As waters warm, researchers keep a wary eye on reef life cycles.
The divers’ lights pierce the night-time darkness 18 metres below the rolling waves of the Gulf of Mexico. As the beams pan across a coral reef, they illuminate whitish spheres nestled in the pale yellow ridges of female coral mounds. Triggered by some unknown signal, these eggs start to rise, a few at a time, like little helium balloons. Male corals nearby begin to release sperm, which resembles drifting smoke, or milk stirred into black coffee. Dispersed by currents, the gametes gradually ascend towards a reproductive rendezvous at the surface.
“It’s a marvellous sight of nature that most people will never see,” says Larry McKinney, director of the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, Texas. McKinney was part of a team of scientists who spent four nights last week scuba-diving and observing the annual coral spawning at the Flower Garden Banks National Marine Sanctuary, located in the Gulf about 175 kilometres southeast of Galveston, Texas.
For McKinney, the event is not only a natural wonder, but also a key indicator of reef health. “Spawning events are sort of the canary in the coal mine for reefs,” he says. Enviornmental stressors that can affect spawning include overfishing and coastal development and — to a degree that has become an increasing concern in the Gulf — water temperature.