The submarine volcano eruption off El Hierro Island: Effects on the scattering biota and the evolution of the pelagic community

Abstract

The submarine volcano eruption off El Hierro Island (Canary Islands) occurring on 10th October 2011 promoted dramatic perturbations in the water column leading to changes in the pelagic fauna. In order to study the response of the scattering biota, we combined acoustic data with hydrographic profiles and concurrent sea surface turbidity indexes from satellite imagery. We also monitored the evolution of the plankton and nekton communities through the eruptive and post-eruptive phases. Decrease of oxygen, acidification, rising temperature and dumping of chemicals in shallow waters resulted in a reduction of epipelagic stocks and a disruption of diel vertical migration (nocturnal ascent) of mesopelagic organisms. Futhermore, decreased light levels at depth caused by extinction in the volcanic plume resulted in a significant shallowing of the deep acoustic scattering layer. Once the eruption ceased, the pelagic biota restored to baseline levels, but no evidence of a volcano-induced bloom was apparent in the plankton community.