Dive Dry With Dr. Bill
Would You Like Yours Black… Or Green?
By Dr. William Bushing
For some reason many people think just because I have a Ph.D. in marine ecology and evolution, and many decades of experience diving both here off Catalina and around the world, that I should know everything about all of the estimated 10 to 14 million species on Planet Ocean. If I did, life would become very boring as I would have nothing left to learn. I might as well take up golf… or maybe shuffleboard! Others know that having a Ph.D. usually means you know more and more about less and less. Although I am by training a kelp marine botanist, I try to take a more rounded approach by studying all the critters that interact within what’s left of our kelp forests today.
Recently a diving friend, Michael Francisco from Sharky’s Eco Dive Center, forwarded a video of a sea turtle filmed off Catalina by another dive friend, Suzy Degazon. He referred to it as a black sea turtle which threw me. Most of the sea turtles we have been seeing around Catalina the past two years have been green sea turtles and that’s exactly what the one in the video looked like. We’ve also had hawksbill, loggerheads and leatherbacks seen off the West Coast lately.
Now Henry Ford is reported to have said buyers of his Model T cars could have them in any color they wanted as long as it was black. In researching this column, I found that not all sources agree he actually said that. When it comes to turtles, I might have said you can have them in any color you want as long as it’s green… and not black! And, yes, I actually said (er, wrote) that. I’ve since discovered I may be quite off base with that thanks to research I did following the viewing of the video and my exchanges with Michael and Suzy.
Back in the Dark Ages when I studied marine biology at Harvard, we liked to believe that a species was relatively easy to define. In the textbook I wrote for my class on evolution at Toyon Bay in the early 1970s, I stated “A SPECIES is a group of organisms similar in their morphology, behavior and physiology but not identical; and capable of interbreeding to produce viable offspring.” This is why a horse and a donkey are separate species even though they can mate and produce offspring in the form of mules. The mule cannot breed and is therefore not “viable.”
As I researched the topic of black and green sea turtles further, I discovered that it is more complex than I ever imagined. First I found statements that the black and green sea turtles were simply names for the same species (Chelonia mydas) as I’d always thought. Then I found sources that said the black turtle was restricted to the eastern Pacific (that is off the west coasts of North and South America) and the green turtle was found in the South Pacific and off Asia wrapping around Africa to the Atlantic Ocean and the East Coast of North America.
Some scientists felt that the differences in shell coloration were sufficient to classify them as separate subspecies with the green-shelled western and central Pacific (and Indian and Atlantic Oceans) version known as Chelonia mydas mydas and the eastern Pacific form off our coast as Chelonia mydas agassizii. Other researchers looked at physiological factors such as blood chemistry, genetics and behavior and came up with additional distinctions between the two. Some marine biologists even suggested that the one on our side of the ocean should be an entirely separate species, Chelonia agassizii. Are you as confused as I am now? I thought so!
I had to keep Googling to muddy up the waters even further. In doing so, I discovered that the so-called black version was also found off Asia and we’ve definitely seen the green version off our coast. Therefore, they apparently aren’t prevented from mating by geographic isolation! I have thanks to the barrier of the San Pedro Channel.. sniff! The presence of both morphological types in the two primary distribution areas suggests to me that they are probably just variations of the same species. I still prefer the old species definition of my youth. Too many people today want to split hairs and separate critters based on factors that WE humans judge to make them different. Easier to make a name for yourself that way, but… the turtles may have a different opinion!
I found this investigation an interesting exercise in biology. It highlights the fact that even the experts don’t agree. As I said, I don’t know everything about every species. Turtles certainly are a long way from my area of expertise unless you count the snapping turtles I used to catch in our creek back in my Chicago childhood. However, based on this inquiry, apparently you can teach an old “Doc” a new trick… at least until another marine biologist decides these are one and the same species!
© 2015 Dr. Bill Bushing. For the entire archived set of over 650 “Dive Dry” columns, visit my website http://www.starthrower.org