Marine Fungus Found to Kill Toxic Red Tide Algae

A Tiny Destroyer in the Mediterranean

A microscopic fungus discovered in Mediterranean waters may hold the key to combating one of the ocean's most persistent environmental threats. Scientists have formally described a new species — and entirely new genus — of marine chytrid fungus named Algophthora mediterranea, which can infect and kill toxic algae responsible for so-called harmful algal blooms (HABs), commonly known as red tide. The findings, published in the journal Mycologia, have drawn attention from marine biologists worldwide.

The name says it all: Algophthora combines the Latin word for alga with the Greek phthora, meaning destruction. First detected in Spanish coastal waters in 2021 by researchers at the Institut de Ciències del Mar (ICM) in Barcelona, led by Dr. E. Garcés and Dr. A. Reñé, the organism was later formally described by Professor Maiko Kagami and PhD student Núria Pou-Solà at Yokohama National University in Japan.

The Alga It Hunts

The fungus's primary target is Ostreopsis cf. ovata, a benthic dinoflagellate that has been spreading with increasing frequency across the Mediterranean and other temperate seas. During bloom events, Ostreopsis produces a potent toxin called ovatoxin (OVTX), which can trigger a cascade of health symptoms in beachgoers and coastal residents — from runny nose and coughing to shortness of breath, conjunctivitis, and skin irritation. In severe cases, respiratory distress can require medical attention.

Beyond human health, these blooms devastate local marine ecosystems, suffocating seabed organisms and disrupting food webs. Warming seas and coastal nutrient pollution have made such events more frequent and more intense in recent decades, according to NOAA's Harmful Algal Bloom program.

How the Fungus Works

Laboratory experiments revealed that Algophthora mediterranea operates as a lethal parasite: it infiltrates individual algal cells and kills them within days. What makes the discovery especially striking is the fungus's versatility. Cross-infection experiments confirmed it can infect not only Ostreopsis but also other dinoflagellates and diatoms — making it the first known chytrid fungus with such a broad phytoplankton host range. It can even survive on pollen grains, suggesting a remarkable ecological adaptability.

Chytrids are a diverse and ancient group of aquatic fungi, but their role in marine ecosystems has been largely overlooked. This discovery suggests they may influence phytoplankton dynamics far more than previously understood.

Biological Control — Promise and Caution

The potential implications for managing harmful algal blooms are significant. Current control strategies — including clay dispersal, hydrogen peroxide application, and physical barriers — carry environmental risks or are impractical at scale. A naturally occurring parasite that specifically targets toxic algae offers a theoretically cleaner alternative.

However, the researchers are quick to temper expectations. They caution that Algophthora mediterranea should not be viewed as a ready-made biocontrol agent. Its broad host range, while scientifically fascinating, also raises ecological questions: deploying it in open waters could affect non-target algal species that form the foundation of marine food chains. The discovery is best understood, they say, as a window into natural regulatory mechanisms that science is only beginning to map.

This aligns with a broader trend in HAB research. A separate 2025 study published in Communications Biology examined Amoebophrya parasites targeting Karenia mikimotoi blooms in Japanese waters, further underscoring the growing interest in parasitic organisms as ecological regulators of algal blooms.

A New Lens on Ocean Health

The discovery of Algophthora mediterranea is a reminder that the ocean's biological toolkit is far richer than science currently appreciates. As climate change intensifies the conditions that fuel toxic blooms, understanding — and potentially harnessing — the natural enemies of harmful algae may prove essential to protecting both coastal ecosystems and the communities that depend on them.