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Ask the veterinarians and biologists collecting dead manatees along Florida’s Atlantic coast this winter, and they’ll tell you starvation is a slow and excruciating way to die.
Organs stop functioning. Cells break down. Muscles waste away. The starving animals are “dissolving on the inside,” said Pat Rose, executive director of the nonprofit Save the Manatee Club.
A series of algae blooms decimated vast seagrass beds where the sea cows once grazed in the Indian River Lagoon on the Central Florida coast. Now they are dying in record numbers, more susceptible to infection and colder, winter waters.
A reported 1,101 manatees died last year, state records show. That’s up to 10% or more of the estimated manatee population in 2016, the most recent number available. More than 700 of those deaths were on the east coast, a few hundred likely due to starvation. This year, at least 350 manatees have died on the east coast since Jan. 1.
The manatee deaths illustrate how ecosystems already weakened by human activities and a changing climate can plunge into disaster when one event spirals through a food chain. And they are the latest and possibly highest profile casualty in a series of similarly devastating events that plague coastal areas around the globe.
Seagrass meadows suffered widespread declines in Chesapeake Bay along the nation’s mid-Atlantic coast. So did seagrass beds in Rhode Island and western Australia. Salt marshes in New England suffered. Kelp forests died off the California coast.
In each case, some combination of the same toxic factors are blamed. Too much wastewater, too much runoff and too much development leave these coastal ecosystems where people live, fish and play weakened and vulnerable. Climate change, in terms of warming temperatures, marine heat waves, flooding rains and higher sea levels add more stress.
By some estimates, up to 30% of the world’s seagrass was lost in the 20th century. Steeper declines began over the past 20 years and then “really accelerated over the last 10 years,” said Mark Bertness, the Robert P. Brown Professor of Biology at Brown University in Providence, Rhode Island.
That’s concerning, he said, because healthy coastal ecosystems provide huge benefits to humans, in terms of things like storm surge protection, carbon storage and fish nurseries.
Without more urgent action to clean up waterways and combat global warming, more cascading ecosystem collapses are expected along the world’s coasts.
“People around the world are watching (Florida), fearing they could see similar disasters in their lagoons and estuaries,” said Jessie Jarvis, an associate professor at the University of North Carolina Wilmington who is serving as president of the World Seagrass Association.
Central Florida’s dying seagrass
Seagrass evolved over thousands of years as submerged forests that provide food and shelter to a vast array of marine life. Offshore fish species spawn in coastal seagrass. Sea turtles spend part of their lives there. So do seahorses, sharks, dolphins and many birds, including pelicans and herons.
Seven of the world’s 72 species of seagrass are found in the Indian River Lagoon, a ribbon of waterways along 156 miles of the Florida coast. Once billed as one of the world’s most biologically diverse estuaries, researchers valued its economic contribution at more than $7.6 billion a year, including activities such as fishing, boating and tourism. But the lagoon’s health has been in free fall for more than a decade.
Many point to a severe freeze in 2010 as a turning point. Unusually frigid water temperatures killed massive amounts of fish and drift algae. The algae had helped to filter the water, absorbing nutrients such as nitrogen and phosphorus. When the algae died, it released those nutrients into the water. Hundreds of thousands of dying fish dumped an even bigger slug of nutrients, fueling the growth of other, more harmful algae species.
By 2011, massive harmful algal blooms spread across several parts of the lagoon. At the time, scientists called it a “superbloom” for its unprecedented size. But subsequent blooms, especially in 2020, have been even bigger and more devastating.
Thick, pea soup-like algae blocked the light essential to seagrass survival. Tens of thousands of acres died in 2012 and 2013, and the losses continued with more recent blooms. The grass released even more nutrients as it died. Without strong root systems, bottom sediments stirred up and further clouded the water.
Up to 60% of the grass beds in the lagoon were lost, seagrass scientist Lori Morris with a regional water management agency said during a recent community webinar. And the remaining beds have “hardly any grass.” One estimate puts the overall grass lost as high as 90%.
