RRS Charles Darwin Cruise 179, 14 Apr - 17 May 2006. Hotspot ecosystem research in the Setúbal, Lisbon, Cascais and Nazaré canyons on the Portuguese continental margin

Abstract

RRS Charles Darwin Cruise 179 was one of a series of cruises studying the biology, geology, biogeochemistry and physical oceanography of the Portuguese margin canyons. The cruise contributed to the European Union Framework Programme VI Integrated Project HERMES (Hotspot Ecosystem Research on the Margins of European Seas). Four key canyon areas on the European margin are being studied in HERMES: the Portuguese margin, the Irish margin and the Western and Eastern Mediterranean. On the Portuguese margin four canyons had been selected for multidisciplinary studies by the HERMES community: the Nazaré Canyon, Setúbal Canyon, Lisbon Canyon and the Cascais Canyon.

RRS Charles Darwin cruise 179 was divided into two legs (Cartagena to Lisbon, 14 April to 1 May 2006; Lisbon to Falmouth, 1 to 17 May 2006). Leg 1 focused on the upper and middle parts of the Setúbal and Lisbon canyons, which join together at a depth of about 2000m, and the upper and middle Cascais Canyon. Leg 2 sampled the lower Cascais and Setúbal canyons and a wide variety of depths in the Nazaré Canyon. The principal sampling activities were seabed photographic and video imaging (NOCS SHRIMP system), deep-tow 30 kHz sidescan sonar imaging (NOCS TOBI system), coring (Megacorer, Piston Corer and Box Corer), trawling (Agassiz Trawl), and benthic boundary layer particulate biogeochemistry using CTD-mounted Stand Alone Pump Systems (SAPS).

Seabed photo-transects at depths between 300 and 4500m confirmed that large parts of all the canyons were covered in a sediment drape, with little evidence of epifaunal megafauna within the canyon axis, but with localised communities of suspension feeding sponges, cnidarians (soft and stony corals), crinoids and asteroids on rocky ledges around the thalweg (central channel) of the canyons. Photo-transects across the thalwegs of the canyons revealed fascinating changes in the nature of the seabed (e.g. ripple patterns) and fauna (e.g. xenophyophores (giant protozoans) on the flanks of the Nazaré Canyon thalweg). New sidescan sonar images were obtained of the Lisbon and Cascais canyons and the base of the continental slope in the vicinity of the Cascais and Setúbal canyons. Coring and trawling focused on comparable sites at c. 3400m and 4400m in the lower canyons. Burrowing holothurians were evident in all three canyons at c. 3400m, but only in the Nazaré Canyon were they superabundant.

This was the penultimate scientific cruise of RRS Charles Darwin. The ship has given UK and European marine science many years of excellent service. She will be greatly missed, and will be succeeded by RRS James Cook in 2006.

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