Polyps

[reefmister]

I know this question is not directly related to your recent columns, but as I do highly respect your ideas I thought you may have time to answer a small question that has been a great debate of mine.

My question is about polyp extensions. I have found that most people tend to really dwell on this. I have found from my own personal experience and from a variety of readings that polyp extensions may not always be a good sign or at least a sign of total health. With the fact that a corals polyps can be used for light gathering, defense or food gathering, or any combination of one or all of these does it really tell the true story. If a polyp on a particular coral is just used for light absorption, does the fact that it is always extended mean its not getting enough light? and thus needs to extend more of it surface in order to gather in more. Or on the other end if the same light dependant polyp does not extend its polyp completely is that a sign that it does not need to because it is gathering enough with only partial extensions or is it a sign of something wrong.

sorry for the long question.

mike

 

[delbeek]

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My question is about polyp extensions. I have found that most people tend to really dwell on this. I have found from my own personal experience and from a variety of readings that polyp extensions may not always be a good sign or at least a sign of total health. With the fact that a corals polyps can be used for light gathering, defense or food gathering, or any combination of one or all of these does it really tell the true story. If a polyp on a particular coral is just used for light absorption, does the fact that it is always extended mean its not getting enough light? and thus needs to extend more of it surface in order to gather in more. Or on the other end if the same light dependant polyp does not extend its polyp completely is that a sign that it does not need to because it is gathering enough with only partial extensions or is it a sign of something wrong.

Mike: Polyps are extended for a variety of reasons, feeding and gas exchange are the main ones. Also, polyp extension varies from coral genus to genus, as well as species to species. To attribute a purpose or effect to the extension or lack of extension, is probably not possible. Some corals may expand while others will contract under the same situation, and this is perfectly normal behaviour for both of them.

In the outdoor systems we have, they get a LOT of light and most of the Acropora have very good polyp extension whereas other genera do not open their polyps except at night e.g. Caulastrea, Echinophyllia, etc.

In the case of lack of extension in say our Acropora, one that is normally extended, then I would say it could be that the coral has received enough light, or the water flow has decreased or increased, it could be a response to an increase in UV light, or it could be a response to predation or a fish picking at the coral just before I looked at it. You'd have to investigate all the possibilities.

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I know this question is not directly related to your recent columns, but as I do highly respect your ideas I thought you may have time to answer a small question that has been a great debate of mine.

Actually there is a paper I discussed on polyp extension in this month's column.

Aloha!
JCDelbeek