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Coral ReefsCoral reefs are underwater ecosystems made from the skeletons of hard coral colonies. Each colony is composed of multiple polyps called corals—animals with tentacles around a mouth at one end and sac-like bodies at the other that attach to a surface and secrete calcium carbonate for protection. Over thousands of years, these secretions accumulate to form habitats that support about 25% of marine species, even though they cover less than 1% of the ocean floor. Known as the "rainforest of the seas," coral reefs are found in tropical and subtropical waters of more than 100 countries, with larger reef systems concentrated in the Indo-Pacific, Caribbean, and the Red Sea. Shallow water coral reefs rely on a symbiotic relationship with colorful photosynthetic algae called zooxanthellae, which provide coral with nutrients and oxygen in exchange for a protective environment within coral tissue. Deep water corals instead consume plankton and dead organic matter to survive. In the US, coral reefs provide $3.4B in annual economic value through fisheries, coastal protection against wave damage, and tourism. However, stressors such as rising temperatures, ocean acidification, and pollution have weakened reefs and caused coral bleaching. This phenomenon sees corals expel zooxanthellae, turning corals white, depriving them of their food source, and making them susceptible to disease.Explore Coral Reefs

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Watch a time-lapse of hard coral growth, which forms coral reefsOver several weeks in an aquarium, these staghorn coral polyps grew and produced new polyps as they deposited calcium carbonate, which forms the basis of coral reefs. At the 0:28 mark, you can see coral growth healing a damaged branch. Peter Kragh How the environmental diversity of coral reefs provides potential medical treatments for humansAs 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. Coral Reef Alliance From 2023 to 2025, coral reefs experienced their fourth global bleaching eventHeat stress from the 33-month-long event impacted about 84.4% of the world's coral reef area across waters in at least 83 countries and territories, making it the largest such event to date. Due to climate change, about 90% of coral reefs are expected to undergo bleaching annually by 2050, leaving insufficient time for recovery during the winter months between bleaching events. NOAA View the three types of coral reefs, categorized by where they formFringing reefs—the most common type—are built from coral depositing calcium carbonate onto the seafloor closest to the shoreline. Barrier reefs grow further from and parallel to the shore, while atolls are the result of mid-ocean volcanoes or seamounts eroding away and leaving a lagoon surrounded by reefs. How It Works Daily Discover the economic value of coral reefs, which benefit one billion people worldwideThe National Oceanographic and Atmospheric Administration estimates that US commercial and recreational fisheries valued at $200M depend on coral reefs, which provide up to $1.8B in flood protection by absorbing 97% of wave energy. Combined with the benefits from tourism, US coral reefs provide $3.4B in value annually. NOAA View an image and video gallery of coral reefs from around the worldDeveloped by The Ocean Agency, the Ocean Image Bank launched in 2021 with the help of more than 200 ocean photographers, videographers, and science organizations to help engage the public and inspire support for oceans as part of the UN Decade of Ocean Science. Ocean Image Bank The importance of zooxanthellae, the single-celled algae that color coral reefsThese microorganisms enter the cells lining corals' digestive tracts and provide corals with sugars produced via photosynthesis in exchange for a home within this protective tissue. Like sea anemones and jellyfish, each coral species forms a symbiotic relationship with distinct species of zooxanthellae, which provide the coral with unique coloration. Tetiaroa Society The importance of coral reefs since their first appearance hundreds of millions of years agoFormed from calcium carbonate skeletons deposited by hard corals, some estimates suggest these reefs provide habitats for over a million marine species. Spanning massive areas, coral reefs also serve as buffers against extreme weather, such as tropical storms. Seeker Explore coral reefs in Google's "street view"Expanding its mission to map the world, Google Maps partnered with The Catlin Seaview Survey to introduce the first-ever underwater panoramas, making oceanic marvels like the Great Barrier Reef accessible to everyone. With Google Maps, the public... Google Why are coral reefs important?Coral reefs are vital ecosystems that millions of people and countless species depend on. This two-minute video from London's Natural History Museum looks at the ecological and economic significance of coral reefs, including their biodiversity and... YouTube Overview: All about coral reefsCoral 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... National Oceanic and Atmospheric Administration Learn how humans can protect coral reefsWhen diving and snorkeling in environments containing reefs, avoid touching reefs, anchoring on them, or using sunscreen with active ingredients harmful to marine life. Properly recycling and disposing of trash in bins helps reduce microplastics and chemicals that can run off into wastewater and into the oceans. U.S. Environmental Protection Agency Where are warm water coral reefs found?Corals thrive in many marine environments around the world—from warm, tropical waters to deep, cold waters. This two-minute video from PBS focuses on warm water coral reefs and where they can be found. Coral reefs thrive where the water is clear,... PBS LearningMedia How climate change threatens coral reefs, including via warming and acidificationIncreasing 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. National Oceanic and Atmospheric Administration Office of Law Enforcement The marine animals that rely on coral reefs for habitats, camouflage, and foodParrotfish 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. American Oceans Scientists explore innovative solutions to protect coral reefsAs coral reefs are under increasing stress due to climate change, pollution, and other factors, scientists are employing creative solutions to save these crucial marine ecosystems. This National Geographic article explores the various scientific... National Geographic Explore a world map of coral reefs and the extent of coral bleachingThe Allen Coral Atlas provides imagery of shallow water reefs, along with maps of potential bleaching events, bleaching alert areas, and bleaching hotspots derived from satellite imagery of whitening. Coral reefs are most prevalent in the Indo-Pacific, the Caribbean, the Red Sea, and the tropical coasts of South America and Africa. Allen Coral Atlas Watch the life cycle of a coral reef, from fertilizing an egg cell to cloning itselfThrough