Damselfish face climate change: Impact of temperature and habitat structure on agonistic behavior

Reef fishes exhibit a complex behavioral repertoire, and subtle changes in behavior are usu- ally associated to fluctuations in environmental conditions [7]. Thus, reef fishes are important organisms in determining how environmental changes can modulate behavior and help us understand their potential influence on reef ecosystems. Environmental changes were shown to affect fish cognition [11], personality [12], reproduction patterns [13], social interactions, migration and even species diversity of reef dwellers [14]. Some reef-fish populations are sensitive to slight increases in water temperature [15], while others tolerate higher temperature variations [16,17]. The dusky damselfish (Stegastes fuscus) occurs along almost the entire Brazilian coast (from 5˚S to 27˚S), featuring a wide range of thermal gradients. Studies on a related species from the Pacific (Chromis atripectoralis) indi- cated that the thermal optimum is around 1˚C above its regional maximum summer tempera- ture (30˚C; [17]). Damselfishes play an important ecological role by affecting the structure of benthic and coralline communities [18–20] and controlling algal diversity [21]. These species are largely territorial, exhibit aggressive behavior toward other herbivorous species and con- tribute to energy and nutrient transfer in reef environments, as a result of their gardening abil- ity [22]. If global warming projections for the end of this century materialize, ocean water tempera- tures may increase 2–4˚C on average, and important conditions for preserving marine life will

be affected [23,24], including the structural complexity of reefs [25]. In this study we evaluated whether water temperature and structural complexity of the habitat affect mobility patterns, tank occupation, and behavioral profile of the damselfish Stegastes fuscus. For this, we sub- jected the animals to classic mirror test and observed if animals kept at high temperature and barren conditions (mimicking the worst forecast scenario for the future) present significant changes in behavior when compared to fish kept at natural temperature and enriched or bar- ren habitat. As increase in temperature raises the metabolic rate of fish and promotes direct influences in behavior, we suggest that natural aggressive behavior of S. fuscus would be affected. 2. Materials and methods 2.1 Animal sampling and holding conditions Animals were collected from Pirambu´zios beach (6˚03’25”S and 35˚05’53”W), Nı´sia Floresta, Rio Grande do Norte state, Northeastern Brazil, as authorized by the Brazilian Institute of Environment and Natural Resources (IBAMA License Number 62318-1/2018). The tide pools that form at this beach serve as a refuge for various marine communities [26]. The average maximum coastal water summer temperature is 30˚C [27], but reaches 36˚C in the tide pools (critical temperature occurring only at low tide and for short periods of time), salinity remains between 36 and 40ppt, and pH is around 8.0 [28]. Dusky damselfish (S. fuscus) were collected from the tide pools in two sampling moments

(average size and weight of 8.99 ± 1.04 cm, 18.83 ± 4.29 g and 8.27 ± 0.80 cm, 13.41 ± 2.99 g at the first and second capture, respectively) using a cast net (3m diameter, 10mm mesh size). Fish were immediately stored in 30-L containers with seawater and air stones to maintain oxy- gen level. Next, they were taken to the laboratory and placed in glass tanks (33 x 30 x 30 cm; 25L) at the Fish Vivarium, Department of Physiology and Behavior, Federal University of Rio Grande do Norte. Saltwater was previously prepared (Red Sea Salt, Red Sea, Houston, USA) and the tanks filled. Salinity was maintained at 36ppt, and a 12:12H light:dark cycle was established. Every 12 tanks formed a closed recirculating system, in which water was kept aerated and filtered (mechanical, chemical and biological filters) and maintained at a controlled PLOS ONE Temperature and habitat structure on damselfish behavior PLOS ONE | https://doi.org/10.1371/journal.pone.0235389 June 30, 2020 2 / 13 Funding: MMS, JFdS, ALPM and EAV were financed in part by the Coordination for the Improvement of Higher Education Personnel (CAPES). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.