The Wateria

The planet of Dousia is over eighty percent water with a thin atmosphere high in stellar radiation that makes life on the surface challenging. Under the protection of the thick water layers, intelligent life, collectively called the Merma, has developed and thrives.
Collectively, the waters of Dousia are called "Wateria." Wateria is a largely salt-water system that connects nearly ninety-seven percent of the water on the planet into a continguous network. Currents faciliate travel through the system and there are countless civilizations and cultures scattered throughout Wateria.
Within Wateria, there are several distinct aquatic environments though the boundaries between them are often blurred. In addition to their lattitudinal temperatures that most planets encounter, Wateria also hosts distinct environments based on their water depth. The planet can be divided into tropics, temperate and polar as many can be, but must be coupled with the depth qualifier. Wateria has four distinct depths: sunlight, twilight, midnight and abyssal in descending order. Therefore, the proper classifications of environment in Wateria use binomial identifications such as tropic-sunlight, etc.
The temperate and tropical twilight zones are the most populous in Wateria. They are the most comfortable environments with seasonal current changes that historically drove schools of fish and other natural prey in and out of the area on migration patterns. This area is also home to the Sukka, or cyclic currents, that have been used as transportation lanes since prehistory. The use of the Sukka have increased from occasional trade routes with other civilizations along the circuit to a highway of movement. Over the centuries, the Sukka has faciliated cultural exchange and growth among the once distinct cultures along it.
Civilizations can be found across most of Wateria. They are not always as easily accessible as those along any of the shared Sukka. Midnight and even a few abyssal societies are noteworthy throughout the tropic and temperate zones. The sunlight layer acts as a natural buffer between the intense radiation that bombards the planet's surface and few cultures have managed to survive or thrive in this area. However, toward the poles are two frigid regions called Kolakka which both feature their own respective cultures that live within the sunlight layer. Being closer to the poles grants them less intense radiation and societies live in the shallower layers to counteract the cold. Some even exit the water for short periods of time!