The Biosphere 2 coral reef biome
The Biosphere 2 coral reef biome is a large tank of living coral reef organisms (water volume of 2650 m3, water surface area of 711 m2 and 590 m2 of reef benthos). The water of the biome is characteristically very low in dissolved nutrients and phytoplankton. The present community of organisms is largely comprised of macroalgae, including 11 genera of green algae, eight genera of red algae, two genera of brown algae, and some blue-green algae. There are 25 genera of coral and two genera of sponges, but they do not dominate the benthos. Fish comprise 16 genera, with seven genera of echinoids and three genera of crustaceans. The coral reef biome water is presently monitored continuously for temperature, salinity, light, O2, and pCO2, and monitored daily to weekly for alkalinity, ΣCO2, pH, nutrients and δ13CDIC and δ18O water values. There are a number of filtration devices, pumps and aerators which have been used in the past to manipulate water movement and composition, but at present the community has come to steady-state without this machinery. Diel changes in O2 and CO2 allow measurements of community metabolism under different experimental conditions of water chemistry, water motion, seasonal light changes, and temperature. Typical values for community metabolic parameters under steady state conditions are: gross production (P), ∼290 mmol C m−2 d−1, respiration (R), ∼270 mmol C m−2 d−1, P/R, ∼1.1 and community calcification, ∼23 mmol CaCO3 m−2 d−1, or only 8% of gross production. Calcification rate has been altered, 0–140 mmol CaCO3 m−2 d−1,, and is positively correlated to saturation state or CO3−2 concentration. The community metabolism values are about half of a natural tropical algal/coral reef flat, but typical of high latitude, shallow, coral reef lagoonal environments. Even though there are some peculiar characteristics of the Biosphere coral reef, the coral reef biome functions as a recognizable coral reef community. The Biosphere 2 coral reef system offers an excellent opportunity to test questions of how environmental factors influence processes at community and organismal scales.