Near-bottom zooplankton over three seamounts in the east Canary Islands: Influence of environmental variables on distribution and composition.

Abstract The near-bottom zooplankton over three seamounts of the eastern Canary Islands (Amanay, El Banquete and Concepcion) was analyzed, identifying the environmental variables that explain biomass distributions over them. Zooplankton composition changed between adjacent water masses, except for the two deepest assemblages associated with Atlantic Antarctic Intermediate Water (AAIW) and Mediterranean Water (MW). The highest biomass of total zooplankton and of main taxa (e.g. copepods, chaetognaths, siphonophores) were recorded at the seamount summits, i.e., over Amanay-El Banquete (summit depths of 23–24 m) associated with Surface Water (SF) and over Concepcion (150 m) in upper levels of the North Atlantic Central Water (NACW). Biomass minima at the three banks were found at ca. 250–650 m, in the deepest levels of NACW. At ca. 700–1000 m (the level occupied by AAIW) and below 1000 m (MW level) biomass increased again. Near-bottom fluorometry (f5mab, 5 m above bottom) and dissolved oxygen (O2 5mab) were the main variables explaining changes of total zooplankton/main taxa biomass. Biomass minima (250–650 m) coincided with decreases of O2 5mab (3.30–3.99 ml/l at 400–700 m) at deepest depths occupied by NACW. Other variables not included in our models like turbidity (resuspension of particles) may have locally enhanced zooplankton aggregation, as they may locally occur alongside Concepcion at the NACW-AAIW confluence (at ca. 700 m), probably from the effects of internal waves. Our results suggest that observations regarding the attraction of organisms to the stationary substrates of seamounts could be related to elevated chlorophyll fluorescence and O2 5mab concentration. Peaks in those variables apparently enhance zooplankton aggregation.