Abstract

Both climate change and invasive species are threatening coral reef ecosystems globally. These two stressors are often studied singularly despite co-occurring in nature. For reef fishes, ocean warming due to climate change leads to elevated metabolic rates, which can increase feeding rates. Invasive species can also cause major declines in abundance and even extinctions in native prey through predation. Here, we examine the effects of ocean warming on the behaviours of an effective invasive predator, the Indo-Pacific lionfish (Pterois spp.), and their prey, native parrotfish (Scarus iseri and S. taeniopterus), which are keystone herbivores on Caribbean coral reefs. We hypothesized that warming would increase both lionfish predatory behaviours and parrotfish foraging behaviours but would decrease parrotfish anti-predator behaviours. To test this, lionfish and parrotfish were placed in experimental mesocosms heated to 32 °C or 29 °C. Lionfish hunted significantly more at 32 °C than those at 29 °C, but only at midday. Lionfish at 32 °C also rested less and spent more time near parrotfish at midday. Although some parrotfish anti-predator behaviours like sheltering did not differ between temperature treatments, parrotfish activity levels (i.e., feeding, hovering, and swimming behaviours) increased at elevated temperatures. We also examined the effect of temperature on various growth metrics in lionfish and parrotfish but found no difference between treatments. Our findings suggest that climate change can potentially exacerbate the negative, predatory effects of invasive lionfish on native keystone prey, through warming effects on both predator and prey, which could lead to cascading impacts in coral reef ecosystems.