Seagrass is making a surprisingly strong comeback at the Sebastian Inlet, a positive sign for the Indian River Lagoon. Seagrass provides food and shelter for marine creatures ranging from tiny crustaceans to huge manatees, and is the foundation of the lagoon’s ecology.

The Sebastian Inlet District, which has been monitoring seagrass growth since 2008, recently announced that grass beds on the shoals west of the Inlet increased by more than six acres in 2020 and now cover nearly 115 acres. 

That coverage is comparable to 2008 when the Lagoon was healthy prior to the algae superbloom in 2012 that killed more than half of the seagrass in the waterway – a disaster followed by other destructive blooms that further damaged seagrass and slowed recovery.

The latest seagrass survey, conducted by district consultant Atkins North America, produced additional good news besides the increase in acreage – there have been no new scars inflicted by boat propellers in the inlet shoals since the prior survey. In 2019, 34 prop scars were documented.

The positive findings at the Inlet are in stark contrast to the condition of the remainder of the 156-mile-long waterway, where seagrass coverage ranges from none to sparse and deep cuts in the lagoon bottom from propellers are widespread.

Sebastian Inlet is one of only five navigable channels connecting the lagoon with the ocean, and the twice-daily tidal influx of fresh seawater likely accounts for better seagrass recovery near the Inlet.

“The water exchange, or flushing, between the Indian River Lagoon and the Atlantic Ocean has a positive impact on water quality within the Lagoon and has promoted an accelerated resurgence of seagrass beds on the western flood shoal at the inlet as compared to other parts of the lagoon,” the Inlet District said in a statement.

The Sebastian Inlet District began conducting aerial surveys and ground-truthing (snorkeling and wading the flats) on the inlet shoals shortly after it extended a boat channel connecting the Intracoastal Waterway with Sebastian Inlet in 2007. 

Atkins North America marine biologist Don Deis has been in charge of the monitoring since its inception. Deis finds that while six of the lagoon's seven species of seagrass grow on the shoals, the dominant species are shoal grass and Johnson’s seagrass – a threatened species that occurs only here and in Miami's Biscayne Bay.

He says he would like to see manatee grass – a stable, slow-growing, bed-forming species that dominated the shallows before the superbloom – return to pre-bloom coverage.

“The return of manatee grass could be [an additional] sign of recovery,” Deis said.
Seagrass benefits the estuary enormously because it nourishes and shelters many species of plankton, fish, invertebrates and mammals. It also improves water quality by trapping and removing sediments and algae-promoting nutrients from the water and protects the shoreline and lagoon bottom by reducing erosion.