My very lovely mussels have small white-ish dots on the shells and with a ton of effort (scraping with my finger nail) they come off. I am cleaning 4lbs do I need to do this? Dinner guests coming soon!!!
I can't tell from the photo's scale, but looks like they could just be small bits of barnacle - hard and raised slightly from the shells? I wouldn't worry about scraping them off. Just give the shells a good scrub to remove sand, dirt and if there are any "beards", pull those off just before cooking.
Those are likely tiny barnacles and no, you don't need to remove them. As long as they’ve been purged (for sand) and de-bearded they’re good to go. Just remember to discard any that didn’t open while steaming. Also, this is handy! https://food52.com/blog...
Amy and Jacque are right, those are barnacles or limpets, nothing to worry about.
Here's SeriousEats' Kenji's longish article about mussels:
I buy farm-raised mussels and I don't do any prep work before cooking apart from a quick spray of water over the colander.