Diving Physiology in Sea Turtles

A Green Sea Turtle Swims Effortlessly

   Recently, I was swimming in front of Hulihee’s Palace.  About twenty feet below me, a green sea turtle swam out from beneath a coral head and made his way to the surface.  Once there, he gulped air four times over about two minutes.  Following this relatively small bit  of breathing (during the same two minutes I breathed in and out no fewer than 20 times) he headed back down in his leisurely sea turtle fashion.

   This got me to thinking about sea turtles and their ability to stay submerged for long periods.  We, who are swimming on the surface and enjoying a regular supply of good old uncle oxygen, take for granted the relaxed beauty of a sea turtle as he swims nearby through the clear water, not on the surface taking a breath every few strokes.  So independent of breathing do turtles appear, that it is difficult to remember that these are not fish; turtles are air breathing vertebrates.  And so the question arises:  What is their secret?   How is it that a green sea turtle can dive 100 meters and stay submerged for three hours?

After Taking a few Breaths, the Turtle Dives

    As an anesthesiologist, I needed to know a fair amount about respiratory physiology.  This subject is not just lung volumes, but the characteristics of hemoglobin and acid base status.  As it turns out, sea turtles have lungs that are a bit more developed than most other reptiles, but not the equal of the fine alveolar system that we mammals possess.  And their hemoglobin is not that different from ours.  What turtles do better than mammals, is manage their carbon dioxide and pH and, most amazingly, tolerate incredible cerebral hypoxia.

    If you are denied a breath, your pO2 will fall to life threatening levels in 5 minutes.  Our brains are not terribly tolerant of a pO2 below 70 mm Hg.  At that point the neurons (brain cells) die. 

     On the other side of the equation, if you are able to provide pulmonary oxygen but keep the patient apneic (which, in a laboratory, is not quite as big a trick as you might think) the pCO2 will rise about 6 torr per minute.  For every 10 torr rise in PCO2, your pH drops by 0.1.  Mammalian life becomes difficult below a pH of 7.1.  
    

A Turtle Swims By Out On Paul Allen's Reef

   All of that may seem more than a little pedantic, but these are simple facts of mammalian respiratory physiology.  Here are some of the corresponding facts about sea turtle diving physiology.  In an unrestricted dive, loggerhead sea turtle pO2 dropped from 112 to 4 after only 25 minutes.  In that same period, the pCO2 increased only about 10 torr (to about 50 torr) and pH did not decrease by more than .1 to above 7.2.  The numbers associated with carbon dioxide and acid base status speak to an amazing buffering ability in the sea turtle blood.  (an incredible amount of carbon dioxide is converted to some other substance like bicarb).  Isn’t it amazing that a turtle can completely recharge this buffering system in a few breaths?  Or to look at it another way, if you were to carry around all the CO2 you discharge over three hours, you would need a 15 gallon bag (assuming that only 4% of your exhaled gas is carbon dioxide...a percent achieved at minimal exertion.)

A Green Sea Turtle in the Crystal Water of Ho'okena

Before moving on, it is important to note that researchers make a great deal of the unrestricted dive.  Not a lot of information on the biochemistry of sea turtle diving has been accumulated, because it is hard to accumulate data in a truly unrestricted turtle.  Sea turtles are remarkably adapted for diving, with their front legs transformed into hydrofoils and the sleek slope of their carapace.  But more than the physical characteristics, note the  leisurely, oxygen conserving manner in which they swim, which also produces far less carbon dioxide.  Though it seems so nonchalant, the unrestricted dive is critical to the turtle.  When in a tether, (a situation in which monitors may be more easily applied) the turtle struggles, oxygen consumption and the  PCO2 rise and the pH falls.  A struggling, or actively swimming, turtle needs to breath more often. 
    
    Most incredible to me, sea turtles tolerate an unbelievable amount of cerebral hypoxia.  Other turtles have an increased tolerance for brain hypoxia, but no other vertebrate comes close to the tolerance that sea turtles exhibit.  Intracerebral ATP (the biochemical battery of life) is preserved in the face of remarkably low arterial oxygen content.  There are articles on calcium and adenosine metabolism and the ability of the sea turtle to reduce its cerebral metabolic rate.  Medical researchers are very interested in how sea turtles defy the ravages of cerebral hypoxia and study these phenomenon in hopes that it might provide therapy for victims of

Protected Sea Turtles in Kona Spend More Time on the Beach

stroke and other brain injury.
 
     Here in Kona, we get used to observing green sea turtles at the surface.  It is my contention that us hau’olis have created a safe environment where the turtles can live at the surface or on the shore without danger of predation.  In the rest of the watery world, sea turtles spend no more than 6% of their time at the surface.  So when you are snorkeling out by the palace or at City of Refuge and you see a turtle swim out from a resting place near the bottom, just think a bit about what an amazing animal you are observing.   If you are lucky, you may see the turtle compensate for hours of underwater apnea with a few gulped breaths.

A Christmas Gift from Canon D10

Which Costume Are You Wearing This Season?

