Biochemical alterations induced in Hediste diversicolor under seawater acidification conditions Rosa Freitas a, * , Adília Pires a , Anthony Moreira a , Frederick J. Wrona b , Etelvina Figueira a , Amadeu M.V.M. Soares a a Department of Biology & CESAM, University of Aveiro, Aveiro, Portugal b Department of Geography, David Turpin Building, University of Victoria, Victoria, BC, Canada article info Article history: Received 23 February 2016 Received in revised form 30 March 2016 Accepted 4 April 2016 Available online 6 April 2016 Keywords: Invertebrates pH decrease Oxidative stress biomarkers Energy reserves Metabolism abstract Seawater pH is among the environmental factors controlling the performance of marine organisms, especially in calcifying marine invertebrates. However, changes in non-calcifying organisms (including polychaetes) may also occur due to pH decrease. Polychaetes are often the most abundant group of organisms in estuarine systems, representing an important ecological and economic resource. Thus, the present study aimed to evaluate the impacts of seawater acidification in the polychaete Hediste diver- sicolor, a species commonly used as bioindicator. For this, organisms were exposed to different pH levels (7.9, 7.6 and 7.3) during 28 days and several biochemical markers were measured. The results obtained demonstrated that pH decrease negatively affected osmotic regulation and polychaetes metabolism, with individuals under low pH (7.6 and 7.3) presenting higher carbonic anhydrase activity, lower energy re- serves (protein and glycogen content) and higher metabolic rate (measured as Electron transport system activity). The increase on CA activity was associated to organisms osmoregulation capacity while the increase on ETS and decrease on energy reserves was associated to the polychaetes capacity to develop defense mechanisms (e.g. antioxidant defenses). In fact, despite having observed higher lipid peroxi- dation at pH 7.6, in polychaetes at the lowest tested pH (7.3) LPO levels were similar to values recorded in individuals under control pH (7.9). Such findings may result from higher antioxidant enzyme activity at the lowest tested pH, which prevented organisms from higher oxidative stress levels. Overall, our study demonstrated how polychaetes may respond to near-future ocean acidification conditions, exhibiting the capacity to develop biochemical strategies which will prevent organisms from lethal injuries. Such de- fense strategies will contribute for polychaetes populations maintenance and survival under predicted seawater acidification scenarios. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction The continuous release of fossil fuel-derived CO 2 into the at- mosphere is predicted to decrease ocean surface waters pH (a process known as Ocean acidification), with greater impacts into coastal systems, namely estuaries (Tomanek et al., 2011; Melzner et al., 2012), where pCO2 values may exceed 10,000 matm during summer months (Cochran and Burnett, 1996; Ringwood and Keppler, 2002). By the end of the century a pH decrease of 0.3e0.5 units is predicted to occur in open ocean waters (up to ~800 matm in year 2100, Caldeira and Wickett, 2003; Feely et al., 2004; IPCC, 2013; Orr et al., 2005; Raven et al., 2005), and up to 4500 matm in hypoxic estuaries (Melzner et al., 2012). These changes are expected to lead to significant impacts in aquatic ecosystems (Doney et al., 2009, 2012; Fabry et al., 2008; Harley et al., 2006; Kroeker et al., 2011; Nikinmaa, 2013; P€ ortner et al., 2004; P€ ortner, 2008; Widdicombe and Spicer, 2008). In fact, it has been shown that seawater pH is among the most important environmental factors controlling the distribution, physiology, morphology and biochemical performance of marine organisms, namely invertebrates (Dupont et al., 2008; Byrne, 2011; Freitas et al., 2016; Fabry et al., 2008; Kurihara, 2008; Matozzo and Marin, 2011; Wittmann and P€ ortner, 2013). Since seawater acidifi- cation is a major threat to calcifying marine invertebrates because it decreases the availability of carbonate ions required for skeleto- genesis, most studies on seawater acidification have devoted to * Corresponding author. Departamento de Biologia, Universidade de Aveiro, Campus Universit ario de Santiago, 3810-193 Aveiro, Portugal. E-mail address: rosafreitas@ua.pt (R. Freitas). Contents lists available at ScienceDirect Marine Environmental Research journal homepage: www.elsevier.com/locate/marenvrev http://dx.doi.org/10.1016/j.marenvres.2016.04.003 0141-1136/© 2016 Elsevier Ltd. All rights reserved. Marine Environmental Research 117 (2016) 75e84