What is the main cause of red tide?

Classification: Education/Science >> Science and Technology

Problem description:

From the ecological point of view, what is the main cause of red tide?

Analysis:

Red tide is a natural phenomenon and also caused by human factors. Humans have long had relevant records, such as the description of red tide in Exodus of the Old Testament: "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 mark les Cabot, a Frenchman, recorded 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 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.

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 pseudoalgae) 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.

1. Seawater eutrophication is the material basis and the 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 contained in industrial wastewater can proliferate 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.

Secondly, the change of hydrometeorology and physical and chemical factors of seawater is an important reason 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.

Thirdly, 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.

Red tide bacteria under microscope

In recent years, pollution in China coastal waters has intensified and red tide disasters have become increasingly frequent. According to relevant data, in 2003, 2/kloc-0 red tides were recorded in the coastal and offshore areas of Ningbo City, Zhejiang Province, which is near the East China Sea. Among them, three red tides occurred in Xiangshan Port in the red tide monitoring area, with a cumulative area of about 4,026 square kilometers. Red tide organisms are mainly Nitzschia lunata and Prorocentrum serratum. Although there are toxic species of red tide organisms in the above red tide, no red tide toxin was detected, which did not cause poisoning death of large-scale cultured aquatic products. According to the data released by Zhejiang Ocean Monitoring and Forecasting Center, there were 49 red tides in Zhejiang waters in 2003. Red tide has attracted people's attention because of its more and more frequent occurrence density and great influence on people's production and life.

So, how is the red tide formed? After the heavy rain in summer, it is hot and sultry weather. The blue sea water will change color overnight, and the sea breeze will blow an unpleasant smell. There are dead fish, dead shrimp and shellfish floating on the sea. This is the terrible sight when the red tide occurs. Scientists believe that excessive discharge of production and domestic sewage has brought a lot of nutrients such as nitrogen and phosphorus to the ocean, resulting in "eutrophication" of seawater, and some special organisms in the ocean-red tide organisms will multiply rapidly and form red tides.

What is the content of nutrients in seawater to achieve eutrophication? According to relevant data, a Japanese scholar proposed the following formula for dividing standards:

Chemical oxygen consumption × inorganic nitrogen × inorganic phosphorus1500 >1is eutrophication.

Research shows that there are more than 50 species of red tide organisms that can cause red tide in the world. Nocturnal algae, dinoflagellate, Gymnodinium and other 10 species are the most common. The main plankton species forming red tide are different, and the color of red tide is also different. For example, flagellates can cause green red tides, some diatoms can produce reddish-brown red tides, and plankton that really form red red tides are luminous. Scientists can roughly judge the species composition of "red tide" organisms according to the color of red tide.

Eutrophication of seawater is the main cause of red tide. Trace elements such as heavy metals such as iron and manganese, and some special organic substances such as vitamin B 1, B 12, tetrazolium indene, m-diazepine, yeast, decomposition liquid after protein digestion, pulp waste liquid, etc. are all important factors for the mass reproduction of red tide organisms. When the contents of iron, salt and manganese are 10 ~ 20 times higher than those in normal seawater, the number of red tide organisms will increase 10 times. When the content of vitamin B 12 is high, red tide organisms can multiply three times. The occurrence of red tide is also greatly influenced by the sea environment and hydrometeorological conditions. Generally, red tides mostly occur in the sea areas with serious stratification. At this time, the water exchange is poor, and red tides often occur when low-oxygen water masses appear at the bottom. The physical phenomenon caused by the sudden decrease of seawater salinity will also cause the abnormal reproduction of red tide organisms.

Harm of red tide

First, the 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.

Second, the 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.

Third, the 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.

Red tide, the biggest threat to aquatic organisms, is the lack of oxygen in the water. Because red tide organisms multiply and cover the whole sea surface, dead red tide organisms are easily decomposed by microorganisms, thus consuming dissolved oxygen in water, making seawater anoxic or even anaerobic, resulting in a large number of marine life deaths. Hydrogen sulfide and methane produced by seawater hypoxia also have fatal effects on marine life. Some marine organisms, such as many dinoflagellates, can secrete a lot of sticky substances outside cells. This sticky substance and the sticky substance discharged by plankton after death can attach to the gills of shellfish and fish and suffocate them. When some tiny plankton multiply in large numbers, they will also stick to the gills of animals, making it difficult for them to breathe, and even leading to their death in severe cases. In addition, the toxins produced by red tide organisms discharged into water will also have toxic effects on marine organisms. The death of red tide organisms will also promote the reproduction of bacteria. Some kinds of bacteria or toxic substances produced by these bacteria can kill fish, shrimp and shellfish.

When a red tide occurs in a certain sea area, the harm to aquaculture is obvious. From the monitoring of marine environment in recent years, due to the destruction of marine ecological environment and the aggravation of water pollution in some sea areas, marine pollution is becoming more and more serious, and the frequency and scope of red tide are expanding day by day, which has to attract people's attention. But as far as the current technical means are concerned, people can only plan ahead. Doing a good job in monitoring and preventing red tides, doing a good job in disaster prevention and mitigation, and protecting marine ecology are the best ways to reduce the frequency of red tides and their losses.

