Factors influencing seed germination and seedling establishment of the threatened seagrass, Zostera caespitosa: Implications for seed-based restoration

Abstract

The seagrass Zostera caespitosa is undergoing a notable decline within its native range along the Northeast Asian coast. We examined the effects of the seed source population, salinity (0, 15, and 30 psu), and temperature (5 and 20 degrees C) on germination rate and subsequent seedling growth under both field and controlled laboratory conditions to assess the potential for seed-based restoration. Seeds collected from Tongyeong (TY seeds) were larger than those from Jangmok Bay (JM seeds), resulting in an increased germination rate; however, seed size did not influence subsequent seedling growth. In the laboratory experiment, the optimal conditions for seed germination (15 psu and 5 degrees C) differed from those for seedling growth (15 psu and 20 degrees C), for both seed sources. In the field experiment, the seedling density from TY seeds was significantly higher than that from JM seeds during the first three months following germination, with no significant difference by the end of the experiment. These results suggest that additional environmental or biotic factors, such as competition and herbivory, strongly influenced seedling growth and successful establishment. Overall, our findings provide essential insights into the sexual reproduction of Z. caespitosa for seed-based restoration efforts and contribute to increasing public awareness of the conservation and management of this threatened species.