Holothuria mammata is one of the most valuable species of sea cucumber, as well as one of the main target species harvested in the Mediterranean and NE-Atlantic regions. This study aims to describe the reproductive cycle of H. mammata in a coastal area of southwest Portugal. Monthly samplings were carried out for 19 months, with the concomitant collection of environmental data and biometric data. H. mammata had a sex ratio of 1:1.2 (male:female) and a size at first maturity of 142 mm for males and 167 mm for females. The gonadosomatic index (GI) peaked between April and May for both sexes. Gonad development started when days had a shorter photoperiod (9 to 13 h of sunlight) and lower seawater temperature (15 °C) and chlorophyll-a concentrations. The development of new studies to increase the biological and ecological knowledge of the populations of H. mammata is essential to create conditions for the domestication of broodstock in captivity, to allow the development of fishing regulations based on informed decisions and to create precise measures for the conservation of ecosystems.

The sea cucumber Holothuria arguinensis (Koehler and Vaney, 1906) presents an increasing commercial value in Asian markets and its exportation depends exclusively on wild stock harvesting. Production through aquaculture has been acknowledged as an alternative to supply demand and reduce pressure on natural stocks, but there are still bottlenecks to overcome, such as low growth rate and survival. This study focuses on the evaluation of the growth of juveniles of H. arguinensis through substrate enrichment—direct mixing of Sargassum vulgare with sediment—in recirculating aquaculture systems (RAS), for 4 months, with a baseline diet of Saccorhiza polyschides. Compared to the control (no enrichment), sea cucumbers fed with enriched sediment showed the highest specific growth rate (SGR), the highest growth rate (GR) and the lowest size heterogeneity. The results obtained in this study showed a favorable growth of sea cucumbers when in the presence of a substrate enriched with Sargassum vulgare, representing an important step towards the viability of large-scale sea cucumber rearing in Europe.

The high demand of sea cucumbers in international markets, mostly based in Asia, has left a deep impact on the natural stock of many species, leading to an investment in aquaculture techniques in order to mitigate these impacts. This study aimed to determine the effects of stock density in rearing broodstock of Holothuria (Panningoturia) forskali Delle Chiaje, 1823, a common species in the Mediterranean Sea and eastern Atlantic with commercial value. To do so, two different density treatments were selected: 1 kg/m² and 2 kg/m². The trial took place over five months and individuals were fed a mixture of frozen microalgae (Tetraselmis sp. and Phaeodactylum tricornutum). At the end of the trial, the effects of stock density on the individuals’ condition were assessed by analysing different variables, namely their fresh and gutted weight, evisceration and mortality rates, gonadosomatic index and oocyte size and even biochemical content, such as protein and lipid content in muscle bands. No significant differences were found between density treatments regarding any of the parameters assessed, aside from mean oocyte diameter. Individuals from the lower‐density treatment presented a smaller mean oocyte diameter, supplied with fewer oocytes, than individuals in both the higher‐density treatment and the baseline group. Regardless of this one difference, all trial individuals were able to maintain their elevated gonadal developmental stage for a full period of five months past their reproductive peak, with female holothurians subjected to the higher‐density treatment showing signs of increasing vitellogenic reserves, a considerable advantage in aquaculture broodstock rearing.

The ever-growing demand for sea cucumbers is a threat to these echinoderms and their habitats; however, a way to relieve stock pressure lies in meeting demand through aquaculture. As such, this study aimed to improve the growth and survival percentage of Holothuria arguinensis during larval development, settlement and juvenile growth. Three diets of microalgae (Diet RbPt = Rhodomonas baltica + Phaeodactylum tricornutum; Diet RbSm = Rhodomonas baltica + Skeletonema marinoi; Diet RbCc = Rhodomonas baltica + Chaetoceros calcitrans) were administered daily to the larval phase. Additionally, three substrates were supplied (pvc rolls, wavy pvc plaques and tile) at three different depths in order to determine the most favourable for settlement. Lastly, the potential benefits on growth and survival from introducing macroalgae (Sacchoriza polyschides) in the juvenile diet were assessed over a period of 6 months. Despite larvae under diet RbPt having presented a larger mean width, H. arguinensis fed with Diet RbCc presented a higher settlement survival at the end of the trial. No preferences were noted among the tested substrates, regardless of diet. Lastly, juveniles with added S. polyschides in their diet showed increased growth in mean weight and length when compared to individuals that were not fed with this seaweed.

