The Baltic (Ostsee) was a nice little limnoral sea like a large lake half-connected to the worlds oceans. It is dead now below the top oxic level. It is maybe 250m deep in its middle, really comparable to a Very Great Lake, and all of us shorenations of it have long since tacitly made use of it: that place in the center of it is where Sweden, Germany, Poland, postsoviet succssor states et al. all are dumping toxic waste, munitions, and such crap. I mean, we have killed it already. Its dead. So it cant get deader. So we can use it as a dump. In the process we are probably creating a nice mineral reserve for some other species in a few million years. No oil was needed t0 kill that sea, industrial civilization upstream along all the rivers discharging into it was enough.

the north sea is still alive. But its pretty empty there now. a few fish, diminutive in comparison to what used to be. Algal blooms a regular occurrence now; also a new thing. Sharks trying to move in from the south as water warm. Some american mussel is currently wiping out preshore communities. not going very well in the north sea.

the deeper atlantic margin, I believe is still somewhat OK. I dont know much about that.

but basically, our seas who were amongst the worlds most productive, are already rid of their biomass, our fleets are currently taking the last big harvest in the southwest pacific, thereafter noone knows where to go.

we can do in the worlds oceans without oil.