This indicator represents the presence of seagrass in the Atlantic Ocean and Gulf of Mexico. It originates from the National Oceanic and Atmospheric Administration’s Marine Cadastre.
Reason for Selection
Seagrasses provide food and habitat for a range of marine and estuarine wildlife, including fish, sea turtles, shrimp, crabs, oysters, and more. They also produce oxygen, filter water, control erosion, and buffer storms. Seagrasses serve as an important indicator of the overall health of coastal ecosystems because they are sensitive to water quality and require sufficiently clear water for sunlight to penetrate (NPS 2021, NOAA 2021, NWF 2021).
Input Data
Mapping Steps
- Convert the polygons from the Marine Cadastre seagrasses layer to raster, snapping to the 2022 Southeast Blueprint extent.
- The data were originally classified into various classes based on the estimated percent cover. Because these classes were not applied consistently across different states, collapse these categories into a single category of seagrass presence.
- Clip to the ‘Atlantic Coastal Plain’, ‘Central Gulf Coastal Plain’, ‘East Gulf Coastal Plain’, ‘Florida Peninsula’, ‘Gulf Coastal Prairies’, ‘Mid East Gulf Coastal Plain’, and ‘Mississippi Alluvial Valley’ subregions, where this indicator was used in Zonation. The source data also covers a few pixels in the Piedmont subregion. We didn’t include data in that subregion due to an oversight in which indicators were used for the Blueprint priorities in that subregion.
- As a final step, clip to the spatial extent of Base Blueprint 2022.
Note: For more details on the mapping steps, code used to create this layer is available in the Southeast Blueprint 2022 Data Download under BlueprintInputs > BaseBlueprint2022 > 6_Code.
Final Indicator Values
Indicator values are assigned as follows:
Known Issues
- Because the data used in this indicator were opportunistically collected based on available state data, this indicator underestimates seagrass presence in some areas and misses some known seagrass locations (e.g., the north shore of Lake Ponchartrain in LA).
- Due to the variety of data sources combined in this indicator, there is significant variation across the Southeast in how rigorously seagrass data is validated. Water turbidity can also influence the quality of validation. NOAA characterizes the level of validation in NC as good, the east coast of FL (particularly the St. John’s River Water Management District) as excellent, the west coast of FL (particularly the Southwest Florida Water Management District) as good, the Big Bend of FL as more challenging due to turbidity, the area immediately surrounding the FL Keys as good, other parts of Florida Bay as challenging due to turbidity, Mobile Bay in AL as good, LA as less consistent, Matagorda in TX as somewhat good, and Laguna Madre in TX as excellent. This indicator is more reliable in areas with strong validation.
- Similarly, variation in the minimum mapping unit used by each data provider causes differences in the size of seagrass patches captured in different parts of the Southeast. For example, some surveys map patches as small as 20 m2, while others do not map patches smaller than 1 acre. As a result, this indicator may underpredict small seagrass patches in areas where survey efforts used a coarse minimum mapping unit.
- In estuarine areas near river deltas (e.g., portions of Mobile Bay in AL), this indicator captures freshwater species of submerged aquatic vegetation in addition to true seagrass.
- While the indicator source data extends into a few pixels in the Piedmont, those pixels are not included in the indicator because they were not used in the Blueprint priorities for that subregion. We didn’t include those pixels due to an oversight in which indicators were used for the Blueprint priorities in the Piedmont subregion. Those pixels are just up and downstream of where I-95 crosses the Occoquan River in Virginia.
Disclaimer: Comparing with Older Indicator Versions
There are numerous problems with using Southeast Blueprint indicators for change analysis. Please consult Blueprint staff if you would like to do this (email hilary_morris@fws.gov).
Literature Cited
National Park Service. Seagrass Meadows. Accessed December 22, 2021. [https://www.nps.gov/subjects/oceans/seagrass-meadows.htm].
NOAA Office for Coastal Management, 2021: Seagrasses. NOAA National Centers for Environmental Information. [https://www.fisheries.noaa.gov/inport/item/56960].
The National Wildlife Federation. Seagrasses. Accessed December 22, 2021. [https://www.nwf.org/Educational-Resources/Wildlife-Guide/Plants-and-Fungi/Seagrasses].
