DO SUDDEN CHANGES IN SALINITY TRIGGER BLOOM FORMATION AND TOXIN PRODUCTION IN THE HARMFUL ALGA PRYMNESIUM PARVUM?

The harmful alga Prymnesium parvum causes massive fish kills in saline rivers around the world. It is believed that such blooms are caused by an increase in salinity due to high evaporation and low discharge during droughts, natural sources of salt, or anthropogenic salt inputs. Dense blooms of P. parvum developed in the Oder River (Poland and Germany) in August 2022 and in June 2024, possibly after growing and being released from a retention basin for saline wastewater. The 2022 bloom was highly toxic, killing large amounts of fish and molluscs, whereas in 2024, P. parvum did not produce detectable amounts of algal toxins (=prymnesins). We aim to identify the causes of bloom formation and to investigate whether sudden changes in salinity trigger toxin production of P. parvum. For that, we compared the environmental conditions preceding both the toxic and non-toxic blooms using monitoring data. We also conducted microcosm experiments on P. parvum cultures (isolated from the Oder River) to investigate the effect of rapid salinity changes on P. parvum toxicity by measuring cell toxin concentrations and gene expression of polyketide synthases genes via qPCR, which have been associated with prymnesin production. This would, for the first time, confirm the role of environmental stressors in the synthesis of prymnesins, representing an experimental model to study environmental triggers of toxin production during harmful algal blooms. This will help us understand the processes causing harmful algal blooms, and to adapt bloom management efforts in rivers with high salt loading.

Presentation Preference: Oral

Primary Presenter: Karla Münzner, Leibnitz Institute of Freshwater Ecology and Inland Fisheries (karla.muenzner@igb-berlin.de)

Authors:

Sven Würtz, Leibnitz Institute of Freshwater Ecology and Inland Fisheries  (sven.wuertz@igb-berlin.de)

Margaret Glenn, Leibnitz Institute of Freshwater Ecology and Inland Fisheries  (margaret.glenn@igb-berlin.de)

Heiner Kuhl, Leibnitz Institute of Freshwater Ecology and Inland Fisheries  (heiner.kuhl@igb-berlin.de)

Stephanie Spahr, Leibnitz Institute of Freshwater Ecology and Inland Fisheries  (stephanie.spahr@igb-berlin.de)

Jan Köhler, Leibnitz Institute of Freshwater Ecology and Inland Fisheries  (koehler@igb-berlin.de)