The influence of thermal extremes on coral reef fish behaviour in the Persian Gulf

Abstract

Despite increasing environmental variability within marine ecosystems, little is known about how coral reef fish species will cope with future climate scenarios. The Arabian/Persian Gulf is an extreme environment, providing an opportunity to study fish behaviour on reefs with seasonal temperature ranges which include both values above the mortality threshold of Indo-Pacific reef fish, and values below the optimum temperature for growth. Summer temperatures in the Gulf are comparable to those predicted for the tropical ocean by 2090-2099. Using field observations in winter, spring and summer, and laboratory experiments, we examined the foraging activity, distance from refugia and resting time of Pomacentrus trichrourus (pale-tail damselfish). Observations of fish behaviour in natural conditions showed that individuals substantially reduced distance from refugia and feeding rate and increased resting time at sub-optimal environmental temperatures in winter (average SST = 21°C) and summer (average SST = 34°C), while showing high movement and feeding activity in spring (average SST= 27°C). Diet was dominated by plankton in winter and spring, while fish used both plankton and benthic trophic resources in summer. These findings were corroborated under laboratory conditions: in a replicated aquarium experiment, time away from refugia and activity were significantly higher at 28°C (i.e., spring temperature conditions) compared to 21 °C (i.e., winter temperature conditions). Our findings suggest that P. trichrourus may have adapted to the Arabian/Persian Gulf environment by downregulating costly activity during winter and summer and upregulating activity and increasing energy stores in spring. Such adaptive behavioural plasticity may be an important factor in the persistence of populations within increasing environmentally variable coral reef ecosystems.

Insights from extreme coral reefs in a changing world

“…Using a combination of field observations and aquaria experiments, D'Agostino et al (2019) showed that during the metabolically challenging summer and winter seasons, the damselfish Pomacentrus trichrourous substantially reduced their feeding rates and movement, but increased feeding and activity during the shoulder seasons when conditions are most benign, presumably to maximize energy intake when physiological demands were more optimal. Individuals also switched diets in a manner that suggest behavioral modification to maximize energy budgets, feeding mainly on plankton in the cooler seasons, but on a combination of plankton and a variety of benthic resources during the hottest time of year when energetic demands would be greatest (D'Agostino et al 2019). Together, these studies suggest that adopting a more flexible behavioral and dietary lifestyle may be necessary to support the physiological and energetic demands presented in thermally extreme seas.…”

Growth impacts in a changing ocean: insights from two coral reef fishes in an extreme environment

“…faster juvenile growth but earlier asymptotic growth for fish living in warmer environments) (Trip et al 2014), suggesting that salinity and perhaps even productivity are exhibiting a strong influence on differences in growth between regions. Interestingly, growth rates of populations within the Oman Sea, where salinity conditions are predominantly stable, were impacted more strongly by salinity fluctuations compared to populations within the Arabian Gulf, suggesting Arabian Gulf's populations may have higher capability of acclimation to seasonal and interannual changes in environmental conditions (Rummer and Munday 2017;D'Agostino et al 2019). While numerous studies have examined the implications of increasing temperature and temperature variability on coral reef fish growth (e.g.…”

“…The pale-tail damselfish (Pomacentrus trichrourus) appears able to mitigate bioenergetic inefficiency associated with the fluctuating and extreme water temperature within the Arabian Gulf by downregulating costly activities during winter and summer, while upregulating activity and increasing energy stores in spring (D'Agostino et al 2019). In this respect, P. trichrourus, P. maculosus and Pomacentrus aquilis all show a degree of feeding plasticity in the Arabian Gulf (Shraim et al 2017;D'Agostino et al 2019), suggesting that such plasticity in feeding may be an important factor in understanding growth rate and overall body size of all three species.…”

“…Furthermore, the two species were chosen because they are phylogenetically and ecologically disparate: L. ehrenbergii is a generalist carnivore, feeding on benthic invertebrates associated with turfing algae (i.e. amphipods, isopods) and small fish (Randall 1995;D'Agostino et al 2019), while P. maculosus is a facultative spongivore/corallivore (Shraim et al 2017).…”

“…Positive effects of high SST on growth rates of both species within the Arabian Gulf may show that high summer water temperatures do not exceed the population's typical temperature range in this region. For example, there was a positive effect of increased maximum SST on growth rate of L. ehrenbergii, potentially indicating that the Arabian Gulf's summer temperature of > 34 °C may not exceed the thermal optimum for this species.Indeed, L. ehrenbergii abundance and predatory activity appear to be highest in summer(D'Agostino et al 2019), suggesting that L. ehrenbergii may still have the aerobic capacity to perform ecological tasks (e.g. swimming, feeding) during the Arabian Gulf's extreme summer temperature.…”