On May 11, Beijing time, according to foreign media reports, in the deepest and coldest areas of the ocean, there are some huge marine organisms, most of which are invertebrates. Compared with squid, sea spiders, worms and other animals, the size of other species in the world is dwarfed. This phenomenon is called "gigantization".
Spider crab
The king squid in sub Antarctic waters is about 14 times longer than the common arrow squid in New Zealand. Sponges deep in the Pacific Ocean can be the size of a van. But why can such huge creatures be created in the depths of these freezing waters? It may be because of survival needs, or it may be caused by some factors in the cold sea water.
An article published in biogeography in 2006 pointed out that the deepest resources of the ocean are very scarce, which is similar to the island ecosystem. Most food comes from shallow water, and only some can reach the depths of the ocean. Alicia bitondo, senior manager of the Monterey aquarium in California, points out that when food is scarce, large size can provide a huge advantage.
Giant squid
Large animals move faster and farther in search of food or mates. Their metabolism is more efficient and their bodies can better store food. Therefore, when food (such as the bodies of large animals) falls into the deep sea, large animals eat more food and store energy for a longer time.
The low temperature in the deep sea will significantly reduce the metabolic rate of animals, which may also contribute to the maximization of deep-sea animals. Organisms in deep-sea ecosystems tend to grow and mature very slowly. For example, Greenland sleeping sharks can be up to 7.3 meters long and 1.5 tons heavy, but they grow all their life and live for hundreds of years. Greenland sharks grow only one centimeter a year and do not reach sexual maturity until they are about 150 years old. Bitondo added that this is partly due to the lack of natural enemies in the deep sea, so these sharks can live so long and grow so large.
Before humans met these giants in the deep sea, they were first found in the waters near Antarctica. Near the south pole, the "gigantization" phenomenon seems to be closer to the sea surface. There are huge sea slugs, sponges, worms, sea spiders and even huge single celled organisms living in shallow water. They are located in the water where scuba diving can be used. The shallowest is only 9.1 meters. "There may be a special factor in Antarctica that allows these huge species to live closer to the surface of the water," said art woods, an ecological physiologist at the University of Montana Woods believes that the gigantism of Antarctic waters may be related to the oxygen supply in cold sea water.
The oxygen concentration of seawater in polar regions is high. However, low temperature will reduce the metabolic rate, so animals in these environments use oxygen very slowly. Since the oxygen content here far exceeds the demand of animals, the conditions restricting their growth may be relaxed. These environments allow animals' bodies and tissues to grow larger without the risk of hypoxia. In other words, adequate oxygen supply is not necessarily the reason for the large size of marine organisms, but at least it creates conditions for this.
But even for polar marine animals, there seems to be an upper limit on size. In a report published in the Royal Society report B in 2017, woods and colleagues studied Arctic sea spiders. They are very large, with a diameter of up to 30.5 cm. The team found that the larger the sea spider, the lower the oxygen level in the body. Aerobic metabolism depends on the oxygen supply. When the oxygen level is too low, the body tissue will suffer from hypoxia. The relationship between sea spider size and oxygen levels suggests that the balance between oxygen supply and demand seems to be changing.
Although there are several hypotheses about how giant marine organisms came into being, no one has determined the specific mechanism that led to their great changes in size in the process of evolution. As Woods said, "nothing is certain in the biological world."