I strongly recommend fortifying all of your bases in preparation for just such events.
They become a lot easier and fun depending on how you construct your defences.

I know its a bit difficult to make out, but behind the spike walls in the below image, i've dug a trench from the ocean in land and then back out to the ocean. This creates a water filled trench that slows and direct enemies.

All you need is the pick.

https://steamcommunity.com/sharedfiles/filedetails/?id=2513393674