns during the summer months in specific areas covered by transplanted P. oceanica fragments with higher (up to 0.25) vector ruggedness measure values. This finding confirmed the essential role of this restored habitat in retaining fine organic particle used as a source of food for deposit-feeding holothurians. This approach is expected to enhance the creation of tailored management plans for sea cucumber populations in coastal regions, facilitating accurate assessments of the impacts of fishing activities on these species.
... Monitoring such benthic organisms can be challenging, primarily due to their cryptic behaviour, patchy distribution, and high body flexibility, which can be reshaped according to the habitat characteristics. Therefore, the most widely used non-destructive sampling techniques for studying sea cucumbers' ecology are based on snorkelling or self-contained underwater breathing apparatus (SCUBA) visual census (Azevedo e Silva et al., 2023;Félix et al., 2024) and mark/recapture techniques (Purcell et al., 2016b;Siegenthaler et al., 2015). In the last decade, advancements in remote sensing technologies have been integrated into marine research, leading to a notable enhancement in bathymetric data resolution. ...
... Holothuria tubulosa (Gmelin, 1788), Holothuria poli (Delle Chiaje, 1923), and Holothuria mammata (Grube, 1840) are common infralittoral sea cucumber species of the Mediterranean Sea, inhabiting soft bottoms with abundant organic matter and Posidonia oceanica (Linnaeus) Delile, 1813 meadows. The removal due to overfishing can result in diminished ecosystem functionality, often leading to loss of ecosystem services in the affected areas, potentially creating cascading effects in other coastal environments (Félix et al., 2024). Consequently, in 2018, the Italian Ministry of Agriculture, Food and Forestry issued Ministerial Decree 156/2018, which effectively prohibits sea cucumber fishing along the national coastline (Pasquini et al., 2022). ...
... Their habitat preferences were shaped by the availability of shelter, food resources, and the complexity of the habitat. In contrast, larger size classes demonstrated a greater tendency to opportunistically investigate less stable and more open sandy environments (Félix et al., 2024). The observed differential cover percentage of detritus among the censused individuals corroborated that smaller-sized classes are generally tended to be less conspicuous due to the accumulation of organogenic detritus, including shell fragments and their bodies. ...
... Holothuria forskali is an understudied species with few studies focusing on its biology and ecology (e.g. Tuwo and Conand, 1992;Santos et al., 2017;David et al., 2020; Azevedo e Silva et al., 2021;Ballesteros et al., 2021;Feĺix et al., 2024). To the best of our knowledge, this is the first study to report growth parameters for this species. ...
... Considering this is the only species of the three with a defensive mechanism against predators (Cuvierian tubules; Muller et al., 1970;Azevedo e Silva et al., 2021), our findings indicate an evolutionary strategy in H. forskali, suggesting accelerated growth during the early stages: Given the reduced predation risk of this species, this growth pattern is inferred as an adaptive response to mitigate higher environmental stress conditions, since larger individuals would be more likely to remain stable in the substrate (Olaya-Restrepo et al., 2018). In fact, H. forskali is the more resilient species of all three to environmental stressors like hydrodynamics (Feĺix et al., 2024). However, it should be noted that K is relative to L∞ so a higher K does not necessarily mean that it is growing faster in absolute terms. ...
... Holothuria forskali is an understudied species with few studies focusing on its biology and ecology (e.g. Tuwo and Conand, 1992;Santos et al., 2017;David et al., 2020;Azevedo e Silva et al., 2021;Ballesteros et al., 2021;Feĺix et al., 2024). To the best of our knowledge, this is the first study to report growth parameters for this species. ...
... Considering this is the only species of the three with a defensive mechanism against predators (Cuvierian tubules; Muller et al., 1970;Azevedo e Silva et al., 2021), our findings indicate an evolutionary strategy in H. forskali, suggesting accelerated growth during the early stages: Given the reduced predation risk of this species, this growth pattern is inferred as an adaptive response to mitigate higher environmental stress conditions, since larger individuals would be more likely to remain stable in the substrate (Olaya-Restrepo et al., 2018). In fact, H. forskali is the more resilient species of all three to environmental stressors like hydrodynamics (Feĺix et al., 2024). However, it should be noted that K is relative to L∞ so a higher K does not necessarily mean that it is growing faster in absolute terms. ...
Sea cucumbers, integral components of benthic ecosystems, have become subjects of scientific scrutiny owing to their intricate morphology and ecological importance. Due to increasing demand, several species of these echinoderms have become overexploited. As a consequence, NE-Atlantic species became new targets for the international markets. There is a vital need for comprehensive biological data to establish and enhance holothurian fisheries management. In the absence of such data, there is a risk of ineffective fisheries regulations, particularly for susceptible commercial species in the NE-Atlantic, which could lead to overexploitation. Establishing effective fisheries regulations requires a foundation of fundamental biological information, such as growth rates from target populations. This work aims to determine the growth parameters for three commercial sea cucumber species from the NE-Atlantic, in a marine protected area, Holothuria mammata, H. forskali and H. arguinensis. This presents a challenge, as sea cucumbers lack significant calcified structures for age determination, and assessing size is complicated because of their body size plasticity. Thus, a von Bertalanffy model was fitted to length-frequency data using the ELEFAN method with the simulated annealing procedure. Underwater length measurements of the three sea cucumber species, in a relaxed state, were systematically recorded over a span of 18 months, with measurements taken every 1.5 months. The results provide the growth parameters of each species. Models considering seasonal growth were better fits to the data. The three species had different growth rates and periods of no growth coincided with the reproductive season. Mortality was lower for the species growing slower. This is crucial information to support decision-making processes regarding stock management, such as setting limits to fisheries considering stock condition associated with environmental variability.
