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A reef is a chain of rocks or coral or a ridge of sand at or near the surface of water. Coral reefs ecosystems are intricate and diverse collections of species that interact with each other and the physical environment. They are essential to healthy coasts and vibrant economies, playing a critical role in everything from protecting lives and property to supporting thousands of businesses.
The following information is taken from the U.S. Environmental Protection Agency (EPA) and National Oceanic and Atmospheric Administration (NOAA). At the end is an article from the Time magazine that motivated me to get on this project.
Stony corals, a type of coral characterized by their hard skeleton, are the bedrock of the reef. Stony coral colonies are composed of hundreds of thousands of individual living polyps. Polyps are capable of drawing dissolved calcium from seawater, and solidifying it into a hard mineral (calcium carbonate) structure that serves as their skeletal support.
When you look at a coral colony, only the thin layer on its surface is live coral; the mass beneath is the calcium carbonate skeleton that may be decades old. The slow growth of polyps and expansion of the hard skeletal structures build up the permanent coral reef structure over time.
Polyps of reef-building corals contain microscopic algae called zooxanthellae, which exist with the animal in a symbiotic relationship. The coral polyps (animals) provide the algae (plants) a home, and in exchange the algae provide the polyps with food they generate through photosynthesis.
Because photosynthesis requires sunlight, most reef-building corals live in clear, shallow waters that are penetrated by sunlight. The algae also give a coral its color; coral polyps are actually transparent, so the color of algae inside the polyps shows through. The colorful appearance of corals comes from the microscopic algae that live inside the coral cells.
When corals are stressed, they expel these algal symbionts through a process known as coral bleaching. Corals also face serious risks of diseases.
Coral reefs provide habitat for a larger variety of marine life, including various sponges, oysters, clams, crabs, sea stars, sea urchins, and many species of fish. Coral reefs are also linked ecologically to nearby seagrass, mangrove, and mudflat communities. One of the reasons that coral reefs are so highly valued is because they serve as a center of activity for marine life.
Not all corals on the reef are stony corals. Important among other types are the following:
Extensive coral reefs are found in the waters of U.S. and its territories. In the Atlantic Ocean, Gulf of America, and Caribbean Sea these reefs of Florida, Texas, Puerto Rico, and the U.S. Virgin Islands. In the Pacific Ocean, they include Hawaiian Islands, Wake Island, Jonhston Atoll, the Northern Marianas, Saipan, Guam, Kingman Reef, and Palmyra Atoll, Howland Island, Baker Island, Jarvis Island, and American Samoa. More than 60% of U.S. coral reefs are in the extended Hawaiian Island chain. There are coral reefs 100 miles offshore of Texas, and Louisiana in the gulf of America.
Healthy coral reefs provide:
The US Geological Survey estimates that coral reefs in the Atlantic, Caribbean and Pacific Islands regions help generate billions in annual tourism dollars, yielding about $100 million (annually) in commercial fisheries and protect tens of thousands of lives and billions in property and economic activity from flooding and erosion.
The impact of these threats disproportionately affects underserved groups including minority, low-income and indigenous populations that rely on coral reefs for nutrition from small fisheries (food security) and for coastal protection (natural infrastructure) against increasingly intense storms.
Coral reefs are home to one in four ocean species, support fisheries, and protect coastlines from storm surges and rising sea levels. And they are at risk. Last fall, scientists reported that warm-water coral reefs were passing their planetary tipping point, a threshold that, once crossed, leads to large, accelerating, and often irreversible changes.
Photographer Britta Jaschinski spent six months with scientists across the U.K. and Germany as they raced to make these critical ecosystems more resilient, whether by freezing coral sperm in biobanks or controlling coral reproduction.
If corals are too far apart to reproduce naturally, scientists can bring them together to assist fertilization and rear larvae. Selective breeding of the strongest corals can produce more adaptable offspring better equipped to withstand accelerating warming.
During a spawning event, corals package their sperm and eggs together into small bundles into gametes that rise to the water surface. This method of reproduction allows reefs to spread over a broad geographic area while increasing genetic diversity. Corals typically spawn only once a year, get cues from the lunar cycle and the water temperature prompting entire colonies to release their gametes around the same time.
In aquarium experiments, corals are gradually exposed to higher water temperatures, raised by about 1 degC per day to see when they bleach- expelling the algae living inside them and losing their vibrant color. Many start to bleach when temperatures rise just 1-2 degC above their usual summer maximum. After the trials, bleached corals are moved back to cooler water to recover. Studies show corals previously exposed to mild heat stress can sometimes become more tolerant in later events. These experiments help researchers understand which are more likely to survive warming oceans.
In the wild, corals release eggs and sperm into the sea during mass spawning events, but rising temperatures disrupt these delicate cycles. Replicating seasonal temperature changes and natural lunar patterns can trigger these reproductive events in labs.
In 2024, scientists at the Horniman Aquarium's Project Coral lab in London successfully spawned and reared the threatened Pink Sea Fan, marking the first time the species was successfully raised in captivity. "It's not a silver bullet," says Jamie Craggs, principal aquarium curator at the Horniman Museum and Gardens. "Restoration is not going to rebuild the world's reefs. The scale at which we need to act is just far too vast for the current technology that we have. Restoration is about buying time in pockets to give corals at least a fighting chance into the future" she said.
"As climate change and ocean acidification threaten the future of reefs, biobanks can serve as an insurance policy, preserving genetic diversity and allowing scientists to restore reefs in the future.
"Three coral frag plugs contain four 10-month-old Trachyphyllia corals (also known as open brain coral) with diverse genetic makeup. Diversity plays a key role in boosting resiliency, making some corals more resistant to heat stress. Gene editing meanwhile helps scientists understand which genes are responsible for greater thermal resilience."
In 2023, researchers successfully cryopreserved and revived fragments of adult coral for the first time. Using antifreeze and liquid nitrogen, scientists froze coral pieces into a glasslike state before thawing them and returning them to seawater. Within 24 hours of revival, the corals consumed oxygen at rates comparable to those that had never been frozen. The breakthrough arrived at a critical time, as coral reefs worldwide face increasing stress from warming oceans.
Marine biologist Mary Hagedorn and her team say this advancement could eventually allow scientists to store coral for decades. "When you put an organism into liquid nitrogen, it goes into stasis," she says. "It just stops biological time."
Researchers learn about reef restoration, coral resilience, and environmental history from coral fragments, leveraging both living pieces for restoration and dead skeletal parts as historical records.
Samuel Nietzer of the University of Oldenburg, Germany collected gametes after lab-triggered spawning. In his lab, a kind of coral IVF takes place, and new coral larvae develop within a few days.
Traditional reef restoration often relies on fragmenting and replanting existing corals, while lab-controlled breeding can create genetically diverse offspring from carefully selected parent colonies. "When you fragment a coral again and again, you may have hundreds or even thousands of pieces that you can bring out on a reef, but it's genetically all the same," notes Mareen Moeller, Nietzer's colleague and partner. Meaning, they are all equally vulnerable: "Any stressor that comes in will affect all of these fragments exactly the same."
Controlled feeding regimens, water-quality management, and larval settlement support help researchers improve juvenile coral survival rates before out-planting them onto vulnerable reef habitats. These advances also provide critical insights into the species' reproductive biology and resilience to environmental stressors like warming seas and ocean acidification.
An estimated one billion people worldwide benefit directly or indirectly from the ecosystems that coral reefs provide. Climate change is the biggest threat to the world's coral reefs, causing mass bleaching among other things.
