Francisco the Hunter (90.7N, 43.0W in Eastwatch) tells of a moarsman fort just below the outpost on the beach. Located at 92.7N 42.5W. The fort is filled with Tainted Grimy Moarsmen.
Killing all the Moarsmen in the fort causes a few Coral Encrusted Chests to spawn at the top of the Temple. They contain a Huge Tainted Egg, use of the chest is on a 6 day timer.
The chests disappear when the Moarsmen respawn after a couple minutes. See Moarsmen on the Shores for more details.
Coral Encrusted Chest Huge Tainted Egg