Microplastics and Daphnia Swimming Paths

ISEF Category: Animal Sciences

Subcategory: Animal Behavior  ·  Difficulty: Advanced  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

Tiny water fleas can act like living motion sensors. When their water changes, their paths can change too. That makes Daphnia magna a strong model for studying stress from microplastics. You can turn those wiggles into real movement data.

What Is It?

Daphnia magna are tiny freshwater crustaceans. They swim by making short hops and pauses, so their paths look a lot like dots on a map. In clean water, those paths often stay fairly steady. In water with microplastics, the animal may change speed, turn more often, or spend more time drifting in odd bursts.

Researchers can describe these paths with two motion models. Brownian motion looks like a random walk with lots of small, similar steps. Lévy-flight-like motion has many small steps, plus a few longer jumps. Think of it like comparing a toddler pacing in a room to someone wandering with sudden dashes across the hall. If microplastics stress the animal, its swim pattern may shift toward one model or away from it.

Why This Is a Good Topic

This topic gives you a clear variable, a visible response, and a way to collect quantitative data. You can change microplastic exposure and measure movement patterns with video tracking, which makes the project testable and data rich. The topic also connects to pollution, aquatic ecology, and animal stress, so your results have a real-world meaning. You can learn experimental design, motion analysis, and basic statistics in one project.

Research Questions

• How does microplastic concentration affect the average swimming speed of Daphnia magna?
• What is the effect of microplastic particle size on the turning rate of Daphnia magna?
• Does exposure to microplastics change the step-length distribution of Daphnia magna swimming paths?
• To what extent do Daphnia magna trajectories match a Brownian model after microplastic exposure?
• Which microplastic shape, bead or fiber, causes a larger shift in path tortuosity?
• How does exposure time change the fraction of long movement steps in Daphnia magna?

Basic Materials

• Live Daphnia magna culture
• Small clear observation chambers or petri dishes
• Compound or dissecting microscope with camera attachment
• Digital microscope camera or smartphone adapter
• Freshwater or culture medium
• Microplastic samples with known type and size
• Plastic transfer pipettes
• Fine-tipped pipettes
• Glass beakers or cups for separate treatments
• Timer
• Temperature probe
• White background or light box for imaging
• Computer for video storage and analysis
• Cleaning supplies for cross-contamination control.

Advanced Materials

• Live Daphnia magna culture
• Inverted microscope with camera
• Multi-well plates or glass observation chambers
• Microfluidic or controlled exposure chamber
• Stereomicroscope for transfer and sorting
• Fluorescence or labeled microplastics, if available
• Analytical balance
• Particle size characterization tools, such as laser diffraction or microscopy image analysis
• Environmental chamber or temperature-controlled room
• High-resolution video capture system
• Calibration slide
• Reference tracer particles for tracking validation
• Water quality meters for dissolved oxygen, pH, and conductivity
• Statistical software for motion-model fitting.

Software & Tools

• ImageJ: Measures body position and helps extract frame-by-frame movement from video.
• ToxTrac: Tracks animal paths and calculates speed, turning angle, and tortuosity.
• Python: Fits motion models and compares Brownian and Lévy-like movement statistics.
• R or RStudio: Runs summary plots, hypothesis tests, and model comparisons.
• Tracker: Lets you mark and export motion points from video when automatic tracking fails.

Experiment Steps

1. Define the exposure question, then choose one microplastic variable to change first.
2. Set up a tracking method that can capture whole-path movement without losing the animal between frames.
3. Build a control group and a clean-water baseline so you can separate stress effects from normal motion.
4. Plan how you will turn each path into numbers, such as step length, turning angle, and path tortuosity.
5. Decide how you will compare motion models, including which fit statistic or distribution test will decide the better match.
6. Map out replication, randomization, and exclusion rules before you start collecting videos.

Common Pitfalls

• Letting room light change between recording sessions, which can confuse the tracking software and distort path measurements.
• Using mixed microplastic sizes in the same treatment, which makes it hard to tell which particle type caused the movement change.
• Tracking animals that hit the chamber wall too often, which inflates turning rates and weakens the model fit.
• Overcrowding the observation chamber, which changes swimming behavior and creates path overlap in the video.
• Skipping a clean-water control batch, which leaves you unable to tell whether the movement shift came from microplastics or handling stress.

What Makes This Competitive

A stronger version of this project compares more than one microplastic trait and uses a model-based analysis, not just a simple speed change. You can raise the level by testing whether the full path distribution fits Brownian or Lévy-like motion better under each exposure. Good replication, clean controls, and a clear statistical rule for model choice will matter more than a flashy setup. A novel sample type or a careful comparison across particle shape, size, or concentration can make the project stand out.

Project Variations

• Compare beads, fragments, and fibers to see which shape alters Daphnia magna path structure most.
• Test whether short-term and longer-term exposure produce different movement signatures in the same species.
• Compare natural sediment particles, microplastics, and clean-water controls to separate physical irritation from pollution stress.

Learn More

• NOAA Marine Debris Program: Search for microplastic background material and pollution reports on the NOAA website.
• NIH PubMed: Search for review articles on microplastics and aquatic invertebrate behavior.
• USGS Water Resources: Find plain-language reports on water pollution, particle transport, and freshwater monitoring.
• Ecotoxicology and Environmental Safety: Search the journal for studies on microplastics and animal movement.
• MIT OpenCourseWare: Look for free ecology, statistics, and data analysis courses that support experimental design.