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- The effects of stocking density on physiological traits in Holothuria forskali broodstockPublication . Sousa, João; Félix, Pedro M.; Brito, Ana C.; Venâncio, Eliana; Silva, Francisco Azevedo e; Simões, Tomás; Raposo, Andreia; Neves, Marta; Narciso, Luís; Melo, Ricardo; Pombo, AnaThe 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.
- Allometric relationships to assess ontogenetic adaptative changes in three NE Atlantic commercial sea cucumbers (Echinodermata, Holothuroidea)Publication . Silva, F. Azevedo e; Brito, A. C.; Simões, T.; Pombo, A.; Marques, T. A.; Rocha, C.; Sousa, J.; Venâncio, E.; Félix, P. M.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.
- Do broodstock diets influence viability and larval development of Holothuria mammata?Publication . Venâncio, Eliana; Félix, Pedro M.; Brito, Ana C.; Sousa, João; Silva, Francisco Azevedo e; Simões, Tomás; Narciso, Luís; Amorim, Ana; Dâmaso, Luísa; Pombo, AnaThe intensive exploitation of sea cucumbers, mainly exported to Asian seafood markets, has contributed to deplete natural populations of several species. In Europe, the aquaculture production of these echinoderms is minimal, reflecting the low scientific production on the topic. In Portugal, like in Mediterranean countries, there are native species with high commercial value, which can be potential candidates for aquaculture. The control over the reproductive cycle is an important tool for rearing success, which, in turn, decreases the pressure over natural stocks. However, there are very few studies on the larval development of European species and none on the broodstock maturation in captivity. The present work studied the influence of three diets on the gonadal maturation and larval viability and development of Holothuria mammata. After 120-days of captivity the broodstock groups fed with a mixture of live microalgae (Diet 2) and a mixture of live microalgae and extruded dry food (Diet 3) reached the spawning stage, in contrast to the group fed with a mixture of frozen microalgae (Diet 1). Spawning was induced by thermal shock. Larval rearing from broodstock fed on Diet 2, total mortality was observed on the 12th day, after the onset of mid auricularia stage. The stocks of larvae from the broodstocks fed diets 1 and 3 reached the stage of pentactula on the 27th day. The success in spawning induction and embryonic development suggest that H. mammata may accept different types of diets as frozen microalgae mixes or live microalgae and dry feeds and still produce viable offspring. However, it is essential to develop more studies on the reproductive biology of H. mammata to optimize the hatcheries techniques to broodstock conditioning and larval rearing in captivity.
- Comparison of the efficiency of different eradication treatments to minimize the impacts caused by the invasive tunicate Styela plicata in mussel aquaculturePublication . Santos, Pedro M.; Venâncio, Eliana; Dionísio, Maria Ana; Heumüller, Joshua; Chainho, Paula; Pombo, AnaIn 2017, aquaculture producers of the Albufeira lagoon, Portugal, reported an invasion of tunicates that was disrupting mussel production, particularly the tunicate Styela plicata (Lesueur, 1823). A totally effective eradication method still does not exist, particularly for S. plicata, and the effects of the eradication treatments on bivalves’ performance are also poorly understood. Our study examined the effectiveness of eradication treatments using three laboratory trials and five treatments (air exposure, freshwater immersion, sodium hypochlorite, hypersaline solution and acetic acid) for S. plicata, as well as their effects on survival and growth of blue mussel Mytilus edulis Linnaeus, 1758. While air exposure and freshwater immersion caused a 27% mortality rate in S. plicata, the acetic acid treatment was the most effective in eliminating this species (>90% mortality). However, a 33–40% mortality rate was registered in mussels. Both species were not affected by the hypersaline treatment in the last trial, but the sodium hypochlorite treatment led to a 57% mortality rate in mussels. Differences in mussels’ growth rates were not detected. These trials represent a step forward in responding to the needs of aquaculture producers. However, further studies are needed to investigate the susceptibility of tunicates to treatments according to sexual maturation, as well as to ensure minimum mussel mortality in the most effective treatments, and to better understand the effects on mussel physiological performance in the long-term.
