After a fairly uneventful first night dive to collect spawn from the endangered Elkhorn Coral (Acropora palmata), I was ready to go back in.  After searching colony after colony for any signs of spawning, my partner, Justin Zimmerman, and I were ready to go back. We envisioned everyone else coming back with full bottles of spawn and then having to endure the mockery of coming back with zilch. To be honest, I really had no idea what I was looking for.  I’ve seen the photos, I’ve seen the videos, but I’ve never personally witnessed a mass coral spawning.

The water was full of everything else but coral spawn. The most annoying was a huge worm that swam like a corkscrew and exploded when swatted at. After 45 minutes in the water I began to think that the worm's little offspring was starting to infiltrate my ears.  Flashbacks to Star Trek started to kind of freak me out. As we headed back to shore we passed over colony after colony of Elkhorn seemingly mocking us and our giant funnel collecting device.  As we approached the last of the colonies before the sand channel, Justin began to frantically point out an area on one colony, and there as plain as day were a small batch of pink egg bundles waiting to be released. We wouldn’t be going back with an empty bottle, and the mockery would have to wait till the next time I couldn’t back up my bragging (which usually doesn’t take long). 

"To be honest, I really had no idea what I was looking for.  I’ve seen the photos, I’ve seen the videos, but I’ve never personally witnessed a mass coral spawning." - Mitch Carl

Justin and I quickly positioned ourselves to collect the bundles.  The colony arose from the ocean floor to about five feet below the surface.  With nearly empty scuba bottles, a pretty good surge and holding onto a giant plastic funnel, keeping neutral buoyancy was almost laughable.  As we concentrated on not ramming into the coral, not floating to the surface, and not crashing into each other, the eggs began to release.  As I held our giant wind sail, Justin used his now patented hand waving motion (referred to in the scientific literature as “The Justin”) to coax the egg bundles into the funnel.  Once the bundles reached the vortex inside the funnel, they would spin in circles and never proceed into the bottle at the top of the funnel. It seemed like forever as we bobbed up and down frantically breathing, waving and in general, failing. Finally the small patch had given up all the bundles, and we shone our flashlight on the collection bottle. Seven. Seriously, seven egg bundles. 

We headed back to the beach, out of air, out of breath and with hardly anything to show for it.  As we were trudging up the beach, there was no one there to greet us. Everyone was packed up and heading back to the lab. We finally reached some others and asked how everyone else did.  Everyone else was shutout and didn’t see any spawning. We quickly went from zeros to heroes as we triumphantly held up our bottle consisting of our now prized seven bundles. I of course gloated and bragged, but thought to myself, “What did I get myself into?” This was hard work. I’m a professional aquarist who grows glorified rocks.  I’m not used to this kind of stuff.

The SECORE (SExual COral REproduction) group has now been back to collect Elkhorn coral spawn in Rincon, Puerto Rico for three years. After that first night we drastically changed our collection devices from those large cumbersome funnels, to light weight butterfly type nets made out of coat hangers and ladies slips (sometimes you gotta do what you gotta do).  We went from collecting those seven bundles, to collecting millions. We went from raising the larvae in labor intensive static bins, to open systems using Kreisel type devices to keep the larvae constantly moving. All this effort was made to establish what is now the largest captive collections of Elkhorn coral in public aquariums and to learn what it takes to take keep this coral alive and healthy. Since being banned from collection in the early 1980’s and now being an endangered species, not many aquarists have gotten to work with this coral.  Knowing what we know now, we can turn our sites to restoration efforts and to help this coral maintain its current population levels.

“What did I get myself into? This was hard work. I’m a professional aquarist who grows glorified rocks.  I’m not used to this kind of stuff." - Mitch Carl

All the effort of collecting and larval rearing wouldn’t have meant much, if we couldn’t raise these palmata larvae to coral colonies.  Not many people have tried to do this with this species, and those that have, have had pretty dismal success.  The founder of SECORE, Dr. Dirk Petersen, had worked with Acropora tenuis larvae and had successfully raised those, so he gave all of us as much advice as he could.  We would have to take the advice from Dirk, and through trial and error, learn the rest on our own.

The last three years I returned home to Nebraska and to the Omaha Zoo to try to raise these larvae.  The larvae were brought back home on the plane packed in one liter or two liter bottles.  Each liter of water held around 2000 free swimming larvae, all desperately looking for a nice place to settle down and start their life. 4000 larvae were placed into a half filled ten gallon tank with water that was adjusted to the same salinity and temperature as the ocean water these larvae were coming from.  The bottoms of these tanks were covered in specially made clay tiles that were designed to enhance settlement of the larvae.  These tiles had been conditioning in our grow out systems for a couple months now, and had gone through their diatom and algae phase and now were clean and starting to get covered in a nice coat of pink corallines.  A small heater kept the temperature around 84 degrees and two rigid airlines bubbled away and kept a nice circular circulation going in tank.  The lighting was provided by a dual strip light with normal fluorescent bulbs.

