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Fish camouflage – How does it work? March 12, 2006

Posted by Stephan Becker in Coral Reef Organism Behaviour, Uncategorized.

Tropical fish come in a large array of colors as most scuba divers and
snorklers are ready to testify. Although you might already know that changes
in color and markings are common between the juvenile lifestage and
adulthood for members of the same species (oh.. you did not? – welcome then
to the amazing world of coral reef organisms!). Few of us actually know how
exactly this works and what the reasons are for these color changes. Well,
let me assure you, even scientists don’t have all the answers to this
question, but some mysteries have been elucidated and make diving and
snorkeling all the more enjoyable for those among you with an insatiable
thirst for knowledge.

Interestingly enough, some tropical fish do not only change color between
different life stages (juvenile – adult), but are capable of changing color
almost at will… At will? Well, almost… actually, it’s more a response to
the time of day (night colors – day colors), a specific activity (mating), a
threat (hiding), or even mood (ever played ‘find the color of my diving
suit’ with a trumpet fish?).

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So how do they do it? Tropical fishes are covered with irregular shaped
cells called chromatophores that contain pigments. The color saturation of
any chosen pigment area is modified by impulses coming from nerve endings
connected to these chromatophores, but can also be triggered by hormones.
Fish can either concentrate the pigments
in the center of each individual cell – making it appear paler or, in
the contrary, expand the pigmentation over a larger area and thus intensify
the color.

I will always remember that one dive on a Barbadian reef in 2002 when,
observing a trumpet fish floating upside-down besides me for about 15
minutes, I suddenly noticed a frantic color change happening over the entire
body of my playmate… a real firework of colors… until it came to a halt
when it matched exactly the color combination of my wetsuit – a luminescent
turquoise green with greyish-blue stripes… the charming little creature was trying to
interact with me – and matched the color perfectly! I can tell you, underwater
experiences like this really change the way you perceive coral reefs and make
you want to protect its magnificent inhabitants…

Wish you all a beautiful day,

Do you have interesting stories about coral reef organism behaviour to share? I would love to hear them – Please use the “add a comment’ button below.


What a great day! January 15, 2006

Posted by Stephan Becker in Coral Reef Organism Behaviour, Dive & Snorkel Reports.
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Didn’t I tell that we have arrived in Grenada 7 days ago? Oups… how could I have missed that. Nice Caribbean breeze, beautiful bays, great diving! We are here to promote Beautiful Oceans to the local dive centers – and to do loads of diving of course…

Nice reefs, teamin with life: Nurse sharks, eagle rays, French Angel, Grey Angel are the ones that pop immediately into my mind… Not to forget the smaller, but nonetheless very interesting reef inhabitants that deserve close observation because of behaviours that will always blow my mind: Threespot damsels (Stegastes planifrons) defending their little algae patch against any intruder in the back reef zone, Boulder star coral (Monastrea annularis) adopting a flattened growth form to catch more light for photosynthesis in the drop-off zone… it is actually quite fun to apply our course ‘Coral Reef Artchitecture & Organisms’ – even if I have contributet to the writing of that very same course…

But today, we spent most of the time out of the water: at Saint George’s University, Grenada. Loads of student freshmen of this local University take the opportunity to meet local businesses and organizations at a campus fair… shopping around and getting informationabout what to do in their leisure time (if there is any left…). Quite some students were interested in our course, and a few students have even taken a free online preview of the course while we were still on campus showing our course books around… quite quick on the mouse I’d say…:-)

Anyway – more tomorrow from beautiful Spice Island… (By the way, did you know that Grenada provides one third of the world nutmeg production? – certainly deserves its name for that one alone…)

Cheers, Stephan

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