SAPELO ISLAND — Scientists at the University of Georgia’s Marine Institute at Sapelo Island have found that the amount of vegetation along the Georgia coast has declined significantly in the last 30 years, spurring concerns about the overall health of marshland ecosystems in the area. Using data collected by NASA’s Landsat TM 5 satellite, which provided 28 years of nearly continuous images of the Earth’s surface between 1984 and 2011, the researchers found that the amount of marsh plant biomass had dropped 35 percent. They published their findings recently in the journal Remote Sensing.