Coral Spawning: How do they know??

by Michele Hall

"Howard and Mark Thurlow on the Flower Gardens - ©Michele Hall.

Back in August of 1993 Howard and I journeyed to the Flower Garden Banks Marine Sanctuary off the coast of Freeport, Texas to film what was then a relatively newly discovered phenomenon. Once each year on either the 8th, 9th, or 10th night after the August full moon, the entire Flower Gardens Reef spawns. The annual coral spawning was first discovered on the Flower Gardens in 1991, and in 1993 we went to sea with NOAA during their second expedition to document the activity. Howard and Marty Snyderman filmed the coral spawning with their 16mm movie cameras and the footage became the most spectacular sequence in our National Geographic Special, Jewels of the Caribbean.

   Now, nearly a decade later, we were back. Accompanied by Mark Thurlow, we returned to the Flower Garden East Banks Marine Sanctuary Buoy #4. Once again we joined a NOAA research cruise, this time aboard the M/V Spree. But on this trip instead of shooting 16mm film for a television special, we excitedly anticipated capturing footage in high definition and adding this fantastic visual experience to our stock footage library.

   An early morning flight took us from San Diego to Houston International (George Bush) Airport, via Dallas Ft. Worth. By 3:45pm we'd loaded all 20 cases into a rented U-Haul cargo van and were looking for Highway 45 South, which would lead us to Freeport (just west of Galveston). A big dinner at a restaurant across the street from the boat dock (have you ever eaten fried dill pickles?) helped pass the time until Captain Frank Wasson, Melanie Wasson, and the crew of the Spree were ready to accept passengers and gear aboard the boat.

   Later that evening, while fighting off squadrons of massive, turkey-sized, blood-thirsty, fang-toothed, mosquitoes, I glanced at Howard and saw him breaking into a sweat and going pale. He was struggling to set up the hi def camera and housing. His anxiety wasn't in response to the Texas summer weather or the bite one of those mossies had taken out of his neck. Rather, while prepping the camera housing for tomorrow's dive, he'd done a routine pressure test of the o-ring seals. The test had failed. It turns out that when Howard and Bob Cranston pressure tested the housing the previous week to see what depth it could withstand (with thoughts of taking it to 350+ feet to film for our next TV series), a welded seam had cracked. Howard had just discovered the flaw. We'd come all the way to southern Texas with all of our gear, used frequent flyer miles for 3 tickets, and paid $750 in excess baggage (one way!), to get footage of the annual Flower Garden Banks coral spawn, and now it looked like the camera would never make it underwater. As I felt the blood drain from my head, I, too, began to sweat.

   An inconsistent night's sleep on a rocking boat can spur some creative ideas. During the night Howard decided he would try patching the housing's cracked seam with epoxy. The next morning Howard and Mark spent several hours working on the housing. We needed to let the epoxy cure for 24 hours before putting it to the test, so while the patch cured, we dived with still cameras to reacquaint ourselves with the reef. The conditions were great: water temp in the mid- to upper-80's; the air temp surprisingly comfortable. We enjoyed a pleasant breeze, and the fang-toothed mosquitoes were left behind in Freeport.

   The first night out was the 7th night after the August full moon. Jesse Cancelmo, who was also aboard, had seen some corals spawn on the Banks last month on the 7th night after the July full moon. So, with some speculation that there might be a pattern for an early spawning, we prepared for a night dive.

   The sun set at 7:40. Howard and I sat on the upper deck and watched the orange orb settle into a cloudbank, enjoying the evening breeze, and waiting for the sky to darken. Joined by Mark, we entered the water at 8:35. Diving Nitrox 36, I had plenty of bottom time left when, after 65 minutes, my diminished air supply necessitated that I begin my ascent. We saw no spawning activity, although a few others, including Jesse, reported seeing minimal action. But I did see one of the biggest turtles - a loggerhead - that I've ever seen, sleeping under a ledge just below the boat. Her carapace must have been 4-4½ feet long. Her head was huge!