The high demand for sea cucumbers in eastern markets, either as a protein source for human consumption or for medicinal purposes, placed an excessive pressure on natural stocks. Sea cucumber aquaculture, set as a valuable alternative for producers and highly developed in Southeast Asia, still falls short on supply. As a consequence, exploitation of natural stocks expanded from the Pacific and Indian Oceans to the Mediterranean and Atlantic regions, either by foreign fishery or locally, for foreign trade. Still, an increase in aquaculture production is the natural response to satisfy demand and assuage stock decline, an extant reality for several Holothuroidea species. Although some North-eastern Atlantic and Mediterranean species have already been introduced in the international market, European aquaculture of sea cucumbers is inexistent. Yet, sea cucumber farming demonstrates a high viability due to its low-cost maintenance and high market value. Moreover, their position in the food chain and further detritivorous feeding strategy, makes sea cucumbers excellent candidates for Integrated Multi-Trophic Aquaculture and enables their sustainable rearing in Polyculture systems. In either of which the presence of these detritivorous species can actually be advantageous, as they play a significant role in recycling and redistributing nutrients, by filtering sediment and removing its organic matter. However, the key to a significant contribution to the decrease of natural harvesting and towards the development of sustainable rearing systems lies on the holistic control of the species’ life-cycle, as opposed to relying on the capture of wild juveniles for growth or wild broodstocks for reproduction. The project Newcumber – Advances towards the sustainable rearing of sea cucumbers – aims to achieve a sustainable aquaculture of sea cucumbers, using species from the eastern-Atlantic coast. The project is geographically focused on the Sado region (estuary and coastal area), Portugal, and has four main goals: (1) select the species that best fits the general aim, in terms of tolerance to captivity and manipulation, suitable feeding strategies, suitable reproductive biology, nutritional value and market/consumer acceptance; (2) achieve species domestication, aiming for the optimization of somatic growth and gonad maturation, as well as breeding control in captivity (spawning, viable gamete and early stage larvae); (3) aquaculture system assessment, evaluating the success of extensive systems, by comparison to intensive farming, and attempting polyculture, aiming to yield suitable production results; (4) define a market status for the selected species, aiming to determine how it fits the global market, in comparison to others already valued and traded, either through its nutritional balance for human consumption, taste or production viability. Ultimately, the Newcumber project expects to contribute towards the development of sustainable aquaculture practices for Atlantic sea cucumber species, which are currently untargeted for production. This is a relevant step towards the diversification of the national and European aquaculture sectors, creating an added-value from its marine native resources and increasing the global supply of high value products, thus, leveraging rearing systems of marine products. From a conservation standpoint, a sustainable alternative to the high sea cucumber demand will contribute to reduce the growing pressure on wild stocks and has the potential to support restocking programs to help replenish vulnerable or depleted populations.

Holothuria tubulosa (Gmelin, 1788) is a marine invertebrate, belonging to the group Echinodermata, usually known as sea cucumber. Its geographical distribution extends from the Atlantic Ocean to the Mediterranean Sea and it is frequently associated to sandy and rocky areas, as well as sea meadows. Generally, they occur at depths less than 100 m. The sea cucumbers are very sensitive and in conditions of stress they can easily eviscerate, which may lead to the death of the organisms. This study aimed to evaluate the stress induced by the catch, transport and triage of H. tubulosa. One hundred specimens were captured in the Sado Estuary (Setúbal, Portugal) resorting to diving and acclimated in thermic containers (46 L) with seawater and constant aeration, with around 15 animals per container. Acclimation, including transport to MARE-IPLeiria, had the duration of 3 hours. At the facilities, sea cucumbers were weighed, measured and distributed randomly in 3 tanks of 400 L and kept in densities of 20.3 kg m-3. The quality of water was monitored daily, with a measured temperature of 15.1 ±1.1 °C, dissolved oxygen of 6.9 ±0.5 mg L-1, salinity of 34 ±1 and pH of 8.3 ±0.1. The maximum value to the concentration of ammonia, nitrites and nitrates were controlled and was established as 1 mg.L-1. H. tubulosa presented a mean weight of 264.46 ±78.19 g and a submersed mean length of 27.30 ±3.77 cm. Although there were no registered mortalities throughout the trial, evisceration occurred in 3.33% of the individuals. The results suggest H. tubulosa is resistant to catch, transport and handling, representing an advantage for its use in laboratorial trials, with scientific purposes or on a commercial level. Considering the high demand of sea cucumbers worldwide and H. tubulosa 's high tolerance to stress and relatively large size, these organisms present strong advantages for aquaculture.