Here is the full list of all 51 Summer in Mara achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Cook 50 dishes.
Complete all the quests from Rigatta.
Read all the messages on Puni Cave.
Build all the main structures on Home Island.
Complete all the quests from Pilly, Milly & Tilly.
Complete all the quests from Ecco.
Complete all the quests from Litio.
Pay the mortgage on your boat.
Sing the old Navy song on its base.
Complete all the quests from Taima.
Complete all the quests from Napopo.
Catch one fish of every type.
Get all the Koa's backpacks.
Complete all the quests from Aquila.
Get all the Koa's outfits.
Complete all the quests from Mûn.
Defeat the Elit.
Recover all the chrystalis from the Door.
Complete all the quests from Mayo.
Complete all the quests from Akaji.
Complete all the quests from Blu.
Beat Ereti in a race.
Complete all the quests from Noho.
Ask Caleb to take you back to Qälis.
Complete all the quests from Awan.
Complete all the quests from Onzo.
Unlock all the crops on Home Island.
Use the recycle bin 100 times.
Visit all the islands from Mara.
Get the boat to max level.
Complete all the quests from Taka.
Sell objects for a total of 3000 coins.
Complete all the quests from Brram.
Get one farm animal of each type for your island.
Craft 60 objects.
Cook 30 dishes.
Meet Dunna.
Sell objects for a total of 2000 coins.
Unlock the mine.
Sell objects for a total of 1000 coins.
Carry 99 oranges in the backpack.
Craft 40 objects.
The sea is dangerous, next time get back to your boat before getting tired.
Meet Saimi.
Cook 15 dishes.
Craft 20 objects.
Collect 90 objects.
Remember...
Collect 60 objects.
Wake up after the tutorial.
Collect 30 objects.