Thanks! That is a great question, and I was actually able to replicate it for the first time a few weeks ago. This photo is from 2022, and I have tried to replicate that shoot every year and only had luck around the time I coincidentally posted this older photo. These nudibranchs appear at Haystack Rock in Cannon Beach in small numbers in April when there is a negative tide. I use a 100mm macro and a garden pad. The nudibranchs will often come up just a millimeter or so from the surface...