Quantcast

Biodiversity Helps Coral Reefs Thrive and Could Be Used Strategically to Save Them

Insights + Opinion
A healthy coral reef at Swains Island, American Samoa. NOAA / NMFS / PIFSC / CRED, Oceanography Team / CC BY 2.0

By Cody Clements

Coral reefs are home to so many species that they often are called "the rainforests of the seas." Today they face a daunting range of threats, including ocean warming and acidification, overfishing and pollution. Worldwide, more than one-third of all coral species are at risk of extinction.


I am one of many scientists who are studying corals to find ways of helping them survive and recover. As a recent report from the National Academies of Science, Engineering and Medicine shows, researchers are exploring many different strategies. Some, such as managed breeding to make corals more tolerant of stresses, are already being developed at small scales. Others, such as moving corals to colonize new areas, have not been tested yet.

My own work examines whether greater diversity of coral species on reefs can help corals survive and thrive. In a study published earlier this year, my colleague Mark Hay and I found evidence that the answer is yes. This finding could help to inform broader strategies for making coral reefs more resilient in altered oceans.

In Nature, More Is Better

Are ecosystems healthier if they contain many species than if they harbor only a few? This is a central question in ecology. Generally, scientists have found that ecosystems with more diverse foundation species – those that define a system and are inseparable from it, such as trees in a forest – tend to be healthier and function better.

Until recently, no one had applied this test to coral reefs. But we do know that healthy coral reefs are diverse, structurally complex ecosystems dominated by corals. In contrast, reefs that have been damaged by stresses such as coral bleaching events tend to become simplified, less diverse landscapes, often dominated by seaweeds.

For our study we chose a reef area on the southwestern coast of Fiji's main island, Viti Levu, in the South Pacific. Many reefs along this coast have been heavily degraded by overfishing and other human-related activities, reducing coral cover and allowing seaweeds to dominate.

There are hundreds of coral species across the Pacific, but at smaller scales, we found just five species or fewer during preliminary surveys conducted on the degraded reef at our site. Since these conditions mirror what is happening to many reefs worldwide, we saw it as an ideal place to test whether coral diversity matters for the "new normal" that we expect to see on reefs of the future.

Underwater Gardens

Our team created 48 concrete plots on the sea floor of the degraded reef, which served as the bases for experimental coral gardens. We created single-species gardens that each contained one of three coral species – Pocillopora damicornis, commonly known as cauliflower coral; Porites cylindrica, also known as yellow finger coral; and Acropora millepora, one of a number species known as staghorn corals. We also planted mixed gardens containing all three species.

We chose these corals because they are common to reefs across the Pacific and are representative of different coral families that have shown varying responses to a variety of harmful disturbances. In all, each garden contained 18 coral individuals, for a total of 864 corals.

To assess each coral's performance as it grew, we needed to remove them from their plots periodically. So we cut off the tops of hundreds of soda bottles and planted an individual coral in the upside-down neck of each bottle with epoxy putty. We embedded the bottle caps into our concrete slabs so that we could easily unscrew each bottle neck to examine the coral it held, then screw it back into its base. Over 16 months we weighed the corals and tracked other measures of their well-being, including tissue death and colonization of each garden by harmful seaweeds.

Experimental coral gardens on a degraded reef in Fiji. Gardens with a mix of coral species performed better than gardens containing only one species.

Cody Clements / CC BY-ND

We consistently found that corals grown in mixed-species gardens performed better than those in single-species plots. Within four months, coral growth in the mixed-species gardens was even exceeding the best-performing single-species gardens. This suggests that different species may benefit each other in yet unknown ways, at least during early stages of a coral community's development.

Examples of single- and mixed-species coral gardens through time during our 16-month experiment. At four months, mixed-species gardens were outperforming single-species gardens in multiple ways – growing faster on average than even the best performing single-species gardens (Acropora millepora). By 16 months, growth was comparable between mixed-species and Acropora gardens, but aggregate performance of single-species gardens continued to lag behind their mix-species counterparts.

