The massive growth or "algal bloom" that occurred recently in the lake was found to have been due to a dinoflagellate (microorganism) known as Ceratium.
"Dinoflagellate blooms are what we call red tide," said Dr. Macrina Tamayo-Zafaralla, project leader of a research tie-up between the University of the Philippines Los Baños (UPLB) and National Institute of Environmental Science-Japan that is monitoring Taal Lake.
The researchers spotted a wide brownish to reddish-brown portion in Taal Lake last May 17, or six days after typhoon "Caloy" wreaked havoc across Luzon, including Southern Tagalog.
"Ceratium was dominant in the lake in the peak of summer last April," Zafaralla said.
Typhoon "Caloy" was expected to flush out the bloom around fishcages in Taal Lake. However, instead of dissipating the "muddy water," it seemed to have dispersed the dinoflagellates, causing a wider expanse of brownish water with an even higher density of algae away from the fishcages.
The UPLB-National Institute of Biotechnology and Applied Microbiology, headed by director Teresita Espino, a member of Zafaralla’s team, has established that the saxitoxin (potent non-protein poison) in Ceratium is not the same as that secreted by the more commonly known marine dinoflagellate Pyrodinium.
"Saxitoxin causes paralytic shellfish poisoning or PSP which could lead to death through paralysis of internal organs, including the heart," Zafaralla said.
So far, there has been no reported PSP case in Taal Lake.
"We now have two algal species to watch out for in this lake," Zafaralla said.
One is the hepatotoxin-producing cyanobacterium or blue-green alga, Microcystis aeruginosa. This is the same blue-green alga species behind the algal bloom in Laguna de Bay.
Cyanobacterial hepatotoxins are known to cause liver disease and cancerous growth when ingested continuously in large quantities.
The amount of hepatotoxin in the entrails of tawilis (a popular fish species found in Taal Lake) had been below critical levels as of April 2006, according to the UPLB group monitoring the toxin.
"Microcystis and Ceratium blooms are caused by the lake’s becoming more and more enriched with nutrients, specially nitrogen and phosphorus. In other words, they are the offshoot of a polluted Taal Lake," Zafaralla said.
Although volcanic lakes are naturally rich in phosphorus, human activities generate undesirable and excessive amounts of phosphorus in the water.
Among these activities are aquaculture, dumping of garbage along the lakeshore, untreated sewage finding its way into the lake, and livestock and poultry wastes reaching the lake’s tributaries.
"It is high time the lakeshore municipalities come up with an integrated management plan for the entire lake watershed, if we want to prevent the water pollution from getting worse," Zafaralla said.
"The signs of degradation are already here. If the conditions are allowed to prosper, we might witness in our midst the repeat of animals dying and people succumbing to diseases gotten from the lake," she added.