broadcast spawning, coral polyps release reproductive cells for less than an hour, once a year, which fertilize and divide to form a larva called a planula. Guided by light and chemical sensors, planula swim through the ocean, searching for a surface to attach to and grow into an adult polyp, which sprouts copies of itself from its sides. Deep Look The origin of the symbiotic relationship between corals and the algae that feed themAn 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. Natural History Museum An overview of the Coral Triangle, which contains about 76% of global coral speciesSpanning the waters of Indonesia, Malaysia, Papua New Guinea, the Philippines, the Solomon Islands, and Timor-Leste, the region contains more than 600 coral species and over 2,200 of the world's coral reef fish species. It sustains 120 million people with food and other resources, as well as a $12B yearly tourism industry. World Wildlife Fund Read about coral reef restoration efforts, from coral IVF and cryopreservationResearchers have collected coral eggs and sperm from healthy reefs, grown baby corals in lab pools, and released them to help repopulate damaged or lost reefs. Devices such as Coralclip® help attach these corals to existing structures, promoting growth without the use of chemical bonding agents. Corals near extinction can be frozen using liquid nitrogen for future restoration efforts. Great Barrier Reef Foundation Learn about deep water corals and the coral gardens they slowly build in the darkFound throughout the world's ocean basins at depths beyond 200 meters (660 feet), these corals do not rely on photosynthetic organisms for nutrients and instead rely on food that's fallen from the ocean surface. Beyond forming larger reefs over the course of thousands of years, smaller coral gardens are built with the aid of underwater worms. Smithsonian National Museum of Natural History An interactive trip through the Great Barrier Reef, the world's largest living structureIn this online adventure, users can explore the structure and history of Australia's coral reef, learn how scientists gather data and research the environment, view and listen to the organisms that make the reef their home, and simulate the evolution of the ecosystem, which spans the size of Italy, in various simulations. David Attenborough's Great Barrier Reef Visualize how hard corals build reefs using minerals dissolved in seawaterThese organisms—also known as stony corals—form a type of calcium carbonate called aragonite from ions brought to the ocean by rivers that have broken down terrestrial rocks. The accumulation of aragonite protects the soft parts of coral polyps' bodies and creates reef structures when colonies of polyps cement themselves together. California Academy of Sciences View a collection of glass sculptures of cold-water coralsIn "Depicting Dark Waters," British sculptural model maker Alice Baker depicts European deep-water corals—65% of all known coral species—to raise awareness of deep-sea ecosystems threatened by fishing, deep-sea mining, and other industrial activities. The project involved a collaboration with marine biologists from the Netherlands and Sweden. Smithsonian Magazine Artificial coral reef tiles built with 3D printing are helping restore ocean biodiversityIn Hong Kong, nontoxic and biodegradable terracotta clay has been used to create foundational structures resembling brain coral. Natural corals have used these tiles to rebuild water ecosystems, achieving a 98% survival rate. Forbes Asia Climate tipping points are irreversible changes to Earth's environmentEarth's natural systems have prevented these events—including the mass death of coral reefs, loss of the Amazon rainforest, and shutdown of Atlantic currents—but scientists believe they are unlikely to withstand continued stressors from climate change. The New York Times Video and still images are combined with sonar data to create seafloor mapsSonar works by sending thousands of sound pulses per second towards the seafloor, capturing the strength and timing of the returning echo. This data can accurately reveal depth, seafloor texture, and the presence of fish habitats to millimeter resolutions. NOAA Ocean Exploration Take an interactive tour through Australia's Great Barrier ReefThis adventure offers spherical panoramas of marine wildlife, including manta rays, loggerhead turtles, and bottlenose dolphins. The shipwreck of a luxury passenger vessel and coral reef systems are also explored with underwater audio recordings of the environment. Google Arts & Culture Niagara’s bedrock holds 440-million-year-old coral fossilsThe Lockport Dolomite that caps Niagara Falls is composed of fossilized coral reefs from a tropical sea that once covered the region 440 million years ago. Info Niagara Ten US spots to see super blue waterMuch of the ocean coasts of the US are full of upswelled biological murk, opaque and dark. But in some spots, where its fairly calm and the sand is settled and white, the water is sparkling blue. Notable locations include Crater Lake in Oregon or Dry Tortugas National Park in Florida. Travel + Leisure The most unusual festivals in the USThe US is host to some strange festivals that complement its more mainstream music and art conventions. This list of nine odd outings begins with the Mothman Festival in West Virginia (described as a paranormal Comic-Con) and ends with the Florida Keys Underwater Music Festival in the Keys. Atlas Obscura Mineral and chemical sunscreens protect differently but both guard against UV damageUVA rays age the skin, while UVB rays are more directly linked to skin cancer. Mineral sunscreens, with ingredients like zinc oxide, physically block rays, while chemical ones absorb UV and turn it into heat. Science Friday Climate proxies reveal past climate patterns using preserved natural evidenceScientists use physical, chemical, and biological materials preserved in sediments, ice, and fossils to infer historical climate data. These proxies are studied and calibrated against modern climate conditions to interpret ancient environments accurately. USGS Watch city kids encounter the national parksPart of Ken Burns’ "The National Parks: America’s Best Idea" film series, this video follows students from Las Vegas and Miami as they visit national parks. In Death Valley, the students get hands-on lessons in geology, while in Biscayne, they canoe through secluded groves and past coral reefs. PBS Scientists are using CRISPR to crossbreed heat-resistant corals amid warming reefsInside Australia's National Sea Simulator, coral hybrids are genetically engineered to resist the widespread coral bleaching caused by rising global temperatures. Early trials have developed groups with survival rates up to 34 percentage points higher than nonhybrids. (Some readers may experience a paywall.) Science Magazine A simple infographic explaining how coral bleaching worksWhen 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. Modest Fish

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