Coral reefs are fraught with danger for herbivores such as damselfish and tangs. Venturing out from the safety of the reef’s colorful cracks and crevices to feed means risking being devoured by predators that patrol the warm waters. As a result, the small fish tend to stay close to the reef when grazing—leaving “halos” of bare sand stripped clean of seaweed around the reef. Using publicly available satellite images from Google Earth, researchers have for the first time observed these halos from space
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