The traditional method for creating seagrass maps is being improved, and the NOAA Coastal Services Center is at the forefront of this effort. The Center's Coastal Change Analysis Program (C-CAP) is combining established and new technologies to increase the quality of seagrass maps and their utility to coastal managers. This benthic mapping program utilizes equipment and knowledge that might not otherwise be available to most state coastal resource management programs, and the resulting maps are more accurate and take less time to produce.
Thus far the Center has assisted in the production of seagrass maps for all of coastal Massachusetts, North Carolina, and Willapa Bay, Washington. Projects are nearing completion in Indian River and Florida Bay, Florida, and Hudson River, New York. Projects are planned for Puget Sound, Washington; northern California; southwest Florida; and coastal Oregon. The goal is to provide a seagrass base map for the nation available via the Internet. Coastal managers will use this information not only in the permitting and planning process, but also as a tool to measure the health of this resource as maps are compared from one year to the next.
Since much of the nation's nearshore bottomlands are covered with mud or sand, seagrass meadows can be viewed as an oasis of sorts. These underwater fields provide food and shelter for a variety of marine animals. Their environmental impact is also great, as this vegetation reduces sediment re-suspension, filters pollutants, and decreases wave activity.
Improper shellfish harvesting, water quality degradation, shoreline construction, dredging, and even recreational boating are just a few of the activities that can destroy this resource. Negative impacts can be minimized with proper management, but it is difficult to manage something when its extent or even its presence is not apparent.
In the past seagrass maps were prepared from photos and personal observation. A cartographer would take this information and manually transfer it onto a base map. While this approach identified most seagrass beds, the positional uncertainty of the resulting maps was so great that they could not be used in the environmental permitting process.
The new map-making process produces digital data with high spatial precision with much less manual labor. The spatial accuracy of the data is between 1 and 5 meters, a significant improvement over previous map-making methods. This is accomplished using analytical photogrammetric methods using a stereoplotter.
Photogrammetry traditionally is used by specialized surveying firms to produce property maps and topographic charts. The techniques are basically the same for mapping seagrasses. Using a stereoplotter and aerial photographs acquired under stringent environmental conditions, a "stereo-graphic model" is created. This mathematical model incorporates the distortion/displacement qualities of the camera, the position of the aircraft at the time of the photography, and the terrain of the earth's surface. With this model and the measurements taken from the photos and from site visits, visible seagrass meadows are mapped directly into a precise digital format using compilation software. The resulting polygon data can then be brought directly into geographic information system software for analysis or comparison with other data.
For more information on the seagrass mapping project, contact Mark Finkbeiner at the NOAA Coastal Services Center. His phone number is (843) 740-1264; the e-mail address is Mark.Finkbeiner@noaa.gov.
