Eastern Oyster is a forageable item in Coral Island. In other words, you can’t just leave a beetle trap or critter trap somewhere and wait for the resource to come to you. Instead, you must find this Oyster yourself, which can be quite problematic if you don’t know where to look.
So, to get Eastern Oyster in Coral Island, you need to go down to the seabed. Diving is unlocked quite early, in the first days of Summer, so you can quickly start searching even if you just started the game. Then, swim down until you hit a large rock. Turn right and swim further until you find stone steps.
Following the steps, you will dive to a depth of approximately 20-23m. After that, all you have to do is explore the location at this depth., and you will easily find several Eastern Oysters in Coral Island. They spawn at a depth of 20-30m, so you should check every area at this depth.
When you find several Eastern Oysters, you need to immediately give one to the Ocean Scavengables offering in the Crop altar. It doesn’t matter what quality the item is, any will do. As a reward for this offering, you will be able to receive a Dehydrator.
Also, you can put Oysters in the Dehydrator to produce Dried eastern oysters. It will take you 10 hours, but in the end, you can earn 80 Coins for each jar. It is much more profitable than selling Eastern Oyster separately.