Diurnal changes of oxygen budgets in Chlorophyta Ulva pertusa

Chlorophyta Ulva pertusa is easy to polyculture with fish in mariculture farms. Therefore, it has become a useful seaweed for the mitigation of eutrophication in these farms. In order to determine the oxygen budgets for this species, an experiment was conducted to monitor their respiration in culture. A respiration chamber of 750 ml was made by combining two glass funnels of a membrane filter. One g of U. pertusa was set in the chamber. The experiment was carried out on a window side of the rearing laboratory from January 5 to 11, 1997. Seawater in the tank in which was cultured the devil stinger Inimicus japonicus was pumped into the chamber by a peristaltic pump at a rate of 30 ml/min. The inlet water and outlet water of the chamber were drifted alternately to an oxygen electrode cell every 15 minutes. The process of which was controlled by a timer. The dissolved oxygen contents were continuously determined by a DO meter (YSI-57) and recorded on a pen-recorder (EYELA-TR-250). The difference of oxygen content between inlet and outlet was determined after the recordings. The water temperature in the chamber was maintained at 23.4 =+- 0.85degC by a thermostat. Sun light was illuminated the chamber during the day. The oxygen budgets in U. pertusa were affected by the weather. The amount of oxygen supplied by the U. pertusa was 22,238 ml/kg/d on cloudy days, 20,790 ml/kg/d on clear days, and 2,124 ml/kg/d on rainy days. The maximum amount of oxygen supplied was found on cloudy, not fine days. Total amount of oxygen produced during the day was 17,392 ml/kg/h, and the oxygen consumed at night was 4,728 ml/kg. The difference between production and consumption was +12,664 ml/kg. The oxygen produced during the day was 3.68 times greater than the oxygen consumed at night.