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04/28/2026 | Press release | Distributed by Public on 04/28/2026 16:18

“Ruthless Predator” of Red Tide Plankton Revealed in New Study

Published Date

April 28, 2026

Article Content

Scientists at UC San Diego's Scripps Institution of Oceanography have uncovered new insights into the bioluminescence of a unique species of marine plankton that feeds on other plankton, including the harmful algae responsible for red tides and algal blooms.

Red tides occur when certain types of microscopic plankton, called dinoflagellates, rapidly multiply in the ocean, forming dense "blooms" that can discolor the water. The species most frequently behind these bloom events in Southern California is Lingulaulax polyedra (previously named Lingulodinium polyedra), which can produce spectacular bioluminescent displays at night during large bloom events. While this species dominates certain red tide events, it's not without predators.

In a new study published in the Journal of Phycology, Scripps Oceanography researchers investigated one such red tide hunter: Polykrikos kofoidii. This little-understood but globally distributed dinoflagellate is strictly heterotrophic - meaning it's a predatory species - and uses harpoon-like structures to snare prey, including toxic and bloom-forming plankton. Unlike many of the organisms it consumes, P. kofoidiidoes not form blooms, but it is capable of producing light.

Michael Latz, a marine biologist emeritus at Scripps Oceanography and co-lead author of the study, described P. kofoidii as "a ruthless predator," noting that the species has been difficult to study in the lab due to challenges in keeping it alive in culture.

This clip shows how P. kofoidii snares a prey cell of L. polyedra, spearing it with a harpoon-like structure and then reeling it in to engulf it whole. The footage was recorded as part of a separate study on dinoflagellates and is credited to Gregory Gavelis et al.

He and the research team established a laboratory culture of the organism, which was isolated from seawater collected at the Scripps Pier, and examined its light-producing behavior and cellular structure using spectroscopy, advanced microscopy and genetic analysis.

Dinoflagellates are single-celled organisms that are well known for producing flashes of blue-green light, most visibly at night when they are agitated by crashing waves or other movement during red tide events. In most species, this light originates from specialized structures inside the cells called scintillons, which house the molecules responsible for the light-producing chemical reaction. The research team was surprised to learn that this conventional setup was different for P. kofoidii.

"We made new discoveries into how Polykrikos kofoidii and other microorganisms emit light, which could lead to a better understanding of marine ecosystems, as well as the evolution, chemistry and potential functions of bioluminescence," said co-lead author Brittany Sprecher, who conducted the research as a postdoctoral fellow at Scripps Oceanography and is now a postdoctoral researcher at Woods Hole Oceanographic Institution.

Sprecher also noted that beyond its unusual bioluminescence, P. kofoidii stands out for its "fascinating hunting behavior," which is unique among dinoflagellates.

Other dinoflagellate predators, such as the Protoperidinium, also described in the study, snare prey and then envelop them using a feeding veil, called a pallium, digesting them externally before discarding the remains. The most widely distributed heterotrophic dinoflagellate is Noctiluca scintillans, or "sea sparkle," recognized globally for its bioluminescence and its ability to consume many plankton species, including phytoplankton and zooplankton.

"Feeding strategies like these are sophisticated forms of predation for single-celled organisms that have been around for several hundred million years, and yet we still have much to learn about these creatures," said Latz, who has studied dinoflagellate bioluminescence for more than 45 years.

Dinoflagellate differences

Using high-resolution photometry, the team found that the light flashes produced by P. kofoidiiare slower and dimmer than those of other bioluminescent dinoflagellates. Individual flashes lasted longer and rose to peak brightness more gradually, producing a distinct "light signature" that could help scientists identify the species in ocean measurements of natural bioluminescence.

Despite these differences in flash behavior, the color of the emitted light - blue-green with a peak of around 474 nanometers - was similar to that of other glowing dinoflagellates. This indicates that the underlying chemistry of the light-producing reaction is shared across species.

At the cellular level, researchers also identified a key difference in how P. kofoidii organizes its light-producing system. In most dinoflagellates, the molecule responsible for light production - luciferin - is confined to scintillons, but in P. kofoidii, it was spread throughout the whole cell.

"We were surprised to see this fluorescence distributed across the entire cell, rather than concentrated in distinct organelles," said Latz. "This suggests that Polykrikos kofoidii may store or regulate its light-producing molecules in a fundamentally different way from other species."

Confocal microscope image of a live Polykrikos kofoidii cell. The nuclei ("Nu"), nematocysts used for hunting (black arrows), and ingested prey cells (asterisks) are visible. Credit: Brittany Sprecher and Michael Latz

Genetic analysis further illuminated the unique biology of the species, indicating that the evolution of bioluminescence in dinoflagellates may be more diverse than previously thought.

"We are still investigating why and how this organism uses such an unusual setup and whether this trait is found in other understudied dinoflagellates," said Sprecher. "We also identified interesting features in the proteins involved in its bioluminescence."

Challenges and next steps

According to the study authors, the predatory impact of P. kofoidii on red tide populations needs to be further assessed to determine its role in regulating harmful algal blooms.

The research also highlights a potential challenge for ocean monitoring. Because P. kofoidii ingests whole cells of photosynthetic prey that can remain fluorescent inside their bodies, instruments that measure chlorophyll fluorescence could mistakenly count these predators as photosynthetic algae, potentially leading to overestimates of primary production in the ocean.

Scripps Oceanography marine biologist Dimitri Deheyn, a co-author of the study, said the findings open "many new doors" to research, including questions scientists had not previously considered.

"In terms of applications, could P. kofoidii be used to help manage toxic algal blooms that are known to devastate coastal economies? It's possible that growing large cultures could point to future solutions," said Deheyn.

Sprecher added that the study highlights how much remains unknown about bioluminescence across species.

"There is still much to discover when it comes to these organisms, and even well-studied biological processes can hold unexpected surprises," she said.

The study was funded by a National Science Foundation Postdoctoral Research Fellowship in Biology, awarded to Sprecher, and a grant from the National Institute of Neurological Disorders and Stroke to the UC San Diego School of Medicine Microscopy Core.

The authors collect seawater from Scripps Pier to find samples of P. kofoidii. Photo: Brittany Sprecher
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