In the 1980s, the diversity of plant species on the backshore and primary dunes was declining. Since the study, rentals of the 4-wheel drive vehicles have been discontinued. In the lower Laguna Madre area, South Padre Island's bayside is a flat, sandy area a few miles wide that looks like a desert covered with a carpet of blue-green algae. Wading birds like the snowy plover, the piping plover, and reddish egret dot the landscape as they feed on the algae. But more than just birds depend on these algae that convert nitrogen from the air into nitrates.
High tides flush much of the nitrates out into the bay, providing nutrients for aquatic life.
This system provides more detailed resolution for interpreting satellite imagery. Everitt and his colleagues have also been using multispectral digital imagery to characterize marshes near the mouth of the Rio Grande. Salt, brackish, and freshwater marshes each have differing patterns of vegetation, though one vegetation zone may be only centimeters higher above sea level than another. For example, digital video images show bright-pink to red shades in the lower zone of brackish marshes, where maritime saltwort prevails and the mineral salt concentration is less than seawater's 35 parts per thousand. In the next zone, shoregrass appears dark brown.