A day octopus settles on a patch of coral. It will change its coloration from moment to moment depending on whether it wants to blend in or, perhaps, display an aggressive warning.
Spotting an octopus is a matter of chance. It helps if it’s on the move, but the presence of goatfish (in this photo, a manybar goatfish), is sometimes a tipoff.
Square-spot goatfish are quite common and most easily distinguished by the square spot in the yellow stripe along their sides. However, the intensity of the square spot changes, darker during feeding, and fading (as with the fish in the photo) or disappearing altogether while resting or schooling. When the spot disappears, square-spot goatfish are hard to distinguish from yellowfin goatfish.
In my attempts to identify what I see in the water, I use John P. Hoover’s book The Ultimate Guide to Hawaiian Reef Fishes, Sea Turtles, Dolphins, Whales, and Seals. His website is hawaiisfishes.com.
Graham's Island 