Mesopelagic fishes across the tropical and equatorial Atlantic: Biogeographical and vertical patterns

• Published in: Progress in oceanography 2017-02, Vol.151, p.116-137
• Main Authors: Olivar, M. Pilar, Hulley, P. Alexander, Castellón, Arturo, Emelianov, Mikhail, López, Cristina, Tuset, Víctor M., Contreras, Tabit, Molí, Balbina
• Format: Article
• Language: English
• Subjects: Diel migration; Diversity; Hatchetfishes; Lanternfishes; Lightfishes; Midwater trawls; Water masses; Zoogeography
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2016.12.001

•The equatorial and tropical mesopelagic fish community is characterized by high species richness.•Association of mesopelagic fish assemblages with water masses of the mesopelagic layers.•No differences in diel migratory patterns despite hydrographic differences.•Mesopelagic migratory species are capable of traversing the oxygen minimum zone.•Some non-migratory fishes live in the oxygen minimum zone. In this investigation we analysed the changes in fish species occurrences and relative abundances across the tropical and equatorial Atlantic, and their vertical distribution patterns in relation to the different environmental scenarios. The study covers a wide region encompassing different water masses, and marked differences in productivity, from an oligotrophic zone close to the Brazilian coast, to a very productive upwelling region close to the Northwest African upwelling. Fishes were collected with a medium-sized midwater trawl (Mesopelagos), complemented by hauls made with a macrozooplankton net (MOCNESS). Species richness in the region was higher than in subtropical, temperate and cold regions. The total number of species and their overall abundance was lower in the stations closer to the Brazilian coast. Abundant species across the entire region were the gonostomatids Cyclothone alba, Cyclothone acclinidens, Cyclothone pallida and Cyclothone pseudopallida, the myctophid Lampanyctus alatus, the sternoptychid Sternoptyx diaphana, and the phosichthyid Vinciguerria nimbaria. The occurrences and abundances of C. parapallida, Lampanyctus nobilis and Lepidophanes guentheri were related to zones where AAIW waters occupied the mesopelagic layers, while other species such as Cyclothone livida and Polyipnus polli increased their abundance when AAIW disappears from their living depths. The presence of Eastern North Atlantic Central Water (ENACW) was associated with the occurrence of several myctophids (Benthosema glaciale, Ceratoscopelus maderensis, Diaphus holti, Diaphus rafinesquii, Hygophum hygomii, Lampanyctus crocodilus, Myctophum punctatum, Symbolophorus veranyi), and the gonostomatid Cyclothone braueri. In spite of the important differences in hydrographic features across the tropical and equatorial Atlantic, all stations showed either the general night migration into the epipelagic layers carried out by myctophids, phosicthyids, and some stomiids, or the presence of the several species of Cyclothone, sternoptychids and melamphaeids that remain in the mesop