Coral growth in high-nutrient, low-pH seawater: a case study of corals cultured at the Waikiki Aquarium, Honolulu, Hawaii

Fifty-seven species of hermatypic corals have been maintained and grown in high-nutrient seawater at the Waikiki Aquarium, Honolulu, Hawaii. In this study we document the chemical conditions of aquarium water in terms of dissolved nutrients and carbon. Aquarium water is characterized by concentrations of inorganic nutrients that are high relative to most natural reef ecosystems: SiO3∼200 μM; PO4∼0.6 μM; NO3∼5 μM; NH4∼2 μM. In contrast, concentrations of organic nutrients are lower than most tropical surface ocean waters: DOP ∼0.1 μM and DON ∼4 μM. The incoming well-water servicing the facility has low pH, creating over-saturation of carbon dioxide. The coral communities in aquaria took up inorganic nutrients and released organic nutrients. Rates of nutrient uptake into aquaria coral communities were similar to nutrient uptake by natural reef communities. Coral growth rates were near the upper rates reported from the field, demonstrating corals can and do flourish in relatively high-nutrient water. The growth of corals does not appear to be inhibited at concentrations of nitrogen up to 5 μM. Statements implying that corals can only grow in low nutrient oligotrophic seawater are therefore over-simplifications of processes that govern growth of these organisms. Some basic guidelines are given for maintenance of coral communities in aquaria.

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