Seawater is too salty to drink! So how do animals living in the ocean get fresh water?

We often say that water is the source of life, but the water that humans refer to mainly refers to "fresh water". After all, salty seawater, no matter how large the volume, cannot be used to quench thirst. Therefore, in the movie "Waterworld", the most precious thing besides soil is fresh water.

Freshwater resources are limited and precious

However, animals living in the ocean are not as picky as humans. Even if they know that the seawater is too salty to drink, they have no choice but to drink it. However, marine organisms still have their own unique skills in "drinking seawater".

So, how do they get fresh water?

It turns out that marine life also needs to drink fresh water

Desalination skills of marine animals

Many people who have eaten marine fish feel that marine fish itself has a "very salty" taste, and believe that this is closely related to the fact that they drink seawater all year round.

But in fact, even fish living in the sea cannot withstand drinking extremely salty seawater every day, so they have learned to "desalinate seawater" through their own bodies.

Fish need water to provide adequate oxygen

According to scientists' observations, many fish living in the sea have something called "chloride-secreting cells" in their gills. These cells are "seawater desalination devices" secretly installed in the gills of fish.

This cell filters seawater after it enters the fish's gills, helping fish obtain fresh water resources.

Schematic diagram of chloride-secreting cells and their structures

Of course, this purification is not 100%, so many fish will actively use their kidneys to metabolize and excrete excess salt.

It can be said that in order to maintain the salt balance in the body, marine fish take a two-pronged approach, which is probably the wisdom gained from years of evolution.

Schematic diagram of osmotic pressure regulation in marine fish

However, the mechanism of marine fish drinking seawater first and then filtering and purifying it is not applicable to mammals in the ocean. Moreover, for mammals living in the ocean, fresh water is indeed a "must-have", so in this case, they will choose to give up seawater directly.

In short, the way they get fresh water is "food". Many people may wonder how much water can they get from food alone, and is it really enough to drink?

Some mammals in the ocean

In fact, because marine mammals rarely sweat and do not have to face the sun directly in the sea, their need for water is not so great. In this case, they will not deliberately drink seawater.

In addition, there are many animals in the ocean that have their own unique ability to "desalinate seawater", such as the well-known sea turtles. This long-lived creature also needs to drink fresh water.

Sea turtles spend their entire lives in the ocean

The way sea turtles obtain fresh water is actually somewhat similar to that of marine fish. That is, they first drink sea water and then carry out the "desalination" work.

This is why many people always have tears in their eyes when they see turtles crawling onto land. It is not because they love the land deeply, but they are simply excreting salt.

However, after enthusiastic humans discovered this phenomenon, some believed that laying eggs was because the turtles were crying because it was painful, and they also added the saying "all things have feelings". Others believed that this was "eye drops" that the turtles shed in order to keep their eyes moist after leaving the sea.

It looks like "crying", but it is actually "excreting salt"

In short, there are many different opinions, but none of them are correct, because according to scientists' observations, there is something called "salt gland" behind the eye sockets of turtles, which is used to discharge excess salt from the turtle's body. The exit of this salt gland is right next to the turtle's eyes, which is why people have the illusion that the turtle is crying.

It can be seen from this that the salt glands of sea turtles actually have the same function as the "chloride-secreting cells" in the gills of marine fish. Their functions are both to purify seawater and excrete salt from the body.

Schematic diagram of the location of salt glands

So, are marine organisms the only ones that have this "filter"?

Seabirds that also have salt glands

Obviously not, there are some creatures in nature that do not live in the sea, but they inevitably need to drink seawater, such as various seabirds. For example, seagulls and albatrosses, although they appear to belong to the blue sky, they actually also belong to the sea.

When flying over the ocean, it is not only difficult to find a place to land, but also difficult to find fresh water resources. So in order to adapt to the environment, these seabirds have evolved salt glands for excreting salt. After all, it is normal to drink seawater when swimming in the ocean.

