Rehoboth Bay Ulva Identification Project--Finding the Green Under the Sea

Author: Kimberly Cole
Organization: Delaware Coastal Programs

89 Kings Highway
Dover, DE 19901
USA

Phone: 302 739 3451
Fax: 302 739 2048
kcole@state.de.us

Every year more boaters, fishers, and other recreational users place a larger strain on the limited space and natural resources of Rehoboth Bay. At the same time, regional development, agricultural, and industrial activities impact the bay with increased runoff of chemicals and nutrients. A particular genus of macroalgae known as ulva grows in these waters naturally, but has become an increasing problem with greater biomass due to changing water chemistry. Ulva management in Rehoboth Bay has challenged government agencies and local organizations for a number of years. Increases in ulva biomass can lead to an increase in dead organic matter and to reduced dissolved oxygen levels in the bay. Lower dissolved oxygen can have a significant impact on the local aquatic ecology. Increased dead organic loads can cause foul odors and create hazards for boats.

Government agencies have funded ulva collection operations to reduce the impacts of the macroalgae on the ecosystem and recreational opportunities in Rehoboth Bay. Unfortunately, little data exists on the spatial extent of ulva in Rehoboth Bay or the effectiveness of the collection operations. It seems imperative that the agencies funding the operations identify the present extent of ulva in the bay and periodically update that information to determine the effectiveness of their efforts.

This paper describes how the Delaware Coastal Programs (DCP) identified the spatial extent of macroalgae, including Ulva, in Rehoboth Bay in the late spring of 1999. DCP used aerial photography, image processing software, a GIS, and a limited field survey to do this work, which resulted in the identification of 1.88 square kilometers of macroalgae in all but the deepest parts of the bay. The project results illustrate the large potential remotely sensed imagery has in resource management work.