Sigh.

It's clearly some afterbirth/placenta or biological part of a large fish probably a whale.

At 4:00-4:20 it looks like an umbilical cord. You can see veins throughout the entire object.

Many of you are mistaken in thinking this creature is moving when you don't realize that the camera is moving on a mounted vehicle, therefore your perspective is reversed.

There are plenty of undercurrents in the ocean and this is clearly animal waste products flowing in the ocean.

But whatever keeps you glued to nothingness, more power to you.