How Formosa’s toxin caused the mass fish deaths in Vietnam

By VnExpress   July 4, 2016 | 05:39 am PT
Phenol and cyanide are the two poisonous substances to blame.

In the central province of Ha Tinh, a group of scientists has run a survey at two sites in Ron Ma and Son Duong islands, 7.5 kilometers from Formosa’s wastewater output. The seabed at Ron Ma had many big rocks and attaching creatures. Coral scattered, failing to merge and form reefs. The corals that died are mostly of genera Favia, Turbinaria, Favites, Goniastrea, Montipora. Typical coral reef fishes like Holocentridae and Chaetodontidae reduced to a population of less than 30 individuals per 250 square meters of coral reef’s area.


Approximately 35 percent to 40 percent of coral at Son Duong died, most of which are of genera Acropora and Montipora.


There were only a few small and economically insignificant individuals of genera Apogonidae and Macropodusinae. Despite the terrain being cut and holey, the group didn’t find any fish of genus Gobiidae - which is usually found in clean waters.


At Hon La area (Quang Binh Province), the experts found coral to distribute along the coast to a depth of four meters, typically genus Acropora, though 45 percent of which were dead.


There was only 10 percent of coral left at Hon Nom (Vung Chua, Quang Binh Province). Most of dead coral belongs to genera Montipora, Favia, Favites and Goniastrea.


The typical coral reef fishes such as Amphiprioninae have disappeared.


Studies at Cua Tung, Quang Tri Province, show poor creature distribution, and a lack of fishes with economical value. The group of experts didn’t find a trace of lobster’s larvea - though it’s the best time of the year to harvest this crustacean. Above is the individuals of fish found on the seabed.

The experts found the remaining of a dead oyster, the flesh of which decomposed, and many oyster shells scattering the seabed.

The experts found the remains of a dead oyster, which flesh has already decomposed, and many oyster shells scattering the seabed.


At Thua Thien - Hue beach area, the experts surveyed Son Cha Island. Much of coral here died, turning white, mostly genera Montipora, Pachyseris, Galaxea and Pocillopora. Fishes with economical values and typical for coral reef disappeared. Before, the density of fishes with economical values was high, but at the time of the survey, no mother fish group was observed.


The coral reef at Bat Chuoi, northern Hai Van area in Thua Thien - Hue, was also found dead and turned white. A major part of them was of genera Acropora and Montipora.


Seabed sediment at some points was covered in a yellow brown layer.


Dead crab in a coral hole at Bai Chuoi


An individual of caranx ignobilis, a genus of fish, found dead afloat. Besides bio-diversity decrease, another problem that worries the experts is that the death fish phenomenon would lead to the loss of traditional birth places of high economical value fishes.


According to some scientists, some waste substances will be diluted with time, but it might take hundreds of years to revive the coral reef, depending on the degree of pollution.

Photos courtesy of Vietnam Academy of Science and Technology

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