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

notice a conspecific invader, it changed the way fish interact with the intruder. Thus, increased water temperatures seem to affect the behavioral trade-off between signaling and fighting against the intruder, a result that is consistent with our prediction. The locomotor patterns observed in S. fuscus did not indicate loss of swimming velocity (Fig 2), as found in other species of damselfish [52–55]. The decreased aggression observed in increased water temperature may be related to nutritional deficit following temperature rise and complexity loss, as an economic strategy to cope with increased metabolism [4, 56,57]. Therefore, the ecological relations of the damselfish with the coral reef community would be compromised. We observed that fish kept in the barren environment exhibited more aggressive displays than those in a complex environment, similar to what occurs with salmonids [58]. Overall lev- els of aggression tend to be higher in less complex environments [12], given that more aggres- sive animals have preferential access to resources [59] or more mating opportunities [60]. Thus, it seems that barren environments, where there are fewer habitat sharing options, lead to a single solution: increased aggressiveness to guarantee territory, even if it involves more stress and higher energy costs. Although the combination of high temperature and barren condition was the worst for S. fuscus, the enrichment of the 34˚C ambient seemed to compensate thermic stress, as was sug- gested by Goldenberg et al. [61]. Other authors have shown that enrichment increases neuro-

genesis and decreases anxiety-like behavior in fish [62,63]. Several other studies have discussed the importance of environmental complexity, which seems to favor behavioral plasticity [64,65] and decline stress levels [66,67], in addition to affecting reef predation and competition rates [68,69]. The structural complexity of the habitat is related to ecologically diverse environ- ments with high fish abundance [70], because a more complex environment provides elevated niche and resource variability [71], producing areas that can harbor more biological diversity and fish biomass when compared to less structurally complex environments [72,73]. Thus, habitat structure may ultimately change the behavioral pattern of species [74]. As such, the reef ecosystem complexity, which is considered of utmost importance for species diversity and richness [25,75–78], is being threatened by the global warming, and many species that occur exclusively on reefs are endangered. The predicted global warming will affect species distribution and lead to profound changes in the three-dimensional structure of reefs [79]. In our study, we heated the tank water to the tem- perature predicted for the end of this century (34˚C) and maintained it for one month, observing several behavioral effects on the dusky damselfish (S. fuscus) that may have cascading effects on reef community. Rather than overall effects on the reef, our results suggest ocean warming reduces the damselfish ability to maintain their territories and consequently control other spe-

cies’ growth by their gardening role. Losing territory size due to decreased aggressiveness is likely to scale up and affect interaction networks in the reefs (e.g., gardening, competition, predation, foraging, reproduction, navigability, and niche partitioning). Changes in behavior are only the tip of the iceberg of many and much more harmful changes, and strategies to mitigate global warming effects are urgently needed to prevent such a future adverse scenario. Supporting information S1 Data. (XLSX) Author Contributions Conceptualization: Guilherme Ortigara Longo, Ana Carolina Luchiari. PLOS ONE Temperature and habitat structure on damselfish behavior PLOS ONE | https://doi.org/10.1371/journal.pone.0235389 June 30, 2020 9 / 13