Unless humanity achieves United Nations Sustainable Development Goals (SDGs) by 2030 and restores the relatively stable climate of pre-industrial CO₂ levels (as early as 2140), species extinctions, starvation, drought/floods, and violence will exacerbate mass migrations. This paper presents conceptual designs and techno-economic analyses to calculate sustainable limits for growing high-protein seafood and macroalgae-for-biofuel. We review the availability of wet solid waste and outline the mass balance of carbon and plant nutrients passing through a hydrothermal liquefaction process. The paper reviews the availability of dry solid waste and dry biomass for bioenergy with CO₂ capture and storage (BECCS) while generating Allam Cycle electricity. Sufficient wet-waste biomass supports quickly building hydrothermal liquefaction facilities. Macroalgae-for-biofuel technology can be developed and straightforwardly implemented on SDG-achieving high protein seafood infrastructure. The analyses indicate a potential for (1) 0.5 billion tonnes/yr of seafood; (2) 20 million barrels/day of biofuel from solid waste; (3) more biocrude oil from macroalgae than current fossil oil; and (4) sequestration of 28 to 38 billion tonnes/yr of bio-CO₂. Carbon dioxide removal (CDR) costs are between 25–33% of those for BECCS with pre-2019 technology or the projected cost of air-capture CDR.

To meet growing seafood demands, the US aquaculture industry will need to consider farming the open ocean in a responsible manner. However, offshore environments can be energetic (seas > 8 m) making it difficult to maintain surface cage systems. To minimize potential storm damage, submerged culture technologies can be employed to safeguard the infrastructure and product. Steelhead trout (Oncorhynchus mykiss) have potential as an offshore species, though they have open air bladders (physostomous), and need access to air to inflate their swim bladders. To address this concern, three experiments were developed to explore the ability of O. mykiss to cope with extended periods of submergence. The studies used small (~300 g) and large (~1000 g) trout, in cages that ranged from 3.7 to 68 m³, that were submerged for periods of one to four weeks. Data storage tags (DST), sonar and video were used to quantify their ability to manage with submergence. Results indicated differences in growth, condition, and mortality among the treatments. The study suggests O. mykiss can be submerged for days to weeks with no negative effects, but that submergence times >3 weeks can be detrimental. It is therefore recommended that when culturing O. mykiss in areas exposed to severe storms or hazardous environmental conditions (e.g. harmful algal blooms or icing), submersible cages should be utilized to avoid these events up to 3 weeks.