Abiotic variables affect STX concentration in a meso-oligotrophic subtropical coastal lake dominated by Cylindrospermopsis raciborskii (Cyanophyceae) De´ bora Monteiro Brentano a, *, Eduardo L. Hettwer Giehl b , Maurı´cio Mello Petrucio c a Instituto Federal de Educac¸a˜o Cieˆncia e Tecnologia de Santa Catarina, Laborato´rio de Ecotoxicologia, Av. Mauro Ramos, 950, Floriano´polis, SC CEP 88020-300, Brazil b Universidade Federal de Santa Catarina, Programa de Po´s-Graduac¸a˜o em Ecologia, Campus Reitor David Ferreira Lima, Floriano´polis, SC CEP 88040-900, Brazil c Universidade Federal de Santa Catarina, Laborato´rio de Ecologia de A ´ guas Continentais, Campus Reitor David Ferreira Lima, Floriano´polis, SC CEP 88040-900, Brazil 1. Introduction The planktonic freshwater cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju 1972 (Order Nostocales) is filamentous and diazotrophic. Originally identified in tropical/subtropical regions, C. raciborskii has increasingly been found in temperate regions (Padisa´ k, 1997) and is currently considered globally dispersed (Wiedner et al., 2007; Bonilla et al., 2012; Sinha et al., 2012). This cyanobacterium is considered an invasive species due to its successful global expansion, which was assisted by the ability of this species to tolerate a wide range of environmental conditions (Padisa´k, 1997). There is great interest worldwide in this species because it produces toxic blooms that can seriously impact water quality, thus threatening human health (Chorus and Bartram, 1999; Chorus, 2005; Burch, 2008). The toxic secondary metabolites produced by Cylindrosper- mopsis raciborskii include the potent cylindrospermopsin (CYN) (Ohtani et al., 1992; Li et al., 2001) and saxitoxin (STX) (Lagos et al., 1999; Molica et al., 2002, 2005), which is the parent compound of more than 30 naturally occurring analogs (Kellmann et al., 2008). Furthermore, the gene locus that is responsible for the biosynthesis of STX in C. raciborskii has been described by Kellmann et al. (2008). Harmful Algae 56 (2016) 22–28 A R T I C L E I N F O Article history: Received 28 August 2015 Received in revised form 13 March 2016 Accepted 15 March 2016 Available online Keywords: Cyanotoxins Drinking water Environmental protected area Management Toxic cyanobacteria Water supply A B S T R A C T The cyanobacterium Cylindrospermopsis raciborskii is capable of producing toxins including saxitoxin (STX). Few studies have verified the influence of environmental variables on the production of STX and most have only been studied in the laboratory. The goal of this work was to identify the abiotic variables related to STX concentration in situ. The relationship among STX concentration and the physical variables, nutrients and chlorophyll-a (chl-a) concentration was examined in a meso-oligotrophic subtropical coastal lake dominated by C. raciborskii. A generalized linear model was developed, incorporating all variables measured monthly over a 45-month monitoring period. Conductivity and dissolved inorganic nitrogen (DIN) concentration provided the greatest explanatory power for STX concentration in situ. Previous studies suggested that C. raciborskii cells exposed to stress associated with higher ionic concentrations appear to activate the biosynthesis of STX suggesting that STX can elicit changes cell permeability and may contribute to the homeostasis of this organism. An increase of DIN concentration results in a higher concentration of STX which may be related to a reduced metabolic demand, since the uptake of inorganic nitrogen requires less energy than N 2 -fixation. Thus, increased DIN can favor the growth of C. raciborskii population or improve cellular homeostasis, both potentially increasing STX concentration in the aquatic system, which was observed through a delayed response pattern. The developed model, while providing only a moderate predictive power, can assist in the understanding of the environmental variables associated with increases in STX concentration, and in monitoring and minimizing the risks of toxic blooms. ß 2016 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +55 48 3221 0646; fax: +55 48 3224 1500. E-mail addresses: brentano@ifsc.edu.br (D.M. Brentano), eduardo.giehl@gmail.com (E.L.H. Giehl), mauricio.petrucio@ufsc.br (M.M. Petrucio). Contents lists available at ScienceDirect Harmful Algae jo u rn al h om epag e: ww w.els evier.c o m/lo cat e/hal http://dx.doi.org/10.1016/j.hal.2016.03.017 1568-9883/ß 2016 Elsevier B.V. All rights reserved.