It is very difficult to overestimate the value of mollusks in nature, because they are an important link in the food chain. First of all, they act as food for fish, crustaceans, birds and animals. At the same time, mollusks play an important role in biocenotic relationships, and their number in the oceans reaches 2.2 billion tons.
Bivalves are natural filters. When water passes through their mantle cavity, it is purified from microorganisms and organic residues. Numerous experiments show that, on average, each of them thus purifies up to 30 liters of water per day, while reducing its contamination by about 250 times. Recognizing the great importance of mollusks, many world states are now taking measures to recreate aquatic biocenoses to ensure environmental protection. This is done by the resettlement of mollusks in those places where they can become part of biological self-purification.
The great importance of mollusks in human life is associated primarily with their use in food. Food can be mussels, oysters, scallops and many others. The fact is that in their meat there are a lot of elements and vitamins that are absorbed by the human body quite easily. In some European countries they are even bred on purpose. It should be noted that for the life of people the importance of mollusks is not limited to this. In some varieties, pearls of decent size grow. In order for their development to begin, the mantle must be irritated by some body of foreign origin. A pearl can be called formed only when the pearl layer is finally formed. After that, pearls are used to make various jewelry.
The industrial value of mollusks cannot be underestimated. Mother-of-pearl products are made from shells of gastropod varieties, as well as from freshwater pearls. At the same time, an ink bag of squid and cuttlefish is used to produce the highest quality carcasses and brown sepia.
Despite all this, the value of mollusks is not purely positive. There are also negative points. In particular, some of them cause serious damage to agriculture. For example, naked slugs in search of food destroy seedlings of crops and other plants in the garden. A lot of damage is also done by the grape snail. Some types of pulmonary freshwater mollusks act as intermediate hosts for trematodes. A whole series of them relates to stone-cutters. They are actively involved in the destruction of rocks.
In the rivers and reservoirs of the Azov-Black Sea basin, a variety such as draysena is very common. This mollusk is considered the only freshwater species that leads an attached lifestyle. As a rule, it settles in pipes and all kinds of biotechnological structures, which fail during intensive reproduction. There are also species that damage structures in ports and ship bottoms. In this case, we are talking about a shipworm.