In Reply to: Re: Humpback is still hanging around...phytoplankton, too. posted by seahunt on October 13, 2015 at 14:13:28:

Over the last 6 weeks or so, the number of adult nudibranchs has dropped to almost zero at ALL of our usual dive sites. The Stearns aeolid that you mention was laying eggs on a piece of kelp on the sand at Garden Spot. Other than that one, I saw less than half-a-dozen nudis at this usually prolific spot.

It seems to be the natural order of things for a particular nudibranch species population to wax and wane. Typical lifespan is about a year or less. So at first, I thought maybe this was a lifespan issue, but now it seems to be a synchronized event. Is high water temperature or silt inhibiting the growth of substrate (their food source) so that nudi veligers aren't settling? Does stirred-up vis force the adults to hide in crevices or under rocks?

We've watched this phenomenon occur at Golf Ball Reef for about a year. I wish I knew what's going on, but some reefs don't look robust right now.