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Sharks face crisis in 400 million years

Ocean acidification concerns about decreased swimming and hunting

Sharks have ruled the sea for over 400 million years. 400 million years ago, it was a long time before trees first appeared on land, and even before vertebrates landed on land. There have been five threats of extinction, but all sharks have been safely passed.

However, research has shown that the shark's ability to swim and hunt could be seriously compromised in the near future. It is ocean acidification that threatens the survival of sharks that reign over 400 million years as the most feared predators in the ocean.

Ocean acidification refers to a phenomenon in which the pH value of seawater decreases due to high hydrogen ion concentration as carbon dioxide is dissolved in seawater. The oceans of the earth have maintained a weak alkalinity of an average pH of 8.2 for hundreds of millions of years.


However, over the 200 years since the beginning of the Industrial Revolution, the average pH of the ocean has dropped to 8.1, and is expected to fall by 0.3 to 0.4 by 2100. The main cause of ocean acidification is carbon dioxide emitted by the burning of fossil fuels such as coal, oil and gas.

Rapid ocean acidification occurred about 66 million years ago, when the giant asteroid crash destroyed the dinosaurs. Billions of tons of sulfur have been released into the atmosphere, and acid rains have been caused by earthquakes and lava. Existing studies have shown that the pH has dropped by about 0.25 over 100 to 1000 years.

If ocean acidification proceeds at this rate, many marine life will disappear as dinosaurs went extinct. Ocean acidification, in particular, has a devastating effect on invertebrates that use their minerals to form shells and exoskeleton, such as corals and shellfish. Thus, most research on ocean acidification has focused on such animal species.

Calcium phosphate concentration in the scales is significantly reduced

But Dr. Lutz Auerswald, a marine biologist at Stellenbosch University in South Africa, was studying how high acidity of beer or carbonated beverages might affect human teeth while wondering how acidic seawater would affect shark teeth. did.

The researchers captured 13 shark species called 'Puffadder shyshark' in a harbor in Cape Town, classified them into control and experimental groups, and raised them in an aquarium. The control group stayed in an aquarium at pH 8.1, which is close to the current ocean level, and the aquarium in the experimental group was gradually lowered to 7.3 by the researchers.

Two months later, the researchers analyzed the shark's scales with an electron microscope. Because shark teeth and scales are formed of a calcium phosphate substance called dentin, the effects of ocean acidification on scales and teeth are likely to be similar.

As a result, the calcium phosphate concentration in the scales of the experimental group sharks was found to be significantly reduced. The control group showed a decrease of about 25% compared to a 9% decrease. This draws attention in that it can have serious consequences for sharks in many ways.

Pued Ed Shayshaq is very timid and ambushes on the floor until food arrives, so scale erosion may not have a significant effect on hunting. However, scales play an important role in species that hunt and swim fast in large spaces, such as giant white sharks.

Salmon loses sense of smell in acidic seawater

One study found that shark scales can increase swimming speed by up to 12 percent. Because of the damage to the scales can seriously reduce the ability of the sharks hunting. The scales also protect some shark species from other predators. Similarly, tooth decay has a negative impact on shark viability. The findings appear in the latest issue of the journal Scientific Report.

Ocean acidification is fatal for shark predators as well as for fish that feed sharks. Salmon, in particular, has a good sense of smell that can detect predators or find food, and rely on smells to find their way back home to lay eggs.

However, research published by researchers at the US National Oceanic and Atmospheric Administration (NOAA) has shown that when seawater carbon dioxide levels increase, salmon do not hide or dodge, even if they smell like predators. Lowered pH values ​​adversely affect salmon's sense of smell.

Investigating the effects of ocean acidification on the scales of sharks, Ourswald Box says, will be divided between adapting and extinct species as ocean acidification progresses.

Lobsters, for example, are quite resilient in the face of acidification, while abalone is not. Indeed, in ancient times many marine animals survived in much more acidic environments, but many species were also extinct.


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