DOCUMENTING DECADAL SPATIAL CHANGES IN SEAGRASS AND ACROPORA PALMATA COVER BY AERIAL PHOTOGRAPHY ANALYSIS IN VIEQUES, PUERTO RICO: 1937-2000

摘要

Aerial photographs from 1937-2000 of Bahia Salina del Sur on Vieques, Puerto Rico were analyzed to detect and describe spatial changes in the areal cover of sea-grass beds in Bahia Salina del Sur. The images were pre-processed to minimize noise and unsupervised classification was used to detect areas colonized by seagrass. The number of individual seagrass patches, direction, and characteristic of growth were quantified and described. Seagrass coverage increased by 85.8% over the 64-yr period and this increase was best described by a 2nd order polynomial function (r~2 = 0.91). Between 1937 and 2000, the spatial expression of the seagrass patchiness went through discrete episodes characterized by expansion in the number and spatial extent of small patches followed by an increase in patch size and agglomeration of small patches to form large homogeneous areas. Patch growth was limited only by proximity to boundaries (i.e., coastline and reef structures) and a fluctuating physical environment. This study suggests that the overall increase in seagrass cover was linked to the synergy of hurricane impacts, decrease in grazers, and the protective geomorphology of Bahia Salina del Sur. Decreases in areal cover only occurred in concert with known anthropogenic impacts.