Analysis of grazing effects on the biomass dynamics of Ecklonia cava

抄録

Relationships between the rate of biomass change and standing biomass of Ecklonia cava are classified into three types: 1) the rate of biomass change is positive under a stable equilibrium that is maximum biomass, 2) the rate of biomass change is negative for all biomasses, and 3) the rate of biomass change is positive between the maximum biomass and an unstable equilibrium that is the minimum biomass required for a persistent E. cava stand. Where the biomass change is positive, E. cava can grow. If the biomass is larger than the minimum biomass required for a persistent E. cava stand, then the bed will persist by overcoming the instability. On the other hand, if the biomass change is negative for all biomasses or the biomass is smaller than the minimum biomass required for a persistent E. cava stand, then the biomass will eventually become zero. The maximum biomass decreased with increasing attenuation coefficient and water depth. The minimum biomass required for a persistent E. cava stand is formed with feeding rate that exceeds threshold. The feeding rate on the threshold is affected by water depth and the attenuation coefficient that characterizes the amount of light at the seafloor. Value of the minimum biomass required for a persistent E. cava stand is increased with increasing feeding rate and water depth. Vertical distribution of E. cava was affected not only by the amount of light but also by grazing intensity.