Staghorn corals are some of the most important reef builders on Earth, boasting more than 150 species and accounting for roughly 20 percent of all reef-building corals alive today. Like other stony corals, they create external "skeletons" of calcium carbonate, an energy-intensive task that requires help from symbiotic algae.
The success of staghorns is partly due to their lightweight skeletons, which often grow quickly enough to outcompete other corals for sunlight, a resource demanded by their photosynthesizing algae. Some staghorn species can grow 4 to 8 inches (10 to 20 centimeters) per year — a blistering speed by coral standards.
This timescale is still a little slow for humans to appreciate, though, so wildlife videographer Peter Kragh captured it in the surreal time-lapse video below:
Those green tentacles are the coral polyps, toiling away as their skeleton grows beneath them. The green hue comes from their algae, known as "zooxanthellae," which give the polyps food in exchange for a safe home. The algae don't always produce enough food, though, so the polyps also emerge at night to grab plankton.
Kragh is a veteran wildlife videographer and cinematographer, having worked on BBC's "Planet Earth" and "Life" series as well as IMAX films, National Geographic specials and other popular projects. To capture these vivid time-lapse scenes, he filmed corals at an aquarium in San Diego over several weeks.
The video consists of several clips, identified by numbers in the lower-left corner, featuring dramatic shots of polyps feeding and of their skeleton expanding. "Maybe the most interesting part of the video," Kragh tells LiveScience, "is seeing how the new polyps seem to appear out of nowhere and start growing."
Another interesting moment comes in clip 206-2, about 0:28 into the video. It shows a broken coral branch healing, Kragh writes on YouTube, then sprouting new polyps.
Corals in crisis
It's a reminder that although corals are fragile, they can be surprisingly resilient — if they have enough time to recover. Reefs around the world are increasingly at risk from human-induced climate change, which is altering their environments more quickly than most natural shifts they've endured in the past. Rapidly warming seawater has caused a surge of coral bleaching events in recent years, while ocean acidification poses a growing threat to the corals' supply of calcium carbonate.
Staghorn corals are "extremely sensitive to high sea temperatures," according to the International Union for Conservation of Nature, as well as secondary dangers like disease, which may increase with temperature. A critically endangered species of Caribbean staghorn, for example, has suffered major declines since 1980 largely due to white-band disease, a plague that has been linked to climate change.
Coral reefs support biodiverse ecosystems that in turn offer huge economic value to humans — one hectare of reef, for example, has been estimated to provide $130,000 worth of ecosystem services on average, and possibly as much as $1.2 million in some cases. The benefits of coral include fishing and tourism, but also less obvious perks, like development of new medications and protection from hurricanes.
Many corals are capable of bouncing back from adversity, and not only in the safety of an aquarium. While the best way to protect coral reefs overall is to reduce the greenhouse gas emissions fueling climate change, scientists are also investigating ways to strengthen coral reefs in the meantime, from cloud brightening and "assisted evolution" to last-resort ideas like gene storage banks.