Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Oxidative stress biomarkers as potential tools in reef degradation monitoring: A study case in a South Atlantic reef under influence of the 2015–2016 El Niño/Southern Oscillation (ENSO) Laura Fernandes de Barros Marangoni a,b, ⁎ , Camila Dalmolin c , Joseane Aparecida Marques a,b , Roberta Daniele Klein c , Douglas Pinto Abrantes b,d , Cristiano Macedo Pereira b,d , Emiliano Nicolas Calderon b , Clovis Barreira e Castro b,d , Adalto Bianchini a,b,c a Pós-Graduação em Oceanografia Biológica, Oceanographic Institute, Federal University of Rio Grande, Av. Itália, Km 8, Rio Grande, RS 96203-900, Brazil b Coral Vivo Institute, Rua dos Coqueiros, Parque Yaya, Santa Cruz Cabrália, BA 45.807-000, Brazil c Biological Science Institute, Federal University of Rio Grande, Av. Itália, Km 8, Rio Grande, RS 96203-900, Brazil d Museu Nacional, Federal University of Rio de Janeiro, Quinta da Boa Vista, São Cristovão, Rio de Janeiro, RJ 20940-040, Brazil ARTICLE INFO Keywords: Lipid peroxidation Total antioxidant capacity Bleaching Corals Hydrocorals Thermal stress ABSTRACT The third global-scale coral bleaching event, triggered by the 2015–2016 El Niño, presented unprecedented levels of thermal stress and bleaching occurrence. Identification of potential cellular biomarkers in key reef species can greatly improve coral reef resource manager’s ability to make ecological forecasts and develop efficient mitigation strategies. In this context, the present study evaluated ecologically relevant biochemical parameters involved in thermal-stress response in two important reef building species of southwestern Atlantic Reefs – the scleractinian coral Mussismilia harttii and the hydrocoral Millepora alcicornis – aiming to assess their potential to forecast bleaching occurrence in corals/hydrocorals. Bleaching frequency, lipid peroxidation (LPO) and total antioxidant capacity (TAC), as well as thermal stress parameters (Degree Heating Weeks, DHW), were monitored during a six-month period in a reef area under influence of the 2015–2016 El Niño event. LPO is suggested as an informative, cost-effective and logical complement to reef monitoring programs; and TAC basal level as a potential measurement for predicting corals/hydrocorals susceptibility to bleaching. Further, results indicate M. alcicornis as a promising bioindicator in South Atlantic reefs. Findings presented here are expected to improve South Atlantic coral reef monitoring programs, as well as to contribute with potential biomarker- monitoring techniques to be used as additional tools in traditional reef monitoring programs worldwide. Further, observations on oxidative stress responses of a hydrocoral undergoing thermal stress conditions in the field are reported here for the first time. 1. Introduction Despite being the most diverse and productive marine ecosystem on the planet, coral reefs are experiencing extensive degradation world- wide due to climate change (Spalding and Brown, 2015; Hughes et al., 2017). The ecological success of coral reefs is largely attributed to the symbiotic relationship between scleractinian corals and dinoflagellates from the family Symbiodiniaceae, known as zooxanthellae (Hoegh- Guldberg, 1999; LaJeunesse et al., 2018). Tropical corals live close to the upper thermal limit of such symbiosis and heat stress is a primary factor in many large-scale bleaching events (Hughes et al., 2018; Lough et al., 2018). In fact, unusually warm sea surface temperature (SST) constitutes the basis of the National Oceanic and Atmospheric Admin- istration (NOAA) Coral Reef Watch (CRW) monitoring program (http:// coralreefwatch.noaa.gov/satellite/index.php). The process of bleaching, whereby corals and other invertebrates that establish sym- biotic relationships with microalgae expel their symbionts or experi- ence degradation of algae photosynthetic pigments, is one of the main reasons leading to coral reef degradation (Downs et al., 2000). Global climate change impacts (e.g. increasing SST) are being in- tensified by pulse heat stress events, such as El Niño, the warm phase of the El-Niño Southern Oscillation (ENSO) (Claar et al., 2018). According to climate modelling evidence, extreme El Niño occurrences are ex- pected to increase in response to greenhouse warming, leading to https://doi.org/10.1016/j.ecolind.2019.105533 Received 11 January 2019; Received in revised form 21 June 2019; Accepted 27 June 2019 ⁎ Corresponding author. E-mail address: laurafbmarangoni@gmail.com (L.F.d.B. Marangoni). Ecological Indicators 106 (2019) 105533 1470-160X/ © 2019 Elsevier Ltd. All rights reserved. T