FISH-KILLING DIATOM BLOOM IN AN URBAN RECREATIONAL POND: AN INDEX CASE FOR A GLOBAL WARMING SCENARIO?

CASA, V.; BRANCOLINI, FLORENCIA; MIELNICKI, D.; MATALONI, G.

Oecologia Australis

Universidade Federal do Rio de Janeiro

Año: 2020

2177-6199

By the end of the exceptionally warm and stormy autumn of 2018, a fish kill occurredin a small hypertrophic pond located in a recreative green area in Buenos Aires (BA, Argentina).As there were no visible signs of an algal bloom, the causes for the die-off were investigated. On1st June, the pond was sampled while fish, mostly Bryconamericus iheringii (Characidae) andAustraloheros facetus (Cichlidae) were still dying. Despite low turbidity (18.9 NTU) andchlorophyll a concentration values (15.90 µg/L) as compared to similar BA waterbodies, a heavybloom of planktonic araphid diatoms (161,600 ind/mL) was detected, mainly caused byFragilaria saxoplanctonica (Fragilariaceae), Pseudostaurosira neoelliptica (Fragilariaceae) andUlnaria cf. acus (Fragilariaceae). Previous records of high abundances of these or closely relatedplanktonic diatoms around the world were associated with increased temperature and nutrientcontent, yet they did not cause other than nuisance blooms. Fish necropsy showed good bodycondition except for gill damage and mucus accumulation due to a large amount of frustules of these species, mainly P. neoelliptica, interspersed in the gill filaments. Although this is a commoncause for die-offs in marine fish farms, it is unprecedented in freshwater systems, and particularlyin urban waterbodies. Conversely to more common ?and foreseeable- summer cyanobacterialblooms in these systems, this phenomenon was triggered by an autumnal weather anomaly. Thisfact is crucial, as non-summer heat waves and heavy storms are predicted to increase in frequencyand intensity over the subtropical regions, yet their ecological consequences are less perceived,seldom studied, and far from understood. This could be the first documented case of many tooccur in such heavily eutrophicated environments unless effective strategies for eutrophicationcontrol and management are taken.Keywords: climate change; diatoms; fish kill; harmful algal bloom;