On a habitable world completely covered in water, with no land above sea-level, there would presumably be storms of biblical proportions. Suppose this world has oceans so deep that the deeper layers just have too much pressure for life of any kind to survive - from the planet's organisms' point of view, the sea would essentially be bottomless.
Without any seabed for shelter/anchorage, but also without any land to be beached on, would gigantic storms, waves etc. be seriously harmful to underwater creatures? When I say "seriously harmful", I mean so damaging as to make the very existence of complex sunlight-zone life on the world dubious.
Two points for further clarification:
- The animals do not need to surface to breathe.
- Yes, they could potentially take shelter in some kind of floating reef/microbial mat, but ignore that for the purposes of the question.