Collaborative Research: Development of a Swarm of Autonomous Subsea Vehicles to Infer Plankton Growth and Transport

Marine plankton are likely the most important components of marine ecosystems: the phytoplankton produce oxygen as they create organic carbon through photosynthesis, while the zooplankton transfer this organic carbon to top predators such as fish, seabirds, marine mammals, and humans. Despite being relatively weak, plankton swimming behaviors can play an important role in determining their distribution and survival: swimming allows plankton to find food, reproduce, and avoid predators in a dynamic and patchy fluid environment.

These behaviors also influence plankton dispersal and survival by modulating the ocean conditions that the plankton experience. Because it is presently impossible to track individual plankton for long periods in situ, current insights into the trade-offs and benefits associated with plankton behaviors have only been gained from experiments in controlled settings and from numerical models.

Having drifting vehicles that simulate planktonic behaviors would enable unique and powerful insights into how plankton interact with the currents and properties of their environment. During this project, investigators will develop small, next-generation, subsurface, autonomous, buoyancy-controlled vehicles – plankton mimics – to study how relatively simple behaviors of plankton can alter their transport and environment.

By sampling the ocean like planktonic organisms, this unique vehicle swarm will give plankton researchers unprecedented data to validate experimental and model predictions, and, hopefully, reveal previously unknown mechanisms driving planktonic population dynamics.

To accomplish the above goals, a swarm of 20 quasi-Lagrangian underwater vehicles will be fabricated. The vehicles will mimic plankton behavior and will be tracked in 3D for 24–72 hours. These goals will be achieved based on several novel technological advances: 1) improved subsurface localization using the most recent developments in acoustic modem technology at reduced cost, 2) subsurface vehicle communication with surface buoys to relay vehicle information (e.g., data, location) to scientists on a nearby ship to facilitate additional ship-based sampling, and 3) a near-incompressible housing and drag skirts to improve the vehicles’ ability to follow fluid velocities and provide a ‘no behavior’ mode.

The swarm will be optimized to investigate biological-physical interactions at spatial scales up to 10 km, focusing on internal waves and fronts. Ultimate performance tests will target high-frequency internal waves, acquiring vehicle trajectories with a spatial resolution of tens of centimeters vertically, sub-meters horizontally, and a temporal resolution of minutes.

Additional sensors will provide along-track information on ocean temperature, salinity, irradiance, and chlorophyll-a. These data will provide unique time series of physical and environmental data along planktonic trajectories in the ocean. The vehicle swarm will generate multiple tracks showing the environmental properties in 3D along with the physical transport associated with different behaviors in the similar environments.

Such tracks will lead to insights regarding the cues and consequences of behaviors in the plankter’s natural environment.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.