The Ocean Biome was first introduced with the Upbeat Giraffe update.
Below the "sea level," naturally-occurring liquid is not drained out into the background like most liquid is, and it does not despawn if collected via the Matter Manipulator. This basically means they provide an unlimited supply of the liquid found on them (water/poison/lava). The only way to create an area of dry land under the sea level is to replace water with any form of mater, then mine the inner layer of matter, making a small tunnel that can be used. This is useful for getting to the ocean floor and back without any nanosuits once constructed, if the planet is suitable for such exploration (basically, planet conditions apply).
Above sea level, there are only a few islands for dry land, and these islands house Tropical biomes (normal Ocean biomes only). Islands only extend up to around 100 1x1 blocks below the sea level.
The sea is very deep, taking seconds to reach the bottom. The seafloor is a walkable surface spanning the planet entire. Due to its nature, the Oxygen Protection nanosuit is necessary for exploration. The bottom of the sea floor is littered with kelp trees, destructible shells that drop pixels and plants that produce light.
It is possible that this biome, and its subtypes, will house Hylotl cities.
Three subtypes currently exist:
- Frozen Ocean Biomes are found in Frozen star systems and have the cold hazard, making it near impossible to explore without the Cold Protection nanosuit. Of the three subtypes, Frozen oceans are the only subtype that does not change the water into another liquid.
- Toxic Ocean Biomes, which can be found in Radioactive (and possibly Eccentric) star systems, change all surface water into poision and add toxic rain, making them one of the hardest Ocean subtypes to explore, even with the Radiation Protection nanosuit equipped. There appears to be no vegetation on the sea floor.
- Magma Ocean Biomes, found in Fiery star systems, turn all the water into - you guessed it - lava, and like other hot planets, they have extreme heat levels, making the Heat Protection nanosuit a must for exploring them. These are tied with Toxic for the hardest exploration due to overabundance of lava + other creatures that will probably kill you if given the opportunity.