Earth has devoted resources to two completely different worlds of life, two very different types of ecosystems. The basic hierarchy of biodiversity in both worlds is the same, from ecosystems to species to genes, and both face the same threat of extinction. But everything else is very different.
To illustrate this point, I hope to take the reader on a short journey, please come with me to the edge of the ocean. The environment around the ocean is far from the earth and the blue sky, as if it were on another planet. If you don't dive into the sea with any life support equipment, humans will die within 10 minutes. The vast underwater world is rarely visited by humans, let alone carefully observed.
As a result, most of the ocean world exists apart from the many events of the Anthropocene. But in the early years of the 21st century, things are changing rapidly. Humans have reached the farthest and lowest reaches of the ocean, especially where food and other resources can be found and profited from. Our ecological footprint is expanding: the sea is warming and acidifying, coral reefs are disappearing, nearly extinct, and in some places are even permanently destroyed. The high seas are often overfished, with undersea trawling leaving the underwater world with only barren silt and polluted river deltas scattered above the seabed creating dead zones.
Nevertheless, much of the marine biodiversity has been preserved. Populations of many species have shrunk and geographic coverage has narrowed, but few species have been driven to the point of eventual extinction. There is still a place in the ocean for species to interdependent and form healthy ecosystems. Much of the ocean is still intact and in the early stages of development.
Let's start with the beach. Imagine that at low tide, you are standing on the wet sand of the crashing wave area, watching waves of thin waves surging around you, submerging your feet one moment, rolling out the sand under your feet, and then building up the sand on your feet. Then, let's start thinking biologically. At first glance, the crash zone seems to have no signs of life, only water and washed soil. But on the contrary, it is home to many invertebrates, and only traces of them can be found here. In terms of body size, the large bullet-shaped shrimp (sand lice, about the size of a thumb) are large, and most of the others are small creatures that are barely visible with the naked eye.
Such simple habitats live with small benthic communities. There are many oddities about this community, not only in the species it contains, but also in the many higher-level taxonomic categories that these species represent. On land, if you walk to the edge of the forest and carefully identify the animal biodiversity here, you are likely to find representatives of the following 7 phyla: vertebrate phylum (birds, mammals, amphibians), arthropod phylum (insects, spiders, mites, millipedes, centipedes, crustaceans), mollusk phylum (snails, slugs), link animal phylum (earthworms), nematodes phylum (roundworms), tardigrades phylum (tardigrades), and rotifer phylum (rotifers).
And between the sand grains in the shore-lapping area, you can find twice as many phytosanitories as in the above areas, which may make you whisper "God" over and over again, including the endritic animal phylum, the ventral hairy animal phylum, the palatial gastropteral phylum, the motifs phylum, the nematode phylum, the nematode phylum, the troll phylum, the starworm phylum, and the tardigrade phylum. In addition, there are the more common mollusk phylums, polychaete worms, rotifers and crustaceans. The more common body size of small benthic organisms is worm-like because it facilitates rapid movement in tightly packed sand grains. They are always gliding to eat, gliding to avoid predators, gliding to mate and breed.
Research into small benthic communities and their location in coastline ecosystems around the world is still in its early stages, and many of the ways in which these species interact remain a blank in academia. These eccentric inhabitants, who live in some of the most vibrant ecosystems on Earth, are an important part of the biological world. While small benthic animals may only live in narrow habitats with a width of 1 km, the total length of Earth's coastline is 573,000 km, essentially equivalent to the distance from Earth to the Moon. Assuming that the small benthic habitat is the same length and average width is 1 km, its total area is as large as the territorial area of Germany.
Let's move on to the next topic, which is about the well-known coral reefs in the sea. Because coral reefs have exquisite and complex structures and abundant biodiversity, they are often referred to as marine rainforests. Here we will find the home of the drifting creatures. It's a completely different habitat that even many marine biologists aren't familiar with. On the surface of the sea where air and seawater come into contact to form a surface tension, a group of organisms live here. Although sparsely distributed, these organisms can be found in all areas of the sea. They live on floating islets formed by animal tissue, with carcasses of fish and seabirds, as well as fragments of algae, and mucus that is barely visible to the naked eye.
Each of these small islands is inhabited by a group of living organisms. Among the "inhabitants" of the island, many kinds of bacteria can always be found, and possibly archaea. Archaea are very similar to bacteria, but the DNA is very different. These inhabitants, like plants and animals that have just arrived at a true marine island, thrive and thrive here before they run out of all their nutrients.
In the world's oceans and inland seas, bacteria and archaea ride on the debris on the surface of the sea and float under the water. Those free-moving bacteria and archaea obtain matter and energy through photosynthesis. Overall, the result is this: no matter how crystal clear the sea water looks, it is full of active life.
