Establishment of environmental and biological bases to optimise the production of the European clam Ruditapes decussatus (Linnaeus, 1758)

Dissertação para obtenção do Grau de Doutor em AmbienteIn Portugal, aquaculture is greatly supported by the production of Ruditapes decussatus that represents 80 % of the total shellfish production. However, the culture of R. decussatus is clearly limited by the availability of seed, which proceeds exclusively from natural recruitment. In the last few years, the production of this species has clearly decreased due to recruitment failures and to severe mortalities. The development of hatchery technology that will provide an alternative reliable source of clam spat, will allow to overcome this constrain. Production of R. decussatus seed in hatcheries is however a relatively new industry for which most methods have been developed using empirical approaches. Due to the scarcity of information on this species production, the main objective of the present work was the evaluation of the biological and ecological processes involved in the different culture phases (broodstock conditioning, larval culture and on-growing). Concerning broodstock conditioning, the reproductive cycle of the two main Portuguese populations of R. decussatus, as well as its nutrient storage and exploitation strategy were characterized. Moreover, the best broodstock origin and timing of collection were determined, as well as the most adequate conditioning temperature and food to achieve maturation, spawning success and larval viability, limiting factors for the reproduction of this species. In order to optimize the larval management, important information on the energetic utilization during oogenesis and metamorphosis was obtained, contributing to the design of the most suitable diet for the larval phase. Concerning the on-growing phase, the response of R. decussatus to local and seasonal environmental factors was evaluated, aiming to define ecological and production management strategies. Finally, the overall information gathered in the present study allowed the development of a successful R. decussatus production program

What do oysters smell? Electrophysiological evidence that the bivalve osphradium is a chemosensory organ in the oyster, Magallana gigas

The sensing of chemical cues is essential for several aspects of bivalve biology, such as the detection of food and pheromones. However, little is known about chemical communication systems in bivalves or the possible role of the osphradium as a chemosensory organ. To address this, we adapted an electrophysiological technique extensively used in vertebrates & mdash;the electro-olfactogram & mdash;to record from the osphradium in the Pacific oyster, Magallana gigas. This technique was validated using amino acids as stimulants. The osphradium proved to be sensitive to most proteinogenic l-amino acids tested, evoking tonic, negative, concentration-dependent 'electro-osphradiogram' (EOsG) voltage responses, with thresholds of detection in the range of 10(-)(6) to 10(-)( 5) M. Conversely, it was insensitive to l-arginine and l-glutamic acid. The current study supports the hypothesis that the osphradium is, indeed, a chemosensory organ. The 'electro-osphradiogram' may prove to be a powerful tool in the isolation and characterization of pheromones and other important chemical cues in bivalve biology.info:eu-repo/semantics/publishedVersio

The impact of climate Change on bivalve farming: combined effect of temperature and salinity on survival and feeding Behavior of clams Ruditapes decussatus

European clam (Ruditapes decussatus) is one of the most relevant emergent bivalve species from the aquaculture sector in Europe with high economic value. Climate changes represent a potential limiting factor to this activity, directly interfering with the survival and behavior of bivalves. Severe fluctuations in temperature along with periods of heavy rainfall or periods of drought that significantly change the salinity can promote physiological stress in bivalves, resulting in changes in physiological and behavioral responses and, in extreme cases, leading to high mortalities. This study aimed to evaluate the combined effect of temperature and salinity on mortality and feeding behavior of R. decussatus. Juveniles and adults were exposed to combined ranges of temperature (5 degrees C-35 degrees C) and salinity (0-40). Mortality and feeding behavior were registered every 24 h of each 120-h trial. A control temperature range was set between 15 degrees C and 23 degrees C, where mortality and feeding behavior were considered as the normal scenario. Our data suggested salinity 15 as a "turning point," a point from which occurred distinct patterns in mortality and feeding behavior. The results evidently indicate that abrupt reductions in salinity and sharp increases in temperature will lead to high mortality of R. decussatus. Juveniles were revealed to be more sensitive to the increase of temperature in a less saline environment, to suffer greater and faster mortalities, and to be more resistant to extremely high temperatures under more saline conditions. The high temperatures and sporadic heavy rainfall that are predicted to occur in the south of Europe due to climate changes will contribute to compromise the recruitment of European clam, thus threatening the production of this species and consequently impacting the economic sector.info:eu-repo/semantics/publishedVersio

Genetic diversity of two Portuguese populations of the pullet carpet shell Venerupis senegalensis, based on RAPD markers: contribution to a sustainable restocking program

The pullet carpet shell Venerupis senegalensis (=V. pullastra) is a commercially important species in Portugal, Spain, France, and Italy. In Portugal, this species was once abundant in the Ria Formosa (southern Portugal

Reproductive activity and biochemical composition of the pullet carpet shell Venerupis senegalensis (Gmelin, 1791) (Mollusca: Bivalvia) from Ria de Aveiro (northwestern coast of Portugal)

