Quantifying temporal change in seagrass areal coverage: the use of GIS and low resolution aerial photography

Geographical Information Systems and the availability of digital data acquired through governmental agencies provide an opportunity to quantify and detect spatial patterns at large (km(2)) scales. These usually low resolution maps may be useful as inventory tools and, as such, aid in management decisions. This work addresses the suitability of using aerial photographs interpreted at a resolution of 1:24000 when examining temporal change in seagrass cover in Tampa Bay, FL, a subtropical estuary. Temporal change in seagrass areal extent based on two categories of seagrass, i.e. patchy and continuous, was examined. Seagrass cover in Tampa Bay was found to have increased 87% (5750-10759 ha) during the decade of 1982-1992. However, this recovery of seagrass areal extent is only 35% of the areal extent recorded in 1879. Most expansion of seagrass areal extent was found in areas categorized as having continuous cover when compared to patchy cover, suggesting that fragmentation of the seagrass habitat was not occurring. (C) 1997 Elsevier Science B.V.