Sea cucumber communities in the wild have different population sizes because there is a high species interaction within the community. Based on the biological organization that is used to express community structure, species diversity is unique to the community level. The objective is to ascertain the structure of sea cucumber communities along the coast of Pasok Village in the Walea Besar District of Central Sulawesi. Data are collected using transect lines, which are divided into three observation stations with ten sampling plots at each. The research method is descriptive-quantitative. The community structure can be known from the domination index (ID), diversity index (H'), and abundance index (J) used to process the data. The results of the study found the diversity index showed the numbers 1.092, 1.056 and 1.089. The dominance of Holothuria scraba species was 0.2 Indv/m2, Holothuria atra 0.14 Indv/m2, and Bohadscia marmorata 0.08 Indv/m2. The highest abundance value belonged to the species Holothuria atra 0.377 Indv/m2 and the lowest to Bohadscia marmorata 0.305 indv/m2. The results showed that the structure of the Holothuroidea community in Pasokan Pantai Village, Walea Besar District, Central Sulawesi, was in the present category.
The demand for sea cucumbers from the NE-Atlantic is increasing as a consequence of the depletion of stocks that historically supplied Asian markets. Some species from the NE-Atlantic are already showing overfishing signs due to either inefficient policies or their total absence, and they do not offer any margins of sustainability to sea cucumber fisheries. The current lack of knowledge of biological and ecological traits has led to ineffective protection of those species. Holothuria arguinensis is a good example of a temperate sea cucumber species suffering from the effects of unregulated and illegal harvest. This study aims to determine the temporal and spatial distribution patterns of H. arguinensis, assessing density and size-class structure in a NE-Atlantic population, in SW Portugal, as a function of environmental conditions. Sampling was done every 1.5 months at 6 stations defined according to habitat heterogeneity, following the coastline from the mouth of the Sado estuary to marine coastal areas. At each station, there were two habitats (rocky substrate and sandy areas) sampled through SCUBA diving along 30-m random transects, each with three replicates. Individuals were counted and measured (total length) and individual behavioural parameters, such as sheltering and settlement surface, were recorded. Water column parameters, sediment composition, and substrate cover were also recorded. Generalised Linear Models were fit to the data, modelling density and size distribution of the species with respect to environmental conditions. The results indicate that the distribution of H. arguinensis was mainly determined by its ability to deal with physical environmental stressors (current), rather than the chemical properties of the water column or sediment composition. The hydrodynamic features of the region exert the greatest impact on this species’ distribution and help shape habitat usage by different size class groups.
The seasonal variability of the ingested matter found in the digestive tract of the burrowing holothurian Holothuria theeli (Aspidochirotida) was studied on a shallow tidal reef flat at the Puntilla Santa Elena, Ecuador in 1994. H. theeli attained its maximum density at lowest tidal level (0 m) with 3.05 ind m-2 and was concentrated in shallow tide pools. Holothuria theeli fed on invertebrates and microscopic algae. 65% of the gut contents consisted of eight zoobenthic groups, where the most dominant species were meiobenthic crustaceans (46.5% , of which 35.5% were harpacticoid copepods), and microphytobenthos (35%, of which 91% were diatoms). May was the transition period (during water temperature changes) in which the population was dormant after spawning. The seasonal variation in the quantity and type of ingested matter may be related to several related factors, such as: (1) availability of food resources, (2) high food consumption rate in the dry season for energy storage to offset the lean rainy season, and (3) high energetic needs for reproductive activities. Holothuria theeli is a non-selective generalist species, which probably plays an important role in determining benthic community structure in the rocky intertidal at the central coast off Ecuador.
The comparison of population density of Holothuria tubulosa (Gmelin, 1790) and Holothuria polii (Delle Chiaje, 1823) between exploited and non-exploited areas in the Aegean Sea coast of Türkiye Türkiye'nin Ege Denizi kıyılarında Holothuria tubulosa (Gmelin, 1790) ve Holothuria polii (Delle Chiaje, 1823) popülasyon yoğunluğunun av yapılan ve yapılmayan alanlar arasındaki karşılaştırılması Abstract: Increasing demand from the Asian market first led to the collapse of economically valuable sea cucumber stocks in the Indo-Pacific, and then demand shifted to lower value Mediterranean species. The effect of this change in sea cucumber stocks in Türkiye started to be seen after the 2010s. To address it, we carried out a study to compare the population density of the most caught Holothuria tubulosa and Holothuria polii species between exploited and non-exploited areas in the Aegean Sea coast of Türkiye. The study was carried out between September 2018 and March 2020 at 4 stations, two of which are in Çandarlı Bay, where sea cucumber fishing is free, and two in İzmir Bay, where it is prohibited. Samplings between 0-20 m depths were carried out with underwater transect line technique, and at depths deeper than 20 m, with beam trawling operations. A total of 6 sea cucumber species were identified, including Holothuria mammata, Holothuria sanctori, Parastichopus regalis and Holothuria forskali species, apart from the target species H. tubulosa and H. polii. Only one P. regalis individual was recorded in the samplings in waters deeper than 20 m. The mean densities of H. tubulosa and H. polii were found to be higher in İzmir Bay stations than in Çandarlı Bay (p<0.05). The results of this study clearly reveal that the population density of sea cucumber in sampling areas has decreased tens of times compared to the last 5 years.
Estuaries are highly productive ecosystems, which are strongly affected by several anthropogenic pressures. Phytoplankton is a key element for assessing the ecological quality status in these transitional waters. Moreover, understanding physico-chemical and biological drivers is crucial to disentangle their effect on the structure of phytoplankton community. The present work aims to study the effect of the main physico-chemical drivers on the phytoplankton community structure and dynamics in a temperate well-mixed estuary (Sado Estuary). Four sampling stations were analyzed monthly in three regions of the estuary, from 2018 to 2019. Surface water samples were collected to analyze the phytoplankton community and several concomitant physico-chemical parameters. Temperature, turbidity, salinity, and nutrients availability were the drivers that best explained the spatio-temporal patterns observed in the phytoplankton community. The upper estuary was characterized by higher phytoplankton cell abundances and biomass. Three phytoplankton groups stood out in the characterization of the estuarine assemblages: diatoms, cryptophytes, and dinoflagellates. Diatoms were the dominant group most of the year, being dominated by small cell species (single and chain-forming) upstream, and by larger chain-forming species downstream. Cryptophytes had a high contribution to the community in the inner regions of the estuary, while dinoflagellates contributed more for the community composition downstream, where high abundances of harmful algal species were sporadically found. Previous studies on the phytoplankton community dynamics in this estuary are limited to the 1990s. Thus, the present study provides insight into changes in the dominant phytoplankton groups of the Sado Estuary in the last 25 years, namely an increase in cryptophytes over diatoms in the inner estuarine regions, and an increase in dinoflagellates near the estuary mouth.