The present study characterizes the reproductive cycle of Venerupis senegalensis (=V. pullastra) from Ria de Aveiro (Portugal) as well as its nutrient storage and exploitation strategy. The reproductive cycle followed a seasonal cycle that correlated negatively with sea surface temperature, and comprised a ripe stage in winter followed by a spawning period that began in late winter and ended in the early summer. This extended spawning may be an advantageous strategy for the species because it ensures a continuous supply of settlers. Gametogenesis began in late summer/early autumn and intensified with the decrease in temperature during autumn. The condition index increased even during the spawning period, which indicates that there is rapid recovery and that reserves are accumulated during late summer and used later in the gametogenic process. Proteins did not contribute significantly to gametogenesis and the glycogen pattern is typical of conservative species, since gametogenesis depends largely on the amount of glycogen stored. The lipid storage and utilization cycle showed that gametogenesis took place in autumn/winter and that energy reserves were accumulated in summer

Actividad reproductiva y composición bioquímica de la almeja babosa Venerupis senegalensis (Gmelin, 1791) (Mollusca: Bivalvia) de la Ría de Aveiro (costa noroeste de Portugal)

The present study characterizes the reproductive cycle of Venerupis senegalensis (=V. pullastra) from Ria de Aveiro (Portugal) as well as its nutrient storage and exploitation strategy. The reproductive cycle followed a seasonal cycle that correlated negatively with sea surface temperature, and comprised a ripe stage in winter followed by a spawning period that began in late winter and ended in the early summer. This extended spawning may be an advantageous strategy for the species because it ensures a continuous supply of settlers. Gametogenesis began in late summer/early autumn and intensified with the decrease in temperature during autumn. The condition index increased even during the spawning period, which indicates that there is rapid recovery and that reserves are accumulated during late summer and used later in the gametogenic process. Proteins did not contribute significantly to gametogenesis and the glycogen pattern is typical of conservative species, since gametogenesis depends largely on the amount of glycogen stored. The lipid storage and utilization cycle showed that gametogenesis took place in autumn/winter and that energy reserves were accumulated in summer.El presente estudio caracteriza el ciclo reproductivo de Venerupis senegalensis (= V. pullastra) en la Ría de Aveiro (Portugal) así como su estrategia de almacenamiento y explotación de los nutrientes. El ciclo reproductivo de esta especie sigue un ciclo estacional que se correlaciona negativamente con la temperatura del agua del mar, que coincide con un estado de madurez en el invierno, seguido de un periodo de desove que se inicia a finales de invierno y termina a principios del verano. Este periodo de puesta prolongado puede ser una estrategia ventajosa para la especie, ya que garantiza un suministro continuo de larvas. La gametogénesis comenzó a finales del verano/inicios de otoño y se intensificó con la disminución de la temperatura durante el otoño. El aumento del índice de condición, todavía durante la puesta, indica una recuperación rápida y una acumulación de reservas a finales del verano, que serán utilizadas en el siguiente proceso de gametogénesis. Las proteínas no contribuyen significativamente a la gametogénesis y el ciclo de glucógeno es típico de las especies conservadoras, una vez que la gametogénesis depende, en gran medida, de la cantidad de glucógeno almacenado. El almacenamiento de lípidos y su utilización indica la gametogénesis en el otoño/invierno, así como el proceso de acumulación de energía en verano

Aumento de la concentración de elementos traza en tejidos de la almeja Ruditapes decussatus trasplantada a zonas influenciadas por actividades humanas (ría Formosa, Portugal)

To examine the extent to which human activities near the Ria Formosa coastal lagoon influence the accumulation of trace elements (TE) in Ruditapes decussatus, individuals were transplanted from a natural bank located in the lower lagoon to three sites located in clam growth grounds under the influence of a small city (Faro), a fish farming centre (Olhão) and a site near the lagoon inlet (Lavajo). Concentrations were determined in substrate of the clam grounds and in the digestive gland, gills, mantle plus siphons, and remaining tissues of clams in four periods of the year. These measurements were accomplished with the monthly survey of the gametogenic stages, condition index, proteins, glycogen, total lipids, pH and osmolarity of hemolymph. Arsenic, Cu, Mn, V, Cr and Pb were preferentially linked to the digestive gland, while Cd was linked to the gills. TE concentrations in the digestive gland and remaining tissues were higher in winter, most likely reflecting additional inputs associated with rain. The lack of disruptions in biological parameters and the prolonged period of spawning and gonad recovery in clams suggest that the current TE availability in the lagoon has a minor influence on the reproductive cycle and hence on clam production.Para examinar en qué medida las actividades humanas cercanas a la laguna costera ría Formosa influyen en la acumulación de elementos traza (ET) en Ruditapes decussatus, se trasplantaron individuos desde un banco natural situado en la parte baja de la laguna a tres sitios localizados en zonas de cultivo de almejas bajo la influencia de una ciudad pequeña (Faro), un centro piscícola (Olhão) y cerca de la entrada de una laguna (Lavajo). Se determinaron las concentraciones de ET en el substrato de locales y en la glándula digestiva, branquias, manto más sifones, y en los tejidos restantes de las almejas en cuatro períodos a lo largo de un año. Estas mediciones fueron realizadas con el estudio mensual de las etapas gametógenas, índice de condición, proteínas, glicóneo, lípidos totales, pH y osmolaridad de la hemolinfa. El As, Cu, Mn, V, Cr y Pb fueron relacionados preferencialmente a la glándula digestiva, mientras que el Cd fue a las branquias. La concentración de ET en la glándula digestiva y los tejidos restantes fue más elevada en invierno, probablemente reflejando los aportes adicionales asociados con la lluvia. La falta de alteraciones de los parámetros biológicos, el período prolongado de desove y la recuperación de las gónadas en las almejas sugieren que la disponibilidad actual de ET en la laguna tienen una influencia menor durante el ciclo reproductivo y, por lo tanto, en la producción de almejas

