The Effect of Light and Ammonium on Growth, Epiphytes and Chemical Constituents of Gracilaria conferta in Outdoor Cultures

The relationship between Gracilaria conferta growth rate, its epiphytes’ biomass and its chemical constituents was determined under various conditions of irradiance and pulse-fed ammonium concentration in an outdoor culture system. Under summer conditions, high pulse-fed ammonium concentration and relatively low irradiance promoted the growth rate of Gracilaria conferta and inhibited its epiphyte biomass, presenting a competitive relationship. Growth rate of Gracilaria conferta in summer showed an inverse relationship with ash free dry weight, C/N ratio and phycoerythrin to chlorophyll a ratio, and a positive relationship with ash, chlorophyll a and phycoerythrin content. Under winter and autumn conditions, the irradiance became the only limiting factor of growth rate of Gracilaria conferta. These results are related to the common model of relationship between environmental factors and the response of growing seaweeds.