Distribution and diversity of mesopelagic fauna on seamounts of the Madeira-Tore complex (Northeastern Atlantic)

Eva García-Seoane,Rui P Vieira,Ana Moreno,Rui M.A Caldeira,Cátia C Azevedo,Maria J Gaudêncio,Antonina Dos Santos

doi:10.1016/j.rsma.2020.101434

Abstract

Mesopelagic organisms play an important role in the vertical carbon flux through diel vertical migrations. The mesopelagic fauna of three NE Atlantic seamounts (Gorringe Bank, Josephine and Seine) and surrounding oceanic waters were sampled. Echogram scrutiny suggests a diel vertical migration of the mesopelagic fauna. Muggiaea atlantica and Meganyctiphanes norvegica were caught at almost every station and thus, appeared to be ubiquitous. Several taxa were only caught in open oceanic stations (e.g. Lampanyctus alatus, Deosergestes corniculum and Acanthephyra purpurea) whereas others appeared uniquely in the vicinity of the seamounts (e.g. Lophogaster sp., Systellapsis pelucida and most of the cephalopod species). Multivariate analyses, based on presence–absence data, indicated significant differences in the mesopelagic community structure among the different seamounts, and between oceanic and seamount waters. Higher species richness was found in oceanic waters compared to seamounts. No significant relationship was found between the environmental variables salinity and fluorescence and the biological data. Even so, the values of these oceanographic parameters over the seamounts are different from those in oceanic waters. Knowledge of diversity and distribution of mesopelagic fauna will improve our understanding of the pelagic realm.

Highlights

The mesopelagic zone, commonly referred as the twilight zone, is defined as the stratum of the ocean between 200 and 1000 m depth, where light is too low for photosynthesis but sufficient for vision to be effective in capturing prey (Gjøsæter and Kawaguchi, 1980; Robinson et al, 2010)
The aims of this paper are: (i) to describe the taxonomic composition of the mesopelagic community at Gorringe Bank, Seine and Josephine Seamounts and surrounding areas; (ii) to assess the diversity of the mesopelagic community on seamounts and surrounding oceanic deep waters; (iii) to investigate their spatial and vertical patterns and (iv) assess whether there is a relationship between the mesopelagic community composition and environmental variables
The physical characterization of the oceanic and seamount regions (Seine, Josephine and Gorringe Bank), along with the comparison among them were done through vertical profiles of density and fluorescence

Summary

Introduction

The mesopelagic zone, commonly referred as the twilight zone, is defined as the stratum of the ocean between 200 and 1000 m depth, where light is too low for photosynthesis but sufficient for vision to be effective in capturing prey (Gjøsæter and Kawaguchi, 1980; Robinson et al, 2010). Mesopelagic zooplankton and micronekton feed in near-surface waters at night, and migrate to greater depths during day, excreting fecal pellets and dissolved organic matter that fuel pelagic and benthic biogeochemical cycles (Robinson et al, 2010). Mesopelagic fauna form the acoustic deep scattering layer, a strong and ubiquitous sound-reflecting layer in the open ocean (Davison et al, 2013). Fishes are an important subcategory of mesopelagic micronekton, which probably dominates the world total fish biomass (Irigoien et al, 2014)

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