Although not directly related to the thread topic, this is an interesting object to analyze.
There are specific parts of the picture that make me think it's a wing, rather than T&G planking:
The object appears to be quite thick some distance back from the nearest edge, and thicker at the left side of the picture than the right side, giving it a tapered appearance. The sunlit top surface and shaded bottom surface do not appear to be parallel, but form a thick wedge that tapers in two directions, like a wing. This would be an unusual shape for planked construction - perhaps a very thick awning or high-dive platform? The marine growths suggest a long time under water, so if it's a planked structure, when did it become submerged, and what was its original purpose?
The object appears to have a rather sharp edge, nearest the camera, like the trailing edge of a wing, but unlike normal planking.
The object has what appears to be a joint or line approximately parallel to the sharp edge, consistant with the small gap between an aileron and wing surface (or T&G planking).
A second, less promenant line parallels the first, consistant with a dive brake panel (or T&G planking).
A geometrically regular object projects at an angle from the bottom of the object right of center, giving the appearance or a rod or shaft. This might be the remains of an aileron counterbalance weight, the end of which is missing. If the object is a planked construct, this might be a structural element.
What would explain the presence of a planked object on a reef? What would explain an aircraft wing on a reef? In the south pacific, both objects would represent imported objects. A planked tapered structure seems less likely to be present on a coral reef than a WWII aircraft wing. OTOH, if the photo was taken in the Bahamas, then the opposite might be true.
Would a wooden structure have bare patches like the ones visible on the object? Isn't the pattern more commonly seen on aluminum aircraft from WWII?
To duplicate the shape with planking would create a shape that looks very much like part of an aircraft wing. Not impossible, but not likely to be present on a reef, to my very limited knowledge.
It seems likely that somewhere out there in cyberspace is a photo by the same diver of the entire object, not just the awning/diving-platform/dive-bomber object. Perhaps Richie can help find it? (I'm on slow dial-up, and photo searches are unbearably slow for me. Sorry)
<later addition:
http://s3.footagesearch.com/stills/JV04_026.jpg is a photo showing the trailing edge of a wing. Not a great comparision, but the best I could find on short notice.>