The waste problem in the other points of the production chain is indeed massive and solvable. The idea that fresh produce is sent to stores only to have a fraction being bought is a massive waste in both food and introduction of additional middle man. Online markets for food could fix this, but I have yet to see one that can compete on prices. It might happen once transport costs go down.

To go back to marine ecosystem, those that are on the brink of collapse is so mainly because of 3 causes. Pollution, invasive species, and over overfishing towards specific fish stocks. Both invasive species and overpopulation caused by eutrophication could actually use an increase in fishing in order to increase biodiversity, but a common element in both is that no one want to pay for it. To my knowledge it actually common problem in many fresh water lakes.