DARP Seagrass and Coral Injuries

A small boat next to a large vessel as white plumes are stirred up in the water around them
Just before midnight in August of 1994, the 155-foot research vessel Columbus Iselin went aground on a spur and groove coral reef formation in the western portion of the Looe Key National Marine Sanctuary. Photo: NOAA

When boaters unfamiliar or inexperienced with navigating local waters damage our delicate ecosystem, Florida Keys National Marine Sanctuary assesses the extent and severity of the injury. This includes a determination of the amount of habitat that is lost or injured and the extent of the damage to critical resources like seagrass and corals. These data are used in part to determine fines or legal claims, as well as the most feasible and beneficial restoration strategy. If a boater runs aground on the coral reef, the first step is to stabilize any broken or detached corals, giving the injured animals their best chance for survival. This is followed by the development of a detailed plan for comprehensive restoration.

For seagrass injuries, the extent of the injury as well as the volume and depth of the injury is determined, along with assessments of the amount of seagrass and other organisms that are lost or injured. For minor boat propeller scars that are only a few inches deep, the grass may be able to naturally recover by expanding inward from the perimeter of the injury. However, propeller scars that are more than 5–6 inches deep are not likely to recover on their own, and often these continue to enlarge during storm events because the seagrass root system is no longer holding the sediment in place. In these situations, the depression needs to be filled with pea gravel and capped with sediment tubes to stabilize the area. This is followed by the planting of seagrass, typically shoal grass (Halodule wrightii) or manatee grass Syringodium filiforme), along with placement of fertilizer stakes or bird perching stakes to provide a supply of nutrients that will allow the seagrass to become established.

The sanctuary's injury assessment team on a small boat leaving a dock
The sanctuary's injury assessment team on its ways to review a seagrass injury case. Photo: Chad Stolka/NOAA

Boat propellers have caused scars in seagrass beds throughout Florida Keys National Marine Sanctuary. When a boat's propeller strikes and excavates seagrass, it fragments the seagrass bed. This can severely restrict the movement of animals living in needed habitat, leaving barren areas where fish and other animals once flourished.

Responsible Boating

To reduce the chances of damaging seagrass communities, boaters should be familiar with local waters where they plan to boat, stay in deep water and marked channels, wear sunglasses with polarized lenses to read the water, and use up-to-date nautical charts. If you find yourself in water that is too shallow, you should immediately stop, turn your motor off, and trim your motor up to prevent further damage. Wait for high tide and carefully walk your vessel out to deeper water or call for help.

Learn more about responsible boating in Florida Keys National Marine Sanctuary