Effect of the alveolate parasite Perkinsus olseni infection on sexual maturation and spawning efficiency of the clam Ruditapes decussatus

The effect of Perkinsus olseni infection on the reproduction ability of clams has been underestimated so far. Although some studies found evidence of reduction of egg production and delay in gonad maturation after infection, the total effect of the infection is still unclear. In this study, Ruditapes decussatus clams from a naïve population were injected with two different doses of P. olseni parasites, a low dose leading to a light infection and a high dose leading to a heavy infection. Clams were maintained during 2 months for maturation, and at the end of the experiment, the spawning was induced, the number of larvae release and mortality were evaluated. During the maturation period, infection level, gonadal stage, condition index, gross biochemical composition and oxidative status of progenitors were evaluated at days 0, 30 and 60 post-injection. The effects of P. olseni infection on clams showed alterations on biochemical parameters, namely lipid peroxidation, a significant mortality and a delayed gonad maturation, with a greater effect in the highly infected individuals. The reproductive capacity of the clams was impaired in both infected groups showing a lower production and a higher mortality rate of larvae. Finally, this study indicates that the production of natural beds with a high prevalence of P. olseni could be compromised by a deregulation of the natural reproduction cycle and a decrease in larvae production by infected animals, probably due to a combination of lower egg production and lower lipid reserves in larvae from infected clams

Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)

Although the bivalve dredge used on the Algarve coast (southern Portugal) is highly selective for the target species, in some periods of the year the bycatch can exceed the catch of the commercial species. The present study aimed to quantify the bycatch and discards, estimate damage and mortality, and propose management measures to minimize discards and mortality. A total of 15 fishing surveys (60 tows) were performed using two types of dredges (“DDredge” targeting Donax trunculus and “SDredge” targeting Spisula solida and Chamelea gallina). Of the 85257 individuals (392.4 kg) of 52 taxa that were caught, 73.4% belonged to the target species, 22.1% to commercially undersized target species and 4.5% to bycatch species. Bycatch rates were lower for SDredge (13.5% in number and 6.3% in weight) than for DDredge (46.0% in number and 32.9% in weight). Damage and mortality rates were also lower using SDredge (1.3% and 1.0% of the total catches, respectively) than using DDredge (4.0% and 2.8% of the total catches). Survival experiments revealed the diverse vulnerability of the taxa and confirmed the influence of the damage score on the mortality rate. The results gathered in the present study encourage the adoption of a bycatch reduction device to reduce both direct and indirect mortality.This study was performed within the framework of the research project “Science Technology and Society Initiative to Minimize Unwanted Catches in European Fisheries (MINOUW)” funded by the Research and Innovation Action (RIA) of the EU Horizon 2020 programme.info:eu-repo/semantics/publishedVersio

Rebuilding viable spawner patches of the overfished Spisula solida (Mollusca : Bivalvia): a preliminary contribution to fishery sustainability

Populations of commercially important bivalves along the coast of Portugal are depleted as a consequence of natural and anthropogenic causes. A pilot experiment was designed to determine the feasibility of transplanting individuals from natural clam beds to a closed fishing area in an effort to rebuild relatively high-density patches of Spisula solida. For this purpose, clams were equally partitioned into two groups (undersize and legal clams) and transplanted at a density of 40 clams m(-2) into two areas 50 m(2). Transplanted and control clams were sampled to estimate survival, condition index, biochemical composition, and reproductive condition. Generally, the physiological condition of clams was not affected by the method of transplanting. One year after transplanting, survival was 45%. The increase in local abundance of mature clams should facilitate successful fertilization and increase the residual reproductive value of each clam relative to its pre-transplant value. Transplanting undersize clams may be more advantageous because they are more likely to spawn at least once before harvest. The experiments demonstrate that spawner transplants may strengthen S. solida populations and can be used in stock-enhancement programmes which, in conjunction with effective management measures, can contribute to the sustainability of the S. solida fishery.info:eu-repo/semantics/publishedVersio