Swimming in an Unsteady World

Area of Science:

• Fluid dynamics
• Marine ecology
• Biophysics

Background:

• Aquatic animal locomotion occurs in flowing water, necessitating an understanding of interactions with turbulent currents.
• Microscopic invertebrate larvae in fouling communities face challenges in dispersal and recruitment within dynamic aquatic environments.

Purpose of the Study:

• To investigate how the swimming behavior of microscopic larvae affects their transport and interaction with surfaces in turbulent water flow.
• To model larval trajectories considering swimming, sinking, rising, and passive buoyancy in relation to ambient flow and chemical cues.

Main Methods:

• Field measurements of water motion over fouling communities to replicate turbulent flow in a laboratory wave-flume.
• Particle-image velocimetry (PIV) for water velocity and planar laser-induced fluorescence (PLIF) for dye concentration (chemical cues).
• Individual-based modeling of larvae with different motile behaviors (swimming, sinking, rising, neutral buoyancy).

Main Results:

• Swimmers exhibited greater vertical movement in turbulent flow compared to neutrally buoyant larvae.
• Passive sinking and rising larvae showed directional settlement, while swimming larvae were better at colonizing unpredictable surfaces.
• Larvae nearing surfaces should cease swimming to settle; swimming and rising larvae are effective at dispersing away from surfaces.

Conclusions:

• Larval swimming behavior significantly impacts transport, settlement, and dispersal in turbulent aquatic environments.
• Locomotory behavior influences encounters with environmental signals like chemical cues and fluid vorticity near surfaces.
• Understanding larval swimming dynamics is key to predicting population connectivity and ecological interactions in marine fouling communities.