Grazer cues induce stealth behavior in marine dinoflagellates

Area of Science:

• Marine biology
• Phytoplankton ecology
• Zooplankton-phytoplankton interactions

Background:

• Chain formation is a common strategy in phytoplankton, but its ecological drivers and consequences remain unclear.
• Understanding how phytoplankton respond to predation pressure is crucial for marine food web dynamics.

Purpose of the Study:

• To investigate the impact of copepod grazing cues on chain formation in the dinoflagellate Alexandrium tamarense.
• To determine how changes in chain length affect swimming behavior and predator encounter rates.

Main Methods:

• Exposing Alexandrium tamarense chains to waterborne cues from copepod grazers.
• Analyzing cell splitting and chain length changes in response to cues.
• Conducting motion analysis to quantify swimming velocities of single cells and chains.
• Simulating predator encounter rates based on swimming behavior and chain length.

Main Results:

• Copepod cues significantly impaired chain formation, causing cells to split into single cells or shorter chains.
• Single cells exhibited lower swimming velocities compared to chains.
• Two- and four-cell chains had significantly higher simulated predator encounter rates than single cells.
• Grazed two-cell chains swam slower, reducing their encounter rates with grazers.

Conclusions:

• Chain length plasticity and altered swimming behavior are key mechanisms for dinoflagellates to avoid copepod grazers.
• Dinoflagellates can modulate motility and predator avoidance by adjusting chain length.
• The high predator encounter rate for motile chains may explain the lower prevalence of chain formation in motile phytoplankton compared to nonmotile species.