All manner of concrete, steel, and stone rubble from dredging, demolition projects, and other construction is used as artificial reef materials. This material is generally available at very low cost or free from construction companies who are more than happy to get rid of it. Transportation costs determine where this material is used by the Reef Program.
"Higher animals" is a catch-all term for vertebrates other than fish. This is rather self-congratulatory, since the so-called "lower animals" - fishes and invertebrates - are actually the dominant species on the planet, both in numbers and diversity! The four classes of higher animals are: