Sometime between 500 and 600 million years ago, the very first coral species appeared on earth. Of course, no one really knows when they actually appeared or what they originally were. What color were they? Did they sting fish? We guess a lot about them from looking at fossil corals and observing the way coral behaves today. That means we really don’t know that much at all, and likely will never know much. Why? Because 250 million years after they first appeared, they were all gone. All that was left of the earliest, now extinct coral species were odd impressions in stone.
Disappearing Again and Again
Obviously, some coral species survived the first disappearing event. Otherwise, we wouldn’t have any coral reefs today. So what became of the the coral that survived? Well, about 50 million years later they also disappeared, only to have another group of coral species appear nearly 100 million years later. Then, coral disappeared again. Coral has gone through several different disappearing and reappearing acts. Sometimes, coral disappeared at the same time as many other species, during mass extinctions. At other times coral just seemed to quietly slip out of existence for millions of years, leaving few clues why.
Coral in Name
The the name coral is applied to multiple phylum, meaning that that many similar groups of organisms are sometimes called coral. When we speak of reef building coral, the reference usually points to scleractinian coral, or stony corals. The ones that are symbiotic with zooxanthellae (zo-o-zan-thel’-ee) algae and that secrete calcium carbonate skeletons.
It is also important to note that corals existing today are not the same as many of the early organisms identified as coral. The coral-like organisms that that appeared during the Devonian 410 million years ago may be more closely related to sponges (phylum Porifera). About 250 million years ago, when dinosaurs were just coming onto the scene, the reef building corals appeared. Click the link for more information on coral body structure. https://coral.org/coral-reefs-101/coral-reef-ecology/coral-polyps/
Vulnerable to Extinction
Some early coral species were likely vulnerable to extinction. Similarly, some coral reef species today are very sensitive to changes in water temperature, light, salinity and, well, just about everything else. So it makes sense that coral species today may also be very vulnerable to extinction.
One of the surprising factors that put coral reefs at high risk for extinction is that they don’t occupy a lot of surface area. Coral reefs make up a negligible 0.1% of the Earth’s surface, and 0.89% of the world’s oceans. Even during periods of time where coral reefs appear to reach much wider distribution, they still never cover much more than a tiny amount of surface area. The limited distribution has a lot to do with the their need for shallow ocean perches, and warm, clear salt water, conditions found primarily in shallow tropical and subtropical waters. And there aren’t many locations that meet this criteria. So, the loss of even a small area of a coral reef is cause for concern.
The Indo-Pacific region, which stretches from the Red Sea to the western Pacific ocean, accounts for 91.9% of coral covered areas. The Caribbean Sea and Western Atlantic Ocean account for just 7.6%. The Eastern Pacific only accounts for 0.6% . A similar pattern is seen for coral diversity, where the Indo-Pacific area contains the most biodiverse reefs. The reason for the high biodiversity in the Indo-pacific may be because the region acted as a refuge for coral during ice ages when sea levels dropped and during warm periods when sea levels rise. When better conditions returned, coral expanded and populate other areas.
Growth in Geological Time
Another high risk extinction factor is the slow pace of coral reef formation and growth. Even the slowest growing plant species outpace coral reef growth by orders of magnitude. For example, the Saguaro cactus (Carnegiea gigantea) grows to be one inch after 10 years. The iconic baobab (Adansonia grandidieri) reaches four inches after five years, and the white cedar (Thuja occidentalis) grows to be only four inches after 155 years.
Compare this to a coral reef that may grow and 0.02 to 0.04 inches in 1000 years. That puts coral reef growth in the category of geological time. What makes the process even slower is that coral reefs don’t grow at a constant rate, and spend a lot of time not growing at all. A lot of things can slow reef growth, such as fish that eat coral and worms that dissolve and burrow into coral. Storms can produce strong waves that can crush a coral reef into small bits in a matter of hours. With all of these threats, it is really amazing coral reefs exist at all.
Resilient Reefs
Perhaps, however, coral are not as fragile as we think, at least not all of them. While some coral are fragile and do not easily survive even the smallest environmental changes, other coral species weather swings in conditions relatively well. For example, in 2009 there was a bleaching event in the Cayman Islands that raised concern about what would become of one of the best coral reefs in the Gulf of Mexico. There was a concern that warmer water from climate change would wipe out the reef. Fast forward to 2019, where researchers are now studying why the reefs are so resilient.
The intriguing history of disappearing and reappearing that occurs also may indicate that coral is able to survive changes and return again and again. The largest reefs are found the South Pacific, near Indonesia. It may be that in times of trouble, or when temperatures drop, coral seeks refuges in locations where the water is warms and there are numerous shallow sea mounts, near enough to the surface to feed on sunlight. It is also possible that some coral may be able to survive in an arrested free floating phase, biding time until a suitable location and conditions are found.
The Peculiar World of Coral Reefers
As you might expect, simply observing coral reefs in the wild does not satisfy everyone! Some people are so fascinated with corals that they endeavor to bring a piece of the reef home with them. Hence, the “coral-reefer” is born!
Raising coral in a home aquarium has become a wildly popular activity among a continuously growing community. Replicating ocean conditions in a relatively small aquarium is a daunting task, and not easily accomplished. However, this hardly discourages the invested hobbyist! Millions of dollars have been poured into developing technologies that help reefers inch closer to matching their micro-environments to the waters from which the coral was collected. Indeed, many corals that enter the trade are grown in ‘farms’ by a practice known as mari-culturing. Of course, sustainability of these farms has been a topic of debate, and there are ongoing conservation efforts geared toward preventing over-collection in the face of ever-growing demand.
If you’ve ever browsed your local pet store’s aquarium displays, you may have noticed the tiny pieces of these colorful oddities mounted on tiny pedestals. These are coral ‘frags,’ which are tiny pieces of larger colonies that are broken off and grown until they are large enough to be bagged and shipped to the pet store, or often directly to the reefer themselves (in a small flat-rate box, no less!). A wealth of information is available through online resources to anyone interested in taking a dive into this complex and expensive hobby. However, beware. Reefing is a test of patience, and often takes many years of meticulous care to produce the marvelous reef aquariums to which all reefers aspire.
