How dangerous is cyanide to marine life?

Botlles of cyanide were seized by the Philippine Navy from Chinese boats near the BRP Sierra Madre in Ayungin Shoal in the West Philippine Sea (WPS), according to the National Security Council (NSC).

Widely known as a deadly substance, how dangerous is cyanide to a marine environment such as those found in the WPS?

Composed of carbon, hydrogen, and nitrogen, cyanide is a highly toxic chemical compound that poses serious risks to both human health and marine ecosystems, according to the Bureau of Fisheries and Aquatic Resources (BFAR).

Out in the sea, the compound is often used in destructive fishing practices. Cyanide fishing involves dissolving the chemical in seawater and spraying it onto coral reefs to stun fish, making them easier to catch. But the practice causes lasting harm to marine habitats.

Cyanide is extremely lethal because it disrupts the body’s ability to use oxygen at the cellular level.

Fish exposed to cyanide exhibit clear signs of distress, including rapid breathing, gasping for air at the surface, erratic swimming, muscle incoordination, and eventually, death.

Coral exposed to the chemical die, often turning white before becoming overgrown with algae. Unlike damage caused by explosives, cyanide leaves coral structures intact but lifeless.

BFAR emphasized that coral reefs are vital ecosystems that support marine biodiversity and provide livelihoods for coastal communities. 

Coral destruction can lead to long-term environmental and economic consequences.

The use of cyanide in fishing also affects livelihoods and tourism, leading to reduced food supply, loss of income for fisherfolk, unemployment, and a decline in tourism in affected areas.

This is not the first time the Chinese were caught using cyanide.

In October 2025, the Armed Forces of the Philippines (AFP) said its Western Command prevented Chinese fishing boats from conducting illegal fishing activities near Ayungin Shoal in the West Philippine Sea (WPS). Several bottles containing suspected cyanide were also confiscated during the incident.  —RF, GMA News