Coastal Ecological Connectivity between Seagrass Bed and Marine Ranching 30 km Apart: A Case STUDY of Apostichopus japonicus Feeding on Seagrass Debris in the Bohai Sea, China

Coastal ecosystems form interconnected networks that are essential for the maintenance of marine biodiversity. This study investigates the dietary patterns of Apostichopus japonicus (sea cucumber) within a marine ranching ecosystem and reveals the influence of Zostera marina (seagrass) leaves from a distant bed on nutrient availability and trophic connectivity. Samples collected between September 2020 and March 2021 from Xiangyun Bay included A. japonicus, macroalgae, phytoplankton, and seagrass leaves. Stable isotope analysis (delta C-13 and delta N-15), in conjunction with Bayesian mixing models, elucidated the contributions of different food sources to A. japonicus' diet. Macroalgae constituted more than 50% of A. japonicus' diet, while seagrass contributions ranged between 5.7% and 11.3%. The isotopic analysis confirmed the presence of seagrass debris in the marine ranching environment, indicating significant nutrient transport from a remote seagrass bed. This study underscores the crucial role played by macroalgae as the primary source of nutrients for A. japonicus within a marine ranching setting. Furthermore, detecting seagrass debris from a distant habitat highlights previously unrecognized ecological connectivity between seagrass ecosystems and artificial reef environments along coastal areas. This understanding of long-range nutrient transfers is vital for effective management and conservation strategies in coastal marine systems, emphasizing intricate yet significant ecological interdependencies across coastal environments.