Invasion of Ceratium furcoides in subtropical lakes in Uruguay: Environmental drivers and fish kill record during its bloom

The invasive freshwater dinoflagellate Ceratium furcoides is extending its distribution in South America with increasing environmental impacts associated with its bloom. We here report two events related to C. furcoides distribution expansion in Uruguay: (1) the main environmental drivers (physical and chemical factors, extreme wind events and zooplankton composition) of the first appearance and bloom of C. furcoides in 2012 in a subtropical eutrophic shallow lake (Lake Blanca, Uruguay); and (2) a fish kill event of Prochilodus lineatus observed during a bloom of C. furcoides in 2016 in a deep eutrophic lake (Puente de las Americas, Uruguay). The bloom of C. furcoides in Lake Blanca started in spring 2012 (December) after a clear water period with high phytoplankton species replacement after a cyanobacterial bloom of Raphidiopsis raciborskii. Extreme wind during this period may have initiated the bloom of C. furcoides by enhanced cysts resuspension from the sediments. High nutrient availability and low zooplankton grazing, further allowed C. furcoides to expand and reach over 96% of the phytoplankton biomass. In Lake Puente de las Americas, we registered the fish kill of the large-sized benthic Prochilodus lineatus during a bloom of C. furcoides. This bloom caused the oxygen depletion in the hypolimnion and the gills from these fish exhibited massive accumulations of C. furcoides cells compared to the ones collected in non-bloom conditions. Concurring to other studies our results suggest that the C. furcoides bloom likely caused the fish kill of P. lineatus by asphyxia. Our study is the earliest register of a bloom of C. furcoides in Uruguay (in 2012) and discusses the potential environmental effects of its bloom in subtropical lakes.

Automated summary

This study reported two events related to the distribution expansion of the invasive freshwater dinoflagellate Ceratium furcoides in Uruguay: its first appearance and bloom in Lake Blanca in 2012, and a fish kill event of Prochilodus lineatus during a bloom in Puente de las Americas in 2016. The research identified main environmental drivers and potential impacts of C. furcoides bloom, revealing factors such as extreme wind events, nutrient availability, and low zooplankton grazing. The findings suggest that the bloom of C. furcoides likely caused the fish kill of P. lineatus by asphyxia, highlighting the environmental effects of its bloom in subtropical lakes.