Schematic diagram of the location of salt glands in seabirds

However, when people see these seabirds excreting salt, they think they are drinking seawater and spitting it out at the same time, because the excretion of salt from their salt glands is also very obvious, which can be said to be almost the same as that of sea turtles.

Bionics scientists say that the salt glands secrete salt fluid that flows through the nostrils to the mouth and then drips from the mouth, so it looks like seagulls and albatrosses are drinking sea water and then spitting it out.

Seabirds with leaky mouths

In short, animals also know that sea water is too salty to drink, but sometimes they "have to drink it", so after being forced to make this choice, they also choose to evolve themselves.

This ability to desalinate seawater and remove excess salt is indeed something that humans are very envious of, because the world's freshwater resources are actually quite limited, and the huge amount of seawater cannot be drunk, which makes humans very distressed.

Oceans cover approximately 71% of the Earth’s surface

Humans also want to desalinate seawater

As a species with huge demand for fresh water resources, humans have been thinking about what methods can be used to increase fresh water since they made a rough statistical analysis of the world's fresh water resources.

However, many of the current desalination methods are too expensive, so human research on converting seawater into fresh water has been in trouble.

Data shows that in 2008, the amount of fresh water produced by seawater desalination in the world was about 5000×10^4m3/d, of which the Middle East accounted for 55%, the United States accounted for 15%, Europe accounted for 9%, and Asia accounted for 8%. 70% of the fresh water in the Middle East countries with severe water shortages, such as Saudi Arabia and Israel, comes from seawater desalination.

Schematic diagram of global water resources distribution

Later, "bionics" began to enter the scientific and technological arena, allowing many scientists to see the "wisdom" displayed by animals in their long evolution, and that this wisdom, if used properly, can also help humans overcome many difficulties.

Therefore, in recent years, many scientists have tried to imitate the way marine organisms desalinate seawater to obtain fresh water, to help humans obtain more fresh water resources.

Bionics can benefit mankind through biological instincts

For example, they developed a new method called "electrodialysis" based on the method of desalinating seawater by marine fish. Although humans are still unable to achieve large-scale desalination of seawater through this method, this method of using animal wisdom to help oneself is still very good.

As freshwater resources become increasingly scarce, people are still looking forward to the method of desalinating seawater to make progress as soon as possible. After all, as for humans, we have lived on the continent for a long time, and we cannot slowly evolve a "seawater filter" like the creatures introduced above. Therefore, if the freshwater resources on land are exhausted, we can only rely on technology to "transform seawater."

Schematic diagram of the process of transforming seawater

At this point, some people may think that if there is really no water to drink, humans will still drink seawater directly. However, according to scientists' research, people who drink seawater directly at that time may die faster than those who do not drink water.

So, humans can't drink seawater directly?

Clear blue waters

Why can't humans drink seawater directly?

In the eyes of many people, if you want your body to evolve, you must have the courage to take on challenges. It is difficult for humans to evolve if they do not face extreme environments.

This is indeed the case, but it does not mean that humans will immediately gain any "special abilities" after drinking seawater, because evolution often requires a long process of natural selection.

As for why humans cannot drink seawater directly, the main reason is that our body organs do not allow it. After taking in seawater, fish will mobilize their kidneys and other organs to actively process the seawater and excrete the salt. But humans are too weak in this regard, and our kidneys' salt excretion function is really limited.

The kidneys say they have done their best!

According to scientists, the human kidney's salt excretion concentration is limited to 2%, while the salt content of seawater is as high as 3.5%. This means that if we drink seawater directly, our kidneys will not be able to bear this burden.

In order to make it work properly, people have to drink a lot of fresh water to dilute it after drinking seawater directly. This busy work has no essential benefit except tormenting their own organs.

Schematic diagram of dissolved salt in seawater

In addition, seawater contains a large amount of substances that humans cannot directly absorb, some of which are fatal to the human body. In this case, some crew members facing a shortage of fresh water would decide not to drink seawater even if they were dying of thirst, because the more they drink, the thirstier they will become.

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