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.
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.
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.
Holothuria arguinensis, Holothuria mammata and Holothuria forskali are three common sea cucumber species found in the NE Atlantic, traded in international markets and susceptible to capture. Allometric relationships reveal if the scaling relationships between biometric characters are proportional with growth, being a useful tool to understand species growth strategies. Allometric relationships of the three species were estimated and compared between them and with populations from different regions. These allometric relationships revealed that the three species have negative allometric growth. However, they have different growth strategies between them and reveal different regional intra-specific growth strategies when compared to other populations, suggesting ontogenetic adaptation as a consequence of external factors.
Introduction:
The exploitation of the sea cucumber (Holothuria (Panningothuria) forskali) in Ría de Vigo (NW Spain) is recent (2015) and it has been done until now with scarce or no information about some key biological aspects as reproduction, recruitment or growth.
Objective:
To describe the reproductive cycle of H. forskali in Ría de Vigo.
Methods:
We sampled fortnightly throughout 2018. We calculated gonadal condition indices (GCI) and gametogenic stages by classic histological methods.
Results:
The reproductive cycle of H. forskali in the Ría de Vigo is characterized by a sexual resting stage during spring, when temperature and daylight hours are lower; the beginning of gametogenesis during summer, when temperature is higher, daylight hours longer and the sea bottom is rich in nutrients; then, a period of spawns interspersed with a gonadal restoration during autumn and winter, when temperature is lower and food is scarce. Sex ratio is 1:1, however, the studied population is not synchronized, because females initiate maturation earlier. The comparison of the histological results with GCI indices suggest that GCI is a good indicator for gonadal stage. Fishery management strategies, such as a closure period, must be adapted to the reproductive stage. We recommend avoiding fishing between November and February to increase spawning potential ratio and, consequently, recruitment.
Sea cucumbers have an important economic value and high demand. Despite that, there is a lack of knowledge about their biology, ecology and habitat distribution patterns, which is very important for sea cucumber stock management, establishment and sizing of no-take zones, restocking actions and selection of grow-out areas. This work aimed to determine the density, abundance and habitat associations of Holothuria arguinensis for a better understanding of its distribution along the coastal lagoon Ria Formosa and to select suitable areas for grow-out. In the duration of a year, monthly visual censuses were performed in two locations at Ria Formosa along the intertidal zone. The number and length of H. arguinensis´ individuals found were registered, and the coverage of algae and seagrass was estimated. It was found that H. arguinensis was distributed along the lower intertidal zone, linked to Zostera noltii meadows on muddy and sandy bottoms. These areas showed the densest population and the largest sizes of H. arguinensis. However, during the warmer months, H. arguinensis seemed to migrate to deeper waters in the channels, to avoid exposition to high temperatures and solar/UV irradiance during low tides. Areas located in the lower intertidal zone with Z. noltii meadows on sand-muddy bottoms should be selected for H. arguinensis grow-out sites.
Aim
Most projections of how climate change will affect species distributions and phenology are based on a species’ most conspicuous life stage. However, not all life stages are equally sensitive to temperature. Among fishes, spawning adults often have narrower thermal tolerances than other life stages and may constrain population responses to climate change. We tested this hypothesis using data on Nassau Grouper (Epinephelus striatus), an endangered coral reef fish.
Location
Greater Caribbean.
Methods
Species distribution models of spawning and nonspawning adults were compared to determine which environmental variables exerted the greatest influence on grouper distribution. We calculated the thermal niche and ecological niche breadth of both life stages. An earth system model was applied to project how species distribution and phenology shift under two climate change scenarios.
Results
Sea surface temperature and seasonal temperature gradients affected the distribution of both spawning and nonspawning adults, but these life stages differed in their preferred temperatures and reaction to oceanic currents. While the two life stages exhibited similar ecological niche breadth, the thermal niche of spawners was narrower. By 2081–2100, potential spawning habitat was projected to decline under a business‐as‐usual scenario by 82% relative to 1981–2000, whereas suitable habitat for nonspawners decreased by 46%. Poleward shifts in latitude occurred 3.8–4.2 times faster for spawners than nonspawners. These changes were attributed to rising temperatures, whereas hydrographical changes did not have a substantial impact. Spawning phenology changed little, with a slight contraction in spawning season but a large reduction in spawning probability across all months.
Main Conclusions
A narrow thermal tolerance range among spawning fishes indicates that this life stage may be a bottleneck constraining responses to climate change. Future research should consider the reaction of each life stage to changing conditions. Conservation of E. striatus should take shifting distribution and phenology into account, as climate effects may exacerbate population declines due to fishing and reduce the efficacy of conservation measures.
