Algae Blooms and Seagrass Loss

Last update: June 19, 2024
This page will be updated as new information becomes available.

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Thousands of acres of seagrass in Florida have died because of nutrient pollution that has caused algae blooms and left manatees without an adequate food source. Learn more about this issue, projects that are being undertaken, and ways you can help.

The Indian River Lagoon (IRL) stretches for 156 miles along Florida’s east central coast. There are more than 4,400 species of plants and animals—including manatees—that are found in the lagoon watershed. Unfortunately, as the direct result of human derelictions over many decades, the Indian River Lagoon has suffered a series of harmful algal blooms, leading to massive losses in seagrass coverage and, in turn, the recent deaths of a heart-rending number of manatees equal to over 25% of the estimated manatee population.

Trouble for Manatees in the Indian River Lagoon

Note: data is preliminary. As of February 6, 2023, there were 800 confirmed carcasses recovered in 2022. Click to view a full-size version of this map.

An excess of nitrogen and phosphorus in waterways can fuel algae and cause it to grow faster than the ecosystem can tolerate. In the IRL, a combination of improperly treated sewage, leaking septic systems, fertilizers, and stormwater runoff has led to eutrophication. This means that frequent harmful algal blooms have blocked the light necessary for photosynthesis. The result: the tragic loss of more than 90% of the seagrass biomass within the Indian River Lagoon.

Before the IRL can be functionally restored, it will be necessary to prevent new sources of nutrient pollution from entering the lagoon as well as strategically removing or sequestering legacy nutrients to make them unavailable as a source of new Harmful Algal Blooms (HAB). Ideally, seagrasses will begin to reestablish on their own, but the process may be facilitated through the restoration of filter feeding organisms and selective pilot seagrass restoration projects. Ultimately, we must reverse those conditions that lead to the loss of seagrasses in the first place if we are going to restore seagrasses.

In 2021, the U.S. Fish and Wildlife Service (FWS) declared an Unusual Mortality Event (UME) for manatees. A UME involves a significant die-off of any marine mammal population and demands immediate response.

Manatees gathering at warm water locations—such as power plants—along the IRL have faced an additional threat, beginning with the 2020-2021 winter season, because there has been very little seagrass or other vegetation for them to eat in the immediate vicinity. Traveling further for forage would mean deadly exposure to cold water, so the manatees ultimately choose to forgo feeding over dying from the cold.
Between December 2020 and December 2022, over 2,000 manatees perished in Florida. 744 of those deaths occurred in Brevard County, which is considered the epicenter of the Unusual Mortality Event.

In a healthy ecosystem, free-ranging manatee grazing makes seagrass communities more productive.

Manatees have evolved along with seagrass communities for millions of years and primarily crop the grasses rather than uprooting entire plants, which can actually stimulate the grasses to grow. The loss of seagrass in the IRL is largely due to persistent and recurring environmental events that have changed the ecosystem over time—especially from human sources of pollution.

An Update: 2024

As of June 2024, we can be cautiously optimistic as seagrass has started to come back in the Mosquito Lagoon, and large numbers of manatees have been seen feeding on the grasses and appear to be in good body condition. That said, the majority of the Indian River Lagoon remains barren of seagrass, and the manatees now feeding in the Mosquito Lagoon are under increased threat from watercraft collisions. Much of the Mosquito Lagoon is a high-speed boating designation, meaning that manatees are not adequately protected.

Additionally, the Unusual Mortality Event designation remains in effect and will not be closed until experts determine that ‘the criteria under which the UME was declared have resolved or have become persistent’ (NOAA). Of concern is the fact that over the last few summers, very few calves were observed in the area, and in 2024, perinatal deaths have spiked, leading experts to believe that the UME could have a long-lasting effect on manatee reproduction that is not fully understood at this point. During the peak years of the Unusual Mortality Event, the Manatee Rescue and Rehabilitation Partnership (MRP)—a cooperative effort between agencies, organizations, and oceanaria (zoos and aquariums) to rescue, rehabilitate, and release manatees—worked tirelessly to coordinate their efforts in the Indian River Lagoon. New facilities were trained to care for manatees, and several new members joined the partnership to aid in the effort. The MRP continues to expand and train partners, and manatees that have been rehabilitated and returned to the wild are being fitted with satellite trackers. These trackers allow researchers to watch the animal’s progress and gain a greater understanding of how manatees are using the Indian River Lagoon post-seagrass loss.

Additionally, efforts to restore the Indian River Lagoon and improve water quality have been under way for several years. Universities, nonprofits, and for-profit companies are working to restore habitat in the lagoon by planting living shorelines, clams, oysters, and seagrasses. The Indian River Lagoon National Estuary Program has helped fund the creation of a Seagrass Nursery Network, where seagrasses are grown in tanks to be outplanted back into the lagoon. Counties within the IRL watershed are upgrading their wastewater treatment facilities to remove more nutrients from the water and treating leaky septic systems to prevent leeching.

Water quality in the Indian River Lagoon has been improving due to these efforts, but it is important that we continue pushing forward and not become complacent once we see improvement. Save the Manatee Club has been working with our partners on Florida’s east coast to support research and restoration efforts and will continue to advocate for additional protections for manatees and their habitat in the Indian River Lagoon.

What Else Is Being Done to Help Malnourished Manatees?

Save the Manatee Club is a founding member of the Manatee Rescue and Rehabilitation Partnership (MRP), a network of partners who participate in the rescue, rehabilitation, release, and post-release monitoring of sick or injured manatees. We are working together with our partners in the MRP to identify manatees in distress due to devastating seagrass losses in Indian River Lagoon.

Save the Manatee Club and our partners are also working diligently on improving water quality to enable natural regrowth of seagrasses and to replant areas where replanting is feasible now.

See Save the Manatee Club’s Work below for more information on our activities to help manatees during the UME.

An emaciated manatee is rescued by the Florida Fish & Wildlife Conservation Commission (FWC). Photo courtesy FWC.
An emaciated manatee is rescued by the Florida Fish & Wildlife Conservation Commission (FWC). Photo courtesy FWC.

If you are at all concerned that a manatee may be sick, injured, entangled, or orphaned, or if you see a manatee that is being harassed or wearing a "tag" or tracking device, please immediately report it to the Florida Fish and Wildlife Conservation Commission (FWC) 24-hour Wildlife Alert Hotline by calling 1-888-404-3922 (FWCC).

What You Can Do

Excessive human-produced nutrient pollution is a growing threat to all seagrass communities. When combined with the warming effects of climate change and sea level rise, these excess nutrients present an even greater danger to the future of seagrasses wherever they are found.

While there are many large-scale sources of pollution, it’s impossible to overstate the value of individual actions. What you do at home can make a big impact—whether you live near the Indian River Lagoon or not. Most people in the United States live in a watershed (a land area that drains to a river, lake, ocean, or other waterway)!

Please don’t feed or give manatees water. Giving food or water to manatees is illegal and teaches them to associate people and/or boats with handouts, which changes their behavior and puts them in harm’s way.

Here are some examples of direct actions you can take to protect our waterways

While Save the Manatee Club works with our partners to strengthen policies that protect water quality, the individual actions of each Florida resident can make a big difference for the health of our waterways. Learn how to do your part and take Save the Manatee Club's pledge to be Fertilizer-Free for Manatees.

More actions you can take for the environment

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