Wonderful capture. Love the low angle, exposure on the whites, head turn, and crab. You were low enough to get a pleasing bg, but high enough to get some feet in the image (perfect amount, I say).
Maybe a version with just a tad more room all around? Either way, this is a keeper!
Beautiful light and I like the low perspective. The detail is excellent - great detail in the gull's eye, the background is smooth I can see the gull's feet - can't fault it - excellent.