In the A to Z Challenge I will be describing parts of my fictional world I am starting to use for Roleplaying games. Most of this information is not known by my players, not to hide it from them, but because I think tons about a location that I won’t force them to sit through during gaming sessions.
So due to less vegetation in the deeper regions of the sea, most sea civilizations are near land in the 0-600ft depth range (or 0-200m range if you would prefer a very rough translation).
Several different regions of sea elves, merfolk and niads exisit. As well as the cruel Merrow, Saughain, Kuo-toa, and wild wereshark tribes. The deep sea Ooruk who never come above 300ft of depth, and the deep Abolithiar servitors round out the deep regions. Many rumoured sightings are had of both a Kraken and Dragon Turtle in the north waters, and few boats venture far from land.
The southern Kuo-Toa empire stays well out of the way of land creatures. This is due to the water sorcerers of the Matron Mysterium, and the suspicions steming from the night of blazing waters.
I am not sure if my players will want to delve too deep in the oceans, but the hazards of water travel must not be understated. The glowing summer jellies are beutiful but deadly to the touch, and are known to clog waterways every few summers.