Efectos de las dietas algales y el ayuno en el crecimiento, supervivencia y composición de ácidos grasos de las larvas de Solen marginatus (Bivalvia: Solenidae)

The aim of this study was to investigate whether it is necessary to feed Solen marginatus (Pennánt, 1777) larvae externally and the evolution of fatty acids in the neutral and polar lipids during larval development in starved larvae and larvae fed on two different microalgal diets. Larvae were subjected to three different treatments: 1. 10 equivalent cells (Isochrysis galbana, Pavlova lutheri and Chaetoceros calcitrans) plus 20 equivalent cells of Tetraselmis suecica; 2. 80 equivalent cells of I. galbana and 3. starvation during eight days, and then individuals were re-fed on diet 1. The best results for growth were observed in larvae fed on diet 1. Starved larvae reached the best survival rate at day 8 (66%). However, three days after re-feeding all larvae died, suggesting that the “point of no return” was exceeded. In spite of the large size of S. marginatus eggs and the great amount of stored reserves, the larvae need to feed on microalgae to undergo metamorphosis. Non-methyle-interrupted dienoic fatty acids and their precursors 16:1n-7 and 18:1n-9 are of great importance in starved larvae. Saturated fatty acids, especially 16:0, fuel larval development. A certain degree of bioconversion of 18:2n-6 to 20:4n-6 was observed in S. marginatus larvae.El objetivo de este estudio es investigar la necesidad de alimentación externa de las larvas de Solen marginatus (Pennánt, 1777) y la evolución de los ácidos grasos en los lípidos neutros y polares durante el desarrollo larvario en ayuno y usando dos dietas microalgales. Las larvas se sometieron a tres tratamientos distintos: 1. 10 células equivalentes Isochrysis galbana, Pavlova lutheri y Chaetoceros calcitrans) más 20 células equivalentes de Tetraselmis suecica; 2. 80 células equivalentes de I. galbana; y 3. Ayuno durante ocho días, y después los individuos se realimentaron con la dieta 1. Los mejores resultados en crecimiento se observaron en las larvas alimentadas con la dieta 1. Las larvas que ayunaron alcanzaron la mejor supervivencia en el día 8 (66%). Sin embargo, tres días después de volver a alimentarlas murieron todas, sugiriendo que el “punto de no retorno” se sobrepasó. A pesar del gran tamaño de los huevos de S. marginatus y del gran acúmulo de reservas sus larvas necesitan alimentarse externamente para llevar a cabo la metamorfosis. Los ácidos grasos dienoicos no-metilen-interrumpidos y sus precursores 16:1n-7 y 18:1n-9 son de gran importancia para las larvas en ayuno. Los ácidos grasos saturados, especialmente el 16:0, suministran energía para el desarrollo larvario. Se ha observado cierta bioconversión de 18:2n-6 en 20:4n-6 en las larvas de S. marginatus

Genetic Variability in Ruditapes Decussatus Clam Combined With Perkinsus Infection Level to Support Founder Population Selection for a Breeding Program

[Abstract] Clam farmers worldwide face several challenges, including irregular seed supply and high mortalities due to pathogenic organisms such as "Perkinsus olseni". In Europe, there is a high unmet consumer demand for native clam species such as "Ruditapes decussatus". The high market value of "R. decussatus" makes the culture of this species potentially more attractive than that culture of the alien species "Ruditapes philippinarum". Thus, there is a market opportunity in breeding and producing "R. decussatus" at an industrial scale. A selective breeding program to improve "R. decussatus" performance will be carried out in Portugal; and the first critical step to develop such a breeding program is the establishment of a founder population. In this study, intra- and interpopulation genetic diversity was assessed using 13 microsatellite markers in eight natural beds located in Portugal, Spain and Italy. Also, allele and genotypic frequencies of each microsatellite locus were assessed discriminating between clams infected and non-infected by "P. olseni". All locations showed similar values for several genetic diversity parameters. Analyses of population differentiation (FST, Bayesian clustering and AMOVAs) revealed five genetically differentiated regions: Rías Altas and Rías Baixas (NW Spain), North/Central Coast of Portugal, Gulf of Cadiz and Adriatic Sea. Significant differences in the allelic and genotypic frequency distribution between infected clams and non-infected ones at four microsatellite loci are reported suggesting that resistance to the disease could have a genetic basis. Moreover, a positive or negative relationship between the frequency of certain alleles and the parasite infection was inferred. Further studies should confirm the potential use of those alleles as genetic markers for "P. olseni" infection. Integrating results of genetic diversity within and between populations and Perkinsus infection levels, a founder population for a "R. decussatu" breeding program is proposed, composed by individuals from Barallobre (Rías Altas), Pontevedra or Cangas (Rías Baixas), Óbidos (North/Central Coast of Portugal), Algarve (Gulf of Cadiz) and Venice (Adriatic Sea).Governo da República Portuguesa; 22390 (16/SI/2016) (CENTRO-01-0247-FEDER-022390)Ministério do Mar (Portugal); FA_01_2017_00

