Secrets of the night oken: strange creatures and mystical glow

When night falls, strange creatures rise from the depths, and the water begins to glow blue. Some phenomena in the ocean can only be seen after dark.

1. The ocean begins to sparkle due to bioluminescence

Dinoflagellates emit blue light when touched, as in this bay of the island of Vaadhu in the Maldives.

You've probably seen similar photos. Night has fallen on an exotic island. Waves are beating on the shore. The water sparkles with a blue, electricity-like color.

The Internet is very fond of photos of this magical bioluminescent bay. You may have heard the stories of bloggers who say that in life everything does not look so magical. Even if it is, bioluminescence (in this case caused by a special plankton called dinoflagellates) — this is an amazing phenomenon of nature.

Dinoflagellates emit blue light only when touched, so they can only be seen on the crest of a wave, around boats, and also when the oars touch the water. These tiny creatures are the main source of bioluminescence on the ocean surface.

The so-called bioluminescent bays, such as in Puerto Rico or Jamaica, are the most famous places to observe such a glow. Nevertheless, this ephemeral phenomenon can be found in many other places of the ocean, where the density of dinoflagellates is especially high.

Sometimes the population of dinoflagellates increases too quickly, and then a much less beautiful glow is formed, which has a red-brown color during the day, also known as "red tide". And some of these dinoflagellates are even poisonous.

An even rarer and more unusual phenomenon than bioluminescent bays is the milky glow of the sea, when the luminous water stretches to the horizon.

The milky glow of the sea has been recorded only a few hundred times since 1915, while most of them were concentrated in the northwestern part of the Indian Ocean and near the Indonesian island of Java. This phenomenon is not explained by dioflagellates, but rather by "bioluminescent bacteria, a large number of which have gathered on the surface of the water," explains Dr. Matt Davis, associate professor of biology at St. Cloud University, USA, who specializes in bioluminescence.

For centuries, sailors have described the milky glow of the sea as a nocturnal, whitish sparkle, similar to a snow cover, but scientists have not been able to study this phenomenon in detail.

In 2005, researchers analyzing archival satellite images found that the milky glow of the sea can be observed from space and that one satellite recorded a huge area in the ocean that had a strange glow for three consecutive nights a decade earlier.

2. Animals glow in the dark

Bioluminescence, the emission of visible light by the body as a result of a natural chemical reaction, is characteristic of marine animals such as fish, squid and shellfish. In deep waters, most species are bioluminescent and are the main source of light.

In shallow water, most bioluminescent fish emit light only at night.

"Black—eyed fish have a special organ under the eye that they can rotate to emit light coming from bacteria [accumulating in this organ], and they use it to hunt and communicate with other animals," says Matt Davis.

Camouflage, protection, hunting are some of the reasons why fish emit light. Squid, for example, uses light in a very sophisticated way. These nocturnal animals have a mutually beneficial relationship with the luminescent bacteria that accumulate in their mantle. With the help of them at night, squids control their color depending on the brightness of the light of the Moon, and thus reduce their own in order to disguise themselves from predators.

3. The light of the moon provokes the biggest orgy on the planet

There's nothing more romantic than moonlight, especially if you're a coral on the Great Barrier Reef. One night a year, in spring, moonlight provokes the world's biggest orgy. More than 130 species of corals simultaneously release germ cells into the water within an interval of 30-60 minutes.

Mass breeding on the Great Barrier Reef is one of the most extraordinary examples of synchronized behavior on earth.

When the germ cells, sperm and eggs, are released, they hang for a second, creating a ghostly resemblance to the shape of a reef, before plunging into an underwater storm of fertilization.

Dr. Oral Levy, a marine biologist and ecologist and professor at Bar-Ilan University, Israel, has studied this extraordinary phenomenon.

"It's a really amazing phenomenon... we know that this event will happen every year in November, a few nights after the full moon, usually 3-5 days," he says. — It is always incredible, in particular, I am amazed every time how coral species multiply at the same time at night at the same hour year after year."

He adds:

"As soon as this happens, it shocks me every time how everything becomes so alive and synchronized. It's almost a spiritual experience when you begin to understand the power of nature in all its glory. The light of the moon provokes this phenomenon, as it serves as a synchronizer and a kind of "alarm clock", most likely, together with other environmental phenomena, such as sunset time, water temperature and tide, to signal the time of the release of germ cells (sperm and eggs)." It is likely that corals have photoreceptors that determine the phases of the moon, thus understanding when to release germ cells.

4. Sharks and seals rely on the light of the sky

For many seals, nights with moonlight mean danger. During the winter months, there are about 60,000 Cape Fur seals on the island Sea Falls Bay, in South Africa, are at risk of being eaten by a great white shark, which are guarding seals at the entrance and exit of the water.

According to a study conducted in 2016, it was hypothesized that swimming at night on a full moon, seals are at greater risk of being eaten by sharks, as the bright moonlight highlights their silhouette on the surface, making them easy prey for predators underwater. However, most shark attacks on seals occur at dawn. Researchers who studied the number of attacks at dawn were surprised that when the moon was full, predators hunted less in the morning. The researchers put forward the theory that moonlight combined with incipient sunlight could reduce the hunting abilities of sharks, and that at this time of day they no longer had an advantage over seals.

Also, the seals could navigate by another parameter — the stars. Common seals (Phoca vitulina) they can determine where the north star is and follow it, the study shows. During an experiment using a simulated night sky, seals swam towards the brightest star.

In the wild, seals need to move across the open sea to find a feeding place that can be hundreds of kilometers away.

Researcher Dr. Bjorn Mock spoke out at the time:

"Seals can remember the location of the stars in relation to the feeding area at sunset and dawn, when they see both the stars and the earth."

5. Unusual animals rise to the surface every night

Under the cover of night, animals that are rarely found migrate to the surface of the ocean in search of prey. Humboldt squid is one of the brightest marine animals that can be seen on the surface of the water.

During the day, it usually lives in the depths of the eastern Pacific Ocean in the waters of the deep-sea shelf off the western coast of North and South America, and every night it, like many other marine animals, migrates upwards in search of food. Vertical migration is a process when marine animals rise to the surface at sunset and sink back to the depth at dawn. Such a phenomenon is a very common phenomenon.

"Humboldt squid follows its main prey, the so—called luminous anchovies," explains Professor Paul Rodhouse, professor emeritus at the British Institute for Antarctic Research and former head of its Department of Biological Sciences. And the glowing anchovies, in turn, follow the vertically migrating zooplankton. Since many marine animals depend on zooplankton, "the remaining links in the food chain will follow it," says Professor Rodhouse.

"It's a huge daily movement of biomass," explains Rodhouse. "More than a thousand meters. Some squid migrate more than a kilometer a day."

Humboldt squid is one of the most stunning species rising to the surface of the water every night. For his ability to change color and glow bright red, he is called the "red devil". And despite the fact that they are smaller than 13-meter giant squid, they can reach one and a half meters in length. These very aggressive predators grab food with strong tentacles and suckers and tear with their teeth. There have even been several attacks on people in history.

But even such ferocious animals become victims of even larger predators, such as swordfish or sharks.

"Of course, they are all active at night to avoid attacks by larger predators," says Professor Rodhouse, "So in order to reduce the risk of being eaten, they have to go down into deep dark waters at night."