Degradation Rate and Influencing Factors of Sacharina japonica Debris from the Sanggou Bay Mariculture Ecosystem

Abstract:

When mariculture Sacharina japonica decay, a large amount of nutrients will be released into the ocean, which will affect the stability in the marine ecosystem. In a 27-day experiment, we investigated the decay rate of Sacharina japonica in the Sanggou Bay and how this process be affected by environmental condition. To determine the effects of the sediment and dissolved oxygen (DO), we set up two conditions including the sediment-containing group and the sediment-free group, and other two conditions about DO including aerobic or anaerobic group. Fluxes of DIN, DON, TN, DIP, DOP and TP were determined during the incubation period. The results were shown as follows: (1) At the end of experiment, the fluxes of DIN, TN, DIP and TP in sediment-containing group were 1.234, 1.802, 0.028, and 0.033 µmol/(g×d) respectively, which were significantly higher than those in the sediment-free group, suggesting that sediment could promote the decay of kelp. However, the flux of DON [0.568 µmol/(g×d)] was significantly lower than that of the sediment-free group. (2) Anaerobic conditions facilitated the release of P from kelp debris and more DOP was released than DIP. The decay rates of TP, DIP and DOP were significantly higher in the anaerobic conditions. However, the release rate of DIN and TN [0.097 μmol/(g×d)] under anaerobic conditions was only 8% and 71% of those under aerobic conditions respectively. (3) The N:P ratio significantly increased to 207.83±301.37 in the sediment-containing group, whereas it decreased to 9.38±6.55 under the anaerobic condition, both of which were distinct from the control group 16.82±1.26. These values were also largely different from the value of Redfield (16:1). Our results suggested that the decay of S. japonica detritus was a fast process and that intensified detritus decay could alter the concentrations and structure of nutrients.