Fig. 1. Conceptual diagram showing comparison of healthy ecosystem with eutrophic ecosystem. In a healthy ecosystem, nutrient inputs (e.g. nitrogen and phosphorus) takes a key role of maintaining the balance between the growth of macroalgae (red algae, brown algae, and/or green algae) and phytoplankton and their predator species as well as high water clarity. Appropriate density of phytoplankton and algae species contributes to the optimum DO level for fish species, and consequently, humans can take benefits from the marine environment. On the other hand, in a eutrophic ecosystem, large amount of emissions and nutrient inputs from farms, urban areas, factories, and sewage treatment plants are into the marine environment triggers rapid growth of phytoplankton, exceeding the consumption capacity of zooplankton and fish. This growth causes lower water clarity and decreased light penetration, lower DO, and decreased hydrophytes. Consequently, harmful algae blooms abnormally occur as well as water contamination and fish kill.