For critically endangered aquatic species, restorative aquaculture and ex-situ conservation may represent the last opportunity to halt extinction trajectories; however, spawning induction, larval rearing, and feeding, depend on understanding species-level ecology. Pinna nobilis , a marine bivalve currently on the brink of extinction, has never yet been successfully kept for multiple generations in captivity. We tested the impact of diet on captive growth of juveniles recovered from mussel farms and maintained in a recirculating aquaculture system, comparing three diets: mixed live microalgae, commercial optimized mix of microalgae, and conditioned seagrass detritus. Seagrass detritus produced the highest mean growth rates in both small (150–190 mm) and large (190–220 mm) size classes, with significantly higher growth observed in the large size class. These results indicate that seagrass detritus constitutes a significant natural food source for this species, providing experimental evidence of a recently hypothesized direct trophic link mediated by heterotrophic bacteria in seagrass meadows. Our findings contribute to both the ecological understanding of P. nobilis and practical guidance for the formulation of optimal diets in captive rearing. This knowledge is essential for the establishment of effective ex-situ conservation programs aimed at promoting growth and reproduction of this iconic Mediterranean species.

Deposit-feeding sea cucumbers are highly potential extractive species within Integrated Multi-Trophic Aqua- culture (IMTA) systems. This study investigated the feasibility of the sea cucumber Holothuria sanctori in pilot- scale IMTA systems with finfish and shellfish over a six-month experimental period. The experiment assessed the survival, growth, and bioremediation potential of H. sanctori (mean weight: 77.74 +/- 32.23 g) using two bottom-placed rearing systems (cages and sediment traps) under finfish and mussel aquaculture waste conditions. In the IMTA system with finfish, H. sanctori performed optimally in the cage model, achieving a survival rate of 96 %, and a specific growth rate of 0.10 +/- 0.05 % per day. In the IMTA system with mussels, the sea cucumber's optimal performance was observed in the sediment traps, with a 100 % survival rate, and a specific growth rate of 0.21 +/- 0.08 % per day. Additionally, the bioremediation capacity of H. sanctori was assessed through a comparative analysis of organic matter (OM) content in sediment traps with and without sea cucumbers. Results indicated a reduction in organic content in sediment traps containing H. sanctori, compared to those without sea cucumbers. This study is the first to evaluate H. sanctori co-cultivation with finfish and mussels in IMTA systems, demonstrating its high potential as an extractive species.

The sea cucumber Holothuria sanctori is an Atlanto-Mediterranean deposit feeder that contributes to sediment processing in coastal areas. However, the feeding ecology of this species, including its sediment processing capacity, remains largely unexplored under controlled conditions. This study investigates the effect of sediment granulometry on the feeding behaviour of H. sanctori, focusing on organic matter (OM) selectivity and sediment ingestion. Specimens were tested under five experimental treatments, each containing sediments with particle sizes ranging from 0 to 1000 μm, with standardized OM availability across treatments. A natural simulation with a hard, sediment-free substrate was also included. Data on defecation rate and faecal OM content was collected daily to evaluate sediment processing capacity. Results indicate that H. sanctori optimally selects OM (average OM: 4.2%) and processes sediment (average defecation rate: 1.5 g/day per 100 g biomass WW) in fine particle treatments (< 250 μm). Additionally, the species exhibits an extended sediment processing capacity across a wide range of sediment sizes, including particles up to 1000 μm. The study further revealed that the sea cucumber increases sediment ingestion (by one order, on average) to compensate for reduced OM availability (by 0.15 order, on average), maintaining a constant OM intake. The results suggest that sediment granulometry might not be the primary factor in determining the species’ microhabitat preferences in the natural environment due to its extended capacity to process different sediment granulometries. These findings enhance our understanding of H. sanctori's feeding behaviour and highlight its potential in Integrated Multi-Trophic Aquaculture applications.

Sea cucumbers are deposit feeding members of marine benthic communities. The over-exploitation of sea cucumber natural stocks, especially in the Mediterranean basin, is having negative impacts on the marine ecosystem. This concerns had led the Italian government to take legal actions to preserve these important marine resources. The aim of this study was to evaluate the level of genetic diversity and population structures within two sympatric Holothuria sea cucumber species, H. polii and H. tubulosa, across ten Mediterranean areas along Italy. A 323 bp portion of the COI mitochondrial gene was sequenced in a total of 441 holothurians (251 H. polii, 177 H. tubulosa and 13 from other species). Genetic diversity analyses and analysis of molecular variance (AMOVA) suggest that H. polii and H. tubulosa species are distinct, but within and among populations are homogeneous, indicating active gene flows across the Mediterranean areas investigated. H. polii showed a lower genetic diversity than H. tubulosa, probably related to differences in life history traits. Phylogenetic analyses showed a clear differentiation between the two species, even if six specimens morphologically assigned to a species clustered within the other species, indicating a possible occurrence of hybridization events. These data will be useful in implementing conservation actions for these holothurian genetic resources.

