Research team seeks answers to restore vegetation critical to river’s health
Steve Cobb has fond memories of growing up in Jacksonville and spending time on the St. Johns River.
“I grew up fishing and shrimping and later got a boat, so I’ve spent a lot of time on the river,” Cobb said. “I just fell in love with it.”
Today, as chairman of the board of St. Johns RIVERKEEPER (SJRK), Cobb puts his love for the St. Johns River into action. In May, Cobb served as captain of SJRK’s SAVe Our River’s Grasses Expedition, a four-day research voyage to measure and analyze the river’s significant loss of submerged aquatic vegetation (SAV). Initially launched in 2023, the five-year project seeks to find solutions that will bring back the river’s grasses, which the St. Johns Riverkeeper Lisa Rinaman said are a vital part of the river’s habitat.
“The river grasses are the kidneys of the river – providing biofiltration, fish habitat, flood protection and more,” Rinaman said. “Without them, the St. Johns could turn into a dead zone, which is absolutely unacceptable.”
A ‘double whammy’
Cobb said the “double whammy” of hurricanes Matthew and Irma impacted the river’s eelgrass. “When they hit, combined with higher salinity, higher water, (the grasses) never came back,” he said.
Rinaman agreed.
“We’ve been tracking the loss of eel grass due to saltwater intrusion for more than a decade,” Rinaman said. “But after Hurricane Irma, we saw the water levels were higher for an extended amount of time. We expected the grasses would come back pretty quickly after that – but they didn’t come back.”
Tannins washing into the river darkened the water, Rinaman added, blocking the sunlight from reaching the grasses. Blue green algae also blocks sunlight, further impeding eelgrass growth.
During the recent SAVe Our River’s Grasses expedition, a team of research scientists and biology students surveyed an 80-mile stretch of the river between Doctors Lake and Lake George, measuring grass beds, conducting water quality testing and assessing possible solutions to restore the habitat. Testing sites included spots behind the homes of residents eager to see the river’s health improved.
“Some of these folks have lived in their homes for decades, so we get to hear their stories about their relationship with the river,” Rinaman said. “So, it’s been a great relationship builder for us with so many people.”
Ben Williams, an avid fisherman and founder of Fisherman’s Dock Seafood Market, offers his dock for the research project.
“All of our river communities’ economies depend on a healthy river,” Williams said. “And the health of the St. Johns depends on healthy eelgrass.”
Signs of success
Findings from the five-year project will be analyzed to identify viable solutions to boost eelgrass growth. And already, Rinaman said, there are signs of improvement.
“It’s been out of balance, but we’re seeing some exciting signs that we may have a really good grass season,” she said. “We found some really beautiful, healthy grass near Mandarin.”
Reopening the Rodman Dam – which would allow water from the Silver Springs and Ocklawaha rivers to enter the St. Johns – has also been suggested as a solution.
“By opening it and allowing the fresher, clearer water to make it to the St. Johns, it would offset some of the darker, cloudy water as well as offset saltwater intrusions and allow eelgrass seed to make its way down through the Ocklawaha,” she said. “So, the benefit to eelgrass of reuniting the rivers is multifaceted.”
The Florida Fish and Wildlife commission also has experimented with protective enclosures to spur SAV growth.
“One of the (testing) sites has those enclosures and the grass is as long as your arm,” Rinaman said. “We’re trying smaller enclosures at each of our sampling sites to see if it can be helpful to get at least sections of the grasses to grow to maturity, so they have enough energy to seed and spread.”
Bryce Yazdiya contributed to this article.
