The marine environment of Kerbin is similar to that of Earth. The seas are populated by thousands of sea creatures, belonging to lots of aquatic clades. Many of these are basal lifeforms, overall, as the water is where all life tends to start. The oceans of Kerbin are strewn with fish, and Acanthocerebrans, along with other clades of aquatic Kerbarthropods and Malacopods. The seas also are full of biomes similar to those on land, creating niches which attract all sorts of lifeforms. The Great Kerbinian Ocean is the Largest of the oceans on Kerbin, followed by the Loveheart Ocean. The Koralian sea, which is located between Kafrica and the continent to the west, is a suitable environment for many coral like species. The weirdly cool waters towards the Koralian strait have caused this large continent to have a large desert on its Eastern side.

The coasts are strewn with coral like organisms and aquatic plants, an ecosystem perfect for many organisms to call home. In the deep sea, Tunicans, a Kerbinian clade which is a mishmash of Echinoderm, Tunicate and Hemichordate organisms, Kerbostomes, and Eozoan bilaterians tend to be prolific in deep sea and far away from the coasts. Rivers and estuaries are mostly inhabited by Acanthocerebrans, along with some river-lying fish, and semiaquatic animals, like the crocodile-like Asterosuchids.