Hatchery seed production of flat oysters from the Mar Menor lagoon

The Mar Menor lagoon (SE Spain) suffers a severe eutrophication process aggravated since the collapse of the lagoon in 2016. Together with it, the populations of the flat oyster Ostrea edulis have been decimated in the lagoon, but also in the European seas, where the species and the habitats provided by it have mainly disappeared. The Mar Menor Oyster Initiative’s main objectives are gaining knowledge on the nutrient extraction capability of the Mar Menor flat oyster and developing the required tools for restoration and bioextraction actions. The project RemediOS, within the framework of the Mar Menor Oyster Initiative, aims to obtain flat oyster seed using the decimated local broodstock to provide the initiative with an oyster population to work with. The present work describes the results of the first attempt of Mar Menor local broodstock reproduction in captivity. Larvae produced in the hatchery accounted for 57.5 million, of which 11.8 million were cultured and 0.68 million survived to settlement and metamorphosis

Recovery of eutrophized marine ecosystems using the European flat oyster, Ostrea edulis

The development of tourism and intensification of agriculture has released large amounts of nitrogen and phosphorus into the Mar Menor coastal lagoon in South-east Spain, resulting in a phytoplankton bloom in 2016. This bloom turned the clear and transparent waters turbid and greenish, and killed approximately 85% of benthic macrophytes. Nutrient bioextraction by flat oysters, Ostrea edulis, has been proposed for remediation of these eutrophication events and water quality recovery. This research aims to quantify the clearance rate and investigate the genetic origin of Mar Menor oysters under eutrophized conditions for potential applications to bioremediation projects. Oligotrophic and eutrophic conditions were replicated in the laboratory, and oyster feeding behaviour (i.e. clearance rates, ingestion rates, absorption efficiency and absorption rates) were studied using a flow-through system. The genetic characterization of oysters showed no significant difference between individuals from the Mar Menor and individuals collected from a nearby Mediterranean bed (Tabarca Island). Based on the physiological results observed, oysters were grouped into high-feeder (HF) and low-feeder (LF) categories according to their clearance rate, that was 3-fold higher in the HF group. Different responses in feeding behaviour were observed under eutrophic conditions in both oyster groups. Constraints in the absorption capacity of LF oysters seemed to be related to their reduced filtering activity. Lower body condition of LF oysters was evidenced by their negative scope for growth value. From this work, several conclusions can be drawn for future restoration/bioextraction actions: (i) the recovery of half of the oyster population that existed in the past would act as an effective top-down control on the phytoplankton community; (ii) using clearance rate measurements is recommended to select oysters as broodstock; and (iii) Mediterranean oysters could be used as broodstock in the event that Mar Menor oysters fail to reproduce.We appreciate the work done by Francisco Gomez in the maintenance and feeding of the oyster and support on the physiological measurements. We also appreciate the technical assistance of Susana Sánchez with the genetic analyses. English has been reviewed by Selby Clarke (PhD student, Dalhousie University, Canada). This research has been performed in the scope of the RemediOS Project, developed with the collaboration of the Biodiversity Foundation (Spanish Ministry for Ecological Transition and the Demographic Challenge), through the Pleamar Program, co-financed by the European Maritime and Fisheries Fund (EMFF). Genetic analyses have been financed by the General Direction of the Mar Menor from the Murcia Regional Government (Reference 2021/009284).Peer reviewe

Overcoming Ostrea edulis seed production limitations to meet ecosystem restoration demands in the UN decade on restoration

The European flat oyster, Ostrea edulis, is a habitat-forming bivalve which was historically widespread throughout Europe. Following its decline due to overfishing, pollution, sedimentation, invasive species, and disease, O. edulis and its beds are now listed as a threatened and/or declining species and habitat by OSPAR. Increasing recognition of the plight of the oyster, alongside rapidly developing restoration techniques and growing interest in marine restoration, has resulted in a recent and rapid growth in habitat restoration efforts. O. edulis seed supply is currently a major bottleneck in scaling up habitat restoration efforts in Europe. O. edulis has been cultured for centuries, however, research into its culture declined following the introduction of the Pacific oyster, Crassostrea gigas to Europe in the early 1970 s. Recent efforts to renew both hatchery and pond production of O. edulis seed for habitat restoration purposes are hampered by restoration project timelines and funding typically being short, or projects not planning appropriately for the timescales required for investment, research-and-development and delivery of oyster seed by commercial producers. Furthermore, funding for restoration is intermittent, making long-term commitments between producers and restoration practitioners difficult. Long-term, strategic investment in research and production are needed to overcome these bottlenecks and meet current ambitious restoration targets across Europe

