PS 49-148 - Marine Protected Areas increase the distribution and stability of seagrass, Zostera marina meadows: guideline for Marine Protected Areas on seagrass beds

Background/Question/Methods

Seagrasses are flowering plants that live submerged in the marine environment. Seagrasses play a significant role in carbon sequestration, coastal protection, mitigating climate change and supporting biodiversity. However, seagrasses are in decline globally due to anthropogenic and natural disturbances. When compared to coral reefs and mangroves, seagrass meadows are among the least protected habitats. One of the best-known strategies for protecting or restoring seagrass meadows is establishing Marine Protected Areas (MPAs) that alleviates the impacts of climate change and human activities. However, relatively few studies have assessed the effects of MPAs on seagrass meadows. The main goal of this study is to investigate the effect of MPAs on seagrass population and distribution. This study was conducted on a monotypic meadow of Zostera marina at Tokkiseom (on the northeastern coast of Jeju Island, Korea) which was designated as an MPA in 2016. Morphological characteristics, biomass, density and production of Z. marina in relation to the coincident measurement of environmental conditions were monitored from April 2015 to February 2022. The biological and physiological data of Z. marina were documented before and after the MPAs designation. In addition, the meadow area was measured monthly from May to December 2021 using the drone.

Results/Conclusions

There were no significant differences in water temperature, underwater irradiance and nutrients concentrations between 2014-2016 and 2019-2021. The area of Z. marina meadows has increased rapidly after Tokkiseom was designated as a MPA in December 2016. In April 2015, 20 months before the designation of MPA, the estimated area was approximately 4,438 m². The area was nearly 3.1 times larger (14,026 m²) in October 2019, 34 months after the designation of MPA. This indicates that MPA seems to increase the distribution of Z. marina meadows through a combination of direct and indirect effects. The shoot density in 2019-2021 was higher than that in 2014-2016. However, shoot height, total biomass and leaf productivity conspicuously decreased in 2019-2021 compared to 2014-2016 levels. These results suggest that increased shoot density in a limited space results in intraspecific competition, thereby reducing the size and individual weight of shoot. Thus, determining the optimal scale of protected area to provide for the maintenance of populations of plants and animals is critical to the success of MPAs. This result provides valuable information for designating MPAs on coastal seagrass ecosystems.