Seagrass restoration could help save starving manatees

Last year was a bad one for manatees, when more than 1,000 of the loveable mammals died in Florida. The main cause of the mass mortality event was starvation, which was due to a lack of seagrass, the manatee’s favorite food. Seagrass was scarce in the Indian River lagoon, a 156-mile-long estuary along Florida’s east coast. 

The seagrass was likely killed by a chain reaction from pollution runoff, and some non-profits sued the EPA over their handling of the pollution. The runoff caused phytoplankton blooms, which in turn blocked light from the grass.

Now, a new study published in Frontiers in Marine Science seeks to remedy the problem by investigating the loss of seagrass and assisting with ecosystem restoration.      

“Light is mandatory for growth and survival of seagrasses,” said study co-author Dr. Dennis Hanisak, a research professor at Florida Atlantic University (FAU) Harbor Branch. “Reduced light causes changes in the physiology and the size and shape of seagrass, such as decreased leaf length, leaf width, leaves per shoot, and shoot growth. Seagrasses can cope with reduced light for short periods, however, once poor clarity becomes chronic or recurrent, detrimental effects on survival, resilience, and recovery arise.”

The study showed that from 1943 to 1994, about 7,400 acres of seagrass were lost. Between 2011 and 2019, approximately 58 percent of seagrass was lost. 

“Multiple anthropogenic stressors affect seagrasses by reducing water clarity, particularly at the deep edge of a bed or the light-limited depth of colonization,” wrote the study authors.

“Reduced light also causes changes in the physiology and morphology of seagrass, such as decreased leaf length, leaf width, leaves per shoot, and shoot growth.”

“Seagrasses can cope with reduced light for short periods, but once poor clarity becomes chronic or recurrent, detrimental effects on survival, resilience, and recovery emerge.”

The researchers noted that reduced availability of light is not the only stressor affecting seagrass. They explained that salinity and temperature are two additional stressors, which are not related to physical disturbance or excessive nutrient loads. The research team is working to grow seagrass in an effort to restore some of what has been lost. 

“We are maintaining the seagrass nursery in a ‘ready mode’ so that we can readily partner with agencies and other interested parties in experimentation or pilot studies for seagrass restoration efforts,” said Dr. Hanisak.

This effort to understand the loss of seagrass is critical in reversing the trend and restoring the habitat to hopefully support a healthy population of manatees into the future. The Florida Power & Light Company (FPL) is providing the funding to operate the nursery for at least three years.

“This gift and continued support from FPL is helping our ongoing research in marine science and technology and addressing critical issues affecting our marine ecosystems,” said Dr. Jim Sullivan, executive director of FAU Harbor Branch. 

“With this funding, our researchers are applying unique techniques to help repair the damages to the crucial aquatic plants that are essential to the health of the Indian River Lagoon, and moreover, critical for the survival of our beloved lagoon manatees that are dependent on this dietary staple.”

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By Zach Fitzner, Earth.com Staff Writer