Activity and composition of the benthic fauna in the Whittard Canyon and the adjacent continental slope (NE Atlantic)

Abstract

We compared the sediment and its community on the Celtic continental slope (Goban Spur) with those in a branch of the nearby Whittard Canyon in search for evidence of canyon mediated transport of (labile) organic matter. We studied the megabenthos and macrobenthos biomass and taxonomic composition, measured in situ sediment community oxygen consumption and determined sediment concentrations of particulate organic carbon, phytopigments, and nucleic acids. While the sediment community and activity on the canyon fan was similar to that on the abyssal station near Goban Spur, the sediment within the canyon had relatively enhanced sediment community oxygen consumption rates and higher levels of phytopigments, particulate organic carbon and nucleic acids, particularly towards the canyon head. However, near-bottom sediment traps and transmissometre readings gave no sign of enhanced particle fluxes. Most likely this enrichment is supplied periodically through lateral transport as suggested by increased numbers of filter-feeding macrobenthos. Markedly higher concentrations of sedimentary pigments were found in a second branch of the Whittard Canyon illustrating the complexity of canyon systems and the need for a much more extensive study. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Activité et composition de la faune benthique dans le canyon de Whittard et la pente continentale celtique voisine. Nous avons comparé le sédiment et sa communauté de la pente continentale celtique (Goban Spur) avec ceux d'une branche du canyon voisin de Whittard, pour mettre en évidence le transport relatif de matière organique (labile) par le canyon. Nous avons étudié la biomasse et la composition taxonomique du megabenthos et du macrobenthos, mesuré la consommation d'oxygène in situ de la communauté sédimentaire, et déterminé les concentrations de carbone organique particulaire, des pigments végétaux et des acides nucléiques. Alors que la communauté sédimentaire et l'activité au pied du canyon sont similaires à la station abyssale près de Goban Spur, le sédiment du canyon présente une consommation d'oxygène plus élevée, et des concentrations supérieures de pigments végétaux, de carbone organique particulaire et d'acides nucléiques, particulièrement vers la tête de canyon. Cependant, les données des pièges à particule et les mesures de transmission près du fond n'indiquent pas un rehaussement du flux de particules. Cet enrichissement périodique est dû au transport latéral, comme l'indiquent les densités supérieures de macrobenthos à régime alimentaire de filtreurs. Des concentrations de pigments nettement plus élevées ont été trouvées dans une deuxième branche du canyon de Whittard, ce qui illustre la complexité des systèmes de canyon et la nécessité d'une étude beaucoup plus approfondie.

Distribution of cold-water corals in the Whittard Canyon, NE Atlantic Ocean

“…It funnels organic matter to depth via a variety of mechanisms including tidal currents, internal waves and turbidity flows (Duineveld et al, 2001;Quaresma et al, 2007). The greater hydrodynamic activity in the canyon leads to an increase in organic matter input and increased food quality within the canyon in comparison to less active areas on the open continental slope.…”

“…The canyon floor is sediment-covered with very little exposed rock, other than on the extreme walls (Reid and Hamilton, 1990). Duineveld et al (2001) found that the POC concentrations were higher in the canyon than in the surrounding open slope areas, indicating organic enrichment within the canyon. The surface waters of the upper reaches of the canyon have relatively high biological productivity because of nutrient upwelling along the Celtic Shelf edge (Wall et al, 2010), resulting in increased nutrient transport through the canyon via mechanisms such as internal wave formation and turbidity flows.…”

“…The Whittard Canyon extends from the upper slope to abyssal depths, varying in depth between 200 and 4000 m (Duineveld et al, 2001), with two main branches (Fig. 1).…”

Sediment community responses to marine vs. terrigenous organic matter in a submarine canyon

“…Canyon sediments receive increased POM inputs via both vertical transport, through the water column, and lateral transport, through slope processes. Consequently, canyons may support higher bacterial and faunal densities than surrounding bathyal and abyssal sediments (Vetter and Dayton, 1998;Duineveld et al, 2001;EscobarBriones et al, 2008;De Leo et al, 2010;Cunha et al, 2011). In the Whittard Canyon (Northeast Atlantic), Duineveld et al (2001) report enhanced sediment community oxygen consumption (SCOC) within canyon sediments.…”

The trophic biology of the holothurian <i>Molpadia musculus</i>: implications for organic matter cycling and ecosystem functioning in a deep submarine canyon

“…Deep-sea submarine canyons host hotspots of OM and biomass (Gage et al, 1995;Vetter and Dayton, 1998;Duineveld et al, 2001;Bianchelli et al, 2008;Ingels et al, 2009;Tyler et al, 2009;de Leo et al, 2010;Pusceddu et al, 2010;Vetter et al, 2010). Within canyons, biodiversity is high as a result of their topographic complexity and spatio-temporal variability (Bianchelli et al, 2008;Ingels et al, 2009;Tyler et al, 2009;Vetter et al, 2010).…”