Using combinations of microalgae to condition European flat oyster (Ostrea edulis) broodstock and feed the larvae: Effects on reproduction, larval production and development

Hatchery production of European flat oyster (Ostrea edulis) is erratic and is dependent upon broodstock conditioning and larval rearing conditions, including nutrition at both steps. In this study, the combined effects of broodstock and larval diets upon larval growth, survival, competence and metamorphosis and fatty acid and sterol compositions were studied. Four-year-old broodstock were conditioned in 700-L flow-through tanks (50 oysters per tank) at 19 degrees C and subjected to three dietary conditions in duplicate during 19 weeks. Two mixed diets were supplied continuously at an equivalent of 2 billion cells per day per oyster: Rhodomonas salina + Chaetoceros neogracile (Rs + C) or R. salina + Thalassiosira weissflogii (Rs + Tw), and the third condition was unfed. Samples of microalgae, released larvae (day 0), and larvae at day 9 were collected, and fatty acids (FAs) in neutral (NL) and polar lipids (PL) and sterols were analysed. Larval collection was continuous to estimate numbers of larvae released, which was dependent upon broodstock diet. Oysters fed Rs + C doubled the number of larvae compared to those receiving Rs + Tw - 47.8 compared to 23.1 million larvae, respectively. FAs in NL and PL, as well as sterol composition of released larvae, differed significantly depending upon broodstock diet. Larvae were reared in 5-L cylinders in a flow-through system at 22 degrees C. Larvae were subsequently fed different single and mixed microalgal diets in triplicate, incorporating Tisochrysis lutea (T), C. neogracile (C), and Diacronema lutheri (D), at a constant concentration of 1500 mu m3 mu L- 1 at the outlet of the rearing tank. Larval growth responded to both broodstock and larval diets; whereas, larval survival, competence, and settlement were influenced by both factors and their interactions. Broodstock receiving Rs + C produced larvae that grew faster (5.6-10.8 mu m day-1) than larvae from the other broodstock dietary regimes (4.6-9.6 mu m day-1). Larvae from fed broodstock (Rs + C or Rs + Tw) receiving the bi-specific diet T + C exhibited the highest growth rate (9.5-10.8 mu m day- 1); whereas, those fed the single diet D. lutheri exhibited low growth and competence (4.6-6.1 mu m day- 1; 4%) on day 9. Fed larvae originating from broodstock fed Rs + C exhibited better survival (92-97%) than those released by broodstock fed Rs + Tw (70-93%). Except for those supplied with T, fed larvae exhibited higher settlement when originating from broodstock receiving Rs + C. On day 9, FA and sterol compositions of larvae reflected the biochemical content of the larval diets. Overall, the best results were observed in larvae fed T + C originating from broodstock fed Rs + C

Ostras para mejorar la calidad del agua del Mar Menor

Los ecosistemas costeros están expuestos a una amplia gama de amenazas ambientales que incluyen, entre otras, la degradación de la calidad del agua por exceso de nutrientes, un proceso llamado eutrofización. Este es el caso del Mar Menor (Murcia, España), la laguna salada más grande de Europa. El Mar Menor sufre de eutrofización desde hace décadas debido a la acumulación de muchos nutrientes en el agua, lo que se ve agravado por la falta de organismos filtradores en el ecosistema. Estos animales, como los mejillones y las ostras, pueden ser, de hecho, parte de su salvaciónPeer reviewe

Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow-out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5-L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10-cm layer of coarse grained sand (300–1200 lm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m-2. In the second one-two densities were essayed (0.62 and 1.24 kg m-2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5-L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five-L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow-out system

The combined effects of blue light and dilution rate on lipid class and fatty acid composition of Tisochrysis lutea

International audienceThe lipid class and the fatty acid compositions of microalgae highly influence bivalve larval and post-larval development. Light is an essential environmental factor for microalgal culture, and quantity and quality of light may induce changes in the biochemical composition of the algae. The objective of this study was to investigate the effect of light spectrum (blue vs. white light) on lipid class and fatty acid compositions of Tisochrysis lutea cultured in a chemostat. Two different dilution rates (D) were assayed for each light spectrum: 0.2 and 0.7 day−1. Triacylglycerol (TAG), sterol, and hydrocarbon (HC) content increased sharply at low D. The proportion of alkenones was significantly reduced under blue light. Polyunsaturated fatty acids (PUFA), and particularly n-3 PUFA, content in phospholipids (PL) increased under blue light compared to white light at low D. Thus, blue light raised 22:6(n-3) levels in total lipids of T. lutea at low D. The cultivation of T. lutea in a chemostat at low D under blue light may improve nutritional value as feed for bivalve larvae by modifying the PUFA profile, especially increasing 22:6(n-3)