Coral reefs get their colors from zooxanthellae—microorganisms that line corals' digestive tracts and provide them with sugars in exchange for a home within this protective tissue.

Watch how coral bleaching resembles an organism's immune system attacking itself

Microorganisms called zooxanthellae are in a symbiotic relationship with coral polyps and provide them with food created through photosynthesis. When ocean temperatures or sunlight exceed an optimal range, zooxanthellae release harmful chemicals that irritate coral cells. To protect themselves, corals sacrifice their food source and expel the colorful microorganisms, becoming white.

A simple infographic explaining how coral bleaching works

When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.

The origin of the symbiotic relationship between corals and the algae that feed them

An analysis of fossilized reefs from northern Africa and Germany suggests that shallow water corals and photosynthetic algae formed a mutualistic partnership between 419 and 359 million years ago. The discovery was made by analyzing nitrogen-isotope ratios in the fossils, which differ depending on whether algae are present, due to various chemical processes.

The marine animals that rely on coral reefs for habitats, camouflage, and food

Parrotfish and surgeonfish feed on algae that grow on coral reefs to prevent overgrowth while serving as prey for larger fish across the food chain. Reefs also serve as structures for organisms like sea anemones, which provide shelter for clownfish, and homes for invertebrates such as crabs, lobsters, and shrimp, which help recycle nutrients.

How the environmental diversity of coral reefs provides potential medical treatments for humans

As immobile animals, corals and the organisms that live on them have evolved a suite of chemical compounds to prevent disease and ward off predators they cannot outrun. These include antibiotics, antivirals, and powerful toxins that target the nervous system and are studied for applications involving pain management and neurological treatments.

The anatomy of coral polyps, whose mouths consume food and expel waste

The mouth is surrounded by tentacles that help clear away debris and defend the organism, using stinging cells called nematocysts that resemble those of jellyfish. Connective tissue called coenosarc connects individual polyps within colonies and allows them to share nutrients.

How climate change threatens coral reefs, including via warming and acidification

Increasing ocean temperatures disrupt the symbiotic relationship of corals and algae, causing the former to bleach and weaken, and strengthen storms that can destroy reef structures. Higher greenhouse gas emissions increase dissolved carbon dioxide levels in ocean water, triggering a series of reactions that consume carbonate, a key ingredient in coral reef construction.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Corals are themselves not coral reefs—the term refers to the tiny marine invertebrates that build the rigid reef.

Synthetic pheromones may protect coral reefs by attracting their predators

Researchers in Australia and Japan have developed these nontoxic chemicals to attract crown-of-thorns starfish, which consume corals that make up the Great Barrier Reef. As of 2026, synthetic pheromones have been shown to be effective in lab trials, and future field trials will attempt to lure starfish into areas for mass removal.

Overview: All about coral reefs

Coral reefs aren’t just vibrant underwater landscapes; they are also some of the most biologically diverse ecosystems on Earth. The National Oceanic and Atmospheric Administration (NOAA) offers a comprehensive guide that explores coral reefs in...

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

Can coral live in cold water?

Dive deep beyond the sunlit coral reefs, and you'll discover a world of deep-sea corals. This article from the National Oceanic and Atmospheric Administration (NOAA) explores the ecosystems of deep-sea corals found way below the water's surface....

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

Massive blooms of microscopic plankton called dinoflagellates produce the neon blue light seen in glowing tides.

Why 75% of ocean animals glow

About 75% of ocean creatures can make their own light. It's called bioluminescence—and it all comes down to a special chemical reaction happening inside their bodies.

Water is naturally tinted with a slight blue, but sediments and organics can alter its color

The innate coloration comes from water absorbing red light in the visible spectrum more than green or blue, giving shallow waters in some parts of the Caribbean their turquoise hue. If sand is light, it can be churned up by turbulent water, clouding its appearance. Plankton and other organisms can color water by affecting how the rest of the spectrum is absorbed or reflected.

Artificial coral reefs have been 3D printed from nontoxic, biodegradable terracotta clay, which coral polyps have used as a foundation for rebuilding marine ecosystems.

Fish populations in the Great Barrier Reef have increased after installing waterproof speakers on the ocean floor that played recordings of sounds from healthy coral reefs.

Zoo animals have developed allergies, too

Although scientists do not know if allergies manifest among wild animals—and if animals can survive with them—in a zoo setting, veterinarians have observed zoo animals with common allergy symptoms, including itchiness, crusty skin, and runny eyes. Veterinarians have identified Asian elephants with pollen allergies and at least one jaguar with an allergy to fleas.

