Red tide warning raised in Lianga Bay

SAN FRANCISCO, Agusan del Sur (MindaNews/27 October) — The Bureau of Fisheries and Aquatic Resources in Caraga (BFAR-13) has again declared Lianga Bay in Surigao del Sur positive for toxic red tide following laboratory tests confirming the presence of paralytic shellfish toxins (PST) beyond safe levels.

In its latest advisory released on October 25, 2025, BFAR-13 reported PST levels ranging from 113 to 286.714 micrograms per 100 grams of shellfish meat collected from the coastal waters of Barobo town.

The agency warned the public against harvesting, selling, or eating any shellfish and Acetes species (locally known as “alamang”) from Lianga Bay until further notice.

BFAR 13 stated that fish, squid, shrimp, and crabs caught from the area are safe for consumption, provided they are fresh and thoroughly cleaned by removing the gills and internal organs before cooking.

Lianga Bay has been placed under repeated red tide warnings in recent years. BFAR records show that the bay was also found positive for paralytic shellfish poison in 2022 and 2024.

The ban was briefly lifted when the bay tested negative for PSP on April 16 this year, but the toxins have reappeared.

Marine scientists attribute the recurring outbreaks to nutrient buildup and poor water circulation in semi-enclosed bays like Lianga.

Runoff from agricultural lands and nearby communities is also believed to contribute to algal blooms that generate the toxic organisms responsible for paralytic shellfish poisoning.

According to Dr. Rhodora V. Azanza of the University of the Philippines Marine Science Institute and Dr. Aletta T. Yñiguez, an expert in Pyrodinium dynamics and ecological modelling, the recurrence of toxic red tide events in Lianga Bay reflects the same environmental patterns observed across Philippine coastal waters.

Their research points to nutrient enrichment, weak flushing, and the life cycle of Pyrodinium bahamense—which forms resting cysts in sediments that can germinate under favorable conditions—as the main causes of repeated PSP events.

Yñiguez’s studies using integrated hydrodynamic and ecological models show that long water residence times and bursts of freshwater and nutrient inflows can trigger rapid Pyrodinium growth, leading to spikes in toxin levels among shellfish.

Azanza’s field studies also link recurring red tide episodes to coastal nutrient stress and the increasing occurrence of harmful algal blooms in the country.

BFAR and local authorities continue to monitor toxin levels in Lianga Bay to determine when it will be safe to lift the ban. Residents and fishers have been urged to comply with advisories to prevent paralytic shellfish poisoning cases.

Local fishermen and shellfish gatherers in Barobo and nearby towns continue to suffer losses each time a red tide warning is raised. Authorities said continuous monitoring is being done until toxin levels drop to safe limits.

BFAR and local government units have reminded residents to stay alert and follow advisories to prevent poisoning incidents. (Chris V. Panganiban /MindaNews)