Answer :
"That these little creatures survive in these small pools of water" is the whole noun clause You could replace that whole noun clause with "That fact" which is a noun phrase and have a sentence That fact is amazing where "that fact" would be the subject.
Likewise, this whole noun clause represents A SUBJECT of the sentence because it corresponds with the predicate "is".
Likewise, this whole noun clause represents A SUBJECT of the sentence because it corresponds with the predicate "is".
