The land is still there, same as before. The ocean is full of water, which can be desalinized. We're a long way from not being able to grow enough food,meat or otherwise.
And how much energy is required to desalinized ocean water?
The issue isn't just food supply shortages. It's distribution. The western world is largely obese, wastes a fair portion of the food that it produces and yet tens of thousands can still die from famine every day. If the energy costs associated with distribution goes up then so do food prices. Poor countries are the first to suffer famines. Developed countries have enough funds to to cover the higher food costs so they'll be fine, hopefully.
Ocean rain isn't salty. It's fresh.
Obese people will last longer without food if they can keep from going into shock.
Supply chains that are problemsome are cause to be such by greedy people trying to control the rest of us.