Distribution of meiobenthos in the Nazare canyon and adjacent slope (western Iberian Margin) in relation to sedimentary composition

Abundance of metazoan meiofauna and foraminifera, and biomass and community structure of nematodes, were investigated in the benthic zone along the Nazare Canyon and adjacent continental slope in relation to concentration of organic matter and its suitability as a food source for the meiobenthos. The Nazare canyon sediments were richer in organic carbon (Corg), total nitrogen, and phytopigments than the adjacent open slope. In addition, phytodetritus was fresher in the canyon sediment than on the slope (higher chlorophyll a: phaeopigments). Nevertheless, the abundance of polychaetes, copepods, bivalves, nematodes, total metazoans, and nematode biomass were not always higher in the canyon than on the adjacent open slope. Lower densities occurred in the upper and middle canyon, and living benthic foraminifers were significantly more abundant on the adjacent slope. The stations in the upper and middle canyon contained infinitesimal numbers of foraminifers. Reduced diversity and evenness and high K-dominance of the nematode assemblages in the upper part of the canyon indicated environmental stress, perhaps related to high Corg content and sediment disturbance. Non-selective deposit-feeders dominated the nematode assemblages of the upper and middle parts of the canyon, whereas a more diverse trophic structure was found in the deeper parts and the open slope. Conditions in the upper and middle areas of the Nazare canyon are harsh, and only opportunistic organisms can survive there.