Aquarius Resurfaced: Ecology of fear in plant-eating coral reef fish

In November 2013, during FIU’s first Aquarius mission, researchers used fiberglass models of predatory fish to study how the risk of predation changes the behavior of herbivorous fish (plant eaters) on coral reefs. They used models of the great barracuda (Sphyraena barracuda) and black grouper (Mycteroperca bonaci) to investigate how anti-predator responses vary with predator identity and time of day. Barracudas employ a sit-and-pursue hunting strategy, while groupers employ a sit-and-wait strategy. 

The team examined how the behavior of herbivorous fish (e.g., parrotfish and surgeonfish) changed in the presence of these predator types by measuring the amount of plant life that was eaten around the models. The scientists accomplished this by setting up seagrass feeding plots placed at varying distances from the models and then measuring the amount of seagrass that was eaten at different times of day. They also used cameras to record the different species of herbivorous fish that visited the plots. 

Researchers found that the herbivorous fish responded to both predators in similar ways, but herbivore feeding changed depending on time of day and the distance the feeding plots were from the models. At dawn, herbivores were found to forage more the further they got from the predator models; by mid-day, however, herbivores fed less in the presence of the barracuda model compared to the grouper model. This suggests that the hunger level of the herbivorous fish and differences in the hunting strategy of predators may influence the foraging patterns of herbivorous coral reef fish. Understanding how the time of day, predator species and the herbivore’s response to the predator models influence the role predators play in affecting the behavior of fish on coral reefs.

This research study has broader impacts for teaching us how the decrease in predator abundance due to overfishing can affect coral reef ecosystems. If predator presence can control herbivory on coral reefs, the findings of this research offer insight to the changes that can be expected if predator abundance continues to be reduced.

This work was greatly enhanced by the extended bottom times afforded by saturation diving aboard Aquarius. Throughout the seven-day mission, the aquanaut team spent over 100 hours diving to depths of between 60-108 feet. This project would have taken months to complete if divers were limited to diving from the surface. 

Aquanaut team: 

Additional science team: