Akashiwo sanguinea blooms and anoxia and mass mortality of fish and invertebrate during the 2023–2024 spring-summer "El Niño" in Perú

A description is provided of an exceptional bloom of Akashiwo sanguinea, detailing its geographic extent and duration, as well as its association with anoxic events and mass mortalities of marine fish and invertebrates. Significant economic losses were incurred by the main shellfish producers. This episode occurred in the epicentre of the Humboldt Current Upwelling System in Peru, following an intense El Niño Southern Oscillation (2023–2024) characterised by positive temperature anomalies relative to the historic mean.