The ocean is a strange place after dark
Moonlight sparked the biggest feasts in the world, strange creatures emerged from the depths, and the waves glowed blue. Some phenomena in the oceans can only be witnessed after dark.
Bioluminescence makes marine shimmer
Dinoflagellates emit blue light when they are disturbed, as in this bay on Vaadhoo Island in the Maldives.
You may have seen the photos.
It's nighttime in a very exotic location. Waves broke out on the beach. The water sparkled with electric blue lights.
The Internet likes images of bays of bioluminescence that look magical. You may also have seen the tourist bloggers bemoaning the real event because not enough to turn on the hype.
Even if the latter is true, bioluminescence (in this case usually caused by a planktonic organism called dinoflagellate) is a very amazing natural phenomenon.
Dinoflagellates emit blue light when disturbed, which is why they can be seen glittering above the crest of waves, around the boat or when the hand or oars pass through it.
This tiny creature is the most common source of bioluminescence on the surface of the oceans.
The so-called bioluminescent bays like in Puerto Rico and Jamaica are one of the most famous places to witness the light. However, mortal phenomena can be found throughout the oceans where there is a dense meeting of dinoflagellates.
Sometimes the population of dinoflagellates rises rapidly to cause bloom, which in the afternoon is colored by less attractive reds, sometimes known as red waves. And some, but not all, of these red waves are poisonous.
This little creature provides the most common source of bioluminescence at sea level.
Even strangers and more rarer than bioluminescent bays are "milky sea", where water continues to shine stretching as far as the eye can see.
Milky sea has only been seen several hundred times since 1915, mainly concentrated in the northwest of the Indian Ocean and near Java, Indonesia.
They are not caused by dinoflagellates, but are thought to be the result of "massive accumulated bioluminescent bacteria near the surface", explains to Dr. Matt Davis, Assistant Professor of Biology, St Cloud State University in the US, who specializes in bioluminescence.
Reports by sailors for centuries have described the milky sea as a nighttime whitish glow like snow, but scientists have little chance to investigate the phenomenon of the first hand.
In 2005, researchers analyzing archived satellite imagery found that the milky ocean could be seen from space and that one satellite had captured images of a vast ocean area that had shown strange light for three consecutive nights a decade earlier.
Animals shine in the dark
Squid tail squid has a symbiotic relationship with bioluminescence bacteria.
Bioluminescence, the emission of visible light by an organism as a result of natural chemical reactions, is common among marine life such as fish, squid and molluscs. In the deep ocean most species are bioluminescent, where it is the main source of light.
In the shallower waters, most bioluminescent fish display their lamps at night.
"Flashlights have special pockets under their eyes that can be rotated to expose the light emitted from these bacteria, and they use this light at night to hunt for food and communicate," says Dr. Matt Davis.
Fish flashlights have special pockets under their eyes that are used to expose bioluminescent bacteria.
Ponyfish emits light from bioluminescent bacteria placed in the pouch using transparent muscular leaves, to communicate, she explains.
Camouflage, defense and predation are one of the reasons why fish are considered to emit light.
For example, the tailed squid has an ingenious way of using lights. These nocturnal animals have a mutually beneficial relationship with luminescing bacteria that live in the cavities of the hearth below. At night the squid control the intensity of this light to match the moonlight, and can reduce their silhouette to disguise themselves from predators.
Moonlight sparked the biggest party on the planet
Mass spawning in the Great Barrier Reef is one of the great examples of synchronized behavior on Earth.
Nothing more romantic than a moonlit night, especially if you are a reef on the Great Barrier Reef in Australia.
One night a year in spring, the biggest party on earth is triggered by the moonlight.
More than 130 species of corals simultaneously release their eggs and sperm into the water during the window for only 30-60 minutes.
This bulk spawning event may be the most amazing example of synchronized behavior in the natural world.
When gametes - eggs and sperm cells - are released, they float for a moment, forming a ghost-shaped reef-like replica, before spreading into a snowstorm underwater as the sperm fertilizes the egg.
