The red tides that frequently haunt Guangdong waters are threatening the province's marine ecology and aquatic product cultivation.

Li Lei, a deputy inspector at the Guangdong Provincial Administration of Ocean and Fisheries, said large-scale red tides struck the province 16 times in 2012, covering an area of more than 741 square kilometers.

"Both the number of red tides that struck the province last year and the scale of the affected water were the largest in five years," Li told a news conference on Wednesday.

According to the ocean administration, Guangdong reported an average of 10 red tides annually in previous years. The red tide first hit the province in 1998.

The waters at the mouth of the Pearl River, Daya Bay and Dapeng Bay in Shenzhen, and Zhanjiang Bay in the port city of Zhanjiang, have been hardest hit by red tides in previous years, with a large number of fish and other marine organisms killed, Li said.

Red tide is a discoloration of seawater caused by a large number of single-celled organisms known as red dinoflagellates. The poison they release kills fish and other organisms. Consuming sea creatures affected by red tide will result in severe food poisoning.

Worsening ocean pollution has been cited as the main cause of red tide, which has also been aggravated by recent extreme weather.

Ocean pollution has worsened in Guangdong's inshore waters with rapid economic growth in recent years, Li said.

Last year, more than 91 metric tons of pollutants were poured into the ocean from the province's 28 estuaries, he said.

The Guangdong provincial government has called for concrete and effective measures to be taken, Li said.

Xie Enyi, a professor at the Fisheries College of Guangdong Ocean University in Zhanjiang, said the growing number of red tides in Guangdong's waters were mainly caused by the increasing number of aquatic farms.

"Now many cities and counties in coastal areas have built farms for fish, shrimp, shellfish and other marine organisms for bigger profits," Xie told China Daily on Wednesday.

Xie predicted red tides will increasingly haunt Guangdong unless effective and measures are introduced to prevent and fight ocean pollution.

"Coastal cities and counties should reduce the number of farms cultivating fish and other marine creatures. Instead, more farms for seaweed, kelp, laver and other marine plants should be built to help improve the marine environment," he said.

"Meanwhile, we need to raise the awareness of protecting the sea in the province, particularly along the coastal areas."

He urged government departments to expand and tighten examinations to control red tide and prevent it from spreading.

Guangdong's ocean economy came to more than 1.1 trillion yuan ($177 billion) last year, up 12.3 percent year-on-year.