They occupy the submerged surfaces of manmade structures like locks and dams, bridges, navigation buoys and their anchoring chains, barges, towboats, and pleasure craft.
(They; occupy; the submerged surfaces of manmade structures like locks and dams, bridges, navigation buoys and their anchoring chains, barges, towboats, and pleasure craft)
They
occupy
the submerged surfaces of manmade structures like locks and dams, bridges, navigation buoys and their anchoring chains, barges, towboats, and pleasure craft