I think the artifacts you are noticing were the result of Youtube's stabilization feature. I reverted it back to the original as I noticed them as well and it also seemed to degrade the picture quality of the entire video, however those issues seem to be fixed. The macro lens does cause a bit of distortion, as can be seen around the edges of the shot of the anemonefish eggs @ 2:20 but the subject remains in focus in the centre.