These nudibranchs eat montipora species. In this picture, that is a big population of nudibranchs, and in the white area (lower right) you can see all the egg sacks. (Photo by Adam DeAnda)
Here are three more pictures from Sanjay Joshi, who recently discovered them infesting a prized montipora colony. Look closely. These are being identified as Embletonia sp.
Considering the size of these tiny nudibranchs, seeing their little 3D bodies so well is impressive. You can even see the head of this animal below.
In this next picture, you can even see the tiny eggs in the upper left section of the photograph.