[Coral-List] Strobes blind seahorses?

Douglas Fenner dfenner at blueskynet.as
Thu Apr 1 04:27:04 EDT 2010

     When I take a picture with a flash on my digital camera and I take it 
on the reef in full sunlight in shallow water, it makes little difference to 
the photo.  I suspect that full sunlight in shallow water is about as bright 
as a flash.  Further, I've never seen a warning in the instruction book for 
a camera to not take a photo with flash closer than a certain distance from 
a person.  If it blinded a person or caused any permanent damage, the threat 
of lawsuits would mandate a lot of warnings.  If there is a solar eclipse, 
there are always many warnings not to look directly at the sun because it 
can damage your eyes.  Looking directly at the sun surely focuses too much 
light on a small spot on the retina.
      I know some aspects of goldfish vision that have been tested are quite 
similar to us (the 3 color vision pigments), so my guess is that most fish 
would react similar to humans, though as Keven points out, fish specialized 
for night vision might have greater effects.  Seahorses and relatives are 
diurnal I believe.
      I suspect this is an urban legend.  But I agree with the others that 
hard data is what would be needed to settle the question, and the things I 
am saying are really just speculation.  Charles seems to be on to something, 
if fish in public aquaria don't go blind, then it is unlikely to cause that, 
since they get plenty of flash photos taken of them.

----- Original Message ----- 
From: "Keven Reed" <reedkc at comcast.net>
To: "Julian @ Reefcheck Malaysia" <julian at reefcheck.org.my>; "'Melbourne 
Briscoe'" <mel at briscoe.com>; "'Coral-List'" <coral-list at coral.aoml.noaa.gov>
Sent: Tuesday, March 30, 2010 6:22 AM
Subject: Re: [Coral-List] Strobes blind seahorses?

> 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
> 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
>  www.reefcheck.org.my
>  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
>  Briscoe
>  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
>  ____________________________
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