Abstract

Harmful species genera of Alexandrium, Dinophysis, Protoceratium and Pseudo-nitzschia, are present in Southern Chile, sometimes in bloom conditions or associated to toxic outbreaks. A time series from 2007 to 2013 is considered, to understand the occurrence and distribution of these species in Reloncaví fjord (42°40’S), Puyuhuapi fjord (44°40’S) and Union channel (52°00’S). Diatoms contributed with >98% of total cell density and the highest value (22.6×106 cells l-1) was found during the Spring 2009 in Reloncaví fjord, with Skeletonema costatum, contributing from North to South with 90%, 39% and 28% of total density. The harmful species are numerically subordinated with <1% of total number, the exception are Pseudo-nitzschia cf pseudodelicatissima and P. cf. australis contributing both with 45% of total density in Puyuhuapi fjord. Both species are present in low numbers in the other studied areas, 0.3%, Reloncaví fjord and 5.5%, Union channel. During the studied period, Alexandrium catenella, A. ostenfeldii and Dinophysis acuta in the Reloncaví fjord, were absent, while these species plus D. acuminata and Protoceratiun reticulatum were present in the other areas. The microphytoplankton composition and distribution showed latitudinal changes associated with vertical stability and stratification of water column. The mean (±SD) of species diversity varied from 0.63±0.59 in Reloncavi fjord to 1.3±0.73 and 1.39±0.57 in Puyuhuapi fjord and Union channel, respectively. Although the studied zones are geographic, oceanographic, and climatically different, the abundance of harmful species are regulated by climatic and oceanographic factors of wide geographic coverage and then, microphytoplankton distribution and abundance is locally driven.