Habitat degradation disrupts neophobia in juvenile coral reef fish

Abstract

Habitat degradation not only disrupts habitat-forming species, but alters the sensory landscape within which most species must balance behavioural activities against predation risk. Rapidly developing a cautious behavioural phenotype, a condition known as neophobia, is advantageous when entering a novel risky habitat. Many aquatic organisms rely on damage-released conspecific cues (i.e. alarm cues) as an indicator of impending danger and use them to assess general risk and develop neophobia. This study tested whether settlement-stage damselfish associated with degraded coral reef habitats were able to use alarm cues as an indicator of risk and, in turn, develop a neophobic response at the end of their larval phase. Our results indicate that fish in live coral habitats that were exposed to alarm cues developed neophobia, and, in situ, were found to be more cautious, more closely associated with their coral shelters and survived four-times better than non-neophobic control fish. In contrast, fish that settled onto degraded coral habitats did not exhibit neophobia and consequently suffered much greater mortality on the reef, regardless of their history of exposure to alarm cues. Our results show that habitat degradation alters the efficacy of alarm cues with phenotypic and survival consequences for newly settled recruits.

Coral reef fish predator maintains olfactory acuity in degraded coral habitats

“…These changes may in part be due to alterations in the availability of sensory information that fishes rely upon to inform behavioural decisions when the structural complexity and benthic composition of the reef changes [12, 13]. Because many fishes rely on these sources of sensory information, alterations to habitat composition can have repercussions for the efficiency with which they forage and assess risk, ultimately affecting the ability of individuals to survive [12–16]. …”

“…The damage-released odour effectively acts as an honest indicator of a predation event in the local environment, and through associative coupling of these cues with predator cues (e.g., visual, chemical) prey learn to identify threats [24]. However, the olfactory responses of some prey species become undermined in dead-degraded coral habitats [12, 14–16, 25]. P .…”

“…P . amboinensis living on dead-degraded coral, overgrown by algae, become unable to detect and respond appropriately to conspecific damage-released odours, unlike those living on healthy coral [14–16, 26]. Indeed, laboratory studies confirm that damage-released odours mixed with small volumes of water that have passed over dead-degraded coral, fail to elicit antipredator responses in P .…”

“…Consequently, P . amboinensis are rendered incapable of developing appropriate risk assessments through direct use of damage-released odour, and do not learn predator identities through associative learning processes [14–16, 28]. P .…”

“…amboinensis also stray further away from shelter and have lower activity when living on dead-degraded, compared to healthy, patches of reef [15]. These behavioural changes modify predator-prey dynamics, with the loss of vigilance in prey leading to higher mortality [16, 27–29]. …”