So, on the planet Oceanus, their exist a species, called the Crustaceanoids, who live in an aquatic environment. They are crustaceans, no duh, and are crab like animals. They are exceptionally intelligent, and already have Stone Age level tools. They also have a writing system, which relies on dead Crustaceanoid shells to make markings on. They also have agriculture, growing algae and herding domesticated fish for food. They will be in the plot of my story, but a need a suitable place for these creatures to live. It has to fit the criteria below.
It has to be shielded from waves, as the backwash can carry out Crustaceanoids and destroy crops.
It has to be protected form predators, who often feast on the Crustaceanoids. It must have lots of places or safe hiding spots (the Crustaceanoids are about 6 inches big)
It has to have plenty of flat areas for herding fish, and rocky surfaces for growing food.
So, which aquatic environment could these Crustaceanoids inhabit?