Dr. Oren Levy, a marine biologist and ecologist and Life Sciences Professor at Bar-Ilan University, Israel, has been studying this extraordinary event.
"This is really an interesting phenomenon ... we know this event will happen a few nights after the full moon of November every year, three to five [days] after the full moon," he said.
"It's always amazing, especially I am amazed how every species of coral from year to year spawns at the same hour of the night."
He added: "Once that happens, it's always very interesting to see how it all becomes so alive and synchronized.This is almost a spiritual [event] and you understand the power of nature at its best."
The moonlight triggers the phenomenon by acting as an alignment or "alarm" perhaps with other environmental signals such as sunset time, water temperature and tides to determine the time the gametes [eggs and sperm cells] are released, explains Dr. Levy.
He added that the reef appears to have a photoreceptor that detects the moon phase, which helps with "fine tuning" of the gamete release.
Sharks and seals depend on the heavenly light
Right when you think it's safe to get into the water ... a great white shark hunts at night too.
For some seals, the dangers of a moonlit night spell.
During the winter months, the 60,000 cape seal on the Sea Island in False Bay, South Africa runs the challenge taken by large white sharks patrolling the ocean as they enter and exit the water.
A study in 2016 that hypothesizes that swimming at night when full moon is at greater risk is eaten by sharks because bright moonlight makes their silhouettes on the surface making them an easy food for predators hiding below.
However, most shark attacks on seals occur right after sunrise. The researchers behind the study, which measure shark attacks at dawn, are surprised to find the seals are much less likely to precede at this time if there is a full moon.
The researchers theorize that moonlighting combined with the emerging sunlight can decrease the shark's stealth ability and that the advantage of switching from shark to seal at night turns into days.
And the seals may depend on other space features to navigate - the stars.
Sealing harbor seals (Phoca vitulina) can find a place of lodging and direct it, the researchers have shown.
During tests using the simulated night sky, seals swim toward the brightest star and can orient themselves when the stars revolve around them.
In the wild, seals must navigate the open sea to find places to eat that may be separated by hundreds of kilometers.
Researcher Dr Bjorn Mauck said at the time: "Seals may know the position of stars relative to where to eat during the dawn and dusk when they can see stars and landmarks on the shore."
The strange animals come to the surface every night.
Humboldt's squid is one of the most striking creatures that appears every night.
Under the dark cover is rarely seen creatures migrate to the surface of the sea to feed.
The Humboldt Squid, also known as the jumbo squid, is one of the most eye-catching sea animals you can see hiding on the water's surface.
At noon the squid lurk in the deep waters of the Eastern Pacific Ocean along the deep shelves that stretch across the west coast of America and each night they are one of many marine animals to migrate upward to find dinner.
Vertical migration (or diel) - when aquatic animals swim to the surface at dusk and disappear again at dawn - very common.
"What Humbioldt squid does is to follow their main meal, called lantern fish," explains Professor Paul Rodhouse, an Emeritus Fellow for the British Antarctic Survey (BAS) and former head of the organization's biological sciences. division.
In turn, the lantern fish follows the vertical zooplankton migration.
Because zooplankton relies on so many marine animals, "the rest of the food chain will follow afterwards," says Prof Rodhouse.
"This is a huge movement of biomass every day," says Prof. Rodhouse. "More than a thousand meters. Some oceanic squid may migrate more than 1000m every day. "
He added that almost all pelagic species (animals living in the water column are not near the bottom or beach) that can swim to travel.
The humboldt squid is one of the most striking creatures that appears every night. Their ability to change color and bright red flash when agitated has earned them the nickname "red devil". Though much smaller than their cousins, the giant squid is 13m, they can reach a length of about 1.5 m (almost 5 feet). A very aggressive predator, they capture the prey with strong tentacles and suckers and tear it with a strong beak, and have reportedly attacked occasionally humans.
But even the vicious Humboldts are preyed on by big predators like billfish, swordfish and sharks.
"Of course what they do [actively at night] is to avoid predation by top predators," said Prof. Rodhouse. "Large predators are visual predators and who live on the surface of the water and see their prey."