DISTRIBUTION AND CONDITION OF INTERTIDAL EASTERN OYSTER (CRASSOSTREA VIRGINICA) REEFS IN APALACHICOLA BAY FLORIDA BASED ON HIGH-RESOLUTION SATELLITE IMAGERY

摘要

The eastern oyster Crassostrea virginica is an important component of the ecology of Apalachicola Bay, Florida, and the economy of the region. Although oyster reefs in the Bay occur in both tidal zones, subtidal reefs have received the most attention because they support most of the oyster fishery. The present study provides new information on the distribution, condition, and ecology of the intertidal reefs, and assessed the general utility of high-resolution satellite imagery for routine monitoring of the extent and condition of intertidal oysters. Using online, freely available color imagery and manual interpretation, a total of 782 individual reefs ranging in size from similar to 3 m(2) to 3.9 ha (= 9.7 acres) and covering a total of 94 ha (233 ac) of bottom area were mapped. Field inspection and sampling of 100 individual intertidal reefs on November 12-16. 2016, confirmed wide differences in the number and areal coverage of reefs in the three major geographic regions in the Bay: 433 reefs covering a total of 56 ha (139 acres) in the western area (St. Vincent Sound); 113 reefs covering 8 ha (19 acres) in the central area; and 236 reefs covering 30 ha (75 acres) in the eastern area (St. George Sound). Most reefs in the western portion of the bay consisted of recently dead ("box") oysters in all size classes, suggesting a recent massive mortality event. Mean densities (all size classes combined) of live oysters in the central and eastern areas were 42.9/m(2) (+/- 7.39; 1 SE) and 99.3/m(2) (+/- 13.22; 1 SE), respectively, with an overall mean shell height of 23.6 nun. Size-frequency histograms indicated only two year classes of live oysters, and the largest oyster collected was 84 mm. Although detailed quantitative comparisons with subtidal reefs were not possible, data from the present study suggest that intertidal reefs cover much less bottom area of the bay, but may contain much higher live oyster densities. The present study also demonstrated the use of high-resolution satellite imagery for mapping reefs as small as a few square meters in surface area, and the potential for estimating relative reef condition measured by live oyster density.