Abstract

An increase of the frequency and intensity of harmful algal blooms associated to Paralytic Shellfish Poison (PSP) have occurred in Southern Chile. During the seventies and eighties, Alexandrium catenella and PSP outbreaks in the Magellan region (48º – 55º S) appeared every 8-9 years, but since 1991 they are continuously present. PSP outbreaks and A. catenella variations in its abundances since 1972 are showing that these events have occurred at the end of the La Niña events but prior to an intense or medium intensity El Niño. For the Magellan region, micro-phytoplankton abundance and relative abundance of A. catenella (RA) time series, since 1994 are available. Through non parametric correlations, the standardized anomalies of these variables were contrasted with pluviometry and air temperature standardized anomalies, as well as with the Multivariate ENSO Index (MEI) and the Southern Oscillation Index (SOI). Our findings are showing that both biotic variables exhibit a significant correlation with MEI, pluviometry and air temperature standardized anomalies, but SOI does not always show a significant relationship. And particularly for 1997-1998, corresponding to the second most intense El Niño phenomenon of the last century, a striking increase of phytoplankton abundance and RA occurs. It is suggested that micro-phytoplankton abundance, RA and abundances of another dinoflagellates are linked through teleconnections to the ENSO, showing changes in rain fall pattern, air temperature and probably glaciers melting, and suggesting a macro-scale triggering factor regulating the micro-phytoplankton and A. catenella distributions and abundances, but later would be modulated by local factors. access to oceanic areas and the low sampling frequency.