Off the coast of La Jolla, California, the waters that glow electric blue during red tide events harbor a microscopic hunter with a strange trait: it glows, too, but not like anything else in the bloom. Researchers at the Scripps Institution of Oceanography have now measured the bioluminescent flash of Polykrikos kofoidii, a single-celled predator that feeds on the toxic plankton behind red tides, and found that its light pulses are distinctly slower and dimmer than the rapid, bright bursts produced by its prey.
The findings, published in spring 2026 in the Journal of Phycology by a team led by bioluminescence researcher Michael Latz at UC San Diego, challenge assumptions about why marine microorganisms glow and open new questions about whether a predator’s muted flash could actually help it hunt.
A predator that glows on its own terms
P. kofoidii is a heterotrophic dinoflagellate, meaning it does not photosynthesize. It survives by actively hunting other dinoflagellates, including bloom-forming species like Alexandrium and Gymnodinium that produce the neurotoxins associated with harmful algal blooms. A 2017 paper by Gavelis et al. in Science Advances showed it captures prey using harpoon-like structures called nematocysts, organelles that fire into target cells with remarkable speed. Separate laboratory work by Jeong et al., published in 2001 in the Journal of Eukaryotic Microbiology, quantified its grazing rates, showing it can substantially reduce prey populations in culture over hours to days.
What the Latz team wanted to know was how this predator’s own bioluminescence compares to the light produced by the organisms it eats. To find out, they cultured P. kofoidii from seawater collected at Scripps Pier and measured its light output using spectroscopy, high-resolution photometry, advanced microscopy, and genetic analysis.
A slower, dimmer flash
The spectral peak of P. kofoidii‘s bioluminescence landed at approximately 474 nanometers, placing it in the blue-green range common among marine plankton. Blue-green light travels efficiently through seawater, so the wavelength itself was not a surprise. The flash profile was.
Compared to autotrophic dinoflagellates like Alexandrium, which produce rapid, intense bursts of light, P. kofoidii‘s flash rose more slowly and generated less total light. That pattern held across repeated stimulations of cultured cells, suggesting a stable physiological trait rather than random noise. These spectral and flash-kinetics measurements come from the Latz et al. paper in the Journal of Phycology (spring 2026), which serves as the primary source for the core physical data in this story.
High-resolution imaging revealed a possible structural explanation. In classic bioluminescent dinoflagellates like Lingulodinium, the light-emitting organelles known as scintillons are compact, discrete bodies clustered near the cell surface. In P. kofoidii, the luciferin-containing structures appeared more diffuse and less tightly organized. That architectural difference could account for the slower rise time and lower intensity.
Does a dim glow help a hunter?
In many bioluminescent plankton, the flash is thought to serve as a defense. A bright burst can startle a predator or act as a “burglar alarm,” attracting larger animals that eat the attacker, according to a Scripps Institution of Oceanography overview of red tide bioluminescence. Under that framework, prey species benefit from the fastest, brightest flash they can produce.
A predator faces a different calculus. A cell that glows less brightly and more slowly could, in theory, avoid tipping off light-sensitive prey before striking, particularly in the dark conditions when red tide bioluminescence is most visible. P. kofoidii‘s subdued flash might reduce the chance that its approach is detected, or it might simply reflect lower investment in a trait that no longer serves a primarily defensive purpose.
For now, those ideas remain hypotheses. The Journal of Phycology study did not test behavior during active predation, and no published data yet link P. kofoidii‘s light properties directly to hunting success. The connection between its unusual flash and its feeding ecology is suggestive, not proven.
Lab results vs. open water
All bioluminescence measurements in the study come from laboratory cultures, not from wild populations during active red tide events. That distinction matters. Natural conditions, including variable turbulence, patchy prey distribution, and fluctuating oxygen levels, can influence how and when dinoflagellates flash. A behavior that appears muted in a controlled setting could be amplified in the ocean if, for example, wave-driven mechanical stimulation triggers different response pathways.
Salinity adds another variable. A separate study published in Marine Biology examined how salinity changes affect the bioluminescence intensity of P. kofoidii alongside two other species, Noctiluca scintillans and Alexandrium mediterraneum. That work found P. kofoidii‘s light output is sensitive to salinity shifts, dimming outside a relatively narrow optimal range. If future conditions along the California coast trend toward lower salinity due to increased runoff, this predator’s already faint glow could become even fainter, potentially erasing whatever signaling role it might serve.
No independent experts outside the UC San Diego group have publicly weighed in on the ecological implications. Commentary from harmful algal bloom modelers and sensory ecologists would help clarify whether the unusual flash kinetics observed in the lab hold up in nearshore and open-ocean conditions.
What this means for red tide science
The practical takeaway is specific but meaningful. Scientists have now characterized the bioluminescent machinery of a confirmed natural predator of red-tide plankton and found it to be more complex and idiosyncratic than previously assumed. P. kofoidii is not just another glowing cell in the bloom. Its light is physically different from that of its prey, and understanding why could eventually inform how marine biologists model bloom suppression in warming, freshening coastal waters.
That work is still ahead. The discovery opens a line of inquiry rather than settling a debate, underscoring how much remains unknown about the roles that even faint flashes of bioluminescence play in the microscopic battles shaping coastal ecosystems off Southern California and beyond.
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*This article was researched with the help of AI, with human editors creating the final content.
