Abstract

Since 1972, Alexandrium catenella and Paralytic Shellfish Poison (PSP) for the Chilean fjords are known. This species in about three decades colonized the fjords from south to north (55° to 41°S), blooming at the northern end of the fjords, in 2002, 2006 and 2009, and restricted to south and southeast of the Chiloé Island waters. The last 2016 A. catenella autumn event occurred also in a different geographical area, spreading for the first time to the Pacific Ocean coastal zone and extending its distribution from the southernmost of Chiloé Island (43°S) to Mehuin (39°S). The event lasted about 6 weeks, densities grew up to 5,000 cells ml-1 and PSP reached 15,000 ug STX eq. 100 g-1. Evidences linking this bloom and the 2015-16 El Niño, are presented. These include a southward displacement and prolonged maintenance of the Pacific anticyclone determining a declination of bad weather fronts, high radiation, rainfall absence and high temperatures. In addition, an increase of southerly winds favored coastal upwelling events raising nutrient-rich and poor in oxygen waters. These conditions triggered an intense and extended phytoplankton bloom between 37°S and 47°S at the end of March and mid-April 2016. Afterwards, during the upwelling relaxation, the A. catenella bloom in the final phase of the phytoplankton succession occurred, in waters with an increased stability, calm period, high radiation, and relative high temperatures in shallow waters. The inoculum would have come from the southeast of Chiloé Island and its entry into the Pacific Ocean, would resulted from oceanographic forces