Habitat degradation negatively affects auditory settlement behavior of coral reef fishes

Abstract

SignificanceClimate change is causing widespread damage to the world’s tropical coral reefs, via increases in cyclones and mass bleaching. Healthy populations of reef fishes facilitate recovery from such events, and recruitment of juvenile fish is influenced by acoustic cues that guide larval orientation, habitat selection, and settlement to reefs. Our matched recordings of Australia’s Great Barrier Reef before and after recent severe degradation demonstrate major changes to natural reef sound. In field experiments using these recordings, we show the potential impact of such acoustic changes. Postdegradation reef sounds were less attractive to young fishes than their predegradation equivalents. Reductions in fish settlement, caused by acoustic changes, may threaten the recovery potential of degraded coral reefs.

An overview of fish bioacoustics and the impacts of anthropogenic sounds on fishes

“…For example, Montgomery et al () suggested that the ability of larval reef fishes to locate their home reefs by responding to their characteristic sounds might be affected by changes in the noise level (Stanley et al, ). There are significant differences in the spectral and temporal composition of the ambient sound associated with different coastal habitat types (Radford et al, ) and Gordon et al () recently pointed out that changes in habitats may negatively affect the auditory settlement behaviour of coral‐reef fishes. Acoustic cues guide the orientation, habitat selection and settlement of many fishes, but these processes may be impaired if degradation alters reef soundscapes.…”

Predicting the reef acoustic cuescape from the perspective of larval fishes across a habitat quality gradient

“…We predicted that even if the average sound level at the reef is below detectability at distance, periodic high-amplitude events will enable larval fishes to locate the reef with a higher probability of success than if acoustic cues were not present. In our model, we assumed that fish behaved with positive phonotaxis when a sound was detected, but we emphasize that fishes can show varied behaviors in response to environmental sounds (Radford et al 2011, Gordon et al 2018). This assumption was necessary for our fourth objective and is a behavior that has been observed (as cited above).…”

“…This is in contrast to non-reef based cues, like a sun compass (Mouritsen et al 2013) or magnetic compass (Bottesch et al 2016, O'Connor & Muheim 2017, which may be a long-distance indicator of the natal reef position but will not provide direct information about the type or quality of habitat. The ability of cues to indicate both location and habitat condition is particularly important when considering how reef degradation and changes in reef community structure may affect the cues that advertise that reef (Gordon et al 2018). It follows that the cues of particular interest when considering how fish populations respond to habitat change are the cue types that are reef-based and influenced by habitat alterations.…”

“…Of the reef-based environmental cues considered, auditory cues are hypothesized to operate over distances that would be relevant to navigation (Montgomery et al 2006) and they also may provide information as to the type and condition of the underlying reef habitat (Piercy et al 2014, Kaplan et al 2015, Gordon et al 2018). This role of acoustic cues to larval fishes is predicted because of the biologically produced sounds at coral reefs, the physics of sound itself (relatively current-independent and long-distance propagation), and evidence of larvae responding to reef sounds (Leis et al 2002, Tolimieri et al 2004, Simpson et al 2005, Huijbers et al 2012.…”

Coral Reef Monitoring, Reef Assessment Technologies, and Ecosystem-Based Management

“…Several other acoustic indices such as rates of invertebrate snapping sounds (Butler et al, 2017) and the acoustic complexity index (Pieretti et al, 2011) may also correlate with visual measures of diversity (Nedelec et al, 2015;Bertucci et al, 2016), although the generality of these trends is not fully established (Staaterman et al, 2017). Further, habitat degradation can alter reef soundscapes; lowerquality reefs with poor management sound quieter than wellprotected reefs (Piercy et al, 2014 , Figure 5), and cyclone and bleaching events change dramatically the acoustic profile of a reef (Gordon et al, 2018). Soundscape recordings can therefore be used to compare reef health across both space and time.…”