The Biosphere 2 ocean simulates a Caribbean reef. It is a very large tank with a surface area of 35 x 20 meters (100 x 60 feet). It consists of a southern portion 7 meters deep (21 feet) and a northern shallow lagoon, partially separated by a fringing reef. The mesocosm is housed within a high grade, corrosion resistant 6XN stainless steel container. During construction this steel was coated with a paint epoxy resin to hinder corrosion and to reduce leaching of metals into the ocean water. The total water volume of the Biosphere 2 ocean is roughly 2,600,000 liters (676,000 gallons). The system houses about 25 species of hard corals, 15 species of fish, 25 species of algae, and over a hundred invertebrate species.
The reef system is total enclosed like other biomes within the Biosphere 2 structure. Unlike most aquaria, animals are not fed. In fact this ocean is big enough to allow all organisms to rely on the internal food chain supported by algae and coral photosynthesis. Light levels are relatively low due to a combination of latitude (32.5° North outside of the tropical reef belt) and shading by the overhead glass and space frame structure. Nonetheless, the measured rates of primary productivity, calcification and nutrient uptake are comparable to those of tropical reefs. Survival of hundreds of species with minimal husbandry over almost a decade, demonstrates that the system and its food web are largely self-sustaining.
Four principal types of substrate were incorporated into the reef: Arizona calcium carbonate-rich clay, Arizona limestone boulders and rocks, Caribbean limestone rubble, and Caribbean aragonite sand. Crushed oyster shells fill the cracks and crevices between large rocks. Aragonitic sand covers the foundation sediments the deep ocean, the lagoon, and the beach.
Numerous mechanical systems simulate or substitute for natural environmental processes. A wave generator and a series of five air-lift pumps, are currently available to circulate water within the tank. Only the wave generator is in continuous use. A series of centrifugal pumps circulate water from the ocean to a separate room where the water is supplied to large experimental flow-through tanks and to heat exchange units. Two heat exchange units control the temperature of the ocean. They consist of large tubs containing plastic coils fed with hot or cold water from the Biosphere 2 Energy Center. Manually operated ball valves control the flow of hot and cold water through the coils. A series of filtration systems were initially installed, including algal turf scrubbers, protein skimmers, plate filters, and rotary drum filters. Over the last two years, it has been recognized that the ocean biota is very efficient at recycling nutrients and all mechanical filtration has been interrupted