AUTHOR=Kim Seung Hyeon , Kim Young Kyun , Kim Hyegwang , Lee Kun-Seop 

TITLE=Recolonization Dynamics of Warm Affinity Halophila nipponica in a Temperate Seagrass Meadow With Zostera marina

JOURNAL=Frontiers in Marine Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00500

DOI=10.3389/fmars.2020.00500

ISSN=2296-7745

ABSTRACT=<p>Because <italic>Halophila nipponica</italic> has only recently been reported in the temperate coastal waters of the northwestern Pacific, the recolonization dynamics of this species have not yet been investigated in temperate seagrass meadows. <italic>H. nipponica</italic> typically occurs in monoculture or in mixed meadows with <italic>Zostera marina</italic>, the most abundant seagrass species in this region. In this study, un-bordered and bordered gaps (0.5 × 0.5 m) were created in a mixed seagrass meadow of <italic>H. nipponica</italic> and <italic>Z. marina</italic> at Namhae Island on the southern coast of Korea to compare recolonization dynamics of the two species. Un-bordered gaps were marked using only a steel stake at each corner, while the margins of the bordered gaps were blocked to a sediment depth of approximately 20 cm using stainless steel blades to prevent penetration of seagrass rhizomes. Shoot densities of <italic>Z. marina</italic> and <italic>H. nipponica</italic> were measured in the gaps and in natural reference plots to estimate percent recolonized. In the bordered gaps, a few <italic>Z. marina</italic> seedlings and <italic>H. nipponica</italic> fragments were observed during winter, but no shoots of either species survived to the end of experiment. In the un-bordered gaps, the density of <italic>H. nipponica</italic> increased rapidly, with approximately 60% recovery after 2 months and reaching 85% after 10 months through only asexual reproduction via clonal growth. By contrast, recolonization of <italic>Z. marina</italic> was much slower than that of <italic>H. nipponica</italic>, with only approximately 25% recovery after 10 months through vegetative growth and recruitment of a few seedlings. Thus, small fast-growing <italic>H. nipponica</italic> rapidly recolonized, compared to relatively large slow-growing <italic>Z. marina</italic> in the small-size gaps. Asexual reproduction was the principle reproductive mechanism for the recolonization of both <italic>Z. marina</italic> and <italic>H. nipponica</italic> at the study site. According to our results, gaps created naturally and anthropogenically in mixed seagrass meadows may be primarily recolonized by <italic>H. nipponica</italic> rather than <italic>Z. marina</italic>, leading to a change in the seagrass ecosystem structure in Korean coastal waters.</p>