Changes in phytoplankton vertical distribution during an El Niño event

The west coast of South America is a very productive oceanic region due to cold, nutrient-rich upwelled waters. This region experiences periodic El Niño events that cause a deepening of the thermocline along with the prevalence of warm nutrient-poor superficial water. Sampling conducted during a weak El Niño event in 2014 allowed us to identify changes in phytoplankton vertical distribution at superficial waters along 8 miles offshore the Ecuadorian coast. As such, it was found that phytoplankton mainly occurred at near-surface waters rather than at 10 m depth after the onset of El Niño in terms of both abundance and species richness. The shift in vertical distribution was interpreted as a result of the trapping of cells in a surface layer formed by the stratification of the water column associated with El Niño events. This finding opens the possibility of developing a potential new El Niño indicator.