Figure 2: A setup at Omaha's Henry Doorly Zoo, Omaha, Nebraska for rearing young Acropora palmata colonies (photograph: Mitch Carl).

For the next four days or so the larvae are allowed to explore the clay tiles and pick a nice spot to live.  Some settle almost immediately, while others take the full four days to finally settle down.  Settlement averages around 10%, so right off the bat; you lose 90% of your corals.  During the settlement period the tanks are fed a mixture of food to help the newly settled corals until they incorporate the zooxanthellae into their tissues.  This food mixture was made up of anything I had in the refrigerator.   Not knowing exactly what these newly settled corals would be feeding on, I put everything I had together.  This mixture included oyster eggs, rotifers, Artemia nauplii, golden pearls, Cyclop-eeze and concentrated phytoplankton.  The phytoplankton was a nice liquid to mix everything into, and would perhaps feed all the little wee beasties in the grow out systems and that would in turn feed the Elkhorn corals.  Around the fifth day, the tiles are then moved to the grow out system, to hopefully grow into colonies. 

The grow out systems are a very simple set up. They consist of two stacked 6ftx3ftx18in fiberglass troughs with a 75gal sump. The Sequence Hammerhead pump pumps the water to six returns in each of the troughs. Each return has a valve for control and is outfitted with an eductor for increased water flow.  With this large pump and eductors, a high flow rate can be achieved. The sump is mainly empty except for an ASM protein skimmer and a phosphate reactor. A calcium reactor keeps the alkalinity and calcium levels at or near the levels needed. Lighting is provided by two 400 watt Sunmaster Cool deluxe bulbs positioned relatively close to the water surface.

Algae control is one of the main things to keep in control in order to be successful. The newly settled corals are only a millimeter or two in size when first settled. While so small, these corals are quickly overgrown by algae or cyanobacteria.  Nutrient levels are kept as low as possible, and an army of herbivores is employed to crop any algae that start to pop up.  Astrea snails and blue legged hermit crabs are the best at doing this and not harming the small corals in the process. 

Since Elkhorn coral parents do not pass on their zooxanthellae to their offspring, the newly settled corals need to have  zooxanthellae introduced to them.  If placed in a system with other corals, most will pick up the zooxanthellae they need from the water column.  Elkhorn is only known to use clade A3 zooxanthellae, and weren’t known to use other clades of symbiotic algae. Not having access to that particular clade of zooxanthellae, I used an Acropora yongei that has been in captivity since the early 80’s.  After introducing the coral to the system and some water pik’d tissue, I waited and hoped that they would take it up.  After about two weeks, the first few zooxanthellae cells could be seen in the outer tentacles of the corals.  A few weeks after that, each coral were a tiny brown dot on the surface of the tiles.

The next three months are a crucial stage. The corals grow from a millimeter sized speck, to a coral easily seen with the naked eye and sporting 5-10 polyps. The survival rate the first year was 33%, which has been improved to over 70% the last couple years. During this time the corals are fed once per day, and the tiles are kept as clean as can be.

"Hopefully with this program, the population of Elkhorn coral can be maintained, while others deal with the issues of pollution, habitat destruction, global warming, ocean acidification and overfishing." - Mitch Carl

The Omaha Zoo has raised over 3000 colonies of the endangered Elkhorn coral in the three years of the project. These corals are used for display and to supply other SECORE members for use in their displays. The corals have been shipped to 10 different zoos and aquariums in the U.S., and also overseas to Rotterdam Zoo, from where they were then sent to five other European institutes. This notoriously difficult coral to ship has a 99% shipping success rate, even in 60 hour transports from Omaha, Nebraska to Rotterdam, The Netherlands.

Figure 3: A three month old A. palmata colony. These offspring need to be kept clean of algae, to prevent them from dying off prematurely (photograph: Mitch Carl).

After showing our success in raising these corals in captivity, the SECORE group is now setting its sights on helping out the few colonies of Elkhorn coral remaining in the wild.  By taking our techniques that we’ve learned in closed systems, we would like to have facilities on the water, to raise these corals in open systems. Once at a certain size, these corals can then be returned to the reefs from where they were spawned. Hopefully with this program, the population of Elkhorn coral can be maintained, while others deal with the issues of pollution, habitat destruction, global warming, ocean acidification and overfishing. Whew, looks like we have some work to do!