A tale of two canyon systems : Gollum and Whittard

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Temporal and spatial meiofauna patterns in the Nazaré Submarine Canyon, Northeast Atlantic.

Submarine canyons are characterized by highly heterogeneous habitats, topography and hydrography with enhanced organic matter input. These factors have a profound effect on canyon faunal communities in time and space. As part of the HERMES project, one of the largest European canyons, the Nazaré canyon was sampled in spring-summer in three consecutive years (2005, 2006, 2007), permitting the study of inter-annual patterns in meiofaunal communities at two contrasting habitats at 3500 and 4300 m water depth. Meiofauna standing stocks and structural and functional diversity were investigated in relation to biogeochemical sediment data. Substantially increased sediment sand content in 2006 and consistent phytodetritus levels indicated the occurrence of one or more deposition events between the 2005 and 2006 sampling events. Nematode standing stocks and trophic diversity decreased in the 2006 samples, seemingly followed by a recovery period as observed by community patterns in 2007, when communities were strongly correlated with the increase of quality and bioavailability of the organic matter supplied. Nevertheless, inter-annual variations were not the main driver for the faunal communities; the depth effect on the faunal communities was greater. The community differences between the sampled habitats were markedly greater than what was caused by inter-annual variation, likely because of the contrasting hydrodynamic and food supply conditions. The higher meiofauna/nematode abundances, biomass, and trophic complexity at the 3500 m station, compared to the 4300 m station, was related to the higher food supply, and greater quality and bioavailability at the 3500 m site

High spatiotemporal variability in meiofaunal assemblages in Blanes Canyon (NW Mediterranean) subject to anthropogenic and natural disturbances

14 páginas, 6 tablas, 4 figurasWe investigated the natural and anthropogenic drivers controlling the spatiotemporal distribution of the meiofauna in the submarine Blanes Canyon, and its adjacent western slope (NW Mediterranean margin of the Iberian Peninsula). We analyzed the relationships between the main sedimentary environmental variables (i.e. grain size, Chl-a, Chl-a: phaeopigments, CPE, organic carbon and total nitrogen) and the density and structure of the meiofaunal assemblages along a bathymetric gradient (from 500 to 2000 m depth) in spring and autumn of 2012 and 2013. Twenty-one and 16 major taxa were identified for respectively the canyon and slope, where the assemblages were always dominated by nematodes. The gradual decreasing meiofaunal densities with increasing depth at the slope showed little variability among stations and corresponded with a uniform pattern of food availability. The canyon was environmentally much more variable and sediments contained greater amounts of food resources (Chl-a and CPE) throughout, leading not only to increased meiofaunal densities compared to the slope, but also different assemblages in terms of composition and structure. This variability in the canyon is only partly explained by seasonal food inputs. The high densities found at 900 m and 1200 m depth coincided with significant increases in food availability compared to shallower and deeper stations in the canyon. Our results suggest that the disruption in expected bathymetric decrease in densities at 900–1200 m water depth coincided with noticeable changes in the environmental variables typical for disturbance and deposition events (e.g., higher sand content and CPE), evoking the hypothesis of an anthropogenic effect at these depths in the canyon. The increased downward particle fluxes at 900–1200 m depth caused by bottom trawling along canyon flanks, as reported in previous studies, support our hypothesis and allude to a substantial anthropogenic factor influencing benthic assemblages at these depths. The possible relationships of the observed patterns and some major natural environmental (e.g., surface productivity or dense shelf water cascading) and anthropogenic (e.g. the lateral advection and downward transport of food-enriched sediments resuspended by the daily canyonflank trawling activities) drivers are discussed.This research has been supported by DOS MARES (Ref. CTM2010-21810-C03-03) research project, funded by the Spanish State Research Plan, and to the Consolidated Research Group on Marine Benthic Ecology of the “Generalitat de Catalunya (2014SGR120)”. C. Romano received funding from the People Programme (Marie Curie Action) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement N. PIOF-GA-2013-628146. J. Ingels was supported by a Plymouth Marine Laboratory Post-doctoral Research Fellowship in collaboration with University of Exeter and a Marie Curie Intra-European Fellowship within the 7th European Commission Framework Programme (Grant Agreement FP7-PEOPLE-2011-IEF no. 00879).Peer reviewe

Distribution of Meiofauna in Bathyal Sediments Influenced by the Oxygen Minimum Zone Off Costa Rica

Ocean deoxygenation has become a topic of increasing concern because of its potential impacts on marine ecosystems, including oxygen minimum zone (OMZ) expansion and subsequent benthic effects. We investigated the influence of oxygen concentration and organic matter (OM) availability on metazoan meiofauna within and below an OMZ in bathyal sediments off Costa Rica, testing the hypothesis that oxygen and OM levels are reflected in meiofaunal community structures and distribution. Mean total densities in our sampling cores (400–1800 m water depth) were highest with 3688 ind. 10 cm−2 at the OMZ core at 400 m water depth, decreasing rapidly downslope. Nematodes were overall dominant, with a maximum of 99.9% in the OMZ core, followed by copepods (13%), nauplii (4.8%), and polychaetes (3%). Relative copepod and nauplii abundance increased consistently with depth and increasing bottom-water O2. Meiofaunal composition was significantly different among sites, with lower taxonomic diversity at OMZ sites relative to deeper, oxygenated sites. Vertical distribution patterns within sediments showed that in strongly oxygen-depleted sites less meiofauna was concentrated in the surface sediment than at deeper slope sites. Highest meiofaunal abundance and lowest diversity occurred under lowest oxygen and highest pigment levels, whereas highest diversity occurred under highest oxygen-concentrations and low pigments, as well as high quality of sedimentary pigment (chl a/phaeo) and organic carbon (C/N). The lower meiofaunal diversity, and lower structural and trophic complexity, at oxygen-depleted sites raises concerns about changes in the structure and function of benthic marine ecosystems in the face of OMZ expansions