toxins Article First Evidence of the Toxin Domoic Acid in Antarctic Diatom Species Anna J. Olesen 1, * , Anneliese Leithoff 1 , Andreas Altenburger 2 , Bernd Krock 3 ,Bánk Beszteri 4 , Sarah Lena Eggers 3 and Nina Lundholm 1   Citation: Olesen, A.J; Leithoff, A.; Altenburger, A.; Krock, B.; Beszteri, B.; Eggers, S.L.; Lundholm, N. First Evidence of the Toxin Domoic Acid in Antarctic Diatom Species. Toxins 2021, 13, 93. https://doi.org/ 10.3390/toxins13020093 Received: 31 December 2020 Accepted: 22 January 2021 Published: 26 January 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Natural History Museum of Denmark, University of Copenhagen, Øster Farimagsgade 5, 1353 Copenhagen K, Denmark; alc@science.ku.dk (A.L.); nlundholm@snm.ku.dk (N.L.) 2 The Arctic University Museum of Norway, UiT The Arctic University of Norway, Lars Thørings veg 10, 9006 Tromsø, Norway; andreas.altenburger@uit.no 3 Ökologische Chemie, Alfred Wegener Institut-Helmholtz Zentrum für Polar-und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany; bernd.krock@awi.de (B.K.); lena.eggers@awi.de (S.L.E.) 4 Department of Phycology, Faculty of Biology, University of Duisburg-Essen, Universitätsstrasse 2, 45141 Essen, Germany; bank.beszteri@uni-due.de * Correspondence: anna.olesen@snm.ku.dk; Tel.: +0045-26187142 Abstract: The Southern Ocean is one of the most productive ecosystems in the world. It is an area heavily dependent on marine primary production and serving as a feeding ground for numerous seabirds and marine mammals. Therefore, the phytoplankton composition and presence of toxic species are of crucial importance. Fifteen monoclonal strains of Pseudo-nitzschia subcurvata, a diatom species endemic to the Southern Ocean, were established, which were characterized by morphological and molecular data and then analysed for toxin content. The neurotoxins domoic acid and iso-domoic acid C were present in three of the strains, which is a finding that represents the first evidence of these toxins in strains from Antarctic waters. Toxic phytoplankton in Antarctic waters are still largely unexplored, and their effects on the ecosystem are not well understood. Considering P. subcurvata’s prevalence throughout the Southern Ocean, these results highlight the need for further investigations of the harmful properties on the Antarctic phytoplankton community as well as the presence of the toxins in the Antarctic food web, especially in the light of a changing climate. Keywords: Antarctic; Domoic Acid; Iso-Domoic acid; HAB; Southern Ocean Key Contribution: First report of domoic acid in Antarctic diatoms, which are probably frequent com- ponents of the Antarctic phytoplankton community and thereby the Antarctic foodweb. Domoic and and isodomoic acid C in equal amounts in Pseudo-nitzschia subcurvata cells. 1. Introduction The unique Antarctic marine ecosystem is fueled by phytoplankton, particularly diatoms, capturing energy from the sun. The potentially toxic diatom genus Pseudo-nitzschia is among the most frequently encountered and dominant diatom genera in Antarctic waters, e.g., contributing 13–70% of diatom densities in the Weddell Sea [1,2]. Despite this, nothing is known about the toxicity of the genus in Antarctic waters [2,3], whereas Pseudo-nitzschia is a known producer of the neurotoxin domoic acid (DA) in temperate and tropical waters, causing amnesic shellfish poisoning in humans [1]. DA accumulates in a wide range of planktonic and benthic organisms across the marine food web, such as krill, copepods, fish, and bivalves [1]. In marine mammals, this can e.g., result in acute and chronic poisoning, with effects such as reduced reproduction, seizures, and death [4]. Worldwide monitoring efforts have linked several toxic Pseudo-nitzschia blooms to unusual, large-scale mortality events in a range of marine vertebrates including sea lions, whales, and seabirds [4–6]. Toxins 2021, 13, 93. https://doi.org/10.3390/toxins13020093 https://www.mdpi.com/journal/toxins