Abstract

Oxyrrhis marina has been reported as an active predator in marine ecosystems, leading us to hypothesize that its grazing activity may impact the dynamics of species during red tide (RT) events in the San Jorge Bay (SJB). We conducted a study on developing one of the largest RT events observed in the SJB between June 2018 and May 2019. We isolated and identified the abundant microorganisms present during the bloom using microscopy techniques. Additionally, we evaluated the grazing activity of O. marina as a predator on phytoplankton species previously isolated from the SJB. Controlled laboratory experiments were conducted with O. marina and six different prey species at a concentration of 1x105 cells mL-1 (1:1) under controlled photoperiod, irradiance, and temperature conditions. The results revealed that the most abundant species during the RT event were Prorocentrum triestinum, P. micans, and O. marina. Regarding grazing preference, after 72 h, O. marina exhibited a significantly higher consumption rate of P. triestinum (19 cells mL-1) compared to the less consumed P. micans (8,627 cells mL-1). The observed strong preference of O. marina for P. triestinum suggests its potential role as a key controller of phytoplankton upwelling during RT periods. This study suggests that the diversity of microorganisms during red tide periods in SJB, Antofagasta, would be regulated by physicochemical and biological factors.