Herbivores, displaced by ocean warming, threaten subtropical seagrass meadows

A new study published in Nature Ecology & Evolution describes how subtropical seagrasses are at risk as tropical herbivores move in response to warming oceans

Peer-Reviewed Publication

UNIVERSITY OF SOUTH FLORIDA

 

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RESEARCHERS BEHIND THE RECENT ARTICLE CONDUCTED A SERIES OF COORDINATED EXPERIMENTS IN SEAGRASS BEDS SPANNING SIX COUNTRIES AND 23 DEGREES OF LATITUDE.

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CREDIT: MAGGIE JOHNSON

TAMPA, Fla. (March 6, 2024) – Tropical herbivores are on the move, and that could spell trouble for subtropical seagrass meadows.

As the ocean warms, marine species often travel poleward in search of suitable habitats and food. This phenomenon, known as tropicalization, can expand the range of tropical herbivores such as sea turtles and manatees — which prefer warmer waters — to subtropical regions that have historically supported few marine herbivores.

A new study published in Nature Ecology & Evolution describes how subtropical seagrasses are at risk as tropical herbivores move in response to warming oceans.

“Ocean warming poses multiple threats to marine ecosystems,” said Tom Frazer, co-author of the study, and professor and dean of the University of South Florida College of Marine Science. “Seagrass meadows, which provide forage for herbivores and nursery habitat for many recreational and commercially important fishery species, are already threatened by degraded water quality. This study suggests that the tropicalization of marine ecosystems in response to warming temperatures could further contribute to the decline of these vital habitats.”

The study’s authors used turtlegrass, a foundational seagrass species found throughout the Western Atlantic, Caribbean Sea and Gulf of Mexico, as a model for seagrass meadows. Researchers conducted a series of coordinated experiments in seagrass beds spanning 23 degrees of latitude (including sites in Bonaire, Panama, Belize, Mexico, the Cayman Islands, and the United States) and found that turtlegrass populations at higher latitudes had lower productivity in response to simulated grazing than populations at lower latitudes.

The findings suggest that subtropical seagrasses are less resilient to heavy grazing from marine herbivores, in part because they receive less sunlight relative to their tropical counterparts. As tropical herbivores move into subtropical waters, overgrazing may prevent subtropical seagrass meadows from persisting in these environments.

There’s hope, though, for subtropical seagrasses and the many species they sustain. What’s key, according to the study’s authors, is making sure seagrasses have what they need to thrive.

“If we want to give these meadows the best chance of enduring the anticipated increases in grazing, we need to get them as much light as possible,” said Justin Campbell, lead author and marine biologist at Florida International University. “That means protecting the water quality.”

While overgrazing is not yet a widespread occurrence across the Western Atlantic, it already occurs in subtropical to temperate waters around Australia and in the Mediterranean. This recent study can serve as a clarion call to protect subtropical seagrass meadows before grazing pressure from tropical herbivores increases.

“As tropical herbivores extend their ranges, they are likely to have profound effects on the ecology of seagrass ecosystems in the northern Gulf of Mexico,” said Frazer. “The results of this study indicate clearly that future management of marine ecosystems will need to place a higher priority on protections from pollutants and other stressors to give seagrasses the best chance to cope with warming waters and other climate related changes.”

Seagrass meadows provide food for marine herbivores and nursey habitats for many fish species.

CREDIT

Maggie Johnson

About the University of South Florida

The University of South Florida, a high-impact research university dedicated to student success and committed to community engagement, generates an annual economic impact of more than $6 billion. With campuses in Tampa, St. Petersburg and Sarasota-Manatee, USF serves approximately 50,000 students who represent nearly 150 different countries.  For four consecutive years, U.S. News & World Report has ranked USF as one of the nation’s top 50 public universities, including USF’s highest ranking ever in 2023 (No. 42). In 2023, USF became the first public university in Florida in nearly 40 years to be invited to join the Association of American Universities, a prestigious group of the leading universities in the United States and Canada. Through hundreds of millions of dollars in research activity each year and as one of top universities in the world for securing new patents, USF is a leader in solving global problems and improving lives. USF is a member of the American Athletic Conference. Learn more at www.usf.edu.

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JOURNAL

Nature Ecology & Evolution

METHOD OF RESEARCH

Data/statistical analysis

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Herbivore effects increase with latitude across the extent of a foundational seagrass