Star coral broadcasts eggs and sperm into the water column in mass spawning events, which occur in the Caribbean a few days after the full moon in August. Fertilization occurs quickly when the larvae reach the surface, and then they drift for as much as two weeks before settling on the hard surfaces where they will spend the rest of their lives. Free-swimming larvae are especially vulnerable to ecological changes because they have limited energetic reserves. Scientifically, studying coral larvae has distinct advantages over documenting the response of adult coral to thermal stress.
Logistically, however, studying larvae scientifically is not so easy. "We have to find suitable reefs with known, and therefore roughly predictable, spawning habits," explains Baums. "These reefs have to be close enough to shore that we can get into the water and out to the corals within the first hour of spawning, which always happens at night. When we see that the corals are about to spawn, we set up nets over coral colonies to catch the fragile gametes before they can reach the surface, then we rush back to shore to set up controlled matings and get the young corals back into aquarium tanks before they die." Once spawning started, the scientists worked nearly around the clock for a few days. If they failed to capture enough larvae, or if the larvae died in captivity, the experiment could not be repeated until the following year.
The team successfully collected spawn from two populations of mountainous star coral, one off Key Largo, Florida, and one off Puerto Morales, Mexico. Keeping spawn from the two sites separate, the scientists allowed fertilization to occur in captivity, then they raised the embryos at different temperatures. They recorded the developmental stage and gene expression in the embryos between 12 and 48-to-50.5 hours after fertilization, comparing those embryos raised at normal temperatures with those raised at tempe
|Contact: Barbara K. Kennedy|