EdJ wrote True, but it does not make any difference to the tadpole.
The smaller ornamental ponds do not freeze solid either. The
tadpoles go dormant or hibernate or something. They do
not need open water to breathe.

I have to respectfully disagree. It is a smart precaution to have a space of
open water in the winter. For a couple reasons. Garden ponds have a lot of
organic matter to the amount of water they hold - consisting of critter waste
and plant debris. This mix of stuff decomposes over the winter and gives off
gases which can be toxic to the pond's inhabitants. Garden ponds usually have a
much higher animal to water proportion so while a large pond can deal with the
waste and debris and freeze over, a garden pond becomes toxic. Also natural
ponds have an influx of water from other sources during the winter and lined
garden ponds are closed systems. Without a hole open in the ice the pond
inhabitants can die as the gas cannot dissipate. Often times a new pond can get
'away' the first winter without this precaution but the subsequent winters will
catch up with it.
Tadpoles, like frogs, are ectotherms, or what we used to call cold-blooded.
They slow down in the winter, go dormant, hang out, lay around. They do take in
oxygen, but very little. They need the warmer temperatures to get their engines
going. Their skins are relatively porous and they will absorb whatever toxins
are laying around.
There are a few frogs who produce a glucose in their bodies that allow them to
'freeze' solid but these are frogs that hibernate on land under the ground.


kathy :-)
algae primer
http://hometown.aol.com/ka30p/myhomepage/garden.html