Red tide not only does great harm to fishery and aquaculture, but also directly threatens human health. In the sea area ravaged by red tide, experts remind people to eat seafood carefully and be wary of red tide toxins becoming human "health killers".

Marine phytoplankton is the main organism that causes red tides. There are more than 260 species of marine phytoplankton in the world that can form red tides, of which more than 70 species can produce toxins. Microcystins in red tide algae accumulate in shellfish and fish. After eating by mistake, people may be poisoned or die, so people call red tide toxin "shellfish toxin".

According to Qi Yuan, an associate researcher at Donghai Fisheries Research Institute of Chinese Academy of Fishery Sciences, shellfish poisoning is the most toxic organic substance, including paralytic shellfish poisoning, diarrheal shellfish poisoning, forgetful shellfish poisoning and neurotic shellfish poisoning.

Within 5 to 30 minutes after humans eat shellfish containing paralytic toxins by mistake, mild poisoning will cause tingling around the lips and tongue. Moderate to severe will develop to the arms, legs and neck, and the most serious will lead to respiratory paralysis and death. The symptoms of diarrhea toxin are similar to food poisoning, which has a destructive effect on human liver cells. Amnesia toxin and neurotoxin can make people temporarily lose some memories, but at present, these two kinds of shellfish poisoning have not been found in China.

According to statistics, since the 1960s, 600 people in China have been poisoned by eating poisonous shellfish by mistake, and 29 of them have died. In 2002, more than 50 people in Ningde, Qingtian, Luoyuan and other places in Fujian were poisoned by trypanosoma, and 3 of them died.

At present, many countries have strict regulations on the toxin content in shellfish, and the quality requirements of imported aquatic products are becoming more and more strict. EU inspection of imported aquatic products includes 63 indicators, including chemical indicators of freshness, natural toxins, parasites, microbial indicators, toxic chemicals of environmental pollution, heavy metals and pesticide residues. Due to a complete set of monitoring and management measures for seafood, although toxic red tides often occur along the coasts of European and American countries, seafood poisoning incidents are rare. However, most seafood sold in China market has not been tested for toxins.

Experts remind that toxins are often concentrated in the hepatopancreas of shellfish. When people eat shellfish, they should remove a digestive gland that looks black, which can reduce the chance of poisoning. In the red tide season, seafood should not be eaten too much at a time. Once toxic shellfish is eaten by mistake and symptoms such as numbness of tongue, mouth and limbs appear, artificial vomiting should be carried out first, and gastric lavage and enema should be carried out in the hospital to prevent respiratory muscle paralysis.

Red tide case

The United States and Japan used to be two countries with serious red tides in the world. From the 1950s to the mid-1960s, red tides occurred almost every year along the coast of Florida, USA, resulting in a large number of deaths of fish, shrimp and shellfish, and even turtles and dolphins feeding on these creatures were not spared.

According to the statistics of Japan 1979, red tides account for 8% of all marine pollution incidents. Since 1970, red tide has become an inevitable marine disaster in Japan. Taking Seto Inland Sea as an example, there were five red tides in the decades before 1955, and 39 red tides from 1959 to 1965. During the periods of 1996- 1980 and 15, there were 2,589 occurrences, exceeding 170 on average every year, of which 305 caused serious harm. 1975 and 1976 have more than 300 times each year. According to statistics, during the five years from 1965 to 1973, the fishery economic losses caused by red tides in Japan reached 24 17 billion yen, with an average of tens of billions of yen per year.

In recent years, the frequency and area of red tide in China are getting higher and higher. According to incomplete statistics, from 1980 to 1992, there were nearly 300 red tides in China's sea areas, which was five times that of/kloc-0 in the 1970s. Red tides occur in the South China Sea, the East China Sea, the Yellow Sea and the Bohai Sea, among which the Pearl River Estuary, Zhanjiang Port, Zhoushan Islands, the Yangtze River Estuary, Jiaozhou Bay, Dalian Bay, Liaodong Bay and Bohai Bay are frequent areas.

In 1989 alone, six coastal areas in China were attacked by red tides, and the direct economic loss exceeded 200 million yuan. Among them, from August to June of 65438+ 10, 26,000 mu of shrimp ponds offshore Huanghua City, Hebei Province were affected, with a loss of 30 million yuan, while Tangshan City and Cangzhou City lost 80 million yuan and more than 30 million yuan respectively. 1990 Red tide also caused fishery losses of more than 28 million yuan in the northwest waters of Hainan Island.

Prevent red tide

In order to protect marine resources and environment, ensure the development of marine aquaculture and ensure human health. Avoid and reduce the red tide disaster, and take corresponding measures and countermeasures according to the actual situation to prevent the red tide disaster.