The success of marine stocking programs hinges on releasing hatchery-produced juvenile animals into the optimal marine habitat. This study sought to identify optimal microhabitat features of coastal seagrass meadows for juvenile sea cucumbers Holothuria scabra, a species cultured widely for stock restoration, sea ranching and sea farming. Groups of 25 juveniles were released into 30 replicate 1 m2 open sea pens embedded into sediments in a coastal bay of New Caledonia at sites with varying biotic and physical features. Survival after 8 to 10 d ranged from 0 to 100% and averaged 77%. Boosted regression tree analyses found that different variables affected survival, growth and burying behaviour. Survival was significantly higher at shallow depths with intermediate seagrass cover (~42%). Growth rate was significantly higher at comparable intermediate seagrass cover (~34%) and for smaller juveniles, presumably displaying compensatory growth. Burying frequency of juveniles was largely explained by habitat variables, notably a high organic carbon content of sediments and shallow seawater depths. Juveniles survived better where they buried more frequently, providing empirical evidence of a predatoravoidance mechanism. Our findings reveal that marine animals can display non-linear responses to habitat features such as seagrass cover. These marine invertebrates should be released in habitats that optimize survival, growth and behaviours and be spread among multiple sites to mitigate against stochastic mortality events. This experimental approach offers clear advantages over factorial designs for identifying optimal habitats for captive-release programs.
Due to the heavy exploitation of holothurians over the last few decades, it is necessary to implement fishing regulations aimed at reversing this situation. Holothurians require specific regulations that take into account their biology and ecology. Their behavior to group and form patches as a strategy for feeding, defense and reproduction, makes them vulnerable to overfishing. The higher the population density, the higher the catchability coefficient, and because they are sedentary organisms, the catchability does not change significantly until the density is very low. Hence, the stock assessment of holothurians can be improved by analyzing their spatial distribution. This paper proposes a stock assessment technique that considers the spatial distribution pattern of the sea cucumber Isostichopus badionotus from Yucatan, Mexico. A bioeconomic spatial model was developed to explain the interactions between fishing effort allocation, quasi-profits and the population in the short term. Because of the high price of the species and the low production costs, artisanal fishers preferred to maximize short-term quasi-profits, rather than the long-term benefits they could gain with low fishing mortality rates.
Holothuria mammata is one of the new target species from the Mediterranean and Atlantic. Usually, it inhabits rocky bottoms, staying in crevices and holes during the day and leaving them in the night for feeding on sandy bottoms. However, it can be found in unusual habitats such as seagrass with diurnal and nocturnal feeding. This study provides information for the first time on the behaviour, density and small scale distribution of H. mammata in a seagrass habitat from Ria Formosa (S Portugal). To reach these aims, a mark/recapture methodology was used. Abundance was estimated through R statistical software v.2.15.3 (package “Rcapture”). The minimum area method was applied in GRASS GIS v.6.4.2 for home range. Size distribution was estimated applying a Shapiro-Wilk test. Rayleigh test for randomness was applied to study the directionality of movements. A circular one-way ANOVA was used to test for differences in movement direction. Capture probability was higher on seagrass than sand and the total length of the individuals ranged from 13 to 25 cm. Movement speed was between 4.7 and 14.7 m day⁻¹. Movements were not directional. H. mammata differs in its behaviour from the related Holothuria arguinensis occurring in the same habitat. © Published by Central Fisheries Research Institute (CFRI) Trabzon, Turkey.
Sea cucumbers (Echinodermata: Holothuroidea) are large and abundant members of marine benthic communities. Overexploitation worldwide has raised concern because they have important functions within ecosystems. The ecological roles of commercially exploited sea cucumbers (Aspidochirotida and Dendrochirotida) are reviewed here, focusing on recent literature. Of the more than 70 species commercially exploited, at least 12 regularly bury into sand and mud, playing major roles in bioturbation. Most aspidochirotids are deposit-feeders, reducing the organic load and redistributing surface sediments, making them bioremediators for coastal mariculture. Sea cucumbers excrete inorganic nitrogen and phosphorus, enhancing the productivity of benthic biota. This form of nutrient recycling is crucial in ecosystems in oligotrophic waters such as coral reefs. Feeding and excretion by sea cucumbers also act to increase seawater alkalinity which contributes to local buffering of ocean acidification. Sea cucumbers host more than 200 species of parasitic and commensal symbionts from seven phyla, thereby enhancing ecosystem biodiversity. They are preyed on by many taxa, thereby transferring animal tissue and nutrients (derived from detritus and microalgae) to higher trophic levels. Overexploitation of sea cucumbers is likely to decrease sediment health, reduce nutrient recycling and potential benefits of deposit-feeding to seawater chemistry, diminish biodiversity of associated symbionts, and reduce the transfer of organic matter from detritus to higher trophic levels. Ecosystem-based fisheries management needs to consider the importance of sea cucumbers in marine ecosystems and implement regulatory measures to safeguard their ecological roles.
Sea cucumbers (Echinodermata: Holothuroidea) can contribute to the cycling of nutrients and play important roles as ecosystem engineers; many also have high commercial value. Their success at colonizing marine habitats from the shore to the abyss makes them ideal models for the study of breeding patterns. Here, the reproductive biology of the sea cucumber Holothuria grisea was studied at large and fine scales over 13 months on the northeastern Brazilian coast, to investigate the role of environmental and aggregative factors in this process. Gametogenic maturity peaked in December–February, as indices of spawning activity appeared and aggregative behavior was minimal. Mature individuals disappeared in June–July in both sexes, as the highest frequencies of aggregation and post-spawning stage were recorded. In August–September, gamete synthesis started to increase again in correlation with a higher frequency of individuals in the early gametogenic growth, while the degree of aggregation among individuals in the field was still high. Spawning occurred during the rainy season when chlorophyll-a concentrations were maximal, and the highest frequency of solitary individuals was recorded. The data are consistent with pre-spawning aggregative behavior as a strategy to help synchronize gametogenesis and phytoplankton bloom as a trigger of gamete release to optimize larval feeding. At finer scale, spawning occurred when high water levels coincided with sunset or night time, providing favorable conditions for free spawning and external fertilization. The influence of environmental factors and aggregation in the reproduction of H. grisea could potentially exacerbate its vulnerability to anthropogenic pressures (e.g., fisheries, pollution, habitat loss) along the coast of Brazil.
