Vertical distribution of zooplankton and active flux across an anticyclonic eddy in the Canary Island waters

Abstract

The vertical distribution (0–900 m) of zooplankton biomass and indices of feeding (gut fluorescence, GF) and metabolism (electron transfer system, ETS) were studied across an anticyclonic eddy south of Gran Canaria Island (Canary Islands). Two dense layers of organisms were clearly observed during the day, one above 200 m and the other at about 500 m, coincident with the deep scattering layer (DSL). The biomass displacement due to interzonal migrants in the euphotic zone was more than 2-fold higher than that previously reported for the southern area of this archipelago. The gut flux estimated (0.14–0.44 mgC m−2 d−1) was similar to the values previously found in the Canaries. The respiratory flux outside the eddy (1.85 mgC m−2 d−1) was in the lower range of values reported for this area. Inside the eddy, migrant biomass and respiration rates were 2- and 4- fold higher than in the surrounding waters. Active flux mediated by diel vertical migrants inside the eddy (8.28 mgC m−2 d−1) was up to 53% of the passive carbon flux to the mesopelagic zone (15.8 mgC m−2 d−1). It is, therefore, suggested that the anticyclonic eddy enhanced both migration from deep waters and active flux.