Many hard corals are broadcast spawners—meaning they broadcast large numbers of eggs and sperm into the water.
This typically happens on a certain date, at a certain time, in an event known as synchronized coral spawning. The eggs and the sperm come together in the water to form coral larvae. The larvae are initially attracted to light, so they swim to the surface where they can be swept along with ocean currents. They can travel for days, or even weeks, before they find a reef to settle upon.
The larvae look for hard, rock-like structures on which to settle, and research has shown that they prefer healthy reefs with favorable conditions. Once they settle, the larvae turn into polyps and form coral colonies that continue to grow.
Corals will only reproduce if they are healthy. If they are bombarded by stressors like poor water quality, a marine heatwave, or overfishing, their energy will be directed at survival instead of reproduction. To ensure the future of coral reefs, we must keep corals healthy so they continue to reproduce.