Iridescent ocean bubbles

I took this shot in 1981 in New Zealand shortly after I bought my first medium format film camera, the Mamiya RB 67. I was on a black sand beach on the South Island of New Zealand, and I noticed the bubbles in the ocean foam were turning iridescent as they spread out on the sand. As I leaned down closely to the interesting pattern of color, I could see myself reflecting in each hemisphere. I was shooting Ektachrome 64 at that time, and 64 ISO means the shutter speed had to be fairly slow with overcast conditions. I remember specifically the shutter I was forced to use was 1/30th of a second, not an ideal situation for hand holding the large camera. Plus, the wind was pretty brisk. I couldn't use a tripod because the bubbles didn't last that long. Adding to the challenging set of variables, there was a friendly dog on the beach who really wanted to play. He'd bring me a stick, stepping in the bubbles, and I'd throw it as far as I could to give me a few extra seconds to compose and shoot. I'm sure I took this picture at f/4.5, the largest aperture on the 110mm Mamiya lens. Any aperture smaller would have meant an impossibly slow shutter.