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2025-01-28 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > IT Information >
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The original title: "how much does it take for animals to shit to feed a sea?" They almost disappeared before we figured it out. "
Humpback whales leaping out of the water (photo: Matthew Savoca / EurekAlert) it is not easy to figure out how much the largest animal on earth can eat.
A huge blue figure swam under the surface of the water. Suddenly, a behemoth broke the water, opened its mouth like a tassel, and wrapped dozens of tons of sea water into its mouth. However, it did not have much interest in the sea water and quickly spit it out and then enjoyed hundreds of kilograms of krill left in its mouth.
Blue whale (photo: NOAA Fisheries) the giant whale in the sea is the largest animal on earth, and the blue whale is more likely to be the largest beast in the history of the earth. What we usually call "whales" include baleen whales (Mysticeti, baleen whales) and toothed whales (Odontoceti). As the name suggests, toothed whales have teeth, while living baleen whales have no teeth, and they rely on the baleen in their mouths for filter feeding.
Whale baleen is a comb-shaped structure formed by the arrangement of pieces of baleen plate, each of which can be several meters long. Many baleen whales have laryngeal pleats (throat groove) between the lower jaw and the abdomen, a structure that expands the whale's oral volume to four times its normal size. When eating, baleen whales first swallow a large amount of sea water containing food (usually krill, copepods, fish, etc.), and then squeeze out the sea water, and the whale beard will block the food in its mouth like a sieve.
Baleen (photo: NOAA Fisheries) many baleen whales are famous sea giants, including blue whale, humpback whale, right whale, bowhead whale and so on. However, there is a very basic and seemingly simple question that has been bothering biologists: how edible are these behemoths?
It's not that scientists haven't tried to answer this question. However, whales are so large that it is difficult to keep a few to observe how much they eat. And they live in water, making it difficult to observe directly how much food they eat. So in the past, scientists often had only two choices: one was to estimate food intake based on the stomach contents of dead individuals, and the other was to extrapolate the metabolic rate of whales using animal metabolic models to estimate food intake. however, these models are based on animals several orders of magnitude smaller than whales. Obviously, the results obtained by these methods are not very reliable.
After a decade of pursuit in Monterey Bay Bay in western California, three scientists are standing on an inflatable boat, clutching an antenna, waiting nervously for something. Suddenly, the beep sounded-which meant that they had received a radio signal from the tracker on the blue whale, and the captain immediately accelerated, following the gradually increasing beep, hoping to find the beast that was about to surface. They must arrive before it escapes into the deep sea again, or they will have to wait another 10 minutes.
Since 2010, the team of dozens of scientists has been tracking whales in the Pacific, Atlantic and Southern Oceans. When they go out to sea, they usually form a small "fleet". In addition to small inflatable boats, there are also large research ships, with researchers on board responsible for observation and guidance.
If all goes well, the scientists on the boat will stick out a 6-meter-long carbon fiber rod and attach the adsorption tracker to the whale while the whale is floating. The tracker is equipped with cameras, microphones, GPS, accelerometers and other devices that scientists can use to track whales' movements and analyze how often they eat. At the same time, researchers on the ship had to remotely control drones to take aerial pictures of whales to measure body length, estimate weight and the volume of water swallowed each time, and use sonar detection to calculate the density of food in the water.
(photo: Micha ë l CATANZARITI / Wikimedia Commons;License:CC-BY-SA 3.0) by 2019, the team had marked 321 baleen whales covering seven species (there are only 14 baleen whales left) and estimated the appetite of these beasts. To their surprise, previous scientists seriously underestimated the food intake of large baleen whales, and in some waters, the new estimates were even three times as high as previously known.
For example, a study published in 2008 estimated that all whales in the California current ecosystem consume more than 2 million tons of food a year. However, the team concluded that any blue whale, fin whale or humpback whale population in the area consumes more than 2 million tons of food each year. They also found that during the foraging season (a year can be divided into foraging and breeding seasons according to whale activity), an adult blue whale in the eastern North Atlantic can eat 16 tons of krill a day, consuming about 1500 to 2,000 tons of krill a year, far exceeding the previous estimate of about 500 tons a year. In fact, the academic consensus in the past was that baleen whales consume no more than 5% of their body weight every day, but this study suggests that this proportion may reach 5% to 30%.
The more you feed the whole ocean, the more you row. On land, animal manure can be used as organic fertilizer, while in the ocean, the excretion of whales can be described as moisturizing. When foraging, whales swim between different depths, swallowing and filtering out sea water and excreting feces, like a large mixer, promoting the mixing and exchange of nutrients between the bottom and surface water.
In the droppings of whales, there is a nutrient that has attracted special attention from scientists-iron. Phytoplankton such as diatoms can produce oxygen through photosynthesis, contributing a large amount of primary production (due to the increase in total organic carbon in the ecosystem due to the synthesis of organic matter by primary producers), but this process depends on iron. However, in many sea areas, the content of soluble iron is very low, which limits the growth of phytoplankton. In the waters around Antarctica, the average iron concentration in whale feces can reach 145.9mg / kg (in common iron-rich foods, the iron content in chicken liver is 110mg / kg, beef is 35mg / kg), which is 10 million times higher than that in sea water.