Deposit-feeding sea cucumbers play a key role in marine ecosystems through biotur- bation, burrowing and feeding on organic matter in marine sediments. Many deposit-feeding holothurians have therefore been recommended for integrated multitrophic aquaculture systems (IMTA). We set up an integrated mariculture system of sea cucumber Holothuria scabra and sea- weed Eucheuma denticulatum in Bweleo, Unguja Island of Zanzibar, Tanzania, to investigate the effect of stocking density on the growth and survival of culture species, total organic matter (TOM) and total organic carbon (TOC) content in the sediment. Treatments that included a fixed stocking density (500 g, ca. 200 g m �2 ) of E. denticulatum and 4 sea cucumber stocking densities (monoculture, low, medium and high density; 0, 150 ± 5, 236 ± 24, 345 ± 48 g m �2 , mean ± SD) of medium-sized H. scabra (114 ± 37 g) were established. Stocking density of H. scabra did not influ- ence survival of either species. Seaweed cultured under high stocking density of H. scabra had a higher specific growth rate of 2.33% d �1 than that cultured at the medium or low densities or with- out sea cucumbers. Sea cucumbers cultured at low stocking density had a higher mean growth rate of 0.80 g d �1 compared to those cultured at medium or high densities. TOM and TOC in sed- iments decreased over the experimental period at medium sea cucumber stocking density, while at low and high stocking densities, organic matter accumulated. The study demonstrates that the integration of E. denticulatum and H. scabra at 200 g m �2 enhances seaweed growth and can reduce organic matter content in the sediments.
This research provides evidence for chemical mediation in the initiation of gametogenesis and interindividual fine-tuning among populations of the holothurian Cucumaria frondosa. Initiated in the laboratory by increased day length, the gametogenesis of C. frondosa developed normally when individuals were transferred to an environment in which temperature and photoperiod were held constant and food was withheld. Gonad development and spawning of these sea cucumbers occurred simultaneously with animals that were fed. Individuals collected from the deep aphotic zone showed gonadal indices and histological development of gametes synchronous with populations found in the shallower photic zone. These data strongly suggest that day length and temperature were not the sole factors controlling the onset and development of gametogenesis, but rather that they act synergistically with other mechanisms. Laboratory experiments showed that gametogenic synchrony was less for individuals separately maintained under natural environmental conditions than it was for similarly treated individuals kept in groups. Finally, gametogenesis was initiated by exposure to more developed individuals, even without the photoperiod cue. This induction, effective only between animals of the same sex, became more evident with increasing maturity of the more developed individuals.
Sea cucumbers are highly marketable as a food product due to their nutritional value. Also, it has been suggested that sea cucumbers possess a wide range of bioactive compounds that can be used in the pharmaceutical industry. In this study, the reproductive biology of Holothuria forskali was performed by evaluating the gonadosomatic index
(GI) and histological analyses of the gonadal tubules. The biotechnological potential was assessed through the evaluation of the antioxidant, antimicrobial and antitumor potential. Finally, the fatty acid profile was also evaluated. These three subjects were chosen to increase the interest and to focus the economic potential of this species rearing, predicting that it can be sold in Europe or export to Asia to be used for human consumption or for the pharmaceutical industry. The GI and the histological analysis of the gonadal tubules revealed that the range from February to March corresponds to the peak of gonads maturation. Furthermore, the methanolic fraction revealed the highest antimicrobial potential against Candida albicans with an IC50 of 233.2 mg mL-1. Also, this fraction presented the highest cytotoxic and anti-proliferative activities through the method for measuring cell proliferation method in both cell lines, with an IC50 of 238.2 and 396.0 mg mL-1 for MCF-7 cells respectively and 260.3 and 218.7 mg mL-1 for HepG-2 cells respectively. Regarding the fatty acid profile, the total fat content was 4.83% and the highest values were obtained for palmitic acid (9.96%), stearic acid (11.23%), eicosapentaenoic acid (10.49%) and arachidonic acid (20.36%).
Sea cucumber fisheries are now occurring in most of the tropical areas of the world, having expanded from its origin in the central Indo-Pacific. Due to the overexploitation of these resources and the increasing demand from Asian countries, new target species from Mediterranean Sea and northeastern Atlantic Ocean are being caught. The fishery effects on biometry and genetic structure of two target species (Holothuria polii and H. tubulosa) from Turkey, were assessed. The heaviest and largest individuals of H. polii were found into the non-fishery area of Kusadasi, also showing the highest genetic diversity. Similar pattern was detected in H. tubulosa, but only the weight was significantly higher in the protected area. However, the observed differences on the fishery effects between species, could be explained considering the different percentage of catches (80% for H. polii and 20% for H. tubulosa).
The spatio-temporal abundance and size patterns of Holothuria sanctori, H. mammata and H. arguinensis were studied from February 2009 to January 2010, off Gran Canaria Island. Holothuria sanctori coloration patterns and the influence of bottom rugosity on holothurian abundances were also studied. Holothuria sanctori was the most abundant species with 1.13 ± 0.29 ind m-2, followed by H. mammata with 0.16 ± 0.22 ind m-2 and H. arguinensis with 0.04 ± 0.05 ind m-2. Holothuria arguinensis showed the bigger sizes, with a mean length of 255.07 ± 55.49 mm, followed by H. mammata with 234.29 ± 45.10 mm and H. sanctori with 181.35 ± 29.15 mm. Only 9
Species data held in museum and herbaria, survey data and opportunistically observed data are a substantial information resource. A key challenge in using these data is the uncertainty about where an observation is located. This is important when the data are used for species distribution modelling (SDM), because the coordinates are used to extract the environmental variables and thus, positional error may lead to inaccurate estimation of the species–environment relationship. The magnitude of this effect is related to the level of spatial autocorrelation in the environmental variables. Using local spatial association can be relevant because it can lead to the identification of the specific occurrence records that cause the largest drop in SDM accuracy. Therefore, in this study, we tested whether the SDM predictions are more affected by positional uncertainty originating from locations that have lower local spatial association in their predictors. We performed this experiment for Spain and the Netherlands, using simulated datasets derived from well known species distribution models (SDMs). We used the K statistic to quantify the local spatial association in the predictors at each species occurrence location. A probabilistic approach using Monte Carlo simulations was employed to introduce the error in the species locations. The results revealed that positional uncertainty in species occurrence data at locations with low local spatial association in predictors reduced the prediction accuracy of the SDMs. We propose that local spatial association is a way to identify the species occurrence records that require treatment for positional uncertainty. We also developed and present a tool in the R environment to target observations that are likely to create error in the output from SDMs as a result of positional uncertainty.
