Effects of acid rainfall on juvenile Atlantic salmon (Salmo salar) antipredator behaviour: loss of chemical alarm function and potential survival consequences during predation

Abstract

Many organisms rely on chemosensory cues to mediate predation risks. Recent studies have demonstrated impaired chemosensory detection ability under weak acidification. Because rainfall may lead to episodic acidification of surface water, we assessed the effects of acid rain on chemosensory alarm functions. Under natural conditions, we quantified alarm behaviour of juvenile Atlantic salmon (Salmo salar) exposed to conspecific chemical alarm cues before and following rainfall. Before rainfall, salmon were capable of an alarm response in the study streams. After rainfall, salmon from Devil’s Brook did not respond to the alarm cues whereas the detection of salmon from Catamaran Brook (a comparable stream having higher acid neutralising capacity) was maintained. To relate these findings to predator–prey encounters, we performed a second experiment where we staged encounters between prey (rainbow trout, Oncorhynchus mykiss) and predator (largemouth bass, Micropterus salmoides) exposed to acidified and unacidified rainbow trout chemical alarm cues. Trout exposed to acidified alarm cues survived for a significantly shorter amount of time than trout exposed to unacidified alarm cues, whereas no difference in overall predator behaviour was observed. Our results suggest that episodic acidification in small nursery streams may disrupt the chemical information mediated by the chemical alarm cues that can translate into higher survival costs for prey.

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

“…The ecological consequence of pH-mediated chemosensory impairment to chemical alarm cues was demonstrated in staged encounters between rainbow trout prey and a predator, the largemouth bass (Micropterus salmoides). Bass captured trout faster and in greater proportion when trout alarm cues introduced in test tanks were acidified (pH 6.0) compared with treatments were alarm cues were introduced using neutral pH water [45]. Thus, prey 'naivety' arising from acid-mediated chemosensory impairment led to greater predation cost.…”

“…These behavioural responses to alarm cues have been observed in a range of freshwater fishes, including fathead minnows (Pimephales promelas), finescale dace (Phoxinus neogaeus), pumpkinseed (Lepomis gibbosus) and rainbow trout (Oncorhynchus mykiss) [20,37,44]. However, predator avoidance behaviour was diminished or absent when these alarm cues were presented in experimental treatments acidified using a minute amount of sulfuric acid (often a major contributor to freshwater acidification) [20,38,45]. Furthermore, behavioural responses to basic chemical stimuli from food (amino acids) were significantly reduced under a similar range of pHs (e.g.…”

“…approx. 30 mm) may be sufficient to reduce ambient acidity by 0.2-0.6 pH units [45,98] whereas major rain precipitation events may have more drastic effects on ambient acidity levels [99]. Additionally, in fresh and brackish water with poor buffering capacity, daily fluctuations of nearly 1 pH unit may occur as a function of changing dissolved CO 2 concentrations driven by algal metabolism and growth [100,101].…”

Use of chemosensory cues as repellents for sea lamprey: Potential directions for population management

“…Chemical alarm cues can also induce long-term behavioral responses such as acquired recognition of new predators and morphological and life history changes (Brown, 2003;Chivers et al, 2008). Such dramatic increases in the predator avoidance behavior of individuals detecting alarm cues are known to increase survival during encounters with live predators (Mathis and Smith, 1993;Leduc et al, 2009). Given the demonstrated survival benefit associated with responding to alarm cues, there likely exists strong selection pressure on cue receivers for the 'innate' recognition of conspecific alarm cues and those of closely related species Kelly et al, 2006;Chivers et al, 2007).…”

Predation costs of impaired chemosensory risk assessment on acid-impacted juvenile Atlantic salmon (Salmo salar)

“…Collectively, these experiments indicate that there are potential survival benefits accrued from antipredator behavioural responses to chemical alarm cues, that these benefits can arise from responding to both conspecific and heterospecific cues, and different types of environmental pollutants mediate the availability of information on risk received through chemosensory cues. The widespread occurrence of weak acidification and other aquatic pollutants, both chronic (Clair et al 2002(Clair et al , 2011 and episodic following precipitation events and seasonal fluctuations such as spring snow melts (Baker et al 1996;Laudon and Bishop 2002;Leduc et al 2009) strongly suggests that many populations of freshwater fishes are deprived of an important source of information on predation risk over different ecological time scales.…”