To improve the sustainability of aquaculture practices, a step towards the use of alternative nutrient sources (such as food processing discards) may secure the future of aquaculture sector, namely for emergent species, such as sea urchins. In this context, adult females of the commercial sea urchin Paracentrotus lividus were reared using four feeds based on lettuce discards (72%) and enriched (8%) with an animal-source ingredient (fish Sardina pilchardus, Feed-S; krill Euphausia superba, Feed-K; mussel Mytilus galloprovincialis, Feed-M; anchovy Engraulis encrasicolus discards, Feed-AD). A fifth feed, used as control treatment, was composed of macroalgae (Laminaria sp. and Ulva sp., Feed-UL). Feed performance was evaluated employing a new productive protocol, the Raking method, which propose testing feed effects on sea urchin caviar (oocytes rather than gonads) production. Thus, ingestion rates and absorption efficiency were measured to evaluate feed palatability. Somatic growth and caviar production, expressed introducing the ovosomatic index (OI) instead of the traditional gonadosomantic index, were measured to assess feed productive performances. Caviar quality was assessed by nutritional content and color. Ingestion rate results showed that all feeds were palatable, while findings on absorption efficiency showed differences between the five proposed feeds, with Feed-M and Feed-AD presenting the worst results. Somatic growth was promoted regardless the provided feeds, while OI resulted higher with Feed-K and Feed-M than the other feeds. All produced caviar resulted suitable for human consumption with high protein and fatty acid content, but caviar produced by Feed-UL showed the poorest nutritional profile. Similarly, Feed-UL led to the production of caviar with the lowest quality color, while Feed-S showed the best orange color. Lettuce-based feeds were therefore effective for feeding P. lividus as they stimulated production of high quality caviar. Findings support the exploitation of food discards for the production of eco-friendly feeds for sea urchin aquaculture.

Accurate data on community structure is a priority issue in studying coastal habitats facing human pressures. The recent development of remote sensing tools has offered a ground-breaking way to collect ecological information at a very fine scale, especially using low-cost aerial photogrammetry. Although coastal mapping is carried out using Unmanned Aerial Vehicles (UAVs or drones), they can provide limited information regarding underwater benthic habitats. To achieve a precise characterisation of underwater habitat types and species assemblages, new imagery acquisition instruments become necessary to support accurate mapping programmes. Therefore, this study aims to evaluate an integrated approach based on Structure from Motion (SfM) photogrammetric acquisition using low-cost Unmanned Aerial (UAV) and Surface (USV) Vehicles to finely map shallow benthic communities, which determine the high complexity of coastal environments. The photogrammetric outputs, including both UAV-based high (sub-meter) and USV-based ultra-high (sub-centimetre) raster products such as orthophoto mosaics and Digital Surface Models (DSMs), were classified using Object-Based Image Analysis (OBIA) approach. The application of a supervised learning method based on Support Vector Machines (SVM) classification resulted in good overall classification accuracies > 70%, proving to be a practical and feasible tool for analysing both aerial and underwater ultra-high spatial resolution imagery. The detected seabed cover classes included above and below-water key coastal features of ecological interest such as seagrass beds, “banquettes” deposits and hard bottoms. Using USV-based imagery can considerably improve the identification of specific organisms with a critical role in benthic communities, such as photophilous macroalgal beds. We conclude that the integrated use of low-cost unmanned aerial and surface vehicles and GIS processing is an effective strategy for allowing fully remote detailed data on shallow water benthic communities.

Filter-feeding mussels blend suspended particles into faeces and pseudo-faeces enhancing organic matter flows between the water column and the bottom, and strengthening benthic-pelagic coupling. Inside operating farms, high bivalve densities in relatively confined areas result in an elevated rate of organic sinking to the seabed, which may cause a localized impact in the immediate surrounding. Deposit-feeding sea cucumbers are potentially optimal candidates to bioremediate mussel organic waste, due to their ability to process organic-enriched sediments impacted by aquaculture waste. However, although the feasibility of this polyculture has been investigated for a few Indo-Pacific species, little is known about Atlanto-Mediterranean species. Hence, for the first time, in the present study, we conducted a comparative investigation on the suitability of different Mediterranean sea cucumber species, to be reared in Integrated Multitrophic Aquaculture (IMTA) with mussels. A pilot-scale experiment was accomplished operating within a mussel farm where two sea cucumbers species, Holothuria tubulosa and Holothuria polii , were caged beneath the long-line mussel farm of Mytilus galloprovincialis . After four months, H. tubulosa showed high survivorship (94%) and positive somatic growth (6.07%); conversely H. polii showed negative growth (− 25.37%), although 92% of specimens survived. Furthermore, sea cucumber growth was size-dependent. In fact, smaller individuals, independently from the species, grew significantly faster than larger ones. These results evidenced a clear difference in the suitability of the two sea cucumber species for IMTA with M. galloprovincialis , probably due to their different trophic ecology (feeding specialization on different microhabitats, i.e. different sediment layers). Specifically, H. tubulosa seems to be an optimal candidate as extractive species both for polycultures production and waste bioremediation in M. galloprovincialis operating farms.