First, control the amount of sewage to prevent eutrophication of seawater.

Eutrophication of seawater is the material basis for the formation of red tide. The discharge of industrial wastewater and domestic sewage carrying a large amount of inorganic substances into the sea is the main reason for eutrophication in this sea area. China coastal area is an important base for economic development, with dense population and developed industrial and agricultural production. However, this has also led to a large number of industrial wastewater and domestic sewage discharged into the sea. According to statistics, coastal areas, which account for less than 5% of the national area, discharge nearly 7 billion tons of industrial wastewater and domestic sewage into the sea every year. With the further economic development in coastal areas, the amount of sewage will increase. Therefore, effective measures must be taken to strictly control the excessive discharge of industrial wastewater and domestic sewage into the ocean. According to the seawater standards formulated by the state and the requirements of the Marine Environmental Protection Law, industrial wastewater and domestic sewage discharged into the sea should be strictly treated.

To control the excessive discharge of industrial wastewater and domestic sewage into the ocean, reduce the ocean load and improve the self-purification ability of the ocean, the following measures should be taken: 1, and the method of combining total amount control with concentration control should be implemented to control the excessive discharge of land-based pollutants into the ocean, especially to strictly control the inflow of sewage containing a large amount of organic matter and nutrient-rich salts; 2, in industrial concentration and densely populated areas and industrial and mining enterprises that discharge a large amount of sewage, establish sewage treatment devices and discharge them into the sea in strict accordance with sewage discharge standards; 3. Overcome the centralized discharge of sewage into the sea, especially the polluted rivers with long-term drought. When the runoff suddenly increases, it will be discharged in stages and batches to reduce the instantaneous load of seawater.

Two, the establishment of marine environmental monitoring network, strengthen the monitoring of red tide.

China has a vast sea area and a long coastline, so it is difficult to monitor the ocean nationwide only by the strength of the state and relevant departments. It is necessary to organize the competent marine environmental units, coastal residents, fishing boats, offshore production departments and various social forces to carry out marine monitoring activities that combine professionalism with mass, expand the coverage of marine monitoring, and timely obtain red tides and pollution information closely related to red tides. According to the work plan, the monitoring network organization department can organize all forces to comprehensively monitor the red tide. In particular, the areas prone to red tides, inshore waters, mariculture areas and river estuaries should be closely monitored to obtain red tide information in time. Once red tide and signs of red tide are found, the monitoring network organization can inform the relevant departments in time, carry out follow-up monitoring in an organized and planned way, put forward control measures, and do everything possible to reduce the harm of red tide.

Three, strengthen marine environmental monitoring, to carry out red tide forecasting services.

In order to minimize red tide disasters and reduce losses, we must actively carry out red tide forecasting services. As we all know, the occurrence of red tide involves many factors such as biology, chemistry, hydrology, meteorology, marine geology and so on. At present, there is no perfect forecasting model suitable for forecasting service. Therefore, we should strengthen the research of red tide forecasting model and understand the occurrence, development and attenuation mechanism of red tide. In order to fully understand the mechanism of red tide, we should comprehensively monitor the marine environment and ecology, especially in areas with frequent red tides and sea areas with serious marine pollution, and increase the monitoring frequency and density. When a red tide occurs, it is necessary to track and monitor the red tide and obtain information in time. On the basis of obtaining a lot of data, the formation mechanism of red tide is studied and analyzed, and a forecasting model is put forward to carry out red tide forecasting service. Strengthening marine environmental and ecological monitoring is to provide information for studying and predicting the formation mechanism of red tide; The second is to provide real-time data for red tide control; The third is to better put forward preventive countermeasures and measures.

Fourth, scientific and rational development and utilization of the ocean.

According to the survey data, in recent years, red tides have mostly occurred in coastal sewage outlets, with poor marine environmental conditions, weak tidal current and weak water exchange capacity. The deterioration of marine environmental conditions is caused by unreasonable layout of coastal industries, coastal engineering, salt industry, aquaculture and offshore oil and gas development. In order to avoid and reduce the occurrence of red tide disasters, we should plan marine functional areas and scientifically guide the development and utilization of the ocean from the overall situation. Develop and plan key sea areas, reduce blindness, and achieve active protection, scientific management, comprehensive planning and comprehensive development. In addition, marine aquaculture should actively promote scientific aquaculture technology and strengthen scientific management of aquaculture. Control the discharge of aquaculture wastewater. Maintain good aquaculture water quality.

Verb (abbreviation of verb) to do social education and publicity.

Once a red tide occurs, the consequences are quite serious. Therefore, through newspapers, radio, television, internet and other news media, popular science propaganda about red tide should be carried out to the whole society, and the awareness of disaster prevention should be enhanced through publicity and education. At the same time, it also calls on all sectors of society to attach great importance to marine environmental protection and raise the awareness of the whole people to protect the ocean while fully developing it. Only by protecting the ocean can we constantly ask for wealth from the ocean, otherwise it will bring incalculable losses.