Impactos do ruído antropogênico no comportamento do peixe-donzela, Stegastes fuscus (Cuvier, 1830)

Abstract

Anthropogenic noise is a major threat to biodiversity. Since marine organisms use sound in many activities in their life cycle, increased nautical traffic can have significant effects on critical behaviors, such as foraging and territoriality. The damselfish Stegastes fuscus (Pomacentridae) is a key species influencing the dynamics of shallow reef systems along the Brazilian coast. This species represents an important model to assess the impacts caused by anthropogenic activities. The present work aims to evaluate the impact of noise generated by nautical tourism vessels on the behavior of S. fuscus in subtropical coastal rocky reefs of Arraial do Cabo (22°58'S 42°01'W). For this, in situ experiments were carried out. Territories of S. fuscus were randomly selected from different sampling sites and an underwater loudspeaker was placed in a central position, at least 1 m from the individual's territories, so that it could cover more than one territory (= individual) at once. For each replicate it was applied: Treatment 1: 10 min without sound transmission (control) + 10 minutes of boat playback (200Hz-1kHz) or Treatment 2: 10 minutes without sound transmission (control) + 10 minutes of an artificial sound (400Hz). Tracks were made using 30s of noise and 30s of silence, in a loop for 10 minutes. Behavioral responses were analyzed by remote filming, considering the frequencies of agonistic behaviors (chases/minute), foraging rates (bites/minute) and refuge time (time spent hiding). Observations were divided in three periods of time: 10 min prior to the sound treatment (‘pre’), as our control, the 10 min trials of the soundtrack (‘during’) and the 10 minutes following the sound treatment (‘post’). To evaluate differences between behavior within periods of time a Friedman test was used (α < 0.05). Fish had significant behavior modifications associated with different sound exposures. Individuals increased their refuge time when exposed to sound compared to the moment of pre-exposure (Treatment 1: p = 0.009; Treatment 2, p = 0.008) in both treatments. And also had lower foraging rates during noise exposure period compared to pre-exposure (Treatment 1: p = 0.003; Treatment 2, p = 0.01). Such changes in foraging and territory defense rates may have potential effects on population fitness. Since the species has a functional role as the most abundant territorial herbivore in the system, the detected effects can significantly alter the reef dynamics. The underwater acoustic soundscape is changing rapidly and with it there is an urgent need to assess the impacts of this anthropogenic pressure and provide measures to mitigate this still-neglected impact.