Respuesta :
The underlined part of sentence 3 that feeds the bottom dwellers is used as a noun clause, because it is a part of the noun phrase constant rain of organic matter.
The kind of clause in sentence three is noun clause. A noun clause can take the place of the noun, and is considered a direct object. It tends to contain important and relevant information about a topic. In the excerpt provided, the phrase is dependant on the constant rain of organic matter and the clause indicates what it feeds on to provide additional details.