The result is “bleaching,” which occurs because the reefs’ single-celled occupants – the algae that provide them with energy and give them their marvelous colors – tend to damage the corals at higher temperatures, so the corals push them out.

“If phases like this last too long, the corals starve. In some cases, they are resettled later, but bleaching of coral reefs is on the rise around the world,” cautions Professor Reinhold Leinfelder, a geobiologist and reef specialist at Freie Universität Berlin.

Experts Estimate That the Reefs Are Home to about Two Million Species of Organisms

This phenomenon was first observed on a large scale in 1998, when a heat wave triggered primarily by the Pacific warming phenomenon known as El Niño destroyed 16 percent of all coral reefs worldwide. The bleaching recurred in 2010 and again from 2014 to 2017.

But in addition to climate change, other factors are also adversely affecting the reefs. Overfertilization due to intensive agriculture, overfishing, mass tourism, and plastic waste harm these sensitive ecosystems in various ways at once. All of this means the scientific community has good reason to declare 2018 the third International Year of the Reef, after 1997 and 2008.

At the German kickoff event, Leinfelder, who was a co-organizer, spoke before an audience of 800 diving instructors at the BOOT boating and water sports expo in Düsseldorf in January to bring them on board as enthusiastic multipliers for the cause of protecting reefs and win their support for researchers’ monitoring efforts.

But why does it matter if the reefs die off? That’s too bad for divers, of course, but otherwise? It is actually very important. Aside from reef tourism, which is a mainstay of the economy in many countries, this kind of colorful paradise serves a wide range of functions. A reef’s rough, jagged surface absorbs as much as 95 percent of the energy of incoming waves, so these barriers offer natural coastal protection for thousands of islands and various mainland regions. If they did not exist, sandy beaches would simply wash away.

Reefs also act as nurseries and feeding grounds for many species of fish. One-quarter of the international catch would be lost without them. The multifaceted underwater landscapes are also hot spots for evolution and biodiversity. “About two million species of organisms are estimated to live in the world’s reefs,” says Leinfelder. “And most of them are still unknown to humans.”

Aside from that, they are also an inexhaustible “blue pharmacy.” Many of the substances produced by reef-dwelling organisms are highly effective as medications, including sophisticated antibiotics, pain relievers, and cancer treatments. This comes as no surprise, since reefs are home to so many different life forms that a wide range of clever survival strategies have emerged through evolution. “On a reef, some organisms have to fight to establish a place for themselves and then watch out to make sure others don’t displace them by poisoning,” Leinfelder explains.

Reefs only arise where the ocean floor is rocky and firm. In most cases, large colonies of master reef builders – hard coral larvae – settle in these areas all at once, since “property” like this is in short supply. The larvae first cement a tiny piece of “floor” underneath themselves and then form a chalky “cup” around themselves, working up from the floor. Depending on the coral species and environmental conditions, this reef base can grow upward by anywhere from a few millimeters to centimeters each year, branching out as it grows.

Leinfelder says reefs are like bustling cities. The two have a lot in common. Single-celled algae act as “tenants,” moving into the “buildings” formed by the corals. Through photosynthesis, the algae provide decentralized solar energy. To the sides, fields of algae form. Plant-eating fish and sea urchins act as “gardeners,” puttering around and preventing uncontrolled growth. This also gives rise to lush “vegetable markets.”

Customers also include carnivorous fish, some of whom are like commuters, stopping by the reef from time to time. Cleaner shrimp offer cleaning services for their teeth afterward. Sponges, mussels, and other animals work to keep the water around the reef clean by filtering it. In the process, they take their nourishment from the tiny organic particles they filter out.

Hermit crabs and other crustaceans handle garbage disposal. And there are even demolition contractors: Drilling sponges break down areas of coral that have died off, clearing coveted properties. Coralline algae, the masters of mortar, cement these areas right away so that new hard coral larvae can find firm ground again.

Everyone Can Do Their Part to Help Conserve This Underwater Paradise

A healthy reef even follows along as the ocean floor subsides due to tectonic movements or sea level rise, since the structures simply keep growing – upward, toward the light. But scientists believe shallow-water tropical reefs will probably not survive climate change, even with all the efforts made on their behalf. Over the Earth’s history, there have been several phases when shallow-water tropical reefs disappeared, Leinfelder says.

They always reemerged at some point, however. “Sometimes it took three million years, sometimes five, and sometimes as much as 140 million years, so it’s not much comfort for today.” But the die-off was never as rapid as it is this time, “thanks” to the multifaceted influence of humans. With this in mind, Leinfelder and his team are studying the adaptability of different types of reefs in various places around the world. The researchers hope that some of them might stand in for shallow-water reefs after they die off, at least in part.

“Off the coast of Borneo, for example, there are mud reefs that are viable despite the large amounts of mud deposited due to rain forest logging,” Leinfelder explains. And during the Jurassic, reefs grew in highly nutrient-rich, cloudy waters even though there was not much light, limiting the algae’s ability to photosynthesize. “These kinds of ‘dirty slob’ coral reefs exist in deep water to this day.”

Another kind of reef that is exciting to Leinfelder is “Lazarus reefs,” which consist mainly of sponges, and those where the corals can adapt, like in the Mediterranean: If there is a lot of plankton, they eat more plankton, and if there is a lot of light, they live in symbiosis with single-celled organisms. Stromatolite reefs made of dead microbial mats – almost the “grandfathers” of all reefs – are true artists when it comes to survival: They can withstand almost anything.

Still, these kinds of exotic reefs cannot entirely replace their threatened counterparts, Leinfelder fears. Only one thing could still help the shallow-water tropical reefs: “We need to dramatically slow the pace of climate change and reduce other contributing factors, such as marine pollution and overfishing, to give the reefs more time to adapt.”

Leinfelder does not believe the often-heard argument that people can’t have an impact as individuals is a good excuse. Each and every one of us can indeed do something, from reducing air travel and thereby limiting our CO₂ emissions to eating less fish and choosing only certified fish – and avoiding plastic, 70 percent of which winds up in the environment at some point. “Even choosing the right sunscreen when you snorkel can help,” Leinfelder says. “The synthetic UV filters used in sunscreens also harm the reefs and the organisms that live there.”