[Coral-List] Strobes blind seahorses?

Keven Reed reedkc at comcast.net
Tue Mar 30 13:22:26 EDT 2010

Dear coral-listers,

    Please note that we have gotten off the subject (Anthozoan biology/research and coral ecology).  However, as an optometric physician, I'll offer a couple general comments about a vertebrate; eg, seahorse fish, having its retinal photoreceptor cells (rods & cones) temporally 'bleached'--nothing to do with coral bleaching/loss of zooxanthellae--

    The temporary blind spots of various colors we humans and other vertebrate animals see after the strobe goes off while aimed into our faces, represent the recycling time for the photopigment molecules in the outer segments of our retinal rod and cone cells to flip back and forth between different cis and trans forms of isomers of our visual pigments before future photons can trigger another chemical event to fire a neuron to the visual cortex of our brain, or the fish's brain.  The ratio of rods and cones converging on a ganglion cell varies dramatically between daytime hunting fishes and deep sea fishes.

    Some terrestrial animals and some fishes have a reflective layer under their retina that humans do not, the tapetum lucidum.  The tapetum improves night vision in low light levels via increased internal reflections in the posterior chamber of the eye much the way a starlight scope amplifies a low light signal.  The tapetum is what gives that metallic sheen to fish eyes and is what you see reflecting back to you when your car beams or torch/flashlight catch a raccoon, deer or other nocturnal beast in their eyes at night.

    Having said all this, we should not equate a temporary bleaching, or afterimage spot, to blindness, or permanent retinal damage.  Granted, a dark adapted fish or terrestrial animal will have a more prolonged after image, or temporary visual impairment before recovery than if the strobe goes off in shallow, sunlight water.  I do not believe underwater strobes blind seahorses or any other creature's retina, and I look forward to any data that negates my hypothesis.

Warmest regards,


Keven Reed, O.D.
Orange Park, Florida, USA
mobile:  904-505-7277
office:  904-264-1206

  ----- Original Message ----- 
  From: Julian @ Reefcheck Malaysia 
  To: 'Melbourne Briscoe' ; 'Coral-List' 
  Sent: Tuesday, March 30, 2010 12:24 AM
  Subject: Re: [Coral-List] Strobes blind seahorses?

  Hi Mel
  I only have anecdotal evidence, but some photographers have made the same
  comments to me. Would be interested to hear more evidence for or against. I
  am also a diving instructor!

  Julian Hyde
  General Manager
  Reef Check Malaysia Bhd
  03 2161 5948
  Follow us on Facebook at www.facebook.com/rcmalaysia

  "The bottom line of the Millenium Asessment findings is that human actions
  are depleting Earth's natural capital, putting such strain on the
  environment that the ability of the planet's ecosystems to sustain future
  generations can no longer be taken for granted."

  -----Original Message-----
  From: coral-list-bounces at coral.aoml.noaa.gov
  [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Melbourne
  Sent: Monday, 29 March, 2010 2:55 AM
  To: Coral-List
  Subject: [Coral-List] Strobes blind seahorses?

  I'm hearing in several diving forums that repeated use of strobes in
  underwater photography can blind seahorses. Is this based on evidence (if
  so, what?), or is it speculation and the precautionary principle at work?

  Thanks -
  Mel Briscoe
  Consortium for Ocean Leadership
  and diving instructor
  Sent from my HTC TouchPro 2
  Coral-List mailing list
  Coral-List at coral.aoml.noaa.gov

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