Behaviourally Mediated Phenotypic Selection in a Disturbed Coral Reef Environment

Abstract

Natural and anthropogenic disturbances are leading to changes in the nature of many habitats globally, and the magnitude and frequency of these perturbations are predicted to increase under climate change. Globally coral reefs are one of the most vulnerable ecosystems to climate change. Fishes often show relatively rapid declines in abundance when corals become stressed and die, but the processes responsible are largely unknown. This study explored the mechanism by which coral bleaching may influence the levels and selective nature of mortality on a juvenile damselfish, Pomacentrus amboinensis, which associates with hard coral. Recently settled fish had a low propensity to migrate small distances (40 cm) between habitat patches, even when densities were elevated to their natural maximum. Intraspecific interactions and space use differ among three habitats: live hard coral, bleached coral and dead algal-covered coral. Large fish pushed smaller fish further from the shelter of bleached and dead coral thereby exposing smaller fish to higher mortality than experienced on healthy coral. Small recruits suffered higher mortality than large recruits on bleached and dead coral. Mortality was not size selective on live coral. Survival was 3 times as high on live coral as on either bleached or dead coral. Subtle behavioural interactions between fish and their habitats influence the fundamental link between life history stages, the distribution of phenotypic traits in the local population and potentially the evolution of life history strategies.

Lethal effects of habitat degradation on fishes through changing competitive advantage

“…By contrast, on bleached and dead coral, P. moluccensis moved further away from the patch that increased their vulnerability to piscivores in the area. A similar shift in spatial distribution was found for P. amboinensis in a previous study [21]. The reasons for this are open to speculation, but may involve avoidance of necrotic or novel odours from the live bleached and dead-algalcovered corals, or an attempt to improve camouflage away from the bleached coral [21,39].…”

“…Previous tests between ecologically similar reef fishes have found effects on growth rather than on mortality (reviewed by [15,42,43]). Intraspecific [21] and interspecific interactions involving P. amboinensis both indirectly lead to enhanced mortality through aggression of dominant individuals, forcing subordinates into areas of greater risk. It is unclear whether the detrimental effects of interspecific competition would be ameliorated or compounded by intraspecific competition.…”

“…(b) Behavioural assessment The behaviour of each fish placed on the patch reefs was monitored 40-60 min after placement on the reef following the protocol of McCormick [21]. Briefly, behaviour of the focal fish was assessed over a 3 min period by a scuba diver positioned 1.5 m away from the patch.…”

“…Coral bleaching owing to ocean warming and run-off has caused catastrophic reductions in hard coral throughout the tropics [9,18] and is predicted to increase in frequency and severity [19,20]. While major changes in fish communities associated with coral bleaching have been documented, the mechanisms underlying these changes are poorly understood [21].…”

Learn and live: predator experience and feeding history determines prey behaviour and survival

“…Research over the last two decades suggests that fishes collected in light traps are intercepted as they come into the vicinity of the reef to settle, and most are in the process of metamorphosis to their juvenile form [23][24][25]. At this stage, they also appear to display active and consistent choices of habitat [26,27], and have little post-settlement movement over the initial juvenile phase [28], suggesting that they do not attempt to return to the plankton.…”