Irene Alejo

DISTRIBUTION OF BENTHIC FORAMINIFERA IN COARSE SEDIMENTS, RÍA DE VIGO, NW IBERIAN MARGIN

The distribution of live benthic foraminifera (>63 μm) in box core samples from coarse sediments of the Ria de Vigo (NW Iberian margin) is mainly related to food availability and bottom current range. Live benthic foraminifera are dominated by small forms (63–125 μm). Faunal densities and diversity values suggest that very coarse substrates provide a favorable settlement for live benthic foraminifera. It is suggested that microalgae or bacterial biofilms that colonize shell surfaces are the main food resource for foraminifera. During upwelling events, the food supply to the bottom increases and the environment is colonized by opportunistic species. Moderate- to low-velocity bottom currents favor such pathways. The upwelling not only enhances the density of benthic foraminifera, but also allows the arrival of new species from the shelf. Attached forms are related to relatively high-velocity bottom currents and free living forms to moderate- to low-velocity bottom currents. Live benthic foraminifera inhabit a wide range of sediment depths and are not restricted to the uppermost centimeter. Under relatively high-velocity bottom current regimes, the vertical distribution of live benthic foraminifera is controlled by current strength. In coarse sediments, attached forms commonly considered strict epifaunal, and inhabiting above the disturbance depth, are considered “pseudoepifauna.” Below the disturbance depth, the sediment is not affected by currents and a “true” infauna is recognized.

El efecto de exposición en el patrón sedimen- tario del sector submareal de tres playas en la Ría de Muros y Noia (NO de España)

En este trabajo se presenta la comparacion de los sedimentos superficiales de la plataforma proximal de tres complejos playeros situados en las inmediaciones de la embocadura de la Ria de Muros y Noia. En cada uno de ellos, se han identificado las distintas poblaciones sedimentarias en funcion de los analisis granulometricos realizados. La aplicacion de un analisis estadistico de componentes principales a las fracciones granulometricas, contenido en carbonatos y materia organica, ha permitido diferenciar poblaciones de muestras y la interpretacion sedimentaria de las mismas. Las diferencias observadas en la distribucion de las poblaciones sedimentarias de los tres complejos estudiados son una consecuencia del grado de exposicion de cada complejo al oleaje dominante y de la presencia de afloramientos rocosos sumergidos que ejercen un efecto barrera.