Science Daily has an article about using the ocean to reduce global warming, as I previously wrote about, only inorganically by adding lime to seawater. Producing lime releases CO2, but the reduced pH it provides makes the ocean absorb much much more CO2.
Another thing that I would like to encourage in oceanic farming is the direct feeding of human-farmed sealife, including whales. A few nations do eat whale still, particularly Norway. More and more types of fish are becoming rarer, but most people love seafood and don't want to give it up. In addition, the ocean is quite vulnerable to the famous "Tragedy of the Commons" situation, since fishers have every interest in grabbing as many fish as they can, but the ocean produces a limited number of fish, which goes further down because the human caught fish are now dead (and eaten) and do not reproduce.
However, death is not the only possible change to animal demographics. Well fed animals should have more offspring. Further, the diet of commonly harvested animals is already well known, and at some level, we should be able to modify the food chain so that more food is available to these animals.
As an example, let us take Krill, a common crustation eaten by whales, carnivorous tuna, and occasionally humans. Krill feeds entirely on plankton, which is the also the food of many other commercial fish, such as Herring. Plankton is also the only food source of fish larvae. Clearly, Plankton is the thing to influence.
Plankton are simple plants, and the animals that feed on them. The "plankton" designation covers a large number of species of plants and animals, that have the following traits in common:
* Small size (the largest plankton are about 20 mm long.)
* Not mobile enough to resist ocean currents. (Some species can move several hundred meters per day, but not fast enough before the ocean moves them more.)
Since plankton either are plants ("Photoplankton,") or eat plants, the lime-treatment is a good first start. More carbon in the water means it is easier for the plants to produce the complex sugars that power their metabolism.
We should also fertilize some areas very carefully. If we add too much, an Algal bloom occurs, which leads to a dead zone if the algae decay without being eaten. The dead zone occurs because the dead algae sink to the bottom, and bacteria consume the dead algae, using up all of the oxygen in the water. Plant produced oxygen is consumed by the bacteria before animals use it, so all of the animals die, and plant growth is ended by surface-floating plants that block the light. Therefore, fertilization should mostly occur in areas with strong and changing currents, and not more often than, say, one tanker per month.
For best results, the "fertilizer" should actually be merely water from a dead-zone area, which occurs from water-leached fertilizer from farmland anyway. This will have the effect of a lesser bloom out in the open ocean, where it can actually feed the ocean's animals, and reducing the bloom near the coast, where it quickly grows to pathological dead-zone levels.
Secondly, if we pay every fisher in the world to not fish for a month, this will be significantly more effective. They will notice greatly enlarged catches after the month. That would probably be impractically expensive.