Structure of deep-sea pelagic fish assemblages in relation to the Mid-Atlantic Ridge (45°–50°N)

Pelagic fishes from depths of 250 to 3200 m from 45°N to 50°N were sampled during a mid-Atlantic cruise in 1982. These clustered into 6 assemblages, which were related to the Mid-Atlantic Ridge, the continental shelf edge and oceanic habitats. Spatial distribution of clusters coincided with SST and surface chlorophyll patterns. Cluster distribution further coincided with published mid-depth hydrography indicating that hydrographic recirculation features were an important determinant of community structure. Over the ridge, Melamphaidae, Serrivomeridae, Stomiidae and Centrolophidae increased in abundance. Horizontally, the myctophid Benthosema glaciale indicated the transition from temperate-subtropical to temperate-subarctic waters. The gadid Micromesistius poutassou and the alepocephalid Xenodermichthys copei were characteristic species for the shallow shelf edge assemblage. Vertically, extended depth ranges were stated for assemblages above MAR and the southern leg, as indicated for the species Gonostoma bathyphilum, and Schedophilus medusophagus. This was further tested for the saccopharyngid Saccopharynx ampullaceus. The increase of gelatinous plankton feeders over the ridge, in particular for S. medusophagus, is discussed with respect to a probable increase of gelatinous plankton abundance in the area considered. An error model was developed to address the contamination problem with respect to non-closing devices.