   By the next morning it was time to put the patched camera housing to the test. We were immensely disappointed when Howard took the housing down and immediately heard the 'water alarm' begin beeping. When Howard opened the housing he discovered that the alarm was caused by a malfunction in the water sensor and that the housing was entirely dry inside. After Howard's second test for an hour at 76 feet, the inside of the housing remained dry. We were ready for the real thing -- putting the hi def camera inside, and hoping that filing an insurance claim wouldn't be added to my 'to do' list when we got home. The day proceeded without incident - no camera incidents, that is.

   There was one big incident after sunset: the reef spawned! After dinner, Peter Vize (a scientist on board, from the University of Calgary) gave us a short rundown about what to expect, advising that the best of the spawning would occur between 9:30 and 10pm. Howard and Mark decided that with the support of their rebreathers, allowing them 3 hours or more of bottom time if they wished, they would descend at 8:30. I held off until 9:15, as did almost everyone else, and when at 8:45 I saw numerous spawn slicks floating on the surface, I began to wonder if this was a mistake. But I kept to my decision, and I hit the bottom just after 9:15. It turns out it was a good one, as I saw one after another coral head releasing eggs during my 75 minutes on the bottom. The water visibility dropped drastically during that time as the water column became inundated with eggs and sperm. It was so thick that as I hung off for my safety stop I couldn't see the hang line that I was supposed to clip my camera to before my final ascent. I could barely see the current line drifting behind the swim ladder forty feet away.

   One of the advantages of shooting in hi def video is being able to relive what we saw underwater in the comfort of a dry boat. So Howard and I spent the next morning reviewing and logging the evening's spawning footage. When the boat later moved to the nearby High Island Oil Rig Platform #389, we jumped in for a dive on what has become a spectacular artificial reef that was installed in October 1981 in 412 feet of water. With the establishment of the Marine Sanctuary, this is the only oil and gas structure in the world that exists inside of a marine sanctuary. The first drilling took place the year of installation, and it's still active.

Barracuda trailing fishing leader - ©Michele Hall

I love diving this rig. One glimpse of this structure underwater and you understand the term 'artificial reef.' Reef building corals were first seen in 1990. Six species of coral have been identified growing on the rig. It also supports a fantastic collection of sponges, hydroids and fish. Another dive boat was pulling away from the rig as we approached and called to say that their divers had seen a whale shark. Though we weren't so lucky, we did see a good size barracuda with a stainless steel hook imbedded in its mouth. Mark Thurlow unsuccessfully tried to remove the hook.

   On our second night out, Peter Vise and Emma Hickerson (the Marine Sanctuary's Research Coordinator) correctly predicted that there wouldn't be much coral spawning activity, but that the brittle stars would be pretty active. We dived the West Flower Gardens Banks Buoy #2, and in the hopes of catching the brittle stars in action, we entered the water earlier than on the first night - at 8:20. I traded my 60mm lens for the wide-angle 24mm lens, and I think it was the better choice. Not long into the dive I caught a glimpse of red under the light of my torch, and got my camera in place just in time to photograph a brittle star raised up on it's legs, releasing eggs!

   The sandy bottom of this reef is about 10 feet deeper than on the East Banks' Buoy #4 (85 feet instead of 75) which really limited my bottom time, even with a Nitrox mix of 36. All too soon I was down to 1 minute of no-deco and had to ascend. To comply with the boat's request of no-deco diving, Howard and Mark followed just a few minutes later. Much to Howard's disappointment, he didn't see or film any good spawning activity. We really feel compromised in our productivity because of our limited experience with and knowledge of these reefs and the associated animal behavior.

   While searching a sandy patch the next morning at West Flower Garden Banks Buoy #2, I saw some volcano sponge releasing eggs. Howard was in the vicinity filming barracuda in the open water, and I was able to call to him on my OTS comm to suggest he check it out. He then called to Mark who was exploring elsewhere on the reef and asked him to get the lights and tripod. Before long they were set up and filming! Once again, our OTS comms helped us get the shot.

