The Ocean

Definition of the ocean:

The ocean can not be understood as a single body of water but a labyrinth of countless bridges and tunnels connecting two points. Navigating such a place is already difficult enough and now imagine those bridges and tunels breaking down, reforming and changing directions seemingly without warning.

Those are the Oceans.
Treacherous, deadly and beautiful.

This frickle and unstable construt is in a sensitive balance. The deeper one traverses the closer one gets to the worlds spiralling centre. With that the currents gain stability but also pick up a lot of momentum, strength and are much denser in mana.

Among this there are islands, floating in the water, serving as the ocean floor to those living on them.

To put it into comparison for any potential land living species..
While the upper layers are dangerous, deadly and hard to navigate for your kind, they are tame in contrast to the depths. Your kind struggles navigating and conquering a breeze while my brethren ride a hurricane.

— Satirical side note from the author of this text

Adaptability

The islands are not as stable as continents due to their smaller size and being surrounded on all sides by the currents. They move and with that several shifts can occur. The density of mana, available light, nutrition, flora and fauna. Many animals that aren't highly adaptable move from island to island through the many winding tunnels whenever an islands becomes unsustainable for them.

Thus the need for adaptation is essential for thriving in the oceans of this world.

In general the further one traverses into the centre the stronger and stranger the creatures become.

Navigation

Outside of the laylines, navigation is extremly difficult. Despite sailing in a seemingly straight line it can happen, that one finds themselves on the other side of the world without warning. When seeing land in the distance it can turn out to be an entirely different continent. Navigating the waters requires a specialist. As someone who studied the star skies and learned how to use the many complicated instruments The Navigator is highly sought after.

Thus mapping out the world proved difficult if not impossible. It was agreed upon by all known nations to map out the world alongside the known stable lay lines connecting the continents and to base distance between them off of travelling time. However inaccurate that may be, it is the only measurable option.

It is unknown how many islands or even large masses of land are not discovered, hidden away admits the worlds temperament.