In situ observations show vertical community structure of pelagic fauna in the eastern tropical North Atlantic off Cape Verde

H J T Hoving,A Körtzinger,P Neitzel,R Kiko,B H Robison,P Silva,S Christiansen,H Hauss

doi:10.1038/s41598-020-78255-9

Abstract

Distribution patterns of fragile gelatinous fauna in the open ocean remain scarcely documented. Using epi-and mesopelagic video transects in the eastern tropical North Atlantic, which features a mild but intensifying midwater oxygen minimum zone (OMZ), we established one of the first regional observations of diversity and abundance of large gelatinous zooplankton. We quantified the day and night vertical distribution of 46 taxa in relation to environmental conditions. While distribution may be driven by multiple factors, abundance peaks of individual taxa were observed in the OMZ core, both above and below the OMZ, only above, or only below the OMZ whereas some taxa did not have an obvious distribution pattern. In the eastern eropical North Atlantic, OMZ expansion in the course of global climate change may detrimentally impact taxa that avoid low oxygen concentrations (Beroe, doliolids), but favour taxa that occur in the OMZ (Lilyopsis, phaeodarians, Cydippida, Colobonema, Haliscera conica and Halitrephes) as their habitat volume might increase. While future efforts need to focus on physiology and taxonomy of pelagic fauna in the study region, our study presents biodiversity and distribution data for the regional epi- and mesopelagic zones of Cape Verde providing a regional baseline to monitor how climate change may impact the largest habitat on the planet, the deep pelagic realm.

Highlights

The meso, bathy- and abyssopelagic ocean—the water column below the sunlit euphotic zone—is the largest biome for multicellular organisms on the planet, and is the habitat with the highest faunal biomass as well as the greatest number of individual organisms[1,2]
We provide high resolution baseline data on vertical distribution patterns of pelagic fauna in the Cape Verde region of the eastern Atlantic
These data contribute to the essential ocean variable “zooplankton biomass and biodiversity”, which is still relatively poorly documented, in particular in the Cape Verde region despite it being a hotspot of oxygen minimum e xpansion[88]

Summary

Introduction

The meso-, bathy- and abyssopelagic ocean—the water column below the sunlit euphotic zone—is the largest biome for multicellular organisms on the planet, and is the habitat with the highest faunal biomass as well as the greatest number of individual organisms[1,2]. The first trait is to efficiently extract oxygen from the water, the second is the ability to temporarily reduce metabolic rates when confronted with low oxygen partial pressures, and the third is to use anaerobic metabolism when necessary To facilitate these traits, organisms have evolved specific morphologies and behavioral patterns. Cephalopods and crustaceans inhabiting the OMZ may have increased gill surface area to facilitate oxygen uptake or have a relatively low metabolic r ate[17]. These organisms may visit the OMZ only temporarily, e.g. for hunting or refuge, and migrate back again to more oxygenated waters to compensate their anaerobic metabolic d ebt[18]. The expansion of the Atlantic OMZs has resulted in habitat reduction for billfish in the eastern tropical A tlantic[31]

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Discussion

Conclusion