Left: Healthy seagrass. Right: Sparse seagrass.


SeagrassSeagrass secures the lagoon bottom, reduces erosion, and is an important primary producer for the ecosystem, providing habitat and food for many types of lagoon life. The seagrass scores below clearly show the recent seagrass losses throughout the lagoon, even in the Mosquito Lagoon South, where historically seagrass has thrived.

There are several reasons for these losses. Seagrass needs saltwater and high levels of light to survive. Heavy freshwater drainage into the lagoon negatively impacts seagrass, especially if salinity drops below 10 ppt for long periods of time. Drainage canals and stormwater also bring sediment into the lagoon, which can smother seagrass and prevent light from reaching the bottom. Too much nitrogen and phosphorus feed excessive algae and phytoplankton which reduce the amount of light reaching seagrass on the bottom. Herbicides and poor boating practices can also destroy seagrass beds. Seagrass does not grow in the North Mosquito Lagoon due to natural conditions (NA).

Seagrass (Habitat Quality) Scores

Seagrass Targets

Seagrass transect length targets were established by the SJRWMD for each individual site. The maximum length assigned to each transect is the maximum extent ever observed in the cumulative aerial mapping effort over the 1943–1999 years.

The regulatory (TMDL) target length for each transect allows for a deduction in 10% of the maximum length (an allowance for potential error, difficulty in returning to historical pre-development conditions, etc.).

Even though there are 100 established and monitored transects, three of these transects have no available TMDL targets and data from these three sites were not used in the IRL health assessment.

Seagrass Offsets

Seagrass Offset Classes
Seagrass offset classes based on the data distribution

Percent offsets from the established TMDL target were calculated for all 97 transects from 1994–2016. Results are reported in percent offsets from the established targets summarized by year.

The frequency distribution of the data, as shown in the figure, provided guidance to create the classes to be used in the seagrass transect offsets. Classes in the green ranges met or exceed the transect length targets, while yellow-red shades indicate values below the established targets.

To learn more about how scores were calculated, to see the targets for each region, and to read other sciencey stuff, check out the 2020 Health Assessment Methodology Report.

Seagrass offsets
Histogram of seagrass transect length percent offsets.