Crecimiento y contenido bioquímico comparativo de larvas en postflexión de sardina de tres zonas del Mediterráneo Occidental (Ebro, bahías de Almaría y Málaga)

Late larval stages of sardine (16-23 mm) were sampled during the 2003 spawning season in their nursery grounds located off the Ebro river mouth, on the Catalan coast, and in two bays of the Alborán Sea coasts, the Bay of Almería and the Bay of Málaga. The daily growth analysis of each sampled population revealed faster growth in the Ebro sardine larvae than in both of the Alboran Sea larval populations. This fact is supported by their greater content with age of DNA, RNA and protein. However, the significantly higher carbohydrate content of the Bay of Almería sardine larvae and a higher Fulton’s index, indicative of energy storage of individuals, in both of the sardine populations sampled in the Bays of Almería and Málaga show evident differences in the daily growth of the Alborán Sea larvae from those originating in the Ebro region. Late larval growth in the Alborán Sea sardine tends to favour an increase in body mass rather than in body length. This study hypothesises that the productivity pulses off the Alboran Sea coasts induced by the north and northwestern wind regimes may be responsible for the growth pulses observed in the otolith microstructure.Estados avanzados de larvas de sardina (de 16 a 23 mm) fueron muestreados durante el invierno de 2003 en zonas de alevinaje situadas en la desembocadura del río Ebro, en la costa catalana, y en las bahías de Almería y de Málaga, en las costas del Mar de Alborán. El análisis del crecimiento diario de cada población larvaria muestreada, evidencia un mayor crecimiento en las larvas procedentes del Ebro respecto a las nacidas en el Mar de Alborán. Esta observación se corrobora con un mayor incremento con la edad de los contenidos en DNA, RNA y proteínas de la población larvaria de sardina del río Ebro. Sin embargo, un contenido significativamente mayor de carbohidratos en la población de Almería, así como un mayor índice de Fulton, indicador de energía almacenada en un individuo, en ambas poblaciones del Mar de Alborán, evidencia una estrategia diferenciada de crecimiento de estas poblaciones larvarias con respecto a las procedentes del río Ebro. En consecuencia, las larvas de sardina del Mar de Alborán muestran una tendencia a crecer más en masa que en longitud, como lo evidencia el crecimiento relativo del peso seco, DNA, RNA y proteínas en relación con su longitud estándar. En este estudio se plantea la hipótesis de que los pulsos productivos en el Mar de Alborán, inducidos por el régimen de vientos de norte y poniente, pueden ser responsables de los pulsos de crecimiento larvario, como se evidencia en las microestructuras de los otolitos

Modelling paralytic shellfish toxins (PSTs) transfer and accumulation in populations of two planktonic grazers

A model was developed in this paper in order to study and compare the paralytic shellfish toxin (PST) transfer and accumulation of two different potential PST vectors in the planktonic community, the heterotrophic dinoflagellate in its red form Noctiluca scintillans and the copepod Acartia clausi. Different factors that influence the toxin transfer such as toxin synthesis, grazing on toxic and non-toxic food and population size of PST producers and vectors were considered in the model. Moreover, a laboratory experiment was conducted in order to calculate the detoxification rates of Noctiluca fed on Alexandrium catenella. According to the model results, the two grazers showed a significant difference mainly in the timing of the PST accumulation. Noctiluca exhibited a rapid response to the grazing of Alexandrium with high initial toxin accumulation, followed by a reduction to zero concentration of toxins in a period of almost two days. In contrast, Acartia showed a considerable delay in comparison to Noctiluca to accumulate the same amount of toxin in the population. This delay is linked to the slower reproduction rates that characterize the copepod. The range of the initial values used for the sensitivity analysis of the model is representative of the coastal environment of a Galician ria (embayment located at the NW of Iberian Peninsula), where the two grazers and Alexandrium may co-exist. The model for Acartia showed less sensitivity to these key parameters probably due to the time delay in accumulation of significant amount of toxins. Both grazers showed a rapid (50 h) reduction of ingested toxin, suggesting inefficiency to transfer toxins through predation in the food web