Ostracods – Living Stars of Inner Space0
By Chim Carlson
On my recent trip to Roatan, I and my fellow dive travelers, veterans of countless night dives, were treated to a magical and fascinating first time experience. I only wish photos or videos could be taken to show you what truly amazed us.
Two biologists on the trip, Jim Morin, a retired professor from Cornell University and and Gretchen Gerrish, a professor at University of Wisconsin at La Crosse introduced us to this amazing creature and magical experience.
Professors Jim & Gretchen took the time to explain this phenomenon that only occurs in the Caribbean. They then worked with our hosts at Turquoise Bay & Mayan Princess Resorts to let us experience these unique marine critters on several of our night dives. For many of us, these were the first time the highlight of the night dive was seen without lights.
Jim & Gretchen have been conducting research on bioluminescent ostracods (with their luminescent courtship displays). These species are only found in reef systems in the Caribbean Sea.
Bioluminescent ostracods are extremely small, reaching a maximum length of about two millimeters, their valves are transparent and contain no pigment, but slight coloration may be seen around the heart, gut, eyes and light organ.
They use luminescence during their brilliant mating displays and to deter predators – when attacked an individual releases a cloud of luminescence that shocks and blinds its predator while the ostracod escapes.
Bioluminescent displays by males to attract female mates occur with the coming of darkness at twilight; without darkness these displays would not be seen and mating of the species would cease.
Come night time, bioluminescent ostracods live up to their name. Displays begin during the first truly dark hour of the night when no moonlight is present, typically about 45 to 50 minutes post-sunset, if there is no moon, otherwise after moonset. During this time, male ostracods leave the reef and swim up into the water column and secrete an intricate series of long-lasting pulses of light to attract non-luminescent females of the same species. These coded trains of pulses serve to attract the same species of females’ attention in hopes that at least one will approach the male, allowing for successful mating. The train of light can be produced vertically up or down or diagonal, depending on the species.
It felt very strange to do a night dive without light, as we were instructed to turn off our lights after entering the water and not to turn them back on until we were ready to get back on the boat. I had to admit at first it was a strange feeling and I felt insecure at first. Then as my eyes got used to the ambient light. It wasn’t so bad after all. Then all of sudden in the darkness the string of lights started appearing on the reef and before we know it, the lights were everywhere. It was so beautiful, like we are looking at the stars. Some of us said, ” just like the movie, Avatar.” This was an experience that I would never forget. After we all enjoyed the light show, we continued on our normal night dive.
If you go to Roatan, please tell your dive operation to try to do this type of night dive. It is an amazing experience.
I really believe everyone should experience this phenomenon. I am sure that most people I know, do not know that there are organisms out there that attract mates in such an amazing way!
Here is a website if you want to learn more about a marine bioluminescent ostracod.
Check out the video below to get an idea of what we were treated to.