Starving manatees have been found as far north as Georgia and southward through Miami, said Martine de Wit, veterinarian for the wildlife commission. The deaths have raised critical concerns about this threatened species that was removed from the endangered species list in 2017 and prompted emergency feedings of leafy greens by state and federal officials.
Numerous experts blame partially treated wastewater, failing septic systems, septic tanks where they shouldn’t be, polluted stormwater runoff and its abundance of fertilizers, herbicides and pesticides.
Clean water allows life-giving light
The same challenge faces restoration groups around the country. Improving the water quality is the key to restoring coastal ecosystems everywhere, said Bertness and others.
Seagrass needs more light than any other living plant on the surface of the Earth, said Robert Orth, an emeritus professor at the Virginia Institute of Marine Science. Because their roots are in toxic sediments, it’s hard for the plants to pump oxygen into the leaves.
Too little light proved to be the enemy in New England, where efforts to re-establish and restore one type of seagrass, eelgrass, haven’t worked, Bertness said. New efforts focus on smaller areas where water is clearer, he said, and that’s working better.
Adding filter feeders such as oysters and clams to help clean the water also boosts restoration projects.
In the 64,000-square mile Chesapeake Bay, eelgrass coverage is a fraction of what it was 50 years ago, said Orth, who has been called the “Johnny Appleseed” of seagrass restoration. The bay’s eelgrass has seen a 29% decline in total area since 1991.
Whether or not the eelgrass ever returns is questionable, Orth said. It is temperature and light sensitive, so “unless we figure out a way to get temperatures to drop and make the water clearer, we’re not going to get eelgrass back to anything looking like the past.”
However, seagrass restoration in coastal lagoons along Virginia’s eastern shore has seen better success. Eelgrass declined in the 1930s along its entire north Atlantic range including these seaside lagoons. Eelgrass wasn’t seen in these lagoons until Orth began a restoration program in 2001. Today, after more than 70 million eelgrass seeds were distributed during the past two decades, these lagoons now have 9,500 acres of thriving eelgrass.
“If you get water quality back to where it was, seagrasses will return pretty rapidly,” he said. “If you don’t remove the water quality issues that are influencing it, you’ll never get it back.”
The latest report from the United Nations’ Intergovernmental Panel on Climate Change also concluded water quality improvements can help coastal ecosystems bounce back, be more resilient to the changing climate and provide natural solutions for protecting shorelines from climate change.
Restoration the goal
As the executive director of a coalition of Florida governments known as the Indian River Lagoon Council, Duane DeFreese is all too familiar with water quality concerns.
“We need to get really serious in America about wastewater treatment,” DeFreese said. “We should not be putting these nutrients into surface water and groundwater.”
He remains hopeful water quality can be restored in the lagoon, even though the estimated cost of long-term restoration approaches $5 billion.
Nearly 300 state and federal projects are underway aimed at cleaning up water quality, from muck dredging to removing septic tanks, DeFreese said. The federal infrastructure bill will bring in nearly $1 million a year for the next five years. Even before the manatee deaths started, voters in Brevard County, where the most manatees are dying, had approved a sales tax initiative that will bring in more than $40 million a year for 10 years.
“With every project, we’re making progress,” DeFreese said.
Other work has shown seagrass restoration is expensive and complicated, he said, but not impossible.
“We’re going to get good at seagrass planting within the restoration community, even if that means caging out the marine life to give planted seagrasses a chance to recover,” he said. “Otherwise, it’s almost like putting out a salad buffet. If you put it out now, whether it’s fish, turtles or manatees, whatever you plant will be gone in 10 days.”
Rose remains guardedly optimistic that the water can be cleaned up enough to stop the algae blooms and ensure the manatees’ survival. “We won’t save the manatees in the Indian River Lagoon if we don’t get the water quality right.”
Manatees resort to eating more algae when seagrass disappears
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Citation: Florida’s starving manatees reflect troubles in coastal ecosystems around the globe (2022, March 17) retrieved 6 April 2022 from https://phys.org/news/2022-03-florida-starving-manatees-coastal-ecosystems.html
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