Conventionally, microalgae have been cultivated on land using raceways and photobioreactors. Developments on ocean-based algal culture systems started with possible benefits from large cultivable area, relatively stable temperature, restless waves, and etc., that could help ease resource requirements. In this study, floating algal culture systems were developed, and Tetraselmis sp. MBEyh01L was cultivated in the coastal water of Young-Heung Island, Incheon, Korea. As the results, biomass productivity was positively correlated with solar irradiance, seawater temperature, and wave energy. The highest biomass productivity of 25.6 g/㎡/d was achieved in July with the one-month average of 12.9 g/㎡/d. In order to achieve high biomass productivity, high solar irradiance and high wave energy were crucial. Development of floating culture systems with efficient conversion of wave energy into culture mixing will be needed to improve biomass productivity in ocean-based algal cultivation.