Wow Allison, I gotta use those for the site! You should check out the rest of her pictures. Like already said, Allison is more reffering to muck diving. "trash," I guess is a dirty word, so thats why muck works better! Its a little bit like artificial reefs, Ships are not natural but do provide a good hard surface for corals to grow on. There is a difference between that and anything organic that could dissolve and be part of the water column. Also, things that are hydrophobic like oil are no good either, because of how they react with many animals use of oils (i.e. preening). Plastic, is not good. Its not a good enough surface for corals to form polyps, its not hard like bottles or ships, and therefore, animals can get caught in them. Please if you see plastic PICK IT UP. Some stuff "trash," "muck" whatever you want to call it, is good, and that stuff will usually be taken up pretty soon. Real estate is expensive in the ocean! lets keep our reefs clean, but also remember that some stuff make great homes, even if they are artifical. Thats what makes a lot of muck diving sites great!