Habitat degradation and predators have independent trait-mediated effects on prey

Abstract

Coral reefs are degrading globally leading to a catastrophic loss of biodiversity. While shifts in the species composition of communities have been well documented associated with habitat change, the mechanisms that underlie change are often poorly understood. Our study experimentally examines the effects of coral degradation on the trait-mediated effects of predators on the morphology, behaviour and performance of a juvenile coral reef fish. Juvenile damselfish were exposed to predators or controls (omnivore or nothing) in seawater that had flowed over either live or dead-degraded coral over a 45d period. No interaction between water source and predator exposure was found. However, fish exposed to degraded water had larger false eyespots relative to the size of their true eyes, and were more active, both of which may lead to a survival advantage. Non-consumptive effects of predators on prey occurred regardless of water source and included longer and deeper bodies, large false eyespots that may distract predator strikes away from the vulnerable head region, and shorter latencies in their response to a simulated predator strike. Research underscores that phenotypic plasticity may assist fishes in coping with habitat degradation and promote greater resilience to habitat change than may otherwise be predicted.

Indirect predator effects influence behaviour but not morphology of juvenile coral reefAmbon damselfishPomacentrus amboinensis

“…Damselfish develop larger false‐eye spots ( i.e ., ocelli) when exposed to predators. Ocelli direct predators away from the vulnerable head region and improve subsequent survival (Lönnstedt et al ., 2013; McCormick et al ., 2019).…”

“…The presence of a predator and a non‐predator induced behavioural adjustments in coral reef damselfish without significantly affecting morphology. P. amboinensis juveniles exposed to predators for 6 weeks did not grow deeper bodies or larger ocelli compared to control fish, contradicting the results of similar studies of conspecifics (Lönnstedt et al ., 2013, P. amboinensis over 6 weeks; McCormick et al ., 2019, P. amboinensis over 6 weeks) and heterospecifics (Brönmark & Pettersson, 1994, Crucian carp over 8 weeks; and Svanbäck et al ., 2017, perch over 10 weeks). Fish in the null control group tended to be smaller than other groups after 6 weeks, suggesting that the exposure to a predator or herbivore induced bigger bodies and therefore less vulnerability to predation (Pessarrodona et al ., 2019).…”

“…Ocelli direct predators away from the vulnerable head region and improve subsequent survival (Lönnstedt et al, 2013;McCormick et al, 2019).…”

Coral Degradation and the Flow-On Effects to Reef Fishes

“…Once one individual has learnt that a particular smell or animal is dangerous, they can pass this, wittingly or otherwise, to others nearby who are very attentive to the reaction of their neighbors (a process called social learning). You can imagine that the capacity to rapidly learn predators and update information is important in an environment where new predators may enter and exit the habitat patch regularly (imagine trevally passing through), or they may need to migrate between patches of different habitat types to find mates or new sources of food later in life [3,4].…”

The role of fishes as food: A functional perspective on predator–prey interactions

“…2008; Hoyle & Keast, 1987; McCormick et al. 2019; Mihalitsis & Bellwood, 2017; Webb & Skadsen, 1980). This is understandable, as piscivory is highly uncertain, making it difficult to quantify in situ.…”