A spatio-temporal survey of some echinoderm larvae was conducted along a transect of 28 nautical miles from the Bay of Villefranche, France, halfway to Corsica. Distribution patterns and mechanisms responsible for larval dispersal, viz. water currents, hydroclimate and vertical movements, were studied. The echinoderm larvae exhibited weak vertical migration (a few meters), remaining in the surface layer. They are therefore subjected to hydrodynamic constraints which either limit or promote dispersal away from the nursery beds. Larval concentration decreased with distance from the coast and was generally restricted to within 16 miles of the coast. This distance coincided with the location of a coastal divergence zone where rising subsurface waters confined larvae to the Ligurian Current.
Temperate species of sea cucumber found on rocky subtidal reefs often have a patchy distribution. If rocky reef complexity is important to the temperate sea cucumber Australostichopus mollis then this should be correlated with relative differences in their abundance along the coast. These temperate subtidal rocky reefs present a variety of possible habitat types that can be patchy in their distribution along the coast. Subtidal surveys were conducted along a 2.5-km stretch of coast and counts of A. mollis recorded along with changes in the composition of a number of physical features of reef structure. Abundance of A. mollis decreased from 1 individual/2 m in headland outcrops to 1 individual/20 m and 1 individual/100 m for coastal areas and inner bays respectively. This was associated with a decrease in percentage composition of large boulders, which were between 0.5 and 1 m along their longest diameter and were part of a predominantly rock and boulder substrate. Where sea cucumber abundance decreased for identified location types there was also a corresponding decrease in kelp cover and an increase in open rock faces of a ridged or corrugated structure. Physical features of temperate reef structure, their contribution to overall reef complexity, and location along the coast, are determining factors mediating the distribution and abundance of A. mollis.
Benefits of marine protected areas depend on local ecological and socio-cultural aspects which are critical to the success of the protection measures. In particular, before−after comparisons are indispensable to disentangle the effects of protection from those of different physical and ecological characteristics among areas. Using underwater visual surveys, we assessed whether biomass and abundance of temperate reef fish assemblages and target invertebrates increased inside a no-take area in the Arrábida Marine Park (Portugal) 3 to 4 yr after its establishment. Data were compared to a previous study, conducted 10 yr before protection was effective. Control−effect comparisons after reserve establishment showed a positive response of legal-size demersal fish and below legal-size target invertebrates. The first evidence of protection was found in biomass but not in numbers. Non-target groups and below legal-size demersal fish had a significant interaction among reserve and habitat complexity indices for either density or biomass, suggesting a lack of a reserve effect. Before−after comparisons revealed non-significant patterns of increase in numbers of target species compared to non-target ones. The most important commercial species showed the largest increase in density after protection was established. Significantly higher abundances and proportionally heavier individuals of these species were also found inside the reserve in the control−effect comparisons. These findings are reinforced by an increasing trend in landings which are consistent with the early detection of a reserve effect.
Bioturbators affect multiple biogeochemical interactions and have been suggested as suitable candidates to mitigate organic matter loading in marine sediments. However, predicting the effects of bioturbators at an ecosystem level can be difficult due to their complex positive and negative interactions with the microbial community.
We quantified the effects of deposit-feeding sea cucumbers on benthic algal biomass (microphytobenthos, MPB), bacterial abundance, and the sediment-seawater exchange of dissolved oxygen and nutrients. The sea cucumbers increased the efflux of inorganic nitrogen (ammonium, NH(4) (+)) from organically enriched sediments, which stimulated algal productivity. Grazing by the sea cucumbers on MPB (evidenced by pheopigments), however, caused a net negative effect on primary producer biomass and total oxygen production. Further, there was an increased abundance of bacteria in sediment with sea cucumbers, suggesting facilitation. The sea cucumbers increased the ratio of oxygen consumption to production in surface sediment by shifting the microbial balance from producers to decomposers. This shift explains the increased efflux of inorganic nitrogen and concordant reduction in organic matter content in sediment with bioturbators.
Our study demonstrates the functional role and potential of sea cucumbers to ameliorate some of the adverse effects of organic matter enrichment in coastal ecosystems.
In aquarium experiments and during field observations, Holothuria (Halodeima) atra (Jaeger, 1883) and Stichopus chloronotus (Brandt, 1835) consumed an average of 67 and 59 g dry wt of sediment individual−1 d−1, respectively. A model calculation showed that a mixed population of both species on a reef flat near Lizard Island, GBR has the potential to rework about 4600 kg dry wt yr−1 1000 m−2 which is approximately the weight of the upper 5 mm of sediment in this area. Gut content analyses showed no significant decrease in phycopigments (chlorophylls a and c and fucoxanthin) during gut passage. In both species the oesophagus pigment content was similar to the concentration in sediments directly in front of the individuals. However, pigment content in front of S. chloronotus and in all gut segments of this species were significantly higher than the corresponding values in H. atra suggesting patch selectivity in the former species. Extremely low meiofauna contents in holothurian guts indicated that meiofauna play a negligible part in the nutrition of H. atra and S. chloronotus. In contrast, the ratio of living to dead diatoms was significantly lower in the guts of both holothurian species compared to the adjacent sediment, indicating digestion of the ingested diatoms. In aquarium experiments, feeding and bioturbation activity of both species significantly reduced microalgal biomass (measured as chlorophyll a concentrations) in sediments inoculated with diatoms or cyanobacterial mats.
