Environmental drivers of coastal benthic community composition in the temperate transition zone of Jeju Island, South KoreaResistance, Resilience and Phase Shifts

Garance Perrois¹, Anna B. Jöst¹, Léonard Pons¹, Taihun Kim¹

¹Korea Institute of Ocean Science & Technology, Republic of Korea

Jeju Island, South Korea, lies in a marine climatic transition zone at the boundary between subtropical and temperate zones. Over the past half a century, the coastal waters of Jeju have recorded a rise in annual sea surface temperature by +1.23°C associated with an increase in heat wave and typhoon-frequency and -intensity, highlighting Jeju Island’s significant position as a climate change hotspot.
Jeju’s coastal benthic ecosystems are characterized by high abundance of organisms living at the limit of their physiological tolerance which make them particularly sensitive to changes in their environment. As a result, the sessile benthic communities have gradually changed from macroalgal-dominated to hard coral-dominated and "barren-ground" habitats making Jeju Island an excellent natural playground for climate change-related hypothesis testing.
This study aims to identify the most specific abiotic environmental factors that contribute to explaining the current spatial distribution of the declining temperate and expanding subtropical foundation species in Jeju waters.
Coverage and composition of sessile benthic communities were determined by photo-quadrat analysis at three sites along the island’s south, east, and north coasts. Divergences in community composition between sites were characterized in light of ten quantitative environmental parameters.
Our results show that while the south is defined by hard corals, predominately Alveopora japonica, the east is dominated by the temperate canopy-forming macroalga Ecklonia cava, and the north is characterized by coralline algae. Winter sea surface temperature, water transparency, nutrient concentration, and water movement were the most impactful environmental factors determining which foundation species constitute each distinct benthic community. This study provides valuable baseline information on the impacts of abiotic environmental factors on sessile benthic communities in a temperate transition zone.