What lives for thousands of years, has its structure on the outside, a plant on the inside, feeds at night, and provides shelter for thousands of species? You know the answer already.
Coral. In particular, shallow-water reef-building corals, are some of the most spectacular lifeforms on the planet. With color, dimension, scale, and lifestyle unique in so many ways, from almost every other lifeform. While they fill the ecological role of both plants and rocks, corals are animals. They feed and breed, grow and die, although at spatial and temporal scales that few if any, other animals even come close to.
Coral Hotspots
Collectively, corals support an estimated 25% of all oceanic life. And in one part of the world, they are the basis for almost everything. Encompassing 5.7 million square kilometers, surrounding at least six different countries housing 120 million people, the coral triangle is one of the most species-rich places on the planet. It’s known as the Amazon of the oceans. While only covering 1.6% of the planet’s surface, the region is home to 76% of all species of coral.
Of course, the Great Barrier Reef is the largest single reef of all, with over 2,900 different species of coral, across its 2,300 km of length. As a UNESCO World Heritage Site, a large part of the reef is protected, ensuring habitat for the myriad of fish, invertebrates, birds, whales, and dolphins that depend on coral habitat, and have a place to call home.
Last I’ll mention, but certainly not the least, is the Northwest Hawaiian Island coral reefs, in the Papahānaumokuākea National Marine Monument. Spanning 1,200 nautical miles, with loads of atolls, islands, and shoals, this area is phenomenal. The collection of reefs enables the existence of more than 7,000 species of fishes, invertebrates, plants, sea turtles, birds, and marine mammals. They are also some of the healthiest coral reefs left in the world (because they are some of the least disturbed) and they are thought to comprise the last large-scale, predator-dominated coral reef ecosystem on the planet. Don’t know about you - but after reading that, I want to go and visit.
Coral as an ecosystem
One of the most important functions of coral is its contribution to marine ecosystems. In fact, this is so important, that entire ecosystems are based on the very existence of coral. The stats above outline how many species exist in coral habitats. The existence of these species is of value, but the interactions between them are what keeps them healthy.
Within the foodwebs that exist in these ecosystems, are thousands of feedback loops and dependencies that, as humans, are almost impossible to fathom. An example at a basic level - coral eats zooplankton, fish eats coral, bigger fish eats fish, tuna eats bigger fish, and we eat tuna. Take a significant part out of this chain, and it’s like taking the linchpin off an axel - the wheel is coming off at some stage and whatever that wheel is supporting, is going to crash. For coral, that linchpin is so small, most people don’t even know it exists.
The greatest relationship of all time
One of the coolest interactions between species in coral reefs occurs within the coral itself. While coral is an animal, most species of coral also contain plant-like creatures, called zooxanthellae. I say plant-like because they’re actually photosynthetic cells, meaning they get energy from the sun, and convert it into tissue.
Coral and zooxanthellae have what is called a mutualistic symbiosis - meaning they both benefit by from each another. Zooxanthellae get shelter (protection) as well as the key compounds they need to survive and thrive. In return, coral, get ~90% of what zooxanthellae produce through photosynthesis (glucose, glycerol, and amino acids) which they use to create macronutrients (proteins, fats, and carbs), as well as produce calcium carbonate —> their ‘shell’.
How cool is that?
Zooxanthellae also give corals their ‘pigment; a beautiful color which is what we find so amazing when we visit coral reefs.
What’s with coral bleaching then?
Well, this is an issue that we are seeing all over the world. If you’ve been snorkeling or diving on a coral reef it’s likely you have seen patches of coral that are different shapes, but all the same light, whiteish color. Those corals are dead. We describe them as bleached because they no longer have their color. They no longer have their color, because they no longer have their best buddies, zooxanthellae. They no longer have zooxanthellae, because the water they’re in, is too warm for them to live. In a last-ditch effort to survive, when water gets too warm for zooxanthellae, they literally leave the coral and go to fend for themselves. This leaves coral without the nutrients it needs, and it dies.
There’s a whole series of articles on what is and may happen as a result of this ecological linchpin being pulled. For now, plan to go and enjoy the magic of coral. Hopefully, next time you snorkel or dive around coral, you’ll see them in a new light. They truly are, spectacular creatures in every sense of the word.