Question

The underlined part of sentence 1 is what kind of clause?

Answer 1

The correct answer is noun clause.

The entire sentence is Scientists report that creatures living in the deep sea are in danger of starving to death. The entire dependent clause acts as the object of the sentence (What do the scientists report...?), which means that it cannot be an adverbial clause. Additionally, it is not describing a noun, and therefore it is not an adjectival clause either. Therefore we are left with the noun clause, which is the correct answer here.

Answer 2

The underlined part of sentence
 that creatures living in the deep sea are in danger of starving to death
 is 
adverbial clause
as
adverbial clause is dependent clause that function as an adverb and modifies a verb  so option 1 is correct
hope it helps