Red tide Philippines
Matarinao Bay, where the "red tide" was confirmed recently, covers the coastal waters of the Eastern towns of General MacArthur, Hernani, Quinapondan, and Salcedo. Image Credit: Google Maps

Manila: More than four months after it was deemed toxin-free, "red tide" has returned to Matarinao Bay in Eastern Samar province, the Bureau of Fisheries and Aquatic Resources (BFAR).

The reappearance of the red tide triggered at least in part by changes in weather patterns, according to the Philippine News Agency.

“To safeguard human lives, a local red tide warning is issued in this area as a precautionary advice to the public to refrain from gathering, selling, and eating all types of shellfishes and Acetes sp. locally known as alamang or hipon from the said bay,” BFAR was quoted as saying by the agency.

Red tide is a term used to describe a phenomenon where the water is discolored by high algal biomass or a high concentration of algae. 

It is caused by harmful algal blooms (HABs) triggered by the proliferation of certain types of algae that produce toxins.

The toxins can accumulate in shellfish and other seafood, posing risks to human health when consumed.

In mid-January 2023, BFAR relaxed the shellfish prohibition in Matarinao Bay. Moreover, paralytic shellfish poisoning (PSP) toxin was detected in the shellfish meat sample taken from the bay in Basey Town, Samar, according to a March 21 laboratory investigation.

Results of the agency's tests on shellfish samples revealed that there were more than 60 micrograms (μg) of toxins for every 100 grams of meat, above the allowed limit.

In the past, the Samar province's San Pedro Bay received a red tide notice from BFAR.

Signs of paralytic shellfish poisoning (PSP)

Early PSP symptoms include tingling of the lips and tongue and may progress to tingling of fingers and toes and then loss of control of arms and legs, followed by difficulty in breathing.

Red tide is a term used to describe a phenomenon where the water is discolored by high algal biomass or a high concentration of algae that are toxic to humans.

PSP which can occur minutes after ingesting bivalve shellfish (such as mussels, oysters, and clams) that contain red tide toxins.

What seafoods are safe?

BFAR said fish, squid, crab and shrimp gathered from these areas are safe to eat — provided that all entrails are removed and the marine products are washed thoroughly with running water before cooking.

The agency also urged residents and local government units to heighten their watch against gathering, trading and consumption of shellfish to prevent the incidence of

History of Philippine red tide incidents:

Red tide occurrences in the Philippines have been reported since the early 20th century.

1924: The first recorded red tide event in the country reported along the coasts of Manila Bay and Cavite.

1983: One of the most significant red tide incidents, affecting various coastal areas in the Philippines. This event led to severe economic losses in the fishing and shellfish industry and raised public health concerns.

1998: Affected several areas, including the waters of Bohol, Palawan, Masbate, and other regions. These incidents resulted in the temporary closure of shellfish harvesting areas, impacting local fishermen and the seafood industry.

2008: Red tide outbreaks occurred in various parts of the Philippines, including coastal areas of Cebu, Negros Occidental, and Masbate. These events led to the closure of shellfish gathering and trading, affecting local livelihoods.

2013: Red tide incidents were reported in parts of the Visayas region, particularly in the provinces of Samar, Leyte, and Biliran. Shellfish harvesting was temporarily banned in affected areas due to the presence of toxins.

In recent years, red tide occurrences have continued to be reported in different regions of the Philippines in recent years.

Various coastal areas, including those in Bicol, Western Visayas, Eastern Visayas, and other parts of the country, have experienced periodic red tide episodes, leading to the temporary closure of shellfish harvesting areas and trade restrictions.