Because whales need water to breathe, they often defecate in shallow light transmission zones (photic zone), which provides sufficient "fertilizer" for phytoplankton such as large diatoms near the surface. Next, the krill will eat diatoms to "recover" the iron from the surface water. It is estimated that the iron in krill in the Southern Ocean accounts for about 24% of the total iron in seawater within 200 meters below sea level in the region. Krill is one of the main food sources for many baleen whales. Whales eat them and then defecate, realizing the cycle of iron.
Antarctic krill (photo: Uwe Kils / Wikimedia Commons;License:CC-BY-SA 3.0) "whales are like mobile krill processing plants, fertilizing the ocean and boosting its productivity. With the exception of whales, few species can promote nutrient recycling on such a large scale." Said Matthew Savorca, a marine ecologist at Stanford University and the newsletter author of the new study.
In addition, whales contain large amounts of nitrogen in their feces and urine, and whales' activities at different depths can bring phosphorus from the deep sea to shallow water, which are also essential for life activities. Without whales, many nutrients could sink to the bottom of the sea, depriving biologically rich shallow waters of important sources of nutrients, thereby reducing the total productivity of the entire ocean. Moreover, because the photosynthesis of phytoplankton absorbs carbon dioxide from the atmosphere and stores carbon, whales indirectly expand the "carbon pool" of the ocean by providing "fertilizer" for phytoplankton.
"our results suggest that the contribution of whales to the primary productivity and carbon absorption of global ecosystems may be on an order of magnitude comparable to that of the entire terrestrial forest ecosystem." Said Nicholas Pyenson, director of marine mammal specimens at the American Museum of Natural History, director of marine mammal fossils at the American Museum of Natural History and one of the co-authors of the new study.
Even after death, whale carcasses continue to nourish the ocean-carcasses that sink to the bottom form whale fall, which are quietly and slowly decomposed on the ocean floor, providing food and habitat for many creatures, such as chemosynthetic bacteria and invertebrates. Decomposed whales can also continuously provide carbon for undersea sediments, usually for more than 2000 years, which can be said to be "turned into spring mud to protect flowers".
Whale fall (photo: Craig Smith / NOAA / Wikipedia) A dark past and an uncertain future. With the development of industrialization and the birth of large whaling ships from the late 19th century to the 20th century, whaling brought bad luck to whales around the world. At that time, blubber, whisker and whale meat were very popular. One study estimates that nearly 2.9 million large whales (mainly baleen whales) were hunted and killed worldwide throughout the 20th century. The populations of many species of baleen whales have shrunk significantly and have not yet returned to pre-whaling levels. For example, it is estimated that blue whales in the Southern Ocean consumed 167 million tons of krill per year in 1900, compared with 600000 tons in 2000, a decrease of 99.6 percent.
The sharp decline in the population has also damaged the function of whales as marine "engineers". Today, whales in the Southern Ocean can recycle about 1200 tons of iron a year, compared with about 12,000 tons before the development of the whaling industry. The team estimates that if restored to this level, net primary productivity (annual net primary production) in the Southern Ocean could increase by 11 per cent. "if the whale population returns to the level it was before the development of whaling in the early 20th century, then the function of the marine ecosystem will be largely restored," Pienson said. "
In 1986, the Global Convention on banning Whaling issued by the International Whaling Commission (IWC) came into force, strictly banning commercial whaling. Since then, global whaling has declined significantly. During the decade of the 1960s, the number of large whales killed by commercial whaling worldwide reached 700000, but by the 1990s it had fallen to about 7000.
Although some baleen whale populations are recovering, these marine giants are not "rest easy". Rising surface water temperatures and acidification threaten whales' food sources. In addition to climate change, other man-made factors such as ship collision, entanglement of fishing gear, marine pollution and sound pollution also inhibit the recovery of whale populations.
Whales injured by ships (photo: NOAA, HIHWNMS) Savoka and colleagues are now engaged in further research: "We are studying how new findings can be used to help restore marine ecosystems and bring whale populations back to normal. These efforts are expected to bring benefits such as promoting biodiversity conservation, fisheries development and carbon storage."
Links to papers:
Https://www.nature.com/articles/s41586-021-03991-5
Reference research:
Https://europepmc.org/article/med/24311126
Https://onlinelibrary.wiley.com/doi/10.1111/j.1467-2979.2010.00356.x
Https://nutritionaustralia.org/fact-sheets/iron/
Https://spo.nmfs.noaa.gov/content/emptying-oceans-summary-industrial-whaling-catches-20th-century
Https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/130220
Https://www.pnas.org/content/113/4/868
Http://www.int-res.com/abstracts/meps/v371/p285-295/
Other reference links:
Https://www.eurekalert.org/news-releases/933143
Https://www.eurekalert.org/news-releases/933241
Https://news.stanford.edu/2020/07/15/studying-whales-high-tech-tools/
Https://www.fisheries.noaa.gov/whales
Https://www.fisheries.noaa.gov/national/outreach-and-education/fun-facts-about-wonderful-whales
Https://www.britannica.com/animal/baleen-whale
Https://us.whales.org/whales-dolphins/what-is-baleen/
Http://zhishifenzi.com/depth/depth/7865.html
This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by Li Shiyuan, revision: Erqi
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