A catastrophic marine mortality event caused by a complex algal bloom including the brevetoxin producer Karenia cristata.

Authors

Shauna A Murray, Christopher J S Bolch, Steve Brett, Cheong Xin Chan, Mark Doubell, Hazel Farrell, Greta Gaiani, Hannah Greenhough, Gustaaf Hallegraeff, Tamsyne Smith-Harding, D Tim Harwood, Robert G Hatfield, Neil MacDonald, Ian Moody, Hugo Bastos de Oliveira, Lesley Rhodes, Anne Rolton, Andrew I Selwood, Justin R Seymour, Nachshon Siboni, Anastasiia Snigirova, Nikola Streiber, Craig Styan, Clinton Wilkinson, Kirsty Smith

Published in

Nature ecology & evolution. Jul 06, 2026. Epub Jul 06, 2026.

Abstract

Harmful algal blooms of Karenia brevis (Dinophyceae) are a global anomaly, occurring in one location worldwide, causing severe marine and acute human impacts via brevetoxins (BTXs). During 2025 an unprecedented mass marine mortality occurred in South Australia, across an area of ~20,000 km², persisting for >12 months, resulting in the deaths of ~10⁶ marine animals of >600 taxa, with human health impacts. Using custom metabarcoding, long-read sequencing and targeted qPCR, we characterized the microalgal assemblage. Karenia cristata dominated over the sampling area, in an assemblage with four other Karenia species with varied abundances spatially and temporally. High abundances of K. cristata appeared in the austral autumn, and hydrodynamic processes appear to have entrained cells coastward in the semi-enclosed seas. We isolated the species and characterized it using light and electron microscopy, liquid chromatography-mass spectrometry and toxicity assays. We show that the rare and little-known K. cristata produces substantial amounts of BTXs with a profile (BTX-2, BTX-3, BTX-B5) different from that of K. brevis, with toxicological effects. These findings reveal a BTX-producing Karenia that causes substantial detrimental marine ecosystem impacts, representing an emerging international threat with unknown consequences given changing ocean conditions.

PMID:
42410015
Bibliographic data and abstract were imported from PubMed on 07 Jul 2026.

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