Monday, July 9, 2007

Coral Spawning

I finally witnessed something I've always wanted to see, which is the once-yearly coral spawning event. I had seen videos of this before but had never witnessed it in person. I think once while I was on the great barrier reef I saw the "slick" of coral eggs on the water from land, but I've always wanted to see it up close and in person. Here's the video I shot of this amazing event which took place on Friday night, July 6th, 2007:

Getting to witness this event wasn't as easy as one might think. The corals usually spawn 6 days after the full moon in July. We weren't sure of the exact day, since they can always spawn a day early or late. Since the full moon was on June 30th, there was also a chance they were not going to go until after the full moon at the end of July. On my first attempt I went out to LauLau Bay on July 5th and met up with John, Angleo, Bev, Brie, and EJ. We snorkeled out the main dive cut and explored around for over an hour. It was a beautiful night-snorkel, and the water was nice and calm, but no spawning!

On my second attempt, I was lucky to be in the company of a PhD coral biologist, Dr. Peter Houk ("Dr. Coral") who taught me how to spot the spawning corals. We left in his small boat from Smiling Cove marina at 7pm, since the corals usually spawn between sunset and the moonrise. So friends Pete, Fran, Michelle and I headed out to a spot right next to the Dimple dive site. We saw a spectacular sunset on the way out and the water was as smooth as glass, with Pete guiding us with the GPS course he had plotted and downloaded onto his handheld GPS.

There was a fisherman moored to the Dimple dive buoy, so we picked a spot a little closer to the reef crest and found a nice sandy patch to drop our anchor on. As we were getting geared up, Pete started seeing coral eggs on the surface of the water. So Pete and Fran jumped right in and headed for the shallow water along the reef crest while Michelle and I took a little longer getting our dive gear sorted out in the dark. Unfortunately I experienced some user-induced issues with my camera which rendered it unusable, but Michelle was kind enough to let me borrow hers, since she had two underwater cameras ready to go. (Thank you!) While we were in the water sorting out the cameras, I noticed a "fire worm" or "bristle worm" swimming through the dark water column heading straight for Michelle's light, and it didn't look like it had any plans to stop! (Eurythoe complanata?) I warned her and she tried to get out of the way, but she didn't do a very good job. Luckily it didn't sting her as it brushed against her kicking legs as she swam frantically to avoid it. (They don't call them fire worms for nothing!) Here's a picture I took of one on a reef in the Virgin Islands. You can see the venomous bristles exposed. I've never seen on on the reef here, so I was excited to see my first one in Saipan.

As I made it over to the spot where Pete and Fran were, I could see a lot of eggs in the water column and on the surface, but I couldn't see the actual corals that were releasing the eggs. Finally, Pete flashed his light at me and pointed out a colony of Acropora coral that was loaded with eggs.

It hadn't begun to spawn yet, but it was about to. The trick is to find a coral that is full of the pink eggs and you just have to sit there and wait it out. In my case I sat with my face in this coral for over 30 minutes before it started releasing its tiny eggs. It was sure worth the wait, though! Having my dive gear on made it very easy to sit and watch, (while taking pictures, of course!) even though we were only in about 5 feet of water. When the coral started to release its eggs, Pete came over and used my octopus (my 2nd regulator) to breathe off of as we watched the show. It started slowly at first, just releasing one or two eggs, but then after a few minutes it really started to pump the eggs out. We managed to catch a few other colonies that were in the act of spawning as we made our way back to the boat.

As we relaxed in the boat and enjoyed some great food that Fran had brought along, we saw another neat show, this time it was all the plankton and other small sea critters that our lights were attracting. I started just looking overboard shining my light on the thousands of little pink and red eggs on the surface of the water, but then I started noticing a whole world of little things that were attracted by my light. We saw tiny worms, shrimp-like stomatapods feeding on the coral eggs, and even a tiny cubozoa (box) jellyfish! Coral eggs are actually a egg and sperm combination packet, and after floating on the surface for a while and mixing with all the other sperm/egg packets that were released, they break apart so the eggs can be fertilized by sperm from another colony. As we decided to pull up anchor and head back home, we could start to make out a thin layer of an oil-like substance on the surface of the water which was actually the sperm from the packets that had broken apart.

The ride home was beautiful, as the water was still like glass. We all had our lights shining ahead into the water watching fish jump, bioluminescing critters shine, and the reflection of the stars on the water.

Now, if I could just witness those turtles hatching... !


scubatripp said...

Wow, I’m excited for you and very jealous at the same time!
I had thought this event was going to happen at the end of July!
I missed the boat literally!
Very informative and interesting posts Greg. I look forward to reading more and doing a dive with you one of these days!
I’ve linked you up on my blog, and written a little bit about your entries so the one or two that read mine may drop by yours. If you wouldn’t mind doing the same I’d appreciate it ( and if you have a room for it another to the Saipan DVD. (

Bev said...

You're so lucky to have seen it. Thanks for sharing the video clip for the rest of us to see!

Harry Blalock said...

"User induced camera problems"? Well that's an interesting way of putting it.

edson.limes said...


Is that the staghorn (Acropora) spawning in the video clip? Don't they need some kind of privacy when they know?lol. That's a cool clip Greg, I've always wanted to witness stuffs like that (besides the Discovery channel) and keep posting the pix so that I can use (with your permission & give credit to the photographer) them for outreach purpose to the natives - for some think that corals are just rocks and stones that are used when chewing betelnut.