Causes, characteristics, hazards and preventive measures of red tide

Red tide, red tide, red water, colorless water

A phenomenon that occurs directly or indirectly with the sudden reproduction of plankton. Originally a fishery term, there is no strict definition. There are many cases of water surface discoloration. Ershui (seawater turns green to brown), bitter tide (red tide, seawater turns red), Lan Chao (seawater turns blue) and freshwater bloom are all phenomena of the same nature. There are many kinds of plankton that make up this red tide, but flagellates and diatoms are the dominant species. When a red tide occurs, the density of plankton is generally 102- 106/ml. In the inner bay of Japan, fresh water flows in from spring to autumn. In recent years, with the increase of urban and industrial wastewater, eutrophication has appeared, and red tides occur frequently in Tokyo Bay, Seto Inland Sea and Youming Sea. Red tides sometimes do great harm to aquatic animals such as fish, which is caused by plankton blocking fish gills, causing mechanical obstacles, decomposing after their death, rapidly consuming oxygen, lacking oxygen in water and secreting harmful substances. It is generally believed that it is the result of the comprehensive action of stagnant water, eutrophication, increasing sunshine and rising water temperature.

Red tide is a natural phenomenon and also caused by human factors. Humans have long had relevant records, such as the Old Testament? There is a description of red tide in Exodus: "The water in the river has turned into blood, and the river stinks, so Egyptians can't drink the water here." In Japan, red tides were recorded as early as Yuan Teng's era and Sickle's era. 1803 French mark? Les Capote records that Indians in the Royal Bay of America judged whether mussels were edible by observing the luminous phenomenon of seawater at night. 1831-1836, Darwin recorded the red tide event caused by Chaetomium sp. The coasts of Brazil and Chile in The Beagle Journey. According to reports, red tide was discovered in China more than 2,000 years ago, and it is also recorded in some ancient books or literary works. For example, Pu Songling in Qing Dynasty vividly recorded the luminous phenomenon related to red tide in Strange Tales from a Lonely Studio.

Red tide is a harmful ecological phenomenon that some phytoplankton, protozoa or bacteria in seawater proliferate explosively or gather highly under specific environmental conditions, causing discoloration of water body. Red tide is a historical name, not necessarily red, but actually a general term for many red tides. According to the causes, types and quantities of red tide, water will appear different colors, such as red or brick red, green, yellow, brown and so on. It is worth pointing out that some red tide organisms (such as Gymnodinium, Gymnodinium, Pyrodinium, etc. Sometimes it doesn't make the sea water appear any special color.

With the rapid development of modern chemical industry and agricultural production and the increase of population in coastal areas, a large number of industrial and agricultural wastewater and domestic sewage are discharged into the sea, and a considerable part of them are directly discharged into the sea without treatment, which leads to the increasingly serious eutrophication in offshore and harbor areas. At the same time, due to the increase of coastal development and the expansion of marine aquaculture, it has also brought pollution to the marine ecological environment and aquaculture itself; The development of shipping industry leads to the introduction of harmful alien red tide species; The change of global climate has also led to the frequent occurrence of red tides.

At present, red tide has become a worldwide public hazard. Red tides frequently occur in more than 30 countries and regions, such as the United States, Japan, China, Canada, France, Sweden, Norway, the Philippines, India, Indonesia, Malaysia, South Korea and Hong Kong.

First of all, the occurrence of red tide destroys the normal ecological structure of the ocean, so it also destroys the normal production process in the ocean, thus threatening the survival of marine life.

Secondly, some red tide organisms will secrete mucus and attach to the gills of fish, shrimp, shellfish and other organisms, which will hinder breathing and lead to suffocation and death. Red tide organisms containing toxins will lead to poisoning death after being eaten by marine organisms. Human consumption of seafood containing toxins will have similar consequences.

Thirdly, after a large number of red tide organisms die, the decomposition of the remains will consume a lot of dissolved oxygen in seawater, resulting in an anoxic environment and a large number of shrimp and shellfish die.

Harm of red tide

Damage of Red Tide to Marine Ecological Balance

The ocean is a complex ecosystem in which living things and environment, living things and living things are interdependent and mutually restricted. The material circulation and energy flow in the system are in a relatively stable dynamic balance. When the red tide appeared, this balance was broken. In the early stage of plant red tide, due to the photosynthesis of plants, the water body will have high chlorophyll a, high dissolved oxygen and high chemical oxygen consumption. This change in environmental factors has led to the failure of some marine organisms to grow, develop and reproduce normally, leading to the escape or even death of some organisms, which has destroyed the original ecological balance.

Harm of Red Tide to Marine Fisheries and Aquatic Resources

The main reasons why red tide destroys fish, shrimp, shellfish and other resources are:

1, which destroys the erbium material base of fishing grounds and leads to the reduction of fishery production.

2. The abnormal reproduction of red tide organisms will cause mechanical blockage of economic organisms such as fish, shrimp and shellfish, which will suffocate these organisms.

3. At the late stage of red tide, a large number of red tide organisms died. Under the action of bacterial decomposition, it can cause serious hypoxia in the environment or produce harmful substances such as hydrogen sulfide, resulting in hypoxia or poisoning death of marine organisms.

