FIU Study: With Seagrass Gone, Manatees Resort To Eating More Algae

MIAMI (CBSMiami) - A new Florida International University study found Florida manatees are resorting to eating a "staggering amount of algae" after seagrass died off at the Indian River Lagoon.

University officials said that FIU Institute of Environment Ph.D. student Aarin-Conrad Allen and a collaborative team of researchers have found the first evidence that Florida manatees went from primarily eating seagrasses to primarily eating algae after a 2011 harmful algal bloom decimated local seagrasses.

"Researchers made the discovery by comparing the stomach contents of manatees living in the Indian River Lagoon during the late 1970s and throughout the 1980s to manatees living there between 2013 and 2015."

FIU researchers say that when half the seagrass died in 2011, many manatees starved. Some died.

Last year, the state lost a record 1,100 manatees — and, in the first two months of 2022, more than 100 have died.

"Manatees primarily eat seagrass but do sometimes supplement their diet with algae and other things like freshwater grasses," said Allen, who works in FIU Marine Sciences Assistant Professor Jeremy Kiszka's lab. "The dramatic shift to algae being the primary focal diet item is interesting, because we're not sure what the health implications will be to the manatees."

"The results of our study show what most had already suspected – manatees in the Indian River Lagoon are consuming less seagrass," said United States Geological Survey's Cathy Beck, who pioneered the modified microscope point techniques that were used to examine the stomach samples. "This is not likely due to a change in preference but a change in seagrass availability as a food source. Macroalgae is helping to satiate their hunger, but the long-term implications on manatee health of this monumental shift in diet has yet to be investigated."

The findings were recently published in Estuarine, Coastal and Shelf Science.