THE EFFECT OF OUTDOOR CULTURE CONDITIONS ON GROWTH AND EPIPHYTES OF GRACILARIA-CONFERTA

The relationship between growth rate, dry weight and epiphyte biomass of Gracilaria conferta (Schousboe) J. & G. Feldman was determined as a function of diverse environmental conditions in an outdoor pulse nutrient addition cultivation system. The independent variables were seawater treatments (pH control, interrupted aeration and water recycling), nutrient supply (nitrogen and phosphate) and light quality variations. Controlled pH treatment compensated for low water exchange, only in summer growth studies. Daily interrupted aeration was as efficient as continuous aeration in maintaining growth rates; however, water recycling had a negative effect. Nitrate and ammonium additions were equally effective, but high phosphate levels inhibited growth of Gracilaria conferta. Exclusion of UV light or selective irradiation of green and blue light enhanced growth rates. Dry weight showed a major decrease under a high rate of water exchange and continuous aeration, presumably because of higher oxidation of organic matter. Dry weight was usually inversely related to growth rate. Relative epiphyte biomass decreased with water recycling and additional nitrate and increased when UV light was excluded. Epiphyte biomass did not show a consistent relationship to growth rate of Gracilaria conferta.