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- 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.
- 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.
- Effect of enriched substrate on the growth of the sea cucumber Holothuria arguinensis Koehler and Vaney, 1906 juvenilesPublication . Rodrigues, Tiago; Silva, Francisco Azevedo e; Sousa, João; Félix, Pedro M.; Pombo, AnaThe 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.
- 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.