On this day, 27 years ago, March 19, 1998 (February 21, 1998, the explosive reproduction of plankton caused a "red tide", causing a large number of fish deaths in Hong Kong waters. On March 19, 1998, a "red tide" caused by explosive reproduction of plankton caused a large number of fish deaths in Hong Kong waters. "Red tide" is known as the "red ghost" and is also called "harmful algal bloom" internationally. Red tide, also known as red tide, is an abnormal phenomenon in the marine ecosystem. It is caused by the explosive proliferation of red tide algae in the seaweed family under specific environmental conditions. Seaweeds are a huge family. Except for some large seaweed, many are very tiny plants, some of which are single-celled plants. Due to the different types and quantities of red tide organisms, seawater can appear in different colors such as red, yellow and green. After the red tide occurred, in addition to the seawater turning red, a large number of red tide organisms gathered in the gills of fish, causing the fish to suffocate and die due to lack of oxygen; Second, after red tide organisms die, the algae consume a large amount of dissolved oxygen in the water during the decomposition process, causing fish and other marine life to die due to lack of oxygen. At the same time, it also releases a large amount of harmful gases and toxins, seriously polluting the marine environment and causing the ocean. The normal ecosystem has been seriously damaged; third, fish swallow a large amount of toxic algae. At the same time, the pH value of seawater will also increase, the viscosity will increase, and non-red tide algae plankton will die and decay; red tide algae will also die in large numbers due to explosive proliferation and excessive aggregation. Red tides occur under specific environmental conditions, and there are many related factors, but one of the most important factors is marine pollution. A large amount of waste water containing various organic substances is discharged into seawater, promoting eutrophication of seawater. This is an important material basis for the proliferation of red tide algae. A large number of studies at home and abroad have shown that marine plankton are the main organisms causing red tide. Among the more than 4000 marine plankton in the world, more than 260 can form red tide, of which more than 70 can produce toxins. Some of the toxins they secrete can directly lead to the death of a large number of marine life, and some can even be transmitted through the food chain, causing human food poisoning. At present, more than 30 countries and regions in the world have been affected by red tides to varying degrees, and Japan is one of the countries most affected. In the past decade or so, due to the increasing marine pollution, red tide disasters in my country have also tended to intensify. They have developed from a few scattered sea areas to large sea areas, and some important breeding bases have been particularly affected. The study and prevention of the occurrence and harm of red tide involves many disciplines such as biological oceanography, chemical oceanography, physical oceanography and environmental oceanography. It is a complex systematic project. Red tide is a natural phenomenon and caused by human factors. There have long been relevant records in humans. For example, there is a description of red tides in the Old Testament Exodus: "The water in the river turned into blood, and the river also stinks, so the Egyptians could not drink the water here." In Japan, red tides were recorded as early as the Tengyuan and Sickle periods. In 1803, Frenchman Marc Les Cabot recorded that Indians in the Royal Bay area of America judged whether mussels were edible by observing the phenomenon of seawater luminescence on a dark night. 1831-1836 Darwin recorded red tide events caused by Trichophylla in Brazil and Chile near the sea in Berger's Voyage Records. It is reported that red tide was discovered in China more than 2000 years ago, and there are already some records of red tide in ancient books, documents or literary and artistic works. For example, Pu Songling of the Qing Dynasty vividly recorded the luminous phenomenon related to red tide in his "Liaozhai Zhi Yi". Red tide is a harmful ecological phenomenon in which certain phytoplankton, protozoa or bacteria in seawater explode or accumulate highly under specific environmental conditions, causing the color change of water. Red tide is a historical name. It may not be all red. It is actually a collective name for many red tides. Depending on the causes, types, and quantities of red tides, water bodies will show different colors, including red or brick red, green, yellow, brown, etc. It is worth pointing out that some red tide organisms (such as gonosulcus, gymnodinoflagellates, pyridium, etc.) cause red tides and sometimes do not cause any special color of seawater. Comments: Red tide has become a worldwide public hazard