Seasonal and intratidal distribution of Dinophysis spp. in a Chilean fjord

The spatial and temporal distribution of Dinophysis spp. in a fjord in southern Chile (43°47′S–72°56′W) was studied through experiments performed in a seasonal and intratidal timescales. Seasonal variability was studied through monthly experiments performed between January 2005 and February 2006. Intratidal variability was explored through two 24-h ADCP (acoustic Doppler current profiler) current measurement experiments combined with biological sampling, in order to assess the effect of flow patterns on Dinophysis spp. distribution. We found four species of Dinophysis , which included D. acuminata and D. acuta . The former was the most abundant species in the two samplings, whereas D. acuta was only found in low concentrations near the head of fjord. The persistent saline stratification and the increased temperature during spring–summer were well associated with the increase of D. acuminata cellular concentrations inner Pitipalena Fjord. There, higher concentrations of D. acuminata were observed around the pycnocline in narrow temperature (11.19–12.52 °C) and salinity (19.75–22.59 psu) ranges. During intratidal experiments, decreases in shear instabilities in the up-fjord direction were accompanied by increases in D. acuminata concentrations (maximum 332 cells L −1 in the pycnocline). Our results suggest that the diel variability observed for D. acuminata at the Pitipalena Fjord is mainly influenced by the tidal effect and vertical density gradients (maximum 4.77 sigma-t m −1 ), which was evidenced by the vertical movement of the pycnocline (between 5 and 10 m depth) during the tidal semidiurnal cycle.