I am an entomologist by birth and have a particular interest in marine insects. There are millions of species of insects, and the noisy biomass made up of insects dominates the animal kingdom on the land. Exactly how many insects live in the marine environment is a very interesting question, and the answer to this question is almost zero. From this, a scientific mystery has been created that is puzzling. In the course of my own island research, I found that there are caterpillars living in the roots of the mangrove pillars in the sea below the surface of the water. Mangroves are the closest plants in the mangrove class to the ocean and the most extensive mangroves in the world. But mangroves, a habitat close to land, are still far from coral reefs and deep-sea areas.
In coral reefs and deep-sea areas, insects are hardly found except on the surface of the sea, and the probability of encountering strange long-distance insects on the sea surface is extremely small. Few biologists have ever actually encountered living insects on the surface of the open sea, and I have never encountered them, and Linnaeus and Darwin were completely unaware of their existence. Here, the only known insect is the water weasel, a hemiptera that is common in freshwater waters such as streams, ponds and lakes, and whose long legs can stand on the surface of the water and jump forward. Freshwater water moths feed on other insects such as mosquito larvae, which also live on or near the surface of the water. All marine motleys belong to the same genus. Of this genus, only 5 species have been found living on the surface of the sea. And no one knows what exactly the prey they prey is.
The existence of the genus Mora, which lives above the vast ocean, is an exception and further deepens the biological mystery. Insects have evolved on land, ponds and other freshwater habitats for 400 million years. During this period, their populations continued to grow, and insects could be seen wherever there were plants. In the baptism of evolutionary tides again and again, millions of insect species have evolved and proliferated, and only moray insects have maintained their standing on the surface of the sea. As far as I know, thousands of other invertebrate species, such as crustaceans, sea spiders and polychaete worms, cannot find moray insects in the narrow habitat they occupy.
Conrad Labandeira, a well-known paleontologist and expert in insect ecology, believes that marine insects do not exist in the world, because there are no trees in the sea and there is no leafy vegetation for insects to live and reproduce. Maybe he's right, but there are abundant layered vegetation in shallow areas of the ocean, such as seagrass forests along the Pacific coast. Even such habitats are not occupied by insects, and they are inhabited by other types of invertebrates who play the role of hunters, parasites and cleaners.
Deep-sea scattering layers in the ocean have completely different fauna. It's a very different biological kingdom, with many wonders waiting to be discovered. If you pursue a career in distant-water fishing and don't limit your targets to large fish species such as marlins and tuna, you'll encounter countless other fish at night. After sunset, accompanied by squid and crustaceans, a dense school of fish will rise from a depth of 270 to 360 meters to the surface of the sea. During the day, these animals lurk in the dark deep sea. However, the protection given to them by deep water is not enough, because hunters active in deeper seawater can still see the silhouettes of these animals with the light from above. As a second defense, some species use a "reflection" mechanism, which emits light through the bioluminescent properties of their abdomen—the symbiotic bacteria carried by their own tissues or bodies. The reflected light is about the same as the brightness of the sunlight or moonlight from above, which makes the luminous animals less likely to be found by hunters.
In the deep-sea scattering layer, every interaction between the hunter and the prey, every competition, is an evolutionary arms race, in perfect harmony with the laws of biology. From this perspective, deep-sea sharks, as well as hunting axefish and ear squid, take the game to new heights: these hunters can also glow in their abdomen and can play a stealth role when approaching their prey.
The discovery of the deep-sea scattering layer itself is already breathtaking, and not long ago, marine biologists discovered another miracle in the deep-sea scattering layer, that is, the monster that makes this place home. In 1976, the first largemouth shark was spotted in the deep sea near Hawaii. By 2014, more than 50 largemouth sharks had been captured or observed. Although the great-billed shark is at least 5 meters long and weighs more than 90 kilograms, this large size does not pose a threat to humans. Although its mouth is large, the teeth in its mouth are surprisingly small, and it will not bite anyway. The largemouth shark opens its mouth wide as it preys, swallowing small crustaceans and other plankton like a funnel. This method is the same as that used by other manta rays, whale sharks, elephant sharks and fin whales that are harmless to humans.
On a dark moonless night with huge deep-sea monsters lurking under ships, cruising through vast oceans that have never been discovered, how many earth-shattering secrets are there for the small creatures that live near these big ones to discover? The question has been lingering in the minds of scientists. To find the most secretive and under-known forms of life, scientists have begun a more thorough search for marine microbes, some of which have proven to be the smallest known organisms on Earth.