by Nicole Gadda
Sea turtles, jellyfish, anemones, parrotfish, seahorses, sea sponges, starfish, Nemo, and Dory – coral reefs aren’t nicknamed the “rainforests of the sea” for nothing, you know! Coral reefs are some of the most diverse ecosystems on the planet and are home to over a million species that call these beautiful places home. The most famous coral reef in the world is the Great Barrier Reef in Australia: a 1,430-mile stretch of coral that’s visible from space!
Reefs are made of corals, which are small, immobile marine invertebrates. When corals die, their calcium bicarbonate skeletons form the bedrock of the reef ecosystem. Similar to how a house needs a foundation before it can be built, coral skeletons provide support for new coral polyps to grow on top of. These living corals eventually solidify into the same hard mineral as the rest of the coral skeletons beneath them when they die. Over time, the slow growth of polyps and addition of hard coral skeletons build up huge coral reefs teeming full of diverse fish and marine animals.
Diversity of the coral reef ecosystem starts on a microscopic scale with an algae called zooxanthellae. These algae are classified as a keystone species that plays a vital role in the health of coral polyps. Zooxanthellae live in a symbiotic relationship with coral polyps, which means they exist together in a mutually beneficial relationship. The coral polyps provide the algae with a nutrient-rich place to live, and the algae provides the polyps with food they make through photosynthesis. Additionally, the algae give the coral polyps their colors! Without algae present, the coral reefs would be transparent and the beautiful colors of coral reefs wouldn’t exist!
The coral skeleton structure is like a playground for marine animals; holes, caves, tunnels, and crevices are all formed as a byproduct of the solidified corals for sea animals to swim through and make homes out of. Brightly colored fish swim in and around color reefs, nibbling on the microscopic algae that’s found abundantly on polyps. Parrotfish, in their quest to get to algae, accidentally consume the reef itself, grinding up the coral skeleton with their teeth and excreting it as sand. Just like a carwash, “cleaning stations” are established by species like shrimp, crabs, and catfish, which act like toothbrushes for larger fish and clean out the dead skin, bacteria, and parasites from their flesh, gills, and mouths! Don’t worry, they get paid for their work. “Cleaner” species like this actually consume dead skin, bacteria, and parasites for food and nutrients. On the other end of the food chain, sharks, groupers, and other predatory fish prowl the coral reef, keeping the populations of smaller fish in check and maintaining the balance of the delicate ecosystem.
Coral reefs are incredibly important to the larger diversity of our planet’s entire ocean, as they’re a habitat, feeding ground, spawning ground, and nursery for over 1 million aquatic fish, including many commercially harvested fish that feed our world’s population. Unfortunately, coral reefs face unprecedented threats to their survival. Climate change, ocean acidification, overfishing, and invasive species all jeopardize coral reef ecosystems. These threats can lead to coral bleaching, where stressed corals expel their symbiotic zooxanthellae algae and turn white. If the stress event continues for too long, the coral will die as a result of losing their source of food. Luckily, bleaching events don’t have to be death sentences – coral can recover by taking on new symbiotic algae partners if their stress decreases, although this can take a number of years before the reef can fully recover. Scientists at the Coral Reef Conservation Program at NOAA have discovered ways to grow coral to create coral reef nurseries – essentially a farm for small pieces of coral. Researchers have also developed technology to make these corals more resistant to environmental stresses. Repopulating damaged, struggling coral reefs with these nursery corals can help the reef thrive again, helping them survive environmental stresses due to climate change and ocean warming. There’s still a long way to go and much work to be done, but there’s hope that humanity can replenish, revive, and restore coral reefs – the greater ocean ecosystem, as well as our world’s population, depends on it.
