Two corals during an ocean heatwave on the Florida reef tract

Here are shown two mustard hill corals (Porites astreoides) growing side-by-side, one (right) that has succumbed to heat stress and lost its symbiotic algae, and one (left) that has not. The heterogeneity in stress response observed in corals of the same species on the same reef gives hope that enough genetic diversity remains for natural selection to act upon, and that humans could assist by actively restoring reefs with the descendants of colonies that survive ocean heatwaves, coral-disease outbreaks, and other reef catastrophes. This photograph was taken during USGS research in the Florida Keys National Marine Sanctuary at Hen and Chickens Reef Sanctuary Preservation Area under scientific collection permit number FKNMS-2013-024-A2.