CRMC funds eelgrass mapping effort

July 12, 2016, WAKEFIELD – The R.I. Coastal Resources Management Council (CRMC) recently provided funding to acquire aerial photographs of the southern coastal ponds and Narragansett Bay, which will allow for a multitude of uses including the mapping of submerged aquatic vegetation, or SAV.

The CRMC partnered with the University of Rhode Island’s Environmental Data Center (EDC) and the U.S. Geologic Survey (USGS) for the overflights, which were completed by contractor Quantum Spatial on June 26th. The EDC will be working with the resulting images in the coming months to create maps of SAV in the areas photographed.

The most common type of SAV in Rhode Island is eelgrass—a rooted, flowering plant that grows beneath the water’s surface in small beds or larger meadows. Eelgrass serves many ecological functions, including supporting the marine food web and providing important habitat for many species of fish and invertebrates. Fish such as tautog lay their eggs on the surface of eelgrass leaves. Shellfish such as bay scallops, quahogs, blue crabs and lobsters can be found in eelgrass beds and some species of waterfowl feed on eelgrass.

SAV beds can be degraded by poor water quality and algal blooms, or physically damaged by human activity like shallow-water boating, dredging and filling associated with maintaining navigation channels and basins, and the construction of in-water structures such as docks, which can shade SAV. For these reasons the CRMC has created policies and regulations within its regulatory program to protect SAV by limiting or prohibiting certain activities in areas where SAV is present. Having accurate maps of where SAV is growing in Rhode Island’s coastal waters is crucial to its protection.
The CRMC is part of the RI Eelgrass Mapping Task Force, which is led by the URI EDC, the Narragansett Bay National Estuarine Research Reserve (NBNERR) and Save The Bay. This group has coordinated previous eelgrass mapping efforts and developed a long-term plan for mapping and monitoring SAV throughout the state’s coastal waters. With previous mapping done in 2007, 2012 and now 2016, the EDC will be able to look at trends to determine where and to what degree SAV beds are expanding or shrinking in size throughout Narragansett Bay and the coastal ponds. 

Unlike typical aerial imagery taken when there are no leaves on the trees, the eelgrass images are taken during the growing season, and thus the uses for them are widespread. In addition to tracking eelgrass beds and growth patterns, the CRMC will also be able to use the images for general planning and permitting purposes, including aquaculture, dredging, marinas and shoreline analysis. The NBNERR, with funding from CRMC, has used the images to map coastal wetland vegetation with the help of software that can identify subtle differences in vegetation types. As with eelgrass, this type of analysis can be done on images from different years to track trends over time.

“This kind of long-term observation and monitoring is very important, especially as we try to assess rapid ecosystem shifts resulting from climate change and sea level rise,” said CRMC policy analyst Caitlin Chaffee. “It allows us to document what changes are occurring and helps us determine what the management response should be.”

With this year’s images acquired and mapping begun, the CRMC will now aid the EDC in its efforts to “ground-truth” the eelgrass maps. This involves getting out on the water in boats and confirming the presence or absence of eelgrass with underwater cameras and GPS equipment. The result will be an accurate and reliable set of maps that will greatly aid in coastal decision-making.