Deep macrobenthic communities from Nazaré Submarine Canyon (NW Portugal)

Abstract

Macrofauna community structure within Nazaré Submarine Canyon is analysed and used to assess the potential effects of natural enrichment in this area subjected to accumulation of coastal sediments. A transect including three stations (2894, 3514 and 4141 m) was carried out in the Nazaré Submarine Canyon (NW Portugal) during a cruise of OMEX II programme (Ocean Margin Exchange), in the winter season of 1999. Although data was not collected in order to calculate sedimentation rates, sampling station at 2894 m is located in an area characterised by high levels of sedimentation, thus a high amount of organic matter is expected to be available for the local communities. Faunistic data are discussed in the context of the different features of the stations sampled. Multivariate analysis clearly separates the shallowest station from the other ones, which otherwise appear to be very similar. It also revealed a perceptible gradient along sediment depth at all stations, from shallow to deeper layers. Exceptionally depressed species richness and low evenness values were observed at the 2894 m station. The high number of individuals of a single species, Cossura sp. A, and the atypical diversity, dominance and evenness values obtained for this station support the hypothesis of community disturbance due to organic enrichment.Key words: Deep sea; submarine canyons; NE Atlantic; macrobenthos; community structure; natural organic enrichment RESUMEN: COMUNIDADES MACROBENTÓNICAS PROFUNDAS DEL CAÑÓN SUBMARINO DE NAZARÉ (NW PORTUGAL). -Se analiza la estructura de la comunidad de la macrofauna del cañón submarino de Nazaré y se utiliza para evaluar los efectos potenciales del enriquecimiento natural de esta área sometida a la acumulación de sedimentos costeros. Se realizó un transecto que incluía tres estaciones (2894, 3514 y 4141 m) en el cañón submarino de Nazaré (NW de Portugal), durante una campaña del programa OMEX II (Ocean Margin Exchange), en el invierno de 1999. Aunque no se han obtenido datos para calcular tasas de sedimentación, la estación de muestreo a 2894 m está situada en un área caracterizada por niveles elevados de sedimentación, de modo que es esperable que haya una gran cantidad de materia orgánica disponible para las comunidades locales. Los datos faunísticos se comentan en el contexto de las distintas características de las estaciones muestreadas. El análisis multivariante separa claramente la estación más somera de las otras, que parecen ser muy parecidas entre sí. También revela un gradiente perceptible a lo largo del grosor del sedimento en todas las estaciones, desde las capas someras a las más profundas. En la estación de 2894 m se observaron valores excepcionalmente bajos de riqueza específica y bajos de equitatividad. El elevado número de individuos obtenidos en esta estación refuerza la hipótesis de perturbación de la comunidad debido a enriquecimiento orgánico.Palabras clave: océano profundo, cañones submarinos, Atlántico NE, macrobentos, estructura de la comunidad, enriquecimiento orgánico nat...

Biodiversity of macrofaunal assemblages from three Portuguese submarine canyons (NE Atlantic)

“…Peak or increased densities are often observed at intermediate depths (e.g. at 2560 m in Campeche Canyon, Escobar Briones et al, 2008; at 2715 m in the Whittard Canyon; Duineveld et al, 2001; at 2894 m in Nazaré Canyon, Curdia et al, 2004). In this study, higher densities were encountered consistently in the middle of all three Portuguese canyons (Nazaré : 3461-3522 m; Cascais: 3199-3219 m; Setú bal: 3224-3275 m).…”

“…There are some reports that submarine canyons may yield characteristic and unique faunas, but more often canyon macrofaunal assemblages show high dominance and biodiversity may be reduced locally (Rowe, 1971;Gage et al, 1995;Rogers et al, 2002;Curdia et al, 2004). In their lower sections, where canyons meet the abyssal plain, the faunal assemblages tend to be more similar to the ones in the surrounding environments.…”

Deep-sea scavenging amphipod assemblages from the submarine canyons of the Western Iberian Peninsula

“…The mouths of these rivers flow directly into the canyon heads. Estuarine input results in large quantities of terrigenous organic matter entering the canyon system (Cúrdia et al, 2004). The extent to which this material travels down these two canyons is thought to be limited, in comparison to Nazaré, owing to the rarity of large-scale episodic events, which are a particular feature of down-canyon sediment transport .…”

“…They experience heightened levels of sediment input, with active submarine canyons acting as downward conduits for matter that has been transported along the continental shelf (Vetter and Dayton, 1998). This effect is often amplified in the presence of contributory river systems Cúrdia et al, 2004). Elevated sediment input carries with it substantial quantities of organic matter , providing food for deep-sea scavengers (Sorbe, 1999).…”

An insight into the feeding ecology of deep-sea canyon nematodes — Results from field observations and the first in-situ 13C feeding experiment in the Nazaré Canyon

“…However, because the canyon intersects a large part of the shelf it entraps large quantities of sediment moving along the Portuguese coast and so is recognised as a major sediment pathway among European canyons (Tyler et al, 2009). Besides high rates of sedimentation, OM transport, entrapment, and burial, the Nazaré canyon is hydrodynamically very 20 active and its heterogeneous topography contributes to a complex current regime within, and even beyond, the canyon's borders (Tyler et al, 2009) with significant impacts on the canyon fauna (Curdia et al, 2004;Garcia et al, 2007;Ingels et al, 2009;Koho et al, 2007). Terraces in the middle canyon area are draped in thick layers of muddy turbidites creating a distinct depot centre with little sediment passing beyond the middle canyon section .…”