Some red tide creatures can also secrete toxins that can accumulate
in shellfish, known as shellfish poison, which tend to be more than
acceptable volume of human.
If these shellfish are eaten accidentally, it can cause poisoning
and lead to death. At present, there are more than 10 kinds of
shellfish toxin which is 80 times higher than the cobratoxin,
and more than 100,000 times than general anesthetics such as procaine
and cocaine. According to statistics, there are about 300 cases of
shellfish poisoning in the whole world, and more than 300 people
have died because of it.
There were only two red tide records before the 1970s
in our coastal area. However, the frequency of red tide
has increased significantly since the 1980s, and it is more than
dozens of times a year. In 1989, there was a red tide in the Bohai
and some other sea areas, which resulted in hundreds of millions
of dollars in the loss of shrimp and shellfish. In the next two years,
the extent and duration of the occurrence of red tide was rare.
In 1998, more than 30 days of massive red tide occurred
in the Pearl River estuary of Guangdong province and Hong Kong waters,
resulting in a large number of farmed fish and shellfish deaths,
and the direct economic loss of over 100 million yuan.