Clements and Hay, 2019 / CC BY-ND

Why Is More Better?

The next question is what drove the effects that we observed. We hope to investigate a number of leads in future experiments. For example, farmers commonly observe that planting a diverse mix of crops helps to reduce the spread of infectious diseases among individuals. Could the same be true for coral reefs?

Our initial findings offer both concern and hope for the future of coral reefs. If diversity is integral to coral well-being, then continued species loss could dramatically alter these ecosystems in ways that lead to further reef decline. How many parts can be removed from the "ecosystem engine" before it breaks down?

That said, many of the strategies in the National Academies report involve using biodiversity – both at the genetic and species level – to enhance coral reef resilience. Examples include cross-breeding corals between populations; altering coral genes to give them new functions, such as higher heat tolerance; and moving stress-tolerant corals or coral genes to new locations.

Promising advances in technology, such as mapping coral reefs from the air, may also help researchers assess coral health and determine which species they contain. This baseline information may help better inform management and restoration efforts.

Corals are in trouble, but they aren't down for the count yet. Perhaps harnessing the power of their remaining biodiversity can help give them a fighting chance.

Cody Clements is a postdoctoral fellow at the Georgia Institute of Technology.
Disclosure statement: Cody Clements receives funding from the National Science Foundation, the National Institutes of Health, the National Geographic Society, and the Teasley Endowment to the Georgia Institute of Technology.

Reposted with permission from our media associate The Conversation.

EcoWatch Daily Newsletter

An aerial view of a neighborhood destroyed by the Camp Fire on Nov. 15, 2018 in Paradise, Calif. Justin Sullivan / Getty Images

Respecting scientists has never been a priority for the Trump Administration. Now, a new investigation from The Guardian revealed that Department of the Interior political appointees sought to play up carbon emissions from California's wildfires while hiding emissions from fossil fuels as a way to encourage more logging in the national forests controlled by the Interior department.

Read More
Slowing deforestation, planting more trees, and cutting emissions of non-carbon dioxide greenhouse gases like methane could cut another 0.5 degrees C or more off global warming by 2100. South_agency / E+ / Getty Images

By Dana Nuccitelli

Killer hurricanes, devastating wildfires, melting glaciers, and sunny-day flooding in more and more coastal areas around the world have birthed a fatalistic view cleverly dubbed by Mary Annaïse Heglar of the Natural Resources Defense Council as "de-nihilism." One manifestation: An increasing number of people appear to have grown doubtful about the possibility of staving-off climate disaster. However, a new interactive tool from a climate think tank and MIT Sloan shows that humanity could still meet the goals of the Paris agreement and limit global warming.

Read More
Sponsored
A baby burrowing owl perched outside its burrow on Marco Island, Florida. LagunaticPhoto / iStock / Getty Images Plus

Burrowing owls, which make their homes in small holes in the ground, are having a rough time in Florida. That's why Marco Island on the Gulf Coast passed a resolution to pay residents $250 to start an owl burrow in their front yard, as the Marco Eagle reported.

Read More
Amazon and other tech employees participate in the Global Climate Strike on Sept. 20, 2019 in Seattle, Washington. Amazon Employees for Climate Justice continue to protest today. Karen Ducey / Getty Images

Hundreds of Amazon workers publicly criticized the company's climate policies Sunday, showing open defiance of the company following its threats earlier this month to fire workers who speak out on climate change.

Read More
Locusts swarm from ground vegetation as people approach at Lerata village, near Archers Post in Samburu county, approximately 186 miles north of Nairobi, Kenya on Jan. 22. "Ravenous swarms" of desert locusts in Ethiopia, Kenya and Somalia threaten to ravage the entire East Africa subregion, the UN warned on Jan. 20. TONY KARUMBA / AFP / Getty Images

East Africa is facing its worst locust infestation in decades, and the climate crisis is partly to blame.

Read More