by Evan Culbertson, Aquarist
Northern star coral, Astrangia poculata, is a large polyp stony coral found off the eastern coast of the United States. Colonies are form round clumps with clear, orange or light pink cup-shaped polyps. The colonies are typically found on wrecks and rocks in water deeper than 30 feet. These corals can withstand temperature ranges from 33 to over 75F. It is highly affected by water temperature, growing faster in warmer water than cooler water. Northern star corals are broadcast spawners meaning during reproduction, they release eggs and sperm into the water column where the eggs are fertilized. Fertilized eggs then develop into larvae, called planulae, measuring less than a grain of rice in size. Once the larvae settle onto hard surfaces, they will develop into a single polyp which will begin a new coral colony.
Keeping corals in human care is not a simple task and takes skill and a good deal of mechanical technology. The Virginia Aquarium is equipped to maintain both tropical and local corals on exhibit for guests to see and enjoy. Each coral aquarium is set up to replicate the environment from which the corals come from. Lighting, water quality, water temperature and even water movement is controlled to give the corals the best chance for survival and hopefully to reproduce.(Being able to have the corals I care for reproduce is the biggest compliment for me. It tells me I'm doing a great job!)
Recently, I made a dive trip out to a local underwater reef structure where star corals can be found. I collected a few specimens and brought them back to the Aquarium. I placed them in our Stoney Beauties Exhibit along with other star corals that had been collected in previous years. A few weeks later, I was excited to observe the coral colonies in the exhibit spawning. During the spawning event, staff took pictures and I was amazed at the effort of the corals. I took careful notes on what could have triggered the spawning so I could learn to anticipate it in the future. Shortly after the spawning took place, I removed a sample of water and was able to observe, through a microscope, sperm fertilizing eggs. It was very exciting! New corals created right under my microscope!
As we learn more and more about this species we will be able to share information to other institutions that keep them and further our abilities to reproduce them in our care. I'm looking forward to the next big event!