The sea cucumber stocks off the east and northwest coasts of Sri Lanka were estimated by
surveying 1307 km2 and 1779 km2 by an underwater visual census (UVC)
in June and October 2008 respectively. The presence of twenty-five sea cucumber species
belonging to seven genera; Actinopyga, Bohadschia, Holothuria, Pearsonothuria,
Stichopus, Thelenota and Acaudina was identified in five
hundred sampling sites randomly selected in each area. The overall average density (± SD) of sea cucumbers was higher in the northwest (350 ± 648 ind ha-1) than in
the east (90 ± 130 ind ha-1) and low-value species were predominant in both
survey areas (79 ± 125 ind ha-1 in the east, 244 ± 488 in the northwest) when
compared with medium (10 ± 34 ind ha-1, 105 ± 175 ind ha-1,
respectively) and high-value category (<2 ind ha-1).
The estimated total biomass in the northwest (13 024 t) was roughly four times greater
than the east (3027 t). Holothuria edulis was the most abundant species
in numbers while Holothuria atra had the highest stock biomass in both
areas. Sea cucumber densities were significantly different among the habitat
(p < 0.001) and depth categories. The highest
density was reported in rocky habitat associated with seagrass and / or macroalgae. The
density of low-value species was significantly high in 1–10 m depth category
(p < 0.001) in the northwest while other
commercial groups were dominant in 20–30 m depth range in both areas. Temporal banning of
the fishery for high and medium-value species would be a better management option to avoid
further stock depletion.
The aspidochirote Holothuria forskali is a large common species found in the Atlantic and the Mediterranean. Its reproductive cycle has been determined in a population from Brittany using histological observations of the different classes of gonadal tubules, oocyte size frequencies and evolution of gonad indices. The cycle is annual and synchronous in both sexes. The different phases are well marked and are characterized by a long maturation during summer and autumn followed by a pre-spawning period during winter. Spawning is probably related to the increase in temperature. Most of the mature gametes are released. The resorption of the relict and spent tubules continues during the onset of the next vitellogenesis in the secondary tubules, without a rest period. The reproductive effort, documented from the gonad indices, is very high in this population which is composed of adult individuals.
In the literature, 69 references altogether have reported 76 predators on holothurians. In terms of the number of predatory species, the most important predators are fishes (26 species), seastars (19 species), and crustaceans (17 species). Seastars are the predators most often cited as regularly ingesting large quantities of holothurians. Toxicity seems to be an effective defense against a generalized predator but, against a specialist on holothurians, escape by swimming movements or shedding of a piece of body wall are the only behaviors that occasionally end with a successful escape. Escape behaviors may be a factor in providing the apparent size refuge from predators. Impacts of predators on holothurian populations have rarely been reported or evaluated, and predation on the earliest life stage is unknown.
Worldwide, most sea cucumber fisheries are ineffectively managed, leading to declining stocks and potentially eroding the resilience of fisheries. We analyse trends in catches, fishery status, fishing participation and regulatory measures among 77 sea cucumber fisheries through data from recent fishery reports and fishery managers. Critical gaps in fisheries biology knowledge of even commonly targeted species undermine the expected success of management strategies. Most tropical fisheries are small-scale, older and typified by numerous (>8) species, whereas temperate fisheries are often emerging, mono-specific and industrialized. Fisher participation data indicated about 3 million sea cucumber fishers worldwide. Fisher participation rates were significantly related to the average annual yield. permanova analysis showed that over-exploited and depleted fisheries employed different sets of measures than fisheries with healthier stocks, and a non-metric multidimensional scaling ordination illustrated that a broad set of regulatory measures typified sustainable fisheries. SIMPER and regression tree analyses identified that the dissimilarity was most related to enforcement capacity, number of species harvested, fleet (vessel) controls, limited entry controls and rotational closures. The national Human Development Index was significantly lower in countries with over-exploited and depleted fisheries. Where possible, managers should limit the number of fishers and vessel size and establish short lists of permissible commercial species in multispecies fisheries. Our findings emphasize an imperative to support the enforcement capacity in low-income countries, in which risk of biodiversity loss is exceptionally high. Solutions for greater resilience of sea cucumber stocks must be embedded within those for poverty reduction and alternative livelihood options.
Sea cucumbers are important components of marine ecosystems and also highly valued commodities in Asian markets
because of their use in oriental cuisine and traditional medicine. The increasing demand for sea cucumbers has elicited intense
worldwide capture and many species are currently considered vulnerable or threatened due to overexploitation. The coast of Santa
Catarina State (South Brazil) is the distribution limit of several tropical species in the Western South Atlantic, but little is known
about the sea cucumber species occurring in this region. This study aimed to identify the holothuroids occurring in the littoral of
Santa Catarina State and to survey their abundance and distribution along the coast. Visual and tactile inspections were carried out
following transects in the intertidal zone of 11 locations and subtidal surveys were carried out by diving in two sites. The surveys
indicated the occurrence of three species: Parathyone braziliensis in the intertidal zone, Holothuria (Halodeima) grisea in the intertidal
as well as in the sublittoral, and Isostichopus badionotus in the sublittoral. The most abundant species was H. (H.) grisea, which
occurred in several sites along the coast, up to Lat. 28° 01′ 07.67ʺ S, its likely southern limit of distribution. The species I. badionotus
was for the first time recorded to occur on the continental coast of the State, expanding its area of distribution. This study registers
for the first time the occurrence of P. braziliensis in southern Brazil, expanding its limit of geographic distribution
In the last years, sea cucumbers consumption is increasing in the Asian region, as consequence more than 70% of the sea cucumber fisheries around the world are fully/over exploited or depleted. Therefore, Asiatic markets are looking for new target species mainly from Mediterranean Sea and NE Atlantic Ocean. In this paper, we establish the state of the art of the sea cucumber fisheries in this geographical area, analyze the negative effects of over-exploitation on five species (Holothuria polii, Holothuria tubulosa, Holothuria mammata, Holothuria arguinensis and Parastichopus regalis) through three study cases well documented in Turkey, Spain and Portugal, assess the Holothuria forskali fishery under regulation in NW Spain, and finally suggest some management measures to improve, and/or develop a right regulation for the exploitation of these new resources. The current fishery pressure has already provoked some important negative effects on wild populations of sea cucumbers from Mediterranean and NE Atlantic waters, such as decrease in density, abundance, and genetic diversity, loss of the biggest individuals, increase on the prevalence of some diseases, and even "local extinction" in some places. Most of the countries where these species are being caught, have not legislation for these fisheries. Therefore, an improvement in the biological knowledge of these new target species is mandatory to effectively suggest right management measures to protect stocks, and to favor the development of national, and international legislation to prevent illegal catches. Existing legislation, e.g., that from Galicia (NW Spain) or Turkey, could be used as a starting point to develop a more effective set of rules. Fishery on sea cucumbers by using scuba diving equipment should be forbidden or better regulated because of its heavy impact on wild populations. Current increasing demand on sea cucumbers should be satisfied by aquaculture production; its biotechnology on species from the Mediterranean and NE Atlantic is being already developed with increasing success, which will allow a reduction of fishery pressures on wild populations of these new target species, and the possibility to develop restocking programs.
Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes.
[Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].
The paper presents new data about the reproductive cycle of the holothurian Holothuria forskali. According to these new results, mature and spawning individuals could be found in the Adriatic Sea during summer and winter months. This is contrary to previous data which suggest that the spawning is occurring solely during the winter. Additionally, the new data show that the reproductive cycle of H. forskali in the Adriatic Sea is different from that in Glenan Archipelago, Brittany in the Atlantic Ocean. This is a representative example demonstrating the variations in spawning periods for the same species living in geographically different places.
The data on the qualitative and quantitative distribution of the species Holothuria tubulosa and Holothuria lorskali as affected by bottom types and depth are presented. The material originates from the continental shelf of the Adriatic Sea collected during Pipeta research cruises. Biological material was collected with bottom trawl from the Italian commercial trawler Pipeta in the 1982-1995 period. For the estimation of the abundance of the species Holothuria tubulosa and Holothuria forskali standard 'swept area' method was used. The total mass and the number of individuals of these species were obtained from 833 hauls (21 cruises) of the bottom trawl over a surface area of 39808.191 km of the Adriatic bottom. Obtained results are indicative regarding the fact that there are some differences in the horizontal and vertical distribution between the species Holothuria tubulosa and Holothuria forskali and that tho abundance is affected by sediment type.
Merchant ship observations are summarized for one-degree squares along the eastern shore of the Atlantic between 7 degree and 44 degree N; monthly averages are prepared for several properties including sea surface temperature and its difference from mid-ocean values, offshore Ekman transport, and surface current. The analysis illustrates the seasonal migration of strong near-shore cooling from near Cap Vert in winter to Morocco and the Portuguese coast in summer, with a band of year-round strong cooling between 20 degree -25 degree N (near Cap Blanc). The distributions of offshore Ekman transport and temperature anomaly are in rough agreement. A seasonal response of the longshore surface current field is indicated.
Following a canvassing of sedimentationists an attempt is made to standardize nomenclature of sediment types relative to sand, silt, and clay content. A triangle diagram with boundaries between types, which met with general approval, is submitted and compared with other systems which have been used for the purpose. The new system uses old well established names and has a simplicity and symmetry which make it easily remembered. The boundaries appear to be well located for description of sediments such as those that have been analyzed in large volume from the investigations of the northern Gulf of Mexico (API Project 51), but it is inadequate in describing well sorted sediments with median diameters near the boundaries of sand and silt or silt and clay. The nomenclature suggested applie only to sediment grade sizes so that other names should be used depending on other characteristics of the sediments. Furthermore, the nomenclature should not be applied to sediments containing large percentages of gravel.
Pachythyone rubra is a small, direct-developing sea cucumber, with a limited geographic range in central and southern California. Surveys from 1996 to 1998 in the Santa Barbara Channel revealed spatial patchiness, with high densities immediately adjacent to low or zero densities in similar habitat. To investigate causes of this patchiness, I transplanted and followed survival and recruitment of P. rubra in sites that had high and low densities of P. rubra. This transplant experiment revealed that survival and recruitment of P. rubra vary spatially, along a gradient in environmental conditions, and that these differences may be caused by predation, sedimentation, and food supply. Laboratory predation experiments identified two predators: the lobster Panulirus interruptus and the sea star Pycnopodia helianthoides. Field observations and trials with freeze-dried P. rubra pellets suggested that fish do not eat P. rubra. Population growth of P. rubra was highest in the western region of the Channel Islands that receives cool, nutrient and phytoplankton-rich water suitable for P. rubra feeding and reproduction. Patchiness of P. rubra in this area may result from spatially variable, but intense, predation by P. helianthoides. The eastern region of the Channel Islands has warmer water with less nutrients and phytoplankton, which may be less suitable for P. rubra feeding and reproduction but lacks P. helianthoides, resulting in lower population growth but potentially more stable patches over space and time.
In the Pacific Islands, invertebrates including sea cucumbers are among the most valuable and vulnerable inshore fisheries resources. As human activities continue to force substantial impacts on coral reef ecosystems, the management of inshore fisheries has become an increasingly important priority. Knowledge of the distribution, biology and habitat requirements of a species can significantly enhance conservation efforts. The sea cucumber (Holothuria leucospilota) forms an important part of the traditional subsistence fishery on Rarotonga, Cook Islands, yet little is known of this species' present spatial distribution and abundance around the island. We apply two machine learning approaches and a classical statistical approach to predict the number of sea cucumber individuals from site characteristics. The machine learning methods used are induction of regression trees and instance-based learning. These are compared to the classical statistical approach of linear regression. The most accurate predictions are obtained using instance-based learning, while the most understandable descriptions are obtained using regression tree induction.