Boy, we could use some good news about Florida’s environment.

So here it is:

Seagrass appears to be making a comeback — at least for now, at least to a limited degree and at least in some areas — in the Indian River Lagoon.

Lagoon-wide, seagrass acreage grew back by 24% in just two years, from a record low of 19,821 acres in 2021 to 24,521 acres in 2023, according to the St. Johns River Water Management District’s most recent studies, including biennial seagrass maps and data from in-water surveys conducted in summer 2023 and this past winter.

We say “at least to a limited degree” because the increase still represents only about 30% of the 80,434 acres of seagrass found in 2007, the acreage biologists say is needed for a healthy lagoon.

We say “at least in some areas” because the rejuvenation, although widespread, appears to be primarily in the northern lagoon, including the section known as Mosquito Lagoon.

And we say “at least for now” because we’re seen seagrass revivals in the past that proved to be short-lived.

Healthy seagrass is essential to a healthy Indian River Lagoon. It provides food and shelter for countless invertebrates at the bottom of the food chain and a nursery for juvenile fish that feed on them and the habitat that makes the lagoon one of the most biodiverse estuaries in the world.

Seagrass also is the primary food for endangered manatees. A record 1,101 manatees died in 2022, most from starvation caused by seagrass loss, according to the Florida Fish and Wildlife Conservation Commission.

No algal blooms = seagrass coming back?

As flowering saltwater plants, seagrasses — like land plants — need sunlight to perform photosynthesis (the process of changing carbon dioxide, water and sunlight into energy and oxygen) for food. Anything blocking sunlight — algal blooms, for example — can kill seagrass beds.

A string of massive algal blooms, including the 2011 blue green “super bloom,” killed more than half the lagoon’s seagrass.

And what caused those algal blooms? People did, by polluting the lagoon with algae-feeding nitrogen and phosphorus from fertilizers and sewage. 

People also use herbicides, including Roundup, that kill seagrass and stay toxic longer in salty water.

So if algal blooms kill seagrass, it stands to reason a lack of blooms is behind the current seagrass rebirth.

The improvement in seagrass acreage is “attributed to natural recovery from better water quality,” Ashley Evitt, media outreach manager for the St. Johns River Water Management District, said in an email, citing “numerous septic-to-sewer projects have been completed and planned, wastewater treatment facilities are being enhanced, and a variety of innovative projects are underway.” 

Zack Jud, director of education and exhibits at the Florida Oceanographic Society in Stuart, isn’t so sure.

“The seagrass recovery we are seeing in the northern IRL and Mosquito Lagoon is a bit of a mystery, Jud said in an email. “There have not been any monumental improvements in water quality over the last few years. Brevard’s Save Our Indian River Lagoon Program (the county’s half-cent sales tax) likely had some positive impacts on water quality, and other municipalities have been working to address wastewater and stormwater issues (but the the current seagrass recovery) may just be a result of favorable environmental conditions over the last few years.”

Sex is good

One reason seagrass seems to be recovering faster in the northern lagoon, including Mosquito Lagoon, could be that widgeon grass, the dominant species there, reproduces sexually (via flowers and seeds) rather than the much slower asexual route (via fragments) like most other species, Jud said.

At this year’s Indian River Lagoon Symposium, researchers said that shoal grass, a species thought to primarily reproduce asexually, was also reproducing via seed, and that seeds could survive for several years buried on the floor of the estuary.

“I think this also explains some of the shoal grass recovery I’ve observed farther south in the IRL,” Jud said.

Ironically, part of the seagrass’ success could also be linked to the tragic deaths of 1,900 manatees in 2021 and 2022, which resulted in fewer manatees eating the sparse seagrass acreage.

A 2019 study in Nature by the University of South Florida and the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute reported that manatee herds in some areas of the lagoon have been known to graze on and disturb up to 40% of the seagrass beds, removing 80% to 96% of the seagrass and 50% to 67% of the roots.

Evitt noted that NASA contractors saw manatees grazing the seagrass beds in Mosquito Lagoon throughout 2023, but the seagrass still expanded by about 5,000 acres in that area.

“We just started our 2024 summer in-water surveys, and reports from Mosquito Lagoon show further expansion since last year,” she added.

The lack of resurgence in the southern lagoon, Evitt said, “is due to environmental factors that we are currently evaluating. … While full recovery hasn’t been seen, we have found higher species diversity and percent cover.”

Fingers crossed

There’s cautious optimism that the current seagrass resurgence in the lagoon will continue longer than the come-and-go growth spurts in the past.

One reason: There are numerous efforts along the length of the lagoon to grow and transplant seagrass beds.

These ongoing projects aren’t the reason for the current upswing in seagrass acreage in the lagoon; as Jud noted, most restoration attempts have had limited survival rates; the scale of the recovery is far beyond what the small projects could have achieved; and thousands of acres of seagrass can be found in parts of the lagoon where restoration efforts weren’t conducted.

But they offer hope for the future.

At the Florida Oceanographic Society, Jud said, “we want to develop a better scientific understanding of how to truly make seagrass restoration work so that we’ll have a viable tool at our disposal once water quality improvements are achieved.” (Read about Florida Oceanographic Seagrass Training, Education and Restoration, aka FOSTER, at www.floridaocean.org/seagrasses.

This year’s natural seagrass recovery, he added, “is just a reminder that the Indian River Lagoon is resilient and has not crossed an ecological tipping point … yet. I am cautiously optimistic that this recovery trend will continue into the future, but I am also realistically concerned that one bad water quality event in the IRL could erase much of the recovery we are currently observing.

“This definitely isn’t time to celebrate a major success with respect to seagrass.”

Know your lagoon seagrasses

Here’s a look at the most common species of seagrass in the Indian River Lagoon, courtesy of the St. Johns River Water Management District:

• Shoal grass is the most common and it can be found throughout the lagoon, especially in shallow water. It is considered a pioneer species, often the first seagrass to appear in a barren area, because it can grow and spread quickly to stabilize the sediment.
• Manatee grass is found at depths of several feet throughout the lagoon, often in mixed beds with other species. As the name suggests, it’s the preferred seagrass for hungry manatees.
• Turtle grass can be found at mid-depths in the lagoon south of Sebastian Inlet. It requires the most sunlight of all the seagrasses in the lagoon, making it an excellent indicator of water quality.
• Johnson’s seagrass is found only in southeast Florida, including the southern half of the lagoon. It’s named in honor of J. Seward Johnson Sr., founder of Harbor Branch Oceanographic Institution, now a division of Florida Atlantic University in Fort Pierce. The National Marine Fisheries Service considers Johnson’s seagrass a threatened species under the Endangered Species Act because of its limited ability to reproduce and its limited distribution.
• Star grass can be found in a range of depths throughout the lagoon but is more common in the northern sections. lagoon. Blades of the grass grow from a single stem to form a star-like pattern, giving the species its name.
• Paddle grass, named for the shape of its blades, is the only annual species in the lagoon; the blades are lost in cold weather and reemerge in warm weather. It generally is found in deeper water, mostly south of the Sebastian Inlet.
• Widgeon grass grows in patches in very shallow water throughout the lagoon, including areas with low salinity.