Animals and plants that live at the bottom of rivers, lakes and oceans. According to life style, it can be divided into fixed life, buried life, underwater crawling life, drilling life, bottom swimming life and so on. Such as snails, starfish, sea urchins, snake tails, etc. , is a species that crawls on the bottom of the sea. Their bodies often emit symmetrical, flat or disc-shaped shells. Sponges, anemones, sea lilies, barnacles, oysters, sea squirts and various corals all settle in the basement of water bodies and have strong reproductive capacity. Some of them germinate and reproduce to form groups, and some produce a large number of floating larvae, which will settle down when they meet the right substrate. Stigma worm, amphioxus, ray, flounder, etc. Inhabits in sediments at the bottom of the water, while meretrix meretrix, meretrix meretrix, etc. Dig a hole to live. Some benthic organisms are available for human consumption. Some marine shellfish and freshwater shellfish can produce pearls. It is generally believed that the density of benthos decreases with the increase of depth in waters with soft sediments as the base. For example, the biomass of continental shelf is much higher than that of submarine plain, but in the deep seabed, the species diversity is more obvious than that of continental shelf.
Organisms that often inhabit the bottom or surface of ocean or inland waters are an important ecological type of aquatic organisms. Living freely or fixed at the bottom of the water, except for fresh water, you can live from the coast to the deepest part of the seabed (depth 10 km or more). Freshwater is mainly aquatic plants, mollusks, annelids and so on. Among marine organisms, benthos are the most abundant, including most kinds of invertebrates, macroalgae, a few higher plants and almost ubiquitous microorganisms. Algae and seed plants (such as kelp and leek, which are common in coastal areas) are fixed on the bottom, and most of them only live in shallow water with light transmission. Animals have a variety of lifestyles: most of them live in bottom sediments (such as clams and sea urchins) or make holes in bottom pipes (such as shrimp, clams and caterpillars), which are called benthos; Some are fixed or attached to the surface of rocks or other hard substrates (including animal shells) (such as oysters, barnacles, moss, etc.). ), or crawling on the substrate (such as abalone, snail, etc.). ), known as zoobenthos or zoonoses; Others can swim in the water near the bottom, but will settle at the bottom after a while (such as shrimp), which is called swimming benthos.
Immortal animals include all sponges and bryozoa, and many coelenterates (corals, corals, etc. ), mollusks (oysters, mussels, etc. ), crustaceans (such as barnacles, barnacles, etc. ) and large algae. Animals (such as oysters, mussels, barnacles and bryozoa) and plants (algae) attached to ship bottoms, buoys or other underwater facilities often cause fouling, so they are also called fouling organisms. Benthic animals include most polychaetes, bivalves and some gastropods mollusks, crustaceans, echinoderms and all the half-chordates of enterobranchia. Some of these species, such as ship maggots of mollusks, sea bamboo shoots, wood-boring pests of crustaceans, water fleas, etc. Making holes in wood or rock is called a boring creature. The swimming benthos include many kinds of shrimp, crab and fish, such as flounder, bream and pomfret. These ecological types have different feeding, nutrition and reproduction methods, as well as different requirements and adaptability to physical and chemical environmental conditions such as seawater and sediments, and their biological and ecological characteristics are also very different.
The position of benthos in marine food chain is in marine food chain. Except benthic diatoms, macroalgae and a few seed plants, most benthic organisms are in the middle position (level). The main producers (primary producers) of marine organic matter-phytoplankton, macrobenthic algae and a few autotrophic microorganisms-are the food of phytophagous zooplankton and benthic organisms (such as bivalves, a few gastropods such as abalone and some shellfish). Some benthos feed on macroalgae (such as algae shrimp and abalone); Some feed on phytoplankton or organic debris (such as most bivalves, shrimps and copepods). ) and in the second place in the food chain; Others feed on zooplankton or benthos and belong to the third level of the food chain (such as snails and many shrimps and crabs); Benthic organisms themselves are prey of fish or other animals. Some of them are still the objects of human consumption (such as economic shrimps, crabs and shellfish, and a few fish). The quantitative change law of benthos and its relationship with marine biological production and resource development are the key issues in current research.
After more than half a century's investigation in 1950s, the benthic biomass distribution map of vast sea areas and important economic zones has been drawn. In the shallow sea area of the continental shelf, that is, the nearshore zone with a water depth of about 50 meters, the biomass, productivity and density of benthos are the highest. Generally speaking, in the sea area outside the continental shelf, the biomass (grams per square meter) and density (individuals per square meter) decrease significantly with the increase of depth. Within the continental shelf, it decreases with the decrease of latitude. In high latitudes, the biomass is high and the density is high, but there are fewer kinds of organisms, with a long life cycle and a slow growth rate, which often takes several years to grow. In tropical areas at low latitudes, biomass and density are low, but there are many kinds and short life cycles, and they can grow in one year or several months. In the north temperate zone or the shallow sea in the cold zone, the biomass is often tens to hundreds of grams per square meter, even more than 1000 grams to several kilograms. But in the tropics, there are only a few grams to a dozen grams per square meter of seabed. In the deep sea area, outside the continental shelf, the biomass decreases significantly, reaching the bottom of the ocean abyss, usually below 65,438+0g per square meter. It is estimated that the existing total amount (reserve) of marine benthos in the world is 9.6 billion tons, which is about 15 times of the current total marine catch in the world.