4. Some red tide organisms contain biological toxins or metabolites, which can directly poison fish, shrimp, shellfish and other organisms.

Harm of red tide to human health

Some red tide organisms secrete red tide toxins. Fish and shellfish may not be poisoned in toxic red tide areas, but biotoxins can accumulate in the body, and their content greatly exceeds the acceptable level of human body when eaten. If these fish, shrimp and shellfish are accidentally eaten by people, it will cause human poisoning and even death in severe cases.

At present, there are more than 10 species of shellfish poisoning, which is 80 times higher than cobra venom and 65,438+10,000 times stronger than general anesthetics such as procaine and cocaine. The symptoms of shellfish poisoning are: numbness of lips and tongue, numbness of limbs, dizziness, nausea, chest tightness, unstable standing, abdominal pain, vomiting, etc. In severe cases, coma and dyspnea occur. Human poisoning incidents caused by red tide toxins occur from time to time in coastal areas of the world. According to statistics, there are more than 300 cases of shellfish poisoning caused by red tide toxins in the world, and more than 300 people have died.

The cause of red tide

Red tide is a complex ecological anomaly, and its causes are also very complicated. Although the mechanism of the occurrence of red tide is still inconclusive, the first condition for the occurrence of red tide is that the proliferation of red tide organisms should reach a certain density, otherwise even if other factors are suitable, red tide will not occur. Under normal physical and chemical conditions, the proportion of red tide organisms in plankton is not large, and some flagellates (or dinoflagellates) are food for some fish and shrimp. However, due to special environmental conditions, some red tide organisms proliferate and form red tides. Most scholars believe that the occurrence of red tide is closely related to the following environmental factors.

Eutrophication of seawater is the material basis and primary condition for the occurrence of red tide.

Because a large number of urban industrial wastewater and domestic sewage are discharged into the sea, nutrients gather in the water body, resulting in eutrophication of the sea area. At this time, nutrients such as nitrogen and phosphorus in the water body; The contents of trace elements and organic matter such as iron and manganese are greatly increased, which promotes the reproduction of red tide organisms. The results of red tide detection show that the water body in the red tide occurrence area has been seriously polluted and eutrophic. Nitrogen, phosphorus and other nutrients greatly exceeded the standard. According to research, some metals in industrial wastewater can stimulate the reproduction of red tide organisms. Adding iron chelating agent less than 3mg/dm3 and manganese chelating agent less than 2 mg/dm3 to seawater can make red tide organisms Chrysophyta and Euglena achieve the highest proliferation rate. On the contrary, in seawater without iron and manganese, the population density will not increase even under the most suitable conditions of temperature, salinity, PH and basic nutrition.

Secondly, some organic substances will also promote the rapid reproduction of red tide organisms. The growth of gymnosperms. It is not obvious if it is cultivated with inorganic nutrients, but it grows significantly when yeast extract is added. When soil extract and vitamin B 12 were added, the gymnosperm bright grew particularly well.

Hydrometeorology and the change of physical and chemical factors of seawater are the important reasons for the occurrence of red tide.

Seawater temperature is an important environmental factor for the occurrence of red tide, and 20-30℃ is the suitable temperature range for the occurrence of red tide. Scientists have found that the sudden rise of water temperature above 2℃ in a week is a precursor of red tide. Chemical factors of seawater, such as salinity change, are also one of the reasons for the proliferation of biological factors-red tide organisms. Red tide may occur in the salinity range of 26-37, but thermocline and halocline are easily formed when the seawater salinity is 15-2 1.6. The existence of thermocline and halocline provides conditions for the aggregation of red tide organisms, which is easy to induce red tide. Due to the interaction of runoff, upwelling, water mass or ocean current, nutrients on the seabed rise to the surface, resulting in high eutrophication in coastal waters. The content of nutrients rose sharply, which led to the proliferation of diatoms. Too many of these diatoms, especially the dense diatoms in bones, often cause red tides. These diatoms provide rich bait for noctiluca scintillans, which promotes the rapid propagation of noctiluca scintillans, thus forming a pink noctiluca scintillans red tide. Monitoring data show that when the red tide occurs, the water area is dry and rainy, the weather is sultry, the water temperature is high, the wind is weak, or the tide is slow.

The pollution of mariculture itself is also one of the factors that induce red tide.

With the great development of coastal aquaculture in China, especially the vigorous development of shrimp aquaculture. It has also caused serious self-pollution problems. In shrimp culture, a large number of compound feed and fresh bait are artificially fed. Due to the outdated and imperfect culture technology, the amount of bait is often too large, and the residual bait in the pond increases, which seriously pollutes the culture water quality. On the other hand, because shrimp ponds need to be drained and changed every day, a lot of sewage is discharged into the sea every day. These waters with a large amount of residual bait and feces contain various forms of nitrogen-containing compounds such as ammonia nitrogen, urea and uric acid, which accelerates the eutrophication of seawater, thus providing a suitable biological environment for red tide organisms and accelerating their proliferation, especially under high temperature, sultry and windless conditions. It can be seen that the self-pollution of mariculture also increases the frequency of red tide.