   That evening Peter briefed us telling us to expect the brain coral to spawn that night between 8:45 and 9pm. So we entered the water at 8:20. Howard immediately found a large loggerhead turtle sleeping under a ledge at 93 feet. As I approached the scene I called to him on the comm that another turtle was swimming overhead. This medium-sized female was not bothered by the big movie lights and she began to follow Howard, swimming towards him so that he could barely back up fast enough to get the shot. Off they went down the reef.

   In the meantime, I scanned the reef with my dive light for brain coral heads of the exact species that we were expecting to spawn. And just at 8:46 I heard Peter call out over his comm, "I have one going off here!" Howard called back asking him where he was. Just then I saw packets of spawn floating above a large coral head, and Emma crouched next to it with her video camera. As I looked to her left and saw another one spawning, Howard's voice came over the comm from across the reef, "Mark, over here; set up the tripod over here!" "Good, he has one, too." I thought.

   And so it went for the next 23 minutes. I concentrated my efforts on one of two coral heads, and I could hear Howard and Mark discussing their strategy. All too soon I was out of film and almost out of bottom time.

   How do they know?? How do they do it??? How do these coral animals that have no brains and almost no nervous systems know that it is not only the tenth night after the full moon in August, but that the time is between 8:45 and 9:00 pm? You can take the corals out of the ocean and put them in an aquarium in a dark or lighted room a thousand miles away, and they will still spawn on time. Their ability to spawn exactly on time is completely predictable and an equally complete mystery. Amazing!

   Sunday morning brought us the last dive of the trip at Stetson Banks. When Howard opened the hi def housing to change batteries, he spotted a small drop of water that he's certain came in through the patched seam. So, rather than take a chance on making the situation worse, he packed up the camera and housing, and took stills on the last dive. Amazingly, more elaborate patches on the housing seam failed to prevent leaks after that last coral-spawning dive. Howard was forced to completely disassemble the housing and re-weld the seam. We were amazingly lucky that the first patch held until our coral spawning trip was essentially over!

   As I remember from our dives here in '93, Stetson Bank is a location to be revisited time and again. There's a large area to explore, with lots of juveniles filling nooks and crannies. We saw 4 species of morays - one saw my finger a bit closer than I might have liked, and bit me! But it was purely my fault, as I got too close and too greedy over a photo opportunity when I tried to get the spotted critter to stick his head out of a hole above a beautiful spiked oyster shell. I was wishing for one of Peter Kragh's metal rod pokers, but since I didn't have one I used my finger instead, all the while thinking, "This is a mistake waiting to happen!" Sure enough, with Howard looking over my shoulder, I got bit. He saw me jerk my hand away and asked through his comm, a chuckle in his voice, "Did he just scare you, or did he bite you?" "He bit me!" I replied, and pulled my glove off to show the damage. But we couldn't see the 5 slashes in the skin because of the torrent of green streaming out of my finger. (Howard later described my eyes as 'getting big as saucers' when I saw the gush of blood.) I quickly pulled my glove in place, shot the last frame on my roll of film (of just the oyster shell L) and headed for the boat. The next thing I heard on my comm was Howard recounting the incident to Thurlow. There are no secrets amongst this crew!

   To avoid infection, I lathered my slashed finger with Neosporin ointment. As I sat on the boat typing the week's events into the computer, I had to try very hard not to get the antibiotic goo all over the computer keyboard! I just hope that I'm left with a respectable scar on to accompany my memories of our coral spawning trip... a lasting and fitting memory of this grand Adventure.

   While we motored back to land, I once again sat on the boat's upper deck, packing up our equipment and enjoying the scenery. Images of the last moments of the previous night's dive at the Marine Sanctuary came to mind. I remembered ascending to the decompression lines of the Spree. The underwater night sky glittered. Water visibility had diminished as the masses of spawn rose to the surface. But I could still make out the strobes attached to the down lines, beckoning my return. Other divers were also homing in, and the iridescent green chemical lights hanging from their tank valves flickered like fire flies on a warm summer night. I've always liked watching fire flies, and tonight this illusion mesmerized me as I waited out my safety stop, my thoughts drifting away. What a scene I'd been privileged to witness: nature's magical, mysterious and exquisite renewal.