Why Double Strobes for Underwater Macro Photography

I have two strobes which are INON S2000 and Sea & Sea YS-D1, however, I had never used both of them at the same time. The main reason was there is only one hole on 10 Bar GF1 Housing for fiber optical cable. Eventually, I bought a Double Hole Rubber Bush Set from FUN-IN. 

Actually, it's just an adapter for two fiber optical cables attached on the original hole of the housing by 3M double-sided tape. It's very simple but I know I am too clumsy to make one by myself. Why not just buy one?! Anyway, the set matches to my housing is just USD6.

Why use double strobes for UW macro photography? The following two reasons are my humble opinions about it:

1. Reduce shadow

It's very easy to create shadow when we use only one source of lighting, like the picture shows below. I don't mean shadow is totally wrong or bad for the UW pictures. Shadow can bring more contrast and stereoscopic, however, many details will be lost in shadow.

Last time, I used double strobes to take the pictures of Porcelain Crab. As what we see below, there is less shadow on the subject and the picture is softer.

2. Various Strobe positioning

To avoid the shadow problem I mentioned above, I usually place my strobe on the top of the lens when I use single one. But sometime, the strobe can't illuminate the objects under rocks or corals like the picture below. I don't like to change the position of the strobe too much underwater, so I usually give up taking these kinds of pictures.

There are many ways to position strobes. I use the basic way which is placing two strobes on the two sides of the lens and toward to the center. Thus, I can light up the objects under rocks or corals and reduce shadow at the same time.

The following pictures were taken by double strobes. Whenever I had the difficulty to focus, I also used the Manual Focusing way I shared before.

Remark:
After testing the strobe, I attached the Bush Set by the instant glue to avoid it falls underwater.