In our last post, Aquarium Aquarist Steven Yong gave us a brief tour of the world of coral reproduction—in preparation for this post, describing his recent trip to Curaçao with the SECORE (SExual COral REproduction) Foundation:
The elkhorn coral, Acropora palmata, is one of the most important reef-building coral species in the Atlantic and was once one of the most abundant in the Florida Keys and Caribbean. Unfortunately, an estimated 90–95 percent of the population has been lost since the 1980s due to disease, bleaching, climate change and human influence. This led the species to be listed as Threatened under the Endangered Species Act (ESA) and Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species™.
The SECORE (SExual COral REproduction) Foundation has been organizing field and lab workshops for 10 years. They take techniques developed by aquarists and scientists for reproducing corals and teach and apply them for coral conservation and research. Workshops have been held in Curaçao, Puerto Rico, Guam, Singapore, Mexico and the Philippines. I’ve been involved with SECORE since 2010, when I was able to attend a lab workshop hosted by the Henry Doorly Zoo and Aquarium in Omaha, NE. I was fortunate enough to be invited to attend a coral reproduction and reef restoration workshop in Puerto Morelos, Mexico in August 2014. There, for the first time, I was able to gain hands-on experience working with elkhorn coral and grooved brain coral, Diploria labyrinthiformis. This year, I was invited to work in Curaçao for the mass spawning of the same two species.
I arrived in Willemstad, the capital of Curaçao, on July 31. I would be working with three other aquarists from the Pittsburgh Zoo and PPG Aquarium, Omaha’s Henry Doorly Zoo and Aquarium and Columbus Zoo and Aquarium, as well as scientists at the Caribbean Research & Management of Biodiversity (CARMABI) biological research station. We would be diving every night for two weeks: first for the elkhorn coral spawn, which typically takes place three to eight nights after the full moon from nine to ten o’clock at night; and second for the grooved brain coral spawn, which takes place nine to twelve nights after the full moon from five to six o’clock in the evening.
During the day, we would be preparing to care for the coral larvae by setting up special nurseries and cleaning the special tiles on which the baby corals will eventually settle. At night we monitored all the coral colonies for signs of “setting,” when gamete bundles are visible in the coral polyps before they are released into the water.
Coming from our local Puget Sound waters, which are usually around 53°F in August, the 78° Curaçao reefs felt almost like a soothing bath. The locals found this temperature unseasonably cool, about five degrees below average for this time of year. The elkhorn coral must have felt the same, as none of the colonies spawned. Though we missed our main objective, we did still enjoy several nights of night diving with calm ocean conditions and saw some neat animals such as arrow crabs, reef octopuses and sleeping parrotfish.
Fortunately, some corals are a bit more forgiving when it comes to spawning cues. The grooved brain coral actually spawns twice a year: once in the late spring as again in late summer. We hoped that this flexibility would allow the corals to still spawn, even with the cooler temperatures. Since this species spawns just before sunset, it releases its bundles very quickly with little to no setting. In order to know which corals will spawn, we actually rely on fish behavior. Two local butterflyfish species; the foureye butterfly (Chaetodon capistratus) and banded butterfly (Chaetodon striatus); are able to sense the impending spawn and frantically pick at the coral in anticipation of the highly nutritious gametes. When we saw groups of two to three dozen fish all crowding a particular coral, we knew to tent it with a net. Soon after, the coral released its bundles and they floated up the net and into our collection vial.
Over three nights we collected about 20mL of gametes from five different coral colonies. This amounts to about 153,000 eggs. With a lab fertilization rate of approximately 80 percent, that means we ended up with 123,000 coral larvae!
During this this time, the larvae are very delicate. They are very sensitive to water quality and will die or develop improperly if handled too roughly. So we spent the following days very carefully removing any dead and dying larvae, performing water changes on their holding containers, and tracking cellular development under the microscope.
Once the larvae fully developed to planula and began to swim around looking for a place to settle, we placed our prepared tiles into their holding containers. We also conducted an experiment and exposed the planula to different species of bacteria to see if we could identify specific ones that would stimulate settlement.
Once settled into a primary polyp, the settlement tiles will be moved to flow-through tanks in the CARMABI wet lab, into ocean nurseries for grow out, or shipped to participating institutions for exhibit purposes. Hopefully I’ll get to see the juvenile brain corals if I’m able to participate in the workshop next year!
Interested in coral? Read our coral fact sheet, then come learn more at the Seattle Aquarium, where you can view tropical corals as well as species that make their homes in our local waters!