   Well, the yuletide is upon us.  Time for us to enjoy the spirit of giving.  We can all give a little by being patient with our fellow drivers (especially if they are over 90), making sure our trash goes in the appropriate receptacle and not stepping on the coral.  Just for once, hop down off Mount Crumpet and be the Anti-Grinch.

   Of course, if you are like me, its just as much fun to receive as to give.  Yesterday at K Bay it was both Yuletide and low tide, making the entry a bit painful on the feetsies.   But the water was still well this side of freezing, which was a pretty good gift in and of itself.  It was a little cloudy until one got over by the breakwater and the number of fish was hideously low.  So few butterflyfish were seen that I thought that the Grinch might have snuck into the bay the night before and taken them back to his

 Black Sided Hawkfish   Paracirrhites forsteri, Kahalu'u  12/12

aquarium supply shop to, er, fix the lights.  I fear, though, that no matter how many evil fisherman and aquarists lurk, some other nefarious force is at work...see Al Gore, An Inconvenient Truth.

   I worked my way out towards surfer rock and was rewarded with a big, fat Freckle-Faced Hawkfish.  I know, I know, its called Black-sided now, but if anyone took the trouble to look at the fish, they would see how ludicrous that name change was.  Right, Mr. Freckle?  Anyway, this guy was indeed big and fat.  You only need to hang around the Big Island Grill for an hour or so to realize that from the days of the Alii right up to the present, big and fat is a compliment in these very Sandwich Islands.  This guy was very cooperative and rewarded me with my best picture of a Freckle-faced Hawkfish ever. 

Is it a Two Spot Wrasse?

     A gift like that is nice, but on the other side of Surfer's Rock lurked the 60 inch Plasma with surround
sound.  As I turned into that shallow patch of clear water I was presented with a fish I knew I had never seen before.  He was schooling with immature parrotfish, and bird and saddle wrasses.  Irregular fins and shiny patches, as if some 10 year old girl had glued on miniature sequins, this three inch wrasse was jinking around much like a small elegant coris.  Odd body positions and sudden movement in unexpected directions.  (It is not for nothing that I do not have a super picture of Elegant Coris.  Its a common fish, but a spooky devil.)  I followed this little guy around in the still but shallow water for a few minutes, getting a number of pictures.  I wasn't sure he was ever in great position relative to the camera, so I just kept following and shooting.  I could tell he was a bit darker posteriorly and ventrally, but the irregular fins and the shiny spotted coat was what held my attention.  By the time I was done, I had convinced myself that this was a fish I had never seen before.  And I ask you,  "What better gift can Kris Kringle put in my flipper than a life fish?"

Shortnose Wrasse, imm, Macropharyngodon geoffroy  Kahalu'u 

     The rest of my swim was uneventful and I soon found myself on the beach, looking at the books provided by the Kahalu'u Reef Social Club.  Just after I had decided that my fish was a Two Spot Wrasse, a young lady from the Social Club approached and inquired politely, "Do you have any questions, Sir?"  She was in her mid-thirties, a decade or three younger than many of the Social Clubbies, and substantially less chubby than our hawkfish.  She had a sincere approach and just a hint of a West Virginia twang.  Was she channeling Clarice Starling?  I should have been nicer, but so full of hubris was I, that I said, "No.  But I have some answers."  Who the hell did I think I was, Paul Krendler?  Our relationship took a frosty turn, but I told her of my Two Spot Wrasse, what a great fish it was and how, if she hurried she might find it doing the Watusi behind Surfer's Rock.

    At this point we need to scoot ahead a few hours, the water camera has been soaked, Paul Krendler has had his nap and we are plugging the SD card into the old, but trusty, laptop.  And what we see, after a bit of

Shortnose and Saddle immatures 12/13/12

 photo shopping, is what you see above.  I'm calling it an immature Shortnose Wrasse.  The Canon D10 does not lie.  No wonder amazing sightings need to be corroborated by real evidence.  This individual is intermediate between the two pics that my friend John Hoover has in the Ultimate Guide.  In my copy of Randall, no immature is pictured.

    This was not a life fish...I saw my very first shortnose less than a year ago at Beach 69 and one since on Paul Allen's reef.  How does the appearance of this previously very rare fish jibe with the diasappearance of all the butterflyfish in K Bay?  Good question, no?

     So...am I forgiven?   Stat page for Officer Starling and the entire Social Club.  I'm sorry, already.  We have recently received a commission from Dr. Randall to look for the Silhouette Soldierfish right around the pier.  It might not be Hannibal's dining room on the shore of Chesapeake Bay, but a propeller in the skull may trump a craniotome.  In the meantime, I'll try to be better behaved, the better to avoid the looming lump of coal. Like the T-shirt says at K-mart, "I've been pretty good for the last two weeks."  Or not.

jeff

Christmas is coming, Mr. Freckle's getting fat.

 Won't you please put a flounder in the poke vat.
If you haven't got a flounder, a Saddle Wrasse will do.
If you haven't got a Saddle Wrasse then God bless you.
God Bless You, Pufferfish, God Bless You!
If you haven't got a Saddle Wrasse then
God Bless You.