Massive coral reefs thrive in deep, freezing fjords without any sunlight.

Cold-water coral reefs were largely unknown until the late 20th century when acoustic mapping and ROVs revealed their massive scale. The most prominent species, Lophelia pertusa, thrives at depths between 200 and 1,000 meters where temperatures hover between 4 and 12 degrees Celsius. Unlike shallow-water corals, these organisms lack zooxanthellae, the symbiotic algae that require sunlight for photosynthesis.Instead of using solar energy, these corals are primary carnivores that feed on zooplankton and organic detritus. They use stinging cells on their tentacles to capture food brought by powerful underwater currents. These currents are often concentrated by the unique topography of fjords and continental shelves, providing a constant nutrient stream that allows the reefs to grow slowly over thousands of years.The Røst Reef, discovered off the Lofoten Islands in 2002, is the largest cold-water reef complex ever recorded. It spans approximately 35 kilometers in length and 3 kilometers in width, covering roughly 100 square kilometers. Radiocarbon dating of these structures suggests that some reefs in the Northeast Atlantic have been growing since the end of the last Ice Age, approximately 8,000 to 11,000 years ago.These deep-sea ecosystems are vital biodiversity hotspots, supporting over 1,300 species of fish, crustaceans, and mollusks. Researchers from institutions like the Institute of Marine Research in Norway continue to study these reefs to understand their resilience to ocean acidification. Because cold water absorbs CO2 more readily, these reefs serve as an early warning system for the health of our global oceans.