Increased ammonium levels occurring during benthic algal blooms are potentially toxic to fucalean algae

Abstract

During the spring of 2016, benthic blooms of Acinetospora crinita (Ectocarpales, Phaeophyceae) producing voluminous mucilaginous aggregates frequently occurred at surveyed locations of the west Istrian Coast (northern Adriatic Sea, Croatia). In mucilage-affected macroalgal assemblages, the concentration of ammonium ranged from 50 to 300 μM. To investigate whether ammonium has the potential to harm fucalean species, a selected taxon, Cystoseira compressa was exposed to increased ammonium concentrations in laboratory conditions. Experiments revealed that exposure to 50 μM ammonium severely damaged the thalli while exposure to 300 μM caused complete necrosis of thalli in 2 days. These findings suggest that benthic algal blooms, enhanced by climate change and eutrophication, can negatively affect the populations of fucalean species due to production of ammonium during the decay of mucilaginous aggregates, causing thallus necrosis.