Following the land-based aquaponics movement is a necessity. By expanding it, in coordination with biogas production, waste-handling and standard hydroponics, we can do more, with less. Agriculture for the incipient Seasteader falls into 5 obvious areas of practice, any or all of which benefit from working with nature, climate, and biology rather than against it. Choosing plants which will thrive in, on, or near the ocean is critical for success and efficient use of resources, including space, nutrients, fresh water, and manpower. The five areas are:
- Food & Fodder production (for humans and livestock)
- Fiber and building materials
- Fuel (including bio-diesel, bio-gas/methane, ethanol/methanol and plain combustion)
- Eco-remediation and environmental engineering (dealing with pollutants & waste streams, and physical concerns such as wave attenuation, erosion control, sun shade, and wind breaks)
- Psychological relief of visually austere environments, i.e. landscaping for beauty and comfort
The IMTA model, at home-scale, is primarily to handle animal and food waste. A biogas digester will treat the wastes, producing an organic effluent, that is nutritious to plants and effectively free of pathogens. By 'effectively' I mean the counts are so minuscule as to be undetectable (no lab is likely to certify it is 100% free of pathogens). The simplest way around that is an additional treatment by storage (sealed and anaerobic for 30 days at comfortable temps, less at higher temps), or other means (chlorination, irradiation, etc.).
The above describes waste handling and using the effluent in hydroponics. This is a simple process which hits three of the areas of agricultural practices listed above. To get Aquaponics, you have to include fish and re-utilize the fish wastes, as well... Since the hydroponics will only use 'X' amount of the effluent, the balance can be used, in less complicated hydroponics, to raise Duckweed.
Duckweed is a very adaptable waterborne plant. It has oil that can be pressed, for biodiesel, the resulting mass, when dried is high in protein. It is edible and used raw, in salad, etc.
Some fish are omnivorous. Tilapia is the typical freshwater aquaponics fish, though others are also used. Another choice is the Rio Grand Cichlid/Texas 'Perch' (NOT a Perch, but actually a native, distant cousin to Tilapia).
Basically, for aquaponics, fish eat and eliminate their wastes in their water, the water is then used as hydroponic plant food.
For open-sea pens, multi-trophic aquaponics relies on the same concept, but it's more of an open loop, allowing the water to go pretty much wherever, bring in new nutrients and washing out some nutrients.
Each section of this concept works, and is in practice, in various places. Stacking the process to use the nutrients in a more intensified manner is the innovation.
Macroalgae-Kelp... Kelp farming and Kelp as fish food is already in use, as is feeding Kelp to Abalone, in floating cages. Abalone yielding Mother of Pearl, the occasional pearl, and some great meat, as well. ( http://videos.howstuffworks.com/discovery/28310-dirty-jobs-feeding-some-abalone-video.htm11 )
This would be floating above the fish pens.
Top pen would have a feeder species of fish, that consumes kelp. The middle pen (conjoined), holds the market fish, which are routinely fed a portion of the feeder-fish. The bottom pen holds a shellfish/bottom-feeder, such as prawn, crabs, or even lobster. Any dead fish, from the other pens, can be chunked and fed to the bottom pen.
Now, not quite done... As the poop trickles down, it is collected, from beneath the shellfish and pumped back up, as food for the kelp and additional food for the Abalone.
Summing up, by raising kelp, feeding it to Abalone and feeder-fish, the IMTA should produce a reliable source of Mother of Pearl and Abalone meat, a Marketable fish, and a shellfish. By having a number of these, at various stages of development, there is a steady supply to market.