Enhanced production of Pacific dulse ( Palmaria mollis) for co-culture with abalone in a land-based system: effects of seawater exchange, pH, and inorganic carbon concentration

Abstract

Addition of carbon dioxide to cultured algae is generally considered necessary to maintain high yields and healthy cultures. However, this represents a major cost for commercial production. This study was conducted to determine requirements for dissolved inorganic carbon (DIC) to maintain high growth rates of Palmaria mollis or Pacific dulse. Methods for introducing DIC included additions of NaHCO 3, CO 2, and variable seawater exchange rates. Specific growth rates (SGRs) of P. mollis were positively correlated with ambient concentrations of DIC and cultures supplied with both CO 2 and NaHCO 3 resulted in higher growth rates than those supplied with either inorganic carbon sources alone. A pH of 8.9 resulted in growth rates that were not significantly different from those at pH 8.3. Adopting a seawater flushing regime that increased flushing during the light cycle (seawater exchange rate of 7.5 vol day −1) but lowered flushing during the dark cycle (0.65 vol day −1) resulted in growth rates equal to those obtained by maintaining pH at 8.5 by sparging with CO 2 at a daily exchange rate of 7.5 vol day −1.