When you want black pearls in great quantity, here are some things I suggest.
1: Ragnarok: Vikings bay. Bring a good crossbow to one shot any water scorpions, they drop TONS of black pearls.
2:Extiction: Gachas. Sometimes when taming gachas, you can get one that produces black pearls. They produce in big quantities, and for me is by far the safest and easiest way to get the black pearls. Like if this helps!😄
Just go to eldrich zone on crystal isles and look for big bubbles that have some black clams/oysters inside of them, put your angler fish inside the bubble, harvest, and enjoy the best black pearls harvester in the entire game, super easy, rank up for people to see this.
Ragnarok top right of map there’s a sunken ship surrounded by eurypterid they continuously spawn so you can either use a crossbow to kill then harvest with a pick or get a Tuso or something and rack up pearls
If on the center you can use the a tueso and it’s grab ability to instantly kill alpha mosasaurs by putting them inside the bubble. The bubble beside the skull has three that spawn right next to the bubble at a high consistency. 100 black pearls each one with gear that comes with it