Variation in mesopelagic fish community composition and structure between Mediterranean and Atlantic waters around the Iberian Peninsula

Mesopelagic fish populations are characterised by high species richness and abundance, have been identified as important contributors to the active carbon fluxes in open ocean. We report variability communities of mesopelagic between five zones around Iberian Peninsula, i.e. Balears Alboran Mediterranean, Cadiz, Lisboa Galicia Atlantic. Day night samples were collected from 7 layers water column with a midwater trawl fitted multisampler. Temperature salinity regimes very different on Mediterranean Atlantic sides peninsula, much higher values through entire characterized strong pycnocline. The highest productivity was observed off Lisboa, where Chlorophyll concentrations two orders magnitude than any other zone. Samples western held 22 species, while 67 found lowest diversity dominance Balears, Cadiz In all zones, but particularly those dominated number small low individual biomasses. Benthosema glaciale , Cyclothone pygmaea Ceratoscopelus maderensis common populations, whereas Atlantic, microdon/livida Valenciennellus tripunctulatus warmingii suborbital e most species. (both at surface zone) main environmental factors explaining assemblage composition. A persistent (day-night) deep scattering layer using vessel-based echosounder comprised primarily gonostomatid spp. Night-time observations near Alboran, net collections indicated that Myctophidae, Stomiidae Phosichthyidae migration extended upper 100 m. Sternoptychids Sigmops elongatus seldom reached m their vertical migrations. Night stratified hauls 30 resolution carried out epipelagic zone showed abundances maxima migratory coincided location maxima.