Vertical and small-scale horizontal distribution of cephalopods in the Charlie-Gibbs Fracture Zone of the Mid-Atlantic Ridge

In summer 2009, NOAA surveyed the nekton fauna of the fracture zone on the Mid-Atlantic Ridge halfway between Iceland and the Azores as a small-scale follow-up to a previous large-scale Norwegian expedition. Midwater sampling with a Norwegian Krill Trawl resulted in 64 discrete-depth samples from 12 stations at depths from near-surface to 3000 m. Seven additional bottom samples were collected with a large trawl at depths of 2000-3500 m. The expedition collected 416 cephalopods in ca. 19 species in the vicinity of the fracture zone. Over 50 hrs of ROV video from the Norwegian expedition was also viewed to determine diel migratory patterns of the most common species of cephalopod in the region, Gonatus steenstrupi, for comparison with the NOAA trawl data. We found that trawl stations southeast of the Subpolar Front were generally most diverse. Cluster analysis showed that midwater trawls were more similar in species composition than bottom trawls. Unlike in the ROV observations, the small G. steenstrupi from trawl samples did not appear to participate in diel vertical migration, suggesting that trawl-caught juveniles are ecologically distinct from those visible in submersible videos.