Humans Have Broken a Fundamental Law of the Ocean

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on 19th November, 1969, CCS Hudson Slipped from the cold waters of Halifax Harbor in Nova Scotia and plunged into the open sea. what was the research ship launching on Several marine scientists on board Thought of as the last great, unknown voyage: America’s first full circumnavigation. The ship was bound for Rio de Janeiro, where it would pick up more scientists before passing through Cape Horn – the southernmost point in the Americas – and then traversing the ice-filled northern route through the Pacific back to Halifax Harbor. For.

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On th eway, Hudson Will stop frequently so that its scientists can collect samples and take measurements. One of those scientists, Ray Sheldon, rode Hudson In Valparaíso, Chile. A marine ecologist at Canada’s Bedford Institute of Oceanography, Sheldon was fascinated by the microscopic plankton that seemed to be everywhere in the ocean: how far and wide were these tiny creatures spread? To find out, Sheldon and his colleagues carried buckets of sea water to Hudsonand used a plankton-counting machine to work out the size and number of organisms they found.

life in the ocean, they discovered, followed a simple mathematical rule: the abundance of an organism is closely related to the size of its body. In other words, the smaller the creatures, the more you find in the ocean. For example, krill are a billion times smaller than tuna, but they are a billion times more abundant.


What was even more surprising was how accurate this rule was. When Sheldon and his colleagues organized their plankton samples by order of magnitude, they found that organisms in each size bracket had the same mass. In a bucket of seawater, one third of the mass of plankton would be between 1 and 10 micrometers, another third would be between 10 and 100 micrometers, and the last third would be between 100 micrometers and 1 millimeter. Each time they move up a size group, the number of individuals in that group declines by a factor of 10. The total mass remained the same, while the size of the population changed.

Sheldon thought that this rule might govern all life in the ocean from the smallest bacterium to the largest whale. This spectacle turned out to be true. The Sheldon spectrum, as it became known, has also been observed in plankton, fish and freshwater ecosystems. (Actually, a Russian zoologist saw Soil had the same pattern three decades before Sheldon, but his discovery went unnoticed). “This shows that no one shape is better than any other shape,” says Eric Galbraith, a professor of Earth and planetary science at McGill University in Montreal. “Everyone has cells of the same size. And basically, for a cell, it doesn’t really matter what body shape you are, you just do the same thing.”

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But now it seems that humans have broken this fundamental law of the ocean. In a November paper for the journal science advance, Galbraith and his colleagues showed that the Sheldon spectrum is no longer true for large marine organisms. Thanks to industrial fishing, the total ocean biomass of large fish and marine mammals is much lower than would be under the influence of the Sheldon spectrum. “It seemed to be the pattern that all life is following for reasons we don’t understand,” says Galbraith. “We’ve changed that in the last 100 years or so.”

To find out whether the Sheldon spectrum is still accurate, Galbraith and his colleagues used satellite images and data on plankton from ocean samples, scientific models to predict the abundance of fish and marine mammals from the International Union for Conservation of Nature. brought together the population estimates. Overall, the group estimated the global abundance of 12 major groups of marine organisms, from bacteria to mammals. They then compared the state of today’s oceans with estimates of what they were before 1850, taking into account the fish and mammals that industrial fishing and whaling have pulled out of the water. To simplify things, the researchers assumed that the levels of bacteria, plankton and small fish in 1850 were similar to those of today.

When Galbraith and his colleagues looked at this conjecture from before 1850, they could immediately see that the Sheldon spectrum was largely correct. The researchers found that in landscapes prior to 1850, biomass was remarkably consistent across size brackets. When they summed up all organisms weighing from 1 to 10 grams, it came to 1 billion metric tons. The same was true for all organisms weighing between 10 and 100 grams and between 100 grams and 1 kilogram. Only at the very extreme end of the spectrum – the smallest bacteria and the largest whales – did the measurements begin to differ.

Comparing these estimates from before 1850 to modern-day models told a very different story. Models show that the biomass of fish and all marine mammals larger than 10 grams has decreased by more than 2 billion metric tons since 1800. The largest sized sections have experienced a reduction in biomass of about 90 percent since the 1800s. Many large fish and mammals that used to live in the ocean are no longer there.

“The world I grew up in is gone,” says Kristin Kaschner, a marine ecologist at the University of Freiburg in Germany. Between 1890 and 2001, the population of all whale species declined more than less than 2.5 million 880,000, While populations of some whale species have resumed since the global whaling moratorium in 1986, many are still in danger, And while most fish stocks are fished in a way that allows them to maintain or grow their populations, just over 34 percent of them are overexploited, which means we are removing so many fish from a certain area that their population cannot recover. some of the Fish stocks are being overexploited Japanese anchovies, Alaskan pollock, and South American pilchard. “I think we are moving towards a world where the default is not to have a natural ecosystem in which everything is as you had before human exploitation and intervention,” Kaschner says.

Although the picture is not rosy at this time, looking at the size spectrum of marine organisms could be a helpful indicator of ocean health, says Julia Blanchard, an ecologist at the University of Tasmania in Australia. Blanchard has studied coral reefs and found that while the Sheldon spectrum seems strange, it is a sign that the reef ecosystem is no longer healthy. “If we want to improve this, we can ask what will be the level of fishing that will sustain the size spectrum,” she says.

One problem that fisheries often target Scientist Says BOFFFFs: Large, old, fat, flaccid, female fish. Their large bodies are prized fishermen, but are an important source of BOFFFF new baby fish. Take these away and the size spectrum quickly runs out of kilos. One way to manage this is to encourage the fishing industry to target medium-sized fish, allowing mature ones to replenish dwindling populations.

Of course, overfishing is not the only challenge facing marine populations. A worst-case scenario of 5°C warming would be too hot for 50 percent of fish species, and 1.5° of warming would still be too much for 10 percent of fish, according to a study, Overfishing means that these populations are starting from a much weaker point than they would otherwise. Remove too many fish from the ocean and you reduce genetic diversity, weaken food webs, and allow ocean habitats to deteriorate, all of which make an individual ecosystem more vulnerable to changes. “The important thing is that as soon as you get out of a system and then it’s heated, it’s a lot less resilient to that warming,” says Blanchard.

The good news is that fish species can bounce back. “They are extremely resilient,” says Ken Andersen, a marine ecologist at the Technical University of Denmark. In September, the International Union for Conservation of Nature moved Four Tuna Species Ahead Due to strict fishing quotas and crackdown on illegal fishing, the list of threatened species has declined after their populations have recovered. “It’s easier to stop overfishing than it is to stop climate change,” says Galbraith. “If we reduce fish, if we allow the ecosystem to recover, we can maintain it.”

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