The eruptive process that took place in October 10th 2011 at the island of El Hierro (Canary Islands), gave rise to the novel submarine volcano Tagoro, at 1.8 km south of the island of El Hierro in the marine reserve of “El Mar de las Calmas” (Canary Islands). In order to monitor the impact of the eruption on the marine ecosystem, several multidisciplinary oceanographic cruises were carried out in the affected area. Here we present a detailed study of the dissolved oxygen parameter with data collected in two oceanographic cruises during the eruptive stage. The findings highlight how the emission of reduced species produced by the submarine volcano Tagoro during the eruptive stage generated dissolved oxygen concentrations close to anoxic levels. Maximum oxygen depletion of 86.2% and 92.4% were found in Leg3 and Leg5 cruises respectively. These perturbations affect not only the marine reserve off El Hierro Island but also affect further areas, as it is transported by local currents to the north of the island producing a depletion of 17.7%. Moreover, our results show a volcanic plume with low dissolve oxygen concentration being trapped and transported by an anticyclonic eddy for tens of kilometres (oxygen depletion of approximately 5%). Finally, the Apparent Oxygen Utilization (AOU) parameter by definition should not be taken into account regarding submarine volcanic areas and the interpretation of this parameter should be made with caution. Keywords: dissolved oxygen; hydrothermal vent; submarine volcano; Tagoro submarine volcano.