April 25, 2019
By Andrew Bywater, Life Support Systems Technician
I began trudging waist-deep into black seawater, the chill rising up my torso as the ocean slowly began filling my wetsuit. Weighed down by nets, collection cups, syringes and other scientific equipment, I was convinced why only a few people have had the opportunity to witness what was to come on this moonlit night. Diving into the unpredictable ocean near midnight, as most sane people are asleep in their warm beds, seems like an extreme venture. Only those crazy enough to study an immobile, expressionless living rock can witness one of nature's most spectacular underwater events.
The synchronized spawning of Curacao's coral reefs takes place annually (sometimes multiple times per year for some species) and is critical for the survival of the many species that call this small Caribbean island home. Multiple variables play in to this event, including temperature, day length, light intensity and the lunar cycle. All these factors must line up perfectly to put these animals in the mood (yes, corals are animals, but more on that later).
Floating together at the surface, the group performed one last check of our equipment before our dive leader proclaimed "lights on," so our path down would be illuminated. We emptied our buoyancy control devices and start to sink. As we descend to a depth of 8 meters, we place our coral spawn collection nets in a central, easily accessible area of the reef. The nets are identified by a reflective label that shines likes buried treasure when spotted by our dive lights. This way, each researcher will be able to see the nets as we gather them when the main event begins.
Prior to this dive, a few days were spent in a classroom learning to identify the target corals for the study. A brief daylight dive allowed us to scout the area and pick out particular coral colonies that we expect to spawn. I have been looking at corals my entire life in aquariums, and picking a coral that is about to spawn out of hundreds is just as difficult as it sounds. A "spawning calendar" was given to each diver, published by coral scientists, to estimate the spawning window for each target species.
As I began traversing to the dark unknown, I stuck to my assigned grid. My field of view was limited to about 10 feet in front of me and just a few feet on the sides, thanks to my underpowered handheld flashlight. The ever-present thought of what could be lurking outside of my small visual range was a concern, but the fact that I was surrounded on all sides by creatures that I have dedicated my life to protecting was calming in a weird, nerdy sense.
After 30 minutes into the dive, I had already photographed a sleepy sea turtle, interacted with a Caribbean reef octopus, and spotted more reef fish than I could count. All of these things by themselves would make for a wonderful night dive, but the real reason we were all there was just about to begin, and no classroom PowerPoint could have prepared me for what I was about to see.
A small "puff" of sperm from a great star coral (M. cavernosa) was the first clue. This particular species is a gonochoric broadcast spawner, meaning it has separate male and female colonies. It almost appeared as if this one polyp was testing the waters in a sense, because within seconds the entire colony swelled and released a white cloud into the water column. As sexual reproduction goes, it takes two to tango. Before I could even reach for my collection syringe, a nearby female great star coral made her presence known by releasing hundreds of stringy bundles of brown eggs. How she knew to release her eggs at the same time is still uncertain (although science points to chemical cues), but it couldn't hurt that these corals have had millions of years to perfect the act.
Dating back to the Triassic period, corals have evolved to reproduce both asexually and sexually. Most corals we see today in zoos and aquariums are produced via asexual reproduction: a small fragment is snipped off of a mother colony and left to grow into a colony itself. Genetics tells us that asexual reproduction yields an identical copy. This is a great method to sustainably produce more corals, but in a changing environment it may not be the ideal scenario for their wild counterparts.
Coral sexual reproduction is a rather new venture that is proving successful in coral restoration. With sexual reproduction, new coral individuals are created that could hold the secrets to adaptability. Large coral colonies release millions of potential recruits during each spawning event. Current research is focusing on the post-larval survivability of these coral hopefuls. With less than a 1 percent chance of making it to adulthood, we need to figure out what these animals need to survive. Ex-situ research (performed in a laboratory) offers a controlled environment in which we can further study the water quality and husbandry needs of these fragile corals.
Climate change, pollution and overfishing are all factors influencing the current degradation of the world's coral reefs, and it is a global problem. The value of these ecosystems is estimated to be in the billions of dollars, and the welfare of entire countries relies on coral reefs for sustainability and economic survival.
In the meantime, it is up to our universities, nonprofits, and zoo and aquarium colleagues to direct their efforts towards coral research. Time is running out, but all hope is not lost. A few brilliant coral researchers have recently discovered how to induce broadcast coral spawning in the lab and have published their findings online, for free. The materials and methods are there; we just need to pull together as a community to help these fascinating animals survive for a few more million years.
This opportunity was something I never thought I'd get to experience. My respect and appreciation for the ocean started at a young age, and to finally see first-hand how these amazing creatures have perfected the art of reproduction was humbling to say the least. I will continue to fight for the conservation of coral reefs, and I urge everyone to learn more about these fragile ecosystems and ways to help.