In regard to a person or an object that is hardly noticeable, people say they have a weak presence. Presence means a feeling that a person or an object exists, which speaks for the amount of people’s interest in the object.
Then, which animal has the strongest presence? Is it the elephant which is almost as big as a house, or the whale as big as a few buses put together? Or maybe it is the lion, the king of the jungle, since the world operates within the law of the jungle, or the shark which dominates the ocean.
However, the presence in nature is not always in proportion to the size of the body or strength. There are animals that are small and out of human’s interest and seem insignificant, but live, feeling proud of their presence. They are invertebrates. Even little anchovies have bones, but invertebrates have been treated with contempt by people for the reason that they look unappealing. However, let’s take a look at the reason their presence is never insignificant in nature.
The World That Is Close to Infinity
Animals are divided into two different groups—vertebrates and invertebrates—according to whether or not they have a vertebral column. Invertebrates are animals without a backbone which even a wiggly snake has. You may think their number will not be many, but in actuality, about 97% of all the animals are invertebrates.
The first person to call all the animals without backbones “invertebrates” was the biologist Lamarck. Among Linnaeus’ six basic animal groups—mammals, birds, amphibians, fish, insects, and vermes, he called insects and vermes “invertebrates.”
According to what has been discovered so far, there are about 1,300,000 species of invertebrates worldwide. The only thing they have in common is that they don’t have a backbone. Their methods of reproduction and lifestyles are all different from one another. There are over 30 phyla1 when they are categorized according to their characteristics. It is contrasting to vertebrates which belong to one same phylum called Chordata.
1. A principal taxonomic category that ranks below “kingdom.”
The largest phylum of invertebrate animals is Arthropoda. There are approximately one million different species of arthropods, including spiders, crawfish, and all types of insects, taking up 75% of all organisms. Arthropods have hard shells, and their legs have joints. The second-largest phylum of invertebrate animals are Mollusca. Molluscs have tender bodies without joints, and breathe with gills. Clams, snails, and octopuses are well-known molluscs.
Earthworms and leeches belong to Annelida. They have long cylinder-shaped bodies, and there are about 15,000 known species of them. Platyhelminthes [flatworms] of which the representative animals are planaria, have tender and flat bodies with amazing capacity to regenerate. Echinoderms like starfish have radial symmetry with thorny skin. Coelenterates have tender bodies without division between the mouth and the anus and live in the water. Sea anemones are representative coelenterates.
Besides these ones, countless invertebrates are striding around in the ecosystem though they are hard to be seen. Just Arthropoda alone can be divided into 80 million species, depending on the way it is divided; it is close to infinity.
Invertebrates offer a great contribution to the study of the ecosystem thanks to their exceptionally more species than those of vertebrates. In particular, benthos is an index for evaluating the health of marine ecosystems. Drosophilae and Caenorhabditis elegans are used as specimens for the study of the ecosystem.
Living Organisms Facing Crisis
Snails, which are easily spotted in flower beds on a rainy day, have less mobility, compared with other animals, so there are many endemic species of them living in certain regions. On January 1, 2019, a special snail faced death. It was the last Hawaiian tree snail. The number of Hawaiian tree snails decreased dramatically due to rapid climate change and attacks from wolf snails which are not native to Hawaii. Eventually, they disappeared completely as the last individual of its species died.
In 2019, approximately 30,000 monarch butterflies spent the winter in California, which was 99.4% less than in 1980 when 10 millions of them spent the winter. It is because their habitats decreased as the city grew larger, and because many parts of habitats were polluted by the usage of herbicide and insecticide. A research team from the University of Michigan suggested that the increase of the amount of carbon dioxide may have had a bad influence on the growth of milkweed plants. Milkweed is the only host plant for the monarch butterfly. It means that the climate change has reduced even the survival rate of the larva. The number of monarch butterflies has been reducing every year.
