Mangrove ecosystem boundary interpretation and detection of areal changes on Marco Island, Florida : application of digital image processing and remote sensing techniques

South Florida mangrove ecosystems In the Marco Island area were analyzed for boundary interpretation and extent of areal change in acreage, over time. Medium and high altitude black and white and color infrared aerial photographic imagery were employed for mapping mangrove ecosystems and associated ecosystems. Mapped locations of mangrove ecosystem boundaries were entered onto a computer digitized base map to produce statistical estimates of total acreage, ecosystem acreage ratios and ecosystem areal change from 1952 through 1984. Ratios of the extent and distribution of Rhizophora (fringe and riverine red), Avicennia (black basin), mixed (black and red) mangrove ecosystems, shifted, over time. From 1952 through 1984, total mangrove ecosystem acreage in the Marco Island area declined from 11,285 acres to 8,577 acres. Other ecosystems, primarily upland, declined from 3,506 acres, to 845 acres in 1984. Decline in mangrove ecosystems was characterized as follows: from 1952 to 1984 fringe mangrove ecosystems declined from 1,390 acres to 1,184 acres; riverine ecosystems, (890 acres to 553 acres); black mangrove ecosystems, (4,250 acres to 2,344 acres); and mixed mangrove ecosystems, (4,755 acres to 4,495 acres.) Causes of this decrease in mangrove and other ecosystems, were primarily related to development of Marco Island into residential waterfront property, beginning in 1962.

Comparisons of natural (hurricane) and man-induced (waterfront development) disturbances over thirty-two years are based upon the aerial photography and digitized maps. Man-induced disturbances of mangrove ecosystems are of relatively greater intensity and more permanent than are natural disturbances. Acute man-induced disturbances include dredge and fill development activities. Chronic impacts resulting in altered drainage or impoundment of mangrove ecosystems, are caused by canalization, road building and residential development.

Results of this mapping project were based upon detailed digital maps suitable for fine scale planning and resource management decisions. One criterion for successful classification of mangrove ecosystems is whether a remote sensing technology meets a defined minimum accuracy. Accurate representations of ecosystems depend upon matching a remote sensing technique with the areal scale of the ecosystems. Based upon field validations, results of this study have an accuracy of 98% for mapping the boundaries and areal extent of mangrove ecosystems.