[ben]

i know that the usual thing for coral feeding is sunlight during the day and plankton at night, but if this is the case why do sps extend their polyps during the day?
i know they extend their polyps a lot more at night but, are they feeding on plankton all the time and if so does it matter if we feed them during the day, rather than at night?

cheers
ben

[tommo]

Expanding a polyp is a response to a couple of things. Corals are far more opportunist than they are made out to be and they will respond to an elevated food load during the day once in captivity for a while. Look at sun corals for example you can force them to open in the daytime and in full light by introducing food!

In the wild, most corals keep their polyps closed during the day as they are subject to constant battery from various coral eating fish and inverts that become inactive at night. Its more a mode of protection rather than feeding, and of course, an abundance of plankton at night that can easily reach the corals without planktivorous motile obstacles make this the best time to feed in nature.

Corals that expand polyps massively during the day can also be doing so to take advantage of as much light as possible by increasing their surface area over which this can be absorbed. This is probably especially the case in aquaria, where lighting simply does not match what they recieve in the wild) Look at bubble corals, who are highly adaptable to many light conditions. They do this by expanding and contracting their bubbles on their polyp to increase and repectively decrease their absorption of light! As dominant zoxanthellae then change within the tissue structure to species more efficient at the designated light intensity, this may yet again gradually change in form!

HTMS (it does to me just about)

Tom

[ben]

thanks tom, yeh it makes sense,lol