Not only the Hawaiian tree snail and the monarch butterfly, but also many invertebrates are losing their ground to live on. In case of Korea, Cristaria plicata, which is the biggest freshwater mussel in Korea, feeds on organic matter in a deep river or a lake. However, the change in the water level caused by the construction of artificial structures such as dams and reservoirs for irrigation and frequent droughts has been a great threat to the cockscomb pearl mussel. As the water pollution and the lack of dissolved oxygen have been added on top of that, they are in danger of becoming extinct. Giant water bugs were selected as Korea’s native species to correct the disturbance of the ecosystem as they eat the tadpoles of bullfrogs which are not native to Korea. However, it’s getting harder and harder to find giant water bug as the wetlands such as puddles and banks are disappearing and even the remaining ones are polluted with agricultural pesticide.
Actually, the extinction of invertebrates is not a new issue. According to the report of a research team of Stanford University, published in Science, an academic journal, in 2014, the number of invertebrates has decreased by nearly half in the past 35 years. Recently, London Zoo announced that 20% of the invertebrates are in danger of extinction. As the survival of various animals and plants is being threatened by indiscreet development, overhunting and overfishing, environmental pollution, and climate change, numerous invertebrates who are vulnerable to the environmental changes have been put in the front line of the danger of extinction.
Invertebrates Are Small, but Play Important Roles
What’s going to happen if all clams disappear overnight? The problem won’t end in the level where we can no longer enjoy spaghetti alle vongole or clam chowder. Many invertebrates such as the starfish and gastropods and many vertebrates such as sea otters and birds feed on clams. If all the clams disappear, these animals will be put in danger of extinction, and the tragedy will spread to the whole ecosystem. Like this, most invertebrates are in the basis of the food chain, and many living creatures depend on invertebrates for their survival.
Invertebrates seem weak and insignificant, but the role they play in the ecosystem is tremendous. As it is known well, earthworms make the soil rich and let plants breathe by digging the soil, and they become nourishment to the soil when they die. Sea lice and Cirolana, which belong to the isopods classified within the arthropods, clean up wastes generated in nature or animal and plant carcasses. Snails which belong to Mollusca protect trees from diseases by eating algae2, mold, and bacteria of tree leaves.
2. Photosynthetic microorganisms. There are various kinds including unicellular organisms and multicellular organisms such as marine algae.
If arthropods such as bees, butterflies, and beetles disappear, mankind will immediately worry about what to eat. They travel from one flower to another, collecting honey and eating pollen. This way, they help plants’ cross-pollination and production of fruits. According to the Royal Society of London for the Improvement of Natural Knowledge, 75% of all the crops around the world cannot grow without the animals mediating the cross-pollination.
Coral reefs, the gathering of corals which make the underwater world colorful, are also essential to the marine ecosystem. Corals, which are coelenterates, live in symbiosis with alga, receive nutrients through alga’s photosynthesis, and also become other living organisms’ food. Without corals, some 30,000 species that live with corals lose their habitats. In 2014, the Secretariat of the UN Convention on Biological Diversity suggested that the coral reefs in the Caribbean Sea may become extinct in six years if the emission of greenhouse gases is not reduced.
In 1986, the Council of Europe adopted the Charter on Invertebrates. It states that “invertebrates are the most important component of wild fauna, both in number of species and biomass.” It also states that they are not only an important source of food for animals, but also useful in protecting farming, forestry, animal husbandry, human health, and water purity. They made it clear that some invertebrates may harm human activities but their populations may be controlled naturally by other invertebrates. Now the importance of invertebrates and the necessity of their preservation are being discovered more and more through various studies. The attempt to protect invertebrates is becoming more and more active, too.
There are some proverbs that go, “Even cicada larvae have the ability to crawl” and “Tread on an earthworm and it will squirm.” The message of these proverbs is that we should not look down on people who look insignificant and incapable of doing things because everybody has his or her own talent. What is interesting is that insects from these two proverbs are both invertebrates. Invertebrates have been regarded as the byword of something insignificant for a long time because they are small or look unattractive. However, their true value is ruminated through the proverbs of the human world.
Paul Ehrlich, an American biologist at Stanford University, said that every species plays an important role although it is small in nature just as small rivets keep a big airplane sturdy. James Lovelock, a prominent scientist, also proved through an experiment that the more species of organisms there are, the more stable the ecosystem becomes.
No creature is useless in nature; it is just that humans do not recognize their presence. Mother Nature consists of precious living beings that cannot be replaced with anything else.