Small benthos Before the 1960s, the research objects of benthos were mainly macrobenthos with a diameter exceeding 1mm and macrobenthos with a weight exceeding1g. Since then, people have attached great importance to the investigation and study of a large number of meiobenthos (also known as interstitial animals) living between coastal or underwater sediment particles with a body diameter of 0.4 ~ 1 mm and meiobenthos with a body diameter less than 0.4 mm These small animals are numerous. The meiobenthos are mainly nematodes, crustaceans, Daphnia and Ostracoda, as well as some other groups that have rarely been studied in the past, such as Gastropoda, Kissing Animals, Mouth Animals, Slow-moving Animals and Shrimp. Microorganisms are mainly bacteria and protozoa. Their number far exceeds that of macrobenthos. Although they are small, their biomass is almost the same as that of large animals. The life span of small animals is often short, and the ratio of their yield to biomass (P/B value) is obviously higher than that of large animals. They are the main food source of macrobenthos in a certain sea area and occupy a very important position in the marine food chain.
The biggest feature of adapting to benthic organisms is living at the bottom of mud, which is closely related to the bottom of water. However, the depth of the habitat, the latitude of the sea area, the distance from the shore, the degree of influence by hydrological conditions, the physical and chemical properties of underwater sediments, the nutritional status of the habitat and the members of the biological community in which * * * lives are all related to their survival and development.
The sediments in marine and freshwater areas are mainly muddy flat bottoms (soft bottoms), and rocks or other hard areas occupy a small area, so the most important benthos are flat-bottomed biota-all benthos and most species of benthos.
Animals at the bottom adapt to the bottom, or are slender and flexible (worm-like), or flat and easy to dig and lurk, and have developed pointed feet or heads, as well as water pipe systems for obtaining fresh water and food from the bottom surface, or have special structures that can create water flow (such as water pipes of bivalves, appendages of some shrimps and crabs, tentacles of anemones, water pipe systems of echinoderms, etc.). ). Cave-dwelling or tube-dwelling species have sand pipes made of mucus secreted by themselves or pipes formed by secretions themselves. There are also some animals that can nest on the beach, such as polychaete sea worms and crustacean snails.
The deepest part of the ocean exceeds 10000 meters. The basal environment of intertidal zone and coastal shallow sea is very different from that of ocean in temperature, pressure, light and food supply. Environmental conditions determine the species composition and quantity of benthos at different depths. Benthic organisms in intertidal zone and shallow sea on continental shelf are diverse and complex in composition. Due to the rich sources of nutrients, many species have been greatly developed. Many species, especially those in tropical waters, have a fast growth rate and a short breeding cycle, which can be multiplied in a short time, providing a large number of aquatic foods and industrial raw materials for human beings. Although benthos can survive and develop on the continental slope, the bottom of deep-sea basin and the bottom of ultra-deep abyss (deep-sea trench), due to the limitation of living and living conditions, both the species of fauna and the number of individuals are very poor, especially in deep-sea trench.
The survival, development, distribution and quantitative changes of benthos are not only closely related to water temperature, salinity and nutritional conditions, but also obviously influenced by the physical and chemical properties of seabed sediments. Most benthic organisms have a long or short larval stage in their life history. Larvae float in the water layer and can flow with the water and spread far away, but most larvae have very strict requirements on sediments. For example, barnacles with fixed life, cockroaches and clams living at the bottom are only fixed at the appropriate bottom. This feature limits the distribution range of some benthic animals to some extent.
The habitat activity and distribution of benthos are greatly influenced by sedimentation. The active sedimentary process in the estuary area has affected the settlement, habitat and activities of benthic animals to some extent. In the coarse-grained area with high sedimentation rate, the biomass and density of benthos are very low, which is often difficult to find. However, in areas with less coarse particles and higher organic matter content (better nutritional conditions), there are often a large number of benthos, forming a special biological community. The life activities of benthic organisms often disturb and destroy the bedding structure of seabed sediments under natural conditions, especially a large number of benthic animals that feed on sediments, such as echinoderms, such as sea cucumbers. This activity is called biological disturbance, which not only changes the bedding structure of sediments, but also changes the properties of sediments.
Benthic organisms are closely related to human life. Many benthic organisms are the targets of fishing or aquaculture and have important economic value. Among them, the most important are shrimps and crabs and shellfish, such as prawns, new prawns, claw shrimps, white shrimps, lobsters, swimming crabs, blue crabs, mitten crabs (hairy crabs), clams, clams, scallops, oysters and red snails, as well as sea cucumbers, various algae, flounder and other benthic fish. The global ocean produces more than 3 million tons of shrimps and crabs and about the same amount of shellfish every year, and the output in China's coastal and shallow sea areas is also quite large. There are tens of thousands of tons of prawns in the Gulf of Mexico, warm water in Southeast Asia and the Yellow Sea in China, and tens of thousands of tons of big crabs. The annual output of Scapharca subcrenata, Meretrix meretrix, Meretrix meretrix and oyster is several hundred thousand tons. In addition, there are more benthos (such as many polychaetes, crustaceans and molluscs) that are natural food for economic fish and shrimp, and their quantity also affects the quantity of these economic fish and shrimp resources, so they are paid attention to by human beings. Many benthos are raw materials for medicine or industry. In addition, many benthic organisms are directly or indirectly harmful to human beings, such as most fouling organisms and drilling organisms, as well as natural enemies of economic fish, shrimp, shellfish and algae.
Benthic organisms are an important ecological group in marine life, which has attracted more attention because of its complex structure and ecology and its close relationship with human economy. With the innovation of research methods, marine ecology has made great progress, and the fishing and proliferation industry of biological resources has developed rapidly, which will inevitably promote the all-round development of benthic ecology.