Coral's Prey Response
Ron Shimek
Anyway, this got me to thinking (Ron and Eric just groaned), do corals respond to the addition of iodine because they want iodine, or because they think food is now available? ( Rob recently posted about corals eating plastic that was coated in their food of choice - I have really over-simplified this!!!)
First, I am not sure corals respond at all to iodine. Iodine in some foods may be correlated with some other chemical or even other factor that the corals respond to. Most cnidarians respond to chemicals that are found in their prey, but generally these are protein fragments called polypeptides rather than substances like iodine, simply because iodine is found in about the same amounts in many marine organisms - hence it would be an unlikely marker for food.
Now, if the corals have been being fed food that is not "balanced" in the same way their natural marine food is, they may well respond to natural food by feeding. However, I would look elsewhere than the iodine for the marker. In class room situations, we used to use MSG (mono-sodium-glutamate) to trigger some cnidarians to feed - never tried it with corals, though. Perhaps it is worth a try....
Perhaps not...
Eric Borneman
Ron is right about iodine. This is not known to produce a feeding response, but may produce a retraction response. In corals and anemones, amino acids "leak" out from prey items...both phytoplankton, zooplankton and bacterioplankton...that trigger feeding responses. The specificity can be somewhat specific to the organism, but generally proline and glutathione are the strongest and the most wide ranging stimulants. There are several sources for more information, but a nice summary for corals can be found in Lenhoff, Muscatine and Davis's, Experimental Coelenterate Biology, and for anemones in Shick's, A Functional Biology of Sea Anemones.
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