2:55 PM - 3:10 PM
[ACG41-05] Turbulence effects on zooplanktivory by free-swimming damselfish and anchored garden eels in coral reefs
Keywords:flow, small-scale turbulence, fish feeding, fish locomotion, biomechanics
Water flow has a major impact on feeding of zooplanktivorous fish, as it affects motions of both active predators and their drifting prey. As such, understanding flow conditions in fish habitats and feeding responses to flows are important to predict ecological traits such as adaptation and habitat selection.
Previous studies have mostly focused on effects of uniform flow to simplify hydrodynamic factors but have overlooked effects of turbulence, which is characterized by chaotic changes in flow speed and direction, and ubiquitous in natural fish habitats. Here, we evaluated turbulence in fish natural habitats and investigated effects of small-scale turbulence on feeding in a controlled flume for zooplanktivorous reef fish with different feeding styles: free-swimming hunters (damselfish) and anchored predators (garden eels).
Free-swimming fish and anchored garden eels live in hydrodynamically different habitats; free fish inhabits relatively shallow water (<5 m deep) with rough bottom covered by corals and rocks whereas anchored fish inhabits deeper water (>10 m deep) with smoother bottom mainly covered by fine sand. Turbulence measurements in each habitat showed that the free fish experience relatively faster mean flow and stronger turbulence dominated by wave-driven oscillatory flows whereas anchored fish encounter slower mean flow and weaker turbulence dominated by unidirectional tidal flows.
To understand effects of small-scale turbulence on their feeding, we generated turbulent flows in a flume at levels similar to those measured in reefs. Three-dimensional reconstructions of feeding motions were obtained under three levels of turbulence and two flow speeds in a custom-made flume. Strong turbulence level caused significant reduction in feeding rate of free and anchored fish at slow and fast flow speed, respectively. Under these conditions, free-swimming fish significantly reduced their foraging area, whereas anchored garden eels experienced a significant decrease in their success rate. Turbulence did not significantly affect strike distance, strike duration, strike speed, or reactive distance in either feeding style of fish.
By combining flow measurements in fish habitats with controlled laboratory experiments, we found that free and anchored fish own feeding strategies adapted to their geometries and hydrodynamic conditions in each habitat.
Previous studies have mostly focused on effects of uniform flow to simplify hydrodynamic factors but have overlooked effects of turbulence, which is characterized by chaotic changes in flow speed and direction, and ubiquitous in natural fish habitats. Here, we evaluated turbulence in fish natural habitats and investigated effects of small-scale turbulence on feeding in a controlled flume for zooplanktivorous reef fish with different feeding styles: free-swimming hunters (damselfish) and anchored predators (garden eels).
Free-swimming fish and anchored garden eels live in hydrodynamically different habitats; free fish inhabits relatively shallow water (<5 m deep) with rough bottom covered by corals and rocks whereas anchored fish inhabits deeper water (>10 m deep) with smoother bottom mainly covered by fine sand. Turbulence measurements in each habitat showed that the free fish experience relatively faster mean flow and stronger turbulence dominated by wave-driven oscillatory flows whereas anchored fish encounter slower mean flow and weaker turbulence dominated by unidirectional tidal flows.
To understand effects of small-scale turbulence on their feeding, we generated turbulent flows in a flume at levels similar to those measured in reefs. Three-dimensional reconstructions of feeding motions were obtained under three levels of turbulence and two flow speeds in a custom-made flume. Strong turbulence level caused significant reduction in feeding rate of free and anchored fish at slow and fast flow speed, respectively. Under these conditions, free-swimming fish significantly reduced their foraging area, whereas anchored garden eels experienced a significant decrease in their success rate. Turbulence did not significantly affect strike distance, strike duration, strike speed, or reactive distance in either feeding style of fish.
By combining flow measurements in fish habitats with controlled laboratory experiments, we found that free and anchored fish own feeding strategies adapted to their geometries and hydrodynamic conditions in each habitat.