As oceans warm and organisms that feed on seagrasses move north, they could overgraze parts of the Gulf of Mexico, including areas in the greater Tampa Bay region.
This finding comes from a peer-reviewed study recently published in the journal Nature Ecology & Evolution.
Tom Frazer, the dean of the College of Marine Science at the University of South Florida, was one of dozens of other scientists who researched areas off Florida's Gulf Coast, the Florida Keys, the Cayman Islands, and parts of Panama.
They focused on turtle grass, which is the predominant structural habitat in the Gulf and the broader Caribbean region. It provides foraging areas for many animals that are important both ecologically and economically.
"In Florida, for example, probably about 85% of the fishes that we exploit either recreationally or commercially spend some part of their life history in seagrass beds," Frazer said.
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The researchers observed the effects on how grazing and nutrient pollution might alter the growth characteristics or the productivity of seagrass beds.
Scattered across the turtle grass range, the scientists each carried out the same exact experimental protocol by setting up plots.
They left some unaltered and clipped seagrasses in others to simulate the grazing impacts. Then nutrients were added to simulate nutrient pollution, which is occurring all around the globe.
The group found that seagrasses at the northern end of their range are less resilient in the face of this simulated grazing impact.
"The implication, obviously, is that as the climate continues to warm and animals move northward, at the northern kind of boundaries of the seagrass beds, they're going to be exposed to this stress,” Frazer said.
“And if we don't manage them properly, then those seagrasses will be less resilient, and we could potentially degrade a very, very valuable habitat.”
By the end of the century, the global temperature is expected to rise more than 3 degrees Celsius.
And temperatures within many shallow water areas, where seagrasses grow, have already increased by a degree or more over the past decade, Frazer said.
Manatees and sea turtles are most commonly known to graze on turtle grass in the Gulf of Mexico, but Frazer said warming water will expand the grazing areas for herbivores that don't typically come here, like tropical parrot fish. The phenomenon is known as tropicalization.
"If you get rid of the seagrasses because they're receiving too much grazing pressure, then you've significantly altered how those ecosystems function, and you will ultimately lose a lot of those ecosystem services that seagrasses provide," he said.
Overgrazing is not a widespread occurrence across the Western Atlantic yet, but it already occurs in subtropical to temperate waters around Australia and in the Mediterranean, according to a press release.
However, the scientists still don't understand how climate change will more broadly affect the dynamics of ecosystems.
“While the direct effects of warming are expected to influence individual species, the indirect effects of warming on species interactions remain poorly understood," according to the abstract from the article, "Herbivore effects increase with latitude across the extent of a foundational seagrass."
"In marine systems, as tropical herbivores undergo poleward range expansion, they may change food web structure and alter the functioning of key habitats.”
But if seagrasses have what they need to thrive, there could be hope for subtropical seagrasses and the many species they sustain.
“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 lead author and marine biologist at Florida International University, Justin Campbell.
“That means protecting the water quality.”
The study was done in partnership with FIU, USF, University of Florida, Florida Gulf Coast University, University of South Alabama, Smithsonian Marine Station, Universidad Nacional Autónoma de México, and Texas A&M University, among others.
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