This is specifically reffering to the efficientcy in which you can farm coral treasure rewards.

To understand the OEC 2021 you willl need to know this: 

1. All star enemies in the Tier 5 Juur sea require .2% endurance to kill(5 enemies = 1%).

2. For each group of monsters in the sea, there is a predetermined treasure spawn.

3. Gold Nineshark in Tier 5 Juur Sea drop two treasure chests instead of one.

4. The monsters in the imediate vicinity surrounding a Gold Nineshark have the same treasure spawn as the Gold Nineshark, however, there are other groups of monsters that surround this group that only produces one chest at a time.

In order to farm efficiently, you will need to focus strictly on the double chest spawn group. Any enduance wasted on other monsters will result in a decrease in double chest spawns, and ultimately, less weekly rewards.

(i.e.: if one player fights both sets of enemies at 100% endurance, the death total will be close to 250 goldshark enemies and 250 surrounding area enemies, resulting in about 25 double spawns and 25 single spawns, or 75 coral treasures. If that same player uses 100% endurance to kill 500 goldshark enemies, the result will be around 50 double spawns, or 100 coral treasures.) 

I personally farm around 130-140 paddix island passes, 28-32 Phantom Ship Grappling Hooks, 50-60 Deepsea Safes, and 5-8 Eventide Island Owner's Notes every week using this method. Rewards are subject to change & rng will take its toll but efficientcy will always lead you in the right direction.

 I wish you the best of luck on your adventure my friends (:

Server : Mediah 

Family name : K0PE