- Acondicionamento, Reprodução e Cultivo Larvar de Holothuria tubulosa (Gmelin, 1790)Publication . Venâncio, Eliana Filipa Santos; Pombo, Ana Margarida Paulino Violante; Félix, Pedro; Brito, Ana C.O aumento da procura por espécies de pepino-do-mar nos mercados asiáticos levou a um declínio nas populações selvagens no Indo-Pacífico (i.e.: Apostichopus japonicus, Cucumaria frondosa, Parastichopus californicus). O esforço de pesca foi, assim, intensificado e expandido para áreas do Mediterrâneo e Sul da Europa, onde diferentes espécies são exploradas. O cultivo de espécies europeias (i.e.: Holothuria mammata, Holothuria scabra, Holothuria tubulosa) está a tornar-se crucial para a sobrevivência dos stocks naturais destes equinodermes. No entanto, esta é ainda uma indústria em desenvolvimento, pelo que se torna essencial otimizar o procedimento de reprodução e crescimento em cativeiro. Holothuria tubulosa (Gmelin, 1790) pertence à classe Holothuroidea e ocorre desde o Golfo da Biscaia (Atlântico Nordeste) até ao Mar Mediterrâneo. Esta espécie reproduz-se sexuadamente, apresentando sexos separados (dióicos), não apresentando dimorfismo sexual. Possuem hábitos alimentares principalmente detritívoros, alimentando-se do conteúdo orgânico da areia, lama e biofilmes. H. tubulosa tem sido visto como um novo candidato à aquacultura pois esta espécie é resistente ao maneio e adapta-se facilmente às condições de cativeiro. Este trabalho teve como objetivos a adaptação dos reprodutores às condições de cativeiro, a sua reprodução e o desenvolvimento larvar de H. tubulosa. Neste estudo, procedeu-se ao acondicionamento de 90 H. tubulosa durante 120 dias com diferentes dietas: Dieta 1 - mix de microalgas congeladas (Tetraselmis sp. e Phaeodactylum tricornutum); Dieta 2 - mix de microalgas vivas (Isochrysis galbana e Phaeodactylum tricornutum); Dieta 3 - microalga viva (Phaeodactylum tricornutum) e ração seca extrudida para peixes marinhos. No final do ensaio comparou-se o peso (g), o comprimento (cm), o índice gonadossomático (%) e a maturação das gónadas entre os indivíduos alimentados com dietas diferentes. Os resultados demonstraram não existir diferenças significativas entre os animais alimentados com as três dietas diferentes. A indução da postura dos reprodutores mantidos em cativeiro foi conseguida com sucesso através de choque térmico, isto é, o aumento brusco da temperatura da água. O desenvolvimento larvar foi acompanhado até ao 27º dia. A fase de pré-auriculária surgiu ao 3º dia, como na maioria das holotúrias, enquanto a fase de doliolária apenas surgiu ao 25º dia, apresentando um desenvolvimento larvar lento vi quando comparado com outros pepinos-do-mar (i.e.: Holothuria mammata, Holothuria polii). De uma forma geral, H. tubulosa demonstrou ser um potencial candidato à aquacultura dada a resistência apresentada ao maneio e acondicionamento, a facilidade de desenvolvimento das gónadas em cativeiro, o sucesso na indução e o cultivo larvar até à fase de assentamento.
- Spatiotemporal distribution patterns of the sea cucumber Holothuria arguinensis on a rocky‑reef coast (Northeast Atlantic)Publication . Silva, F. Azevedo e; Brito, A.C.; Pombo, A.; Simões, T.; Marques, T.A.; Rocha, C.; Madruga, A.S.; Sousa, J.; Venâncio, E.; Félix, P.M.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.
- Modelling the distribution of a commercial NE-Atlantic Sea Cucumber, Holothuria mammata: demographic and abundance spatio-temporal patternsPublication . Félix, Pedro M.; Pombo, Ana; Silva, Francisco Azevedo e; Simões, Tomás; Marques, Tiago A.; Melo, Ricardo; Rocha, Cristina; Sousa, João; Venâncio, Eliana; Costa, José L.; Brito, Ana C.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.
- Reproductive biology of the sea cucumber Holothuria mammata (Echinodermata: Holothuroidea)Publication . Venâncio, Eliana; Félix, Pedro M.; Brito, Ana C.; Silva, Francisco Azevedo e; Simões, Tomás; Sousa, João; Mendes, Susana; Pombo, AnaHolothuria 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 (<15ºC), and spawning occurred later, with longer photoperiod (13 to 15 h of sunlight) and higher seawater temperature (>15ºC) 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.