Aerial photos of red tide off the Gulf Coast

The toxic algae grows naturally in warmer oceans in small amounts and is typically harmless. With extended warm periods and unusually-high additions of nutrients from run-off, the algae blooms extensively, posing health risks to wildlife and humans...

A look at anoxygenic photosynthetic bacteria, which do not produce oxygen

Rather than using water to produce organic compounds and release oxygen, purple and green sulfur bacteria take up hydrogen sulfide, carbon dioxide, and light to produce water, elemental sulfur, and a carbohydrate. Other organisms can take up various molecules and elements, such as iron, which can replenish the electrons in pigments involved in light-dependent reactions.

View colorful flowers that grow on cacti and succulents, popular xerophilic organisms

These dry-loving organisms are able to retain the water they need to grow and reproduce in deserts and arid grasslands through a suite of adaptations, including thick, fleshy stems that store abundant water, a waxy coating that helps prevent water loss, and an uncommon form of photosynthesis that loses less water.

Deep sea fish rely on a molecular strengthener to prevent being crushed

Trimethylamine N-oxide (TMAO) stabilizes hydrogen bonds and prevents water and proteins within organisms from being misshapen under immense pressure. Compounds called piezolytes protect cellular membranes from being crushed in regions like the Mariana Trench, where pressures are 1,100 times greater than surface atmospheric pressure.

When caught in the mouths of cardinal fish, seed shrimp release glowing, bioluminescent chemicals, which alert predators of the cardinal fish, prompting the shrimp's ejection.

Fireworks make a loud booming sound after explosion due to air expanding faster than the speed of sound

This shockwave is caused by the rapid release of energy and is one of the key characteristics of fireworks, alongside the bright light show. The colors result from chemicals that absorb light at different wavelengths in the spectrum, with higher-energy compounds leading to darker colors and lower-energy compounds—like strontium chloride—producing colors like orange and red.

Explore the animals that populate the depths of the ocean, from fish and coral in the first few hundred feet, all the way down to the bottom of the Mariana Trench.

During the fall, chlorophyll breakdown in leaves produces color changes

With shorter days and less sunlight, the concentration of the green pigment diminishes, revealing yellow and orange pigments. Red leaves result from trapped sugars, producing new pigments called anthocyanins, which weren't present in leaves during the growing season.

Cerulean eruptions result from sulfur being heated by molten rock

During eruptions, warm-colored lava at temperatures between 700 and 1,200 degrees Celsius (1,300 and 2,200 degrees Fahrenheit) burns minerals as they escape from underground reservoirs. In some volcanoes, such as Indonesia's Kawah Ijen and Ethiopia's Danakil Depression, abundant sulfur compounds that burn with blue flames appear to change the color of the melted rock.

The CCZ is believed to harbor trillions of dollars of valuable minerals and thousands of undiscovered species

Located between Hawaii and Mexico and spanning an area larger than the European Union, the Clarion-Clipperton Zone is the world's region with the most contracts awarded to groups seeking to extract valuable metals by collecting polymetallic nodules. Conservative estimates suggest that 21.1 billion tons of polymetallic nodules exist in this abyssal plain, but about 90% of the species in the area are unknown to scientists.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

Corynebacterium species are particularly responsible for our funky smell

Myriad bacteria contribute to our body odor, but research suggests that Corynebacterium species are strongly associated with the bad smells emanating from adults. Staphylococcus and Cutibacterium genera may also play leading roles.

Why no aquarium has a great white shark

Historically, great white sharks die very quickly in captivity—with the exception of the Monterey Bay Aquarium's successful attempt in 2004. The aquarium held a four-year-old great white for six months. Before that, the longest stint was 16 days. The creatures can only breathe if they are moving forward, making survival difficult in a small tank.

See how fireworks are made and learn how metals like magnesium and copper are responsible for different colors.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

This poison ivy knowledge quiz—accompanied by photos of the plant's varied forms—may help you identify this common rash-inducing growth.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

SpongeBob exemplifies Aristotle's philosophy for living well because he understands that happiness doesn't come from external factors like money, recognition, or power.

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Georgia O'Keeffe's flower paintings are often assumed to be sexual, though the artist claimed she was simply interested in highlighting the beauty of flowers that most people neglect

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

How the most famous Ebola book, The Hot Zone, which sold 3.5 million copies and was translated into 30 languages, got aspects of the disease so wrong.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

Memecoins are a type of cryptocurrency—a form of digital currency with a wide variety of uses—created around popular 'memes,' or viral internet jokes.

Fast-casual restaurant Chili's is experiencing a resurgence, with its parent company recently reporting a nearly 32% increase in sales, thanks to passionate Gen Z fans on TikTok.