Some good stuff in that video, but the key message for most people to get is that we could feed everyone on the planet from the land area of California, if it was farmed intensively, with full nutrient recycling (could be on a ten or twenty year cycle, time doesn’t matter, it only matters that we close the loop), and people were vegan.
Eating animals takes a lot more land (or ocean) than eating plants (about 10 times as much land, and 300 times as much ocean area – most of the deep ocean is essentially nutrient limited desert – with a few notable exceptions where current up-welling or dust deposition deliver nutrients to the surface photic zone allowing plants to flourish).
Getting silt from the bottom of hydro dam lakes could be a great source of mineral enrichment for soils also.
We don’t need to use the ocean, and we can.
We have done some nasty things to the ocean, dumping general and toxic and nuclear waste in it, so it isn’t nearly as pure as it once was.
There is also the problem of periodic toxic algal blooms, so one needs to constantly test seafood – such testing programs are in place in many countries, and they cannot be perfect with current technology (they are good at finding large blooms, but can still miss small ones).
So as people become more risk averse, as we get serious about living a very long time, I expect many people will tend to avoid seafood, for the risk factors involved – that while low in normal conditions, become more significant if one is intending to live for thousands of years, even though testing and screening technologies will undoubtedly get much better (we may all end up with food tasting and testing nanites that we sprinkle on our food and leave for 5 minutes before recovering them and eating the food if it passes all the tests.
I have lived near the sea most of my life, worked on it for 17 years, so am very conscious of just how harsh the marine environment can be. Storms at sea have amazing destructive capacity. And again, we will most likely develop the technology to tame and harness that power, but we’re not there yet. Its hard when you have to design things not simply to withstand massive waves, but also to survive 90ft 40T whales blundering into the system while disoriented by a storm.