When it dries out the mold hypha will disappear but the spores will still be there and develop hypha well conditions are right. The mold is breaking down the mulch. Controlling the moisture in the mulch will keep the mold from reappearing.

So is this not harmful to the plants?

We've got more rain coming in tomorrow, but I can let the mulch dry out a little after that. It's a bit difficult, since the bed is mostly mulch and it retains moisture very VERY well.

I just want to be sure I'm not going to kill off my plants if I do nothing.

Thanks for the quick reply!

As a rule the growth of fungi,or even slime molds, is not hazardous to your plants. The conditions that make growth of these might be since they grow only where all the conditions, including excess moisture, are present. The real cure to molds and fungal growth is to fix the reason they grow where they grow.

Thanks for all the help guys!

I'll try to let things dry out a little a hope that things stabilize.