Abstract The dramatic Mass Mortality Event, MME, of Pinna nobilis populations initially detected in 2016 in the western Mediterranean basin, has also spread rapidly to the central and eastern basin. Unfortunately, there is still a significant lack of information on the status and health of P. nobilis, since only a fragmentary picture of the mortality rate affecting these populations is available. Regarding the Italian coast, several surveys have given only localized or point-like views on the distribution of species and the effect of the MME. Therefore, for the first time, this study investigated P. nobilis densities, distribution and mortality in 164 surveys covering a total of 800 km along the southeast coast of Italy (Apulia region). The geographical scale of this investigation made it the largest ever conducted in Italy, and this was achieved through a rapid and standardized protocol. No live individuals were observed along the 92 km linear transects, allowing us to assess that the P. nobilis populations had totally collapsed, with a mortality rate of 100% in Apulia. The distributional pattern of the species showed a strong overlap with seagrass meadows on meso and macro geographical scale, however this was not the case on a micro scale. This result indicates that although there is a relationship between P. nobilis and seagrass meadows, it is not limited to the habitat patch but crosses the boundaries of seagrass. This observation led us to the conclusion that the distribution of P. nobilis shows a trophic link through the cross-boundary subsidy occurring from seagrass meadows to the nearby habitat, by means of the refractory detrital pathway.

The dramatic Mass Mortality Event, MME, of Pinna nobilis populations initially detected in the western Mediterranean basin, has also spread rapidly to the central and eastern basin. Unfortunately, there is still a significant lack of information on the status and health of P. nobilis , since only a fragmentary picture of the mortality rate affecting these populations is available. Regarding the Italian coast, several surveys have given only localized or point-like views on the distribution of species and the effect of the MME. Therefore, for the first time, this study investigated P. nobilis density of individuals, distribution and mortality throughout 161 surveys along 800 km of coastline in the Apulia region (South-east of Italy). The geographical scale of this investigation made it the largest ever conducted in Italy, and this was achieved through a rapid and standardized protocol. During this monitoring campaign, 90 km of linear underwater transects were surveyed, along which no live individuals were observed. This result allowed to estimate that the P. nobilis populations had totally collapsed, with a mortality rate of 100% in Apulia. The distributional pattern of the species showed a strong overlap with seagrass meadows on meso- and macro-geographical scale, however this was not the case on a micro-scale. This result evidenced that relationships between P. nobilis and seagrass meadows are not limited to the habitat patch, but cross the boundaries of seagrass leading us to suggest that the distribution of P. nobilis hold a trophic link through the cross-boundary subsidy occurring from seagrass meadows to the nearby habitat, by means of the refractory detrital pathway.

Sea cucumbers are widely distributed deposit-feeders that represent an important component of benthic communities worldwide. These echinoderms were recently proposed as candidates in embryo bioassays to provide a new tool in the toxicity assessment of pollutants in marine water and sediments. The aim of this study is to evaluate the usefulness of a new species, Holothuria tubulosa (Gmelin, 1788), as a model organism for sensitive embryo bioassays, defining the acceptability of controls, minimum sample size, embryo density and salinity range. Cadmium (Cd), copper (Cu), lead (Pb), mercury (Hg), sodium dodecyl sulphate (SDS) and 4-n-nonylphenol (NP) were used as reference toxicants to assess specific embryotoxicity endpoints. Sea cucumber sensitivity to marine sediment elutriates were finally assessed by comparing their responsiveness in tandem with that of routinely employed sea urchin embryos. The results showed an acceptability threshold of 10% (abnormal embryos), a minimum sample size of 200 embryos, an embryo density of 200 embryos/mL and an optimal salinity range of 36-37 parts per thousand. The sensitivity to the environmental pollutants and matrices tested revealed values (expressed as EC50) comparable with those of embryos belonging to other marine invertebrates commonly used in bioassays, indicating that this species has a good level of responsiveness. A specific integrative toxicity index (ITI) was applied, combining the frequency of developmental anomalies and weighting their severity. ITI data demonstrated good discrimination of sample toxicity, with a dose-dependent increase of teratogenic effects for all the tested substances, indicating H. tubulosa as a promising species for future assessments of marine pollution. (C) 2021 Elsevier B.V. All rights reserved.