Here is the full list of all 51 Coral Island achievements.
Start dating an NPC
Reach heart 5 with 25 NPCs
Purchase all clothing items
Complete dinosaur collection
Complete gem collection
Ship all crops
Complete artifact collection
Cook 15 recipes
Reach heart 8 with an NPC
Earn 1000k coins
Ship a golden animal product
Earn 500k coins
Clear all the mine gates
Slay 20 enemy types
Heal all the sick coral
Purchase 10 clothing items
Reach heart 5 with an NPC
Earn 250k coins
Ship 30 different crops
Give a gift to 25 NPCs
Ship one crop 1000 times
Ship 5 animal products
Earn 100k coins
Gain access to Giants’ Village
Ship 2 animal products
Slay 10 enemy types
Earn 50k coins
Gain access to Merfolk Kingdom
Craft 15 things
Earn 20k coins
Harvest 100 crops
Earn 10000k coins
Complete bug collection
Complete fish collection
Complete sea critter collection
Complete museum collection
Restore the temple
Reach heart 10 with an NPC
Reach heart 8 with 25 NPCs
Reach heart 8 with All NPCs
Give a gift to all NPCs
Get married
Have 2 children
Cook all recipes
Craft all things
Purchase 50 clothing items
Slay all enemy types
Ship all animal products
Ship everything in the game
Ship one animal product 1000 times
Reach level 10 mastery in everything