Tom Gerald T. Genovia1, Bienson Ceasar V. Navarte1, Lourie Anne R. Hinaloc1 and Michael Y. Roleda1
1 Algal Ecophysiology Laboratory , The Marine Science Institute, University of the Philippines Diliman, Quezon City 1101, Philippines.
The supply of macronutrients nitrogen (N) and phosphorus (P) regulates seaweed photosynthesis, growth, and subsequent flow of photosynthate into various biochemical compounds. This study investigated the growth performance and biochemistry of Kappaphycus alvarezii (strain TR-C5) under control (ctrl/ambient seawater), and one-time (1×, i.e., only at the start of the experiment) and intermittent (5×, i.e., every 10 days) pulse feeding with inorganic nutrient using a commercially available, ammonium-phosphate (16-20-0 NPK composition) fertilizer under hatchery condition for 50 days. Fertilization every 10 days showed significantly higher growth rate, and greater nitrogenous (e.g., chlorophyll a and protein) and carbon-based (carbohydrate) compounds compared to the ctrl and 1× treatments suggesting that the fertilization strategy employed had a direct effect on N and carbon (C) metabolism. Conversely, inorganic nutrient fertilization negatively affected the carrageenan yield and quality (viscosity and gel strength) where the ctrl produced the highest values compared to 1× and 5× treatments. In this regard, the use of inorganic nutrient fertilizer employed by commercial seaweed farmers to enhance production and minimize incidence of e.g., ice-ice disease must be properly managed without compromising carrageenan yield and quality. When additional nutrition is applied, and maximum growth and biomass are already achieved, the farmed Kappaphycus should be allowed to metabolize excess nitrogen for at least 14 days from the last pulse feeding schedule. This will allow the seaweed to allocate C for the production and storage of cell wall polysaccharide.