Coral reefs could be more vulnerable to coastal development than predicted

December 8, 2015, University of Florida
Marine biologist Mike Gil is in Akumal, Mexico. Credit: Mike Gil

For years, many scientists thought we had a secret weapon to protect coral reefs from nutrients flushed into the seas by human activity. Experiments suggested that herbivores such as fish, urchins and sea turtles could keep corals and their ecosystems healthy by eating up extra algae that grew in the presence of these nutrients.

But a new University of Florida study sheds doubt on that idea, underscoring the importance of sustainable growth in coastal areas.

"We found that while herbivores can control the effects of nutrient pollution in small-scale experiments, nutrient pollution at larger, realistic scales can overwhelm them," said Mike Gil, a marine biologist who conducted the study as a at UF. "We can't just focus on protecting fish to keep healthy. We have to take a more holistic approach."

You don't have to be a scuba diver to care about healthy reefs. In addition to sustaining , whales and dolphins, these ecosystems deliver a host of benefits to people, from providing medicinal compounds and seafood to protecting our coastlines from storm surges. Nutrient enrichment can endanger these reefs: As our population grows, paving and development dump runoff laden with nitrogen and phosphorus into nearby bodies of water. Fertilizers intended for lawns and crops find their way into the seas, where sewer pipes might also be disgorging waste, especially in developing nations. The resulting enrichment can cause an overgrowth of algae that harms corals, sea grasses and kelp.

In Akumal, Mexico, where he leads a field course in marine ecology, Gil has seen coral reefs decline and algae increase, even as the population of algae-eating fish remained stable. He wondered if herbivores alone were really enough to defend the reefs. The that gave rise to that idea typically looked at areas of nutrient pollution of a square meter or less, but nutrient pollution zones can cover hundreds of square kilometers. Gil wanted to know if those results would scale up, but he knew larger field experiments weren't a viable option. ("It's not ethical to nuke an entire system with nutrients.") So Gil and his co-authors - fellow doctoral student Jing Jiao and former UF professor Craig Osenberg, now at the University of Georgia - turned to mathematical modeling.

They found that as the area affected by increased, herbivores' ability to control the resulting algae decreased, suggesting that these systems may be more vulnerable than many scientists thought.

Their findings could guide policy-makers in creating sustainable plans for industries such as tourism and fishing, which rely on healthy reefs.

Tourists can help, too - when visiting sensitive areas such as the Yucatán, Hawaii or the Great Barrier Reef, opting for sustainable accommodations and tour operators can reduce impact on reefs, Gil said.

Explore further: Grazing fish can help save imperiled coral reefs

Related Stories

Hawaii to come up with management plan to help coral reefs

November 17, 2015

The state of Hawaii is gathering information from the scientific community and local stakeholders to create a comprehensive coral reef management plan, but officials said Monday they will not yet impose a requested moratorium ...

Fish communities key to balancing nutrients in coral reefs

May 13, 2014

( —Coral reefs are among the most productive—and imperiled—ecosystems in the world. One of the many threats they face is pollution from runoff and poorly treated wastewater, which upsets the delicate balance ...

Recommended for you

Death near the shoreline, not life on land

December 13, 2018

Our understanding of when the very first animals started living on land is helped by identifying trace fossils—the tracks and trails left by ancient animals—in sedimentary rocks that were deposited on the continents.

The long dry: global water supplies are shrinking

December 13, 2018

A global study has found a paradox: our water supplies are shrinking at the same time as climate change is generating more intense rain. And the culprit is the drying of soils, say researchers, pointing to a world where drought-like ...

New climate model to be built from the ground up

December 13, 2018

Facing the certainty of a changing climate coupled with the uncertainty that remains in predictions of how it will change, scientists and engineers from across the country are teaming up to build a new type of climate model ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.