International Journal of Marine Science, 2025, Vol.15, No.3, 118-129 http://www.aquapublisher.com/index.php/ijms 124 was obvious species replacement and turnover between fish community DNA from 0 meters offshore of the coral reef and 250 m ~ 750 m offshore samples, and the abundance of reef groups detected in reef water samples dropped sharply in distant samples (Jaquier et al., 2024). This phenomenon shows that in coral reef environments with relatively mild hydrodynamics and complex terrain, eDNA signals mainly reflect local biomes and have less long-distance transmission. In addition, the seasonal flow and vortex of water masses may also cause eDNA enrichment or dilution in certain regions. Layering and mixing of water columns can also lead to differences in vertical distribution: the concentration and composition of the eDNA of the surface and bottom water bodies may differ depending on the intensity of the turbulent mixing. Figure 1 Species detected using environmental DNA (Adopted from Jaquier et al., 2024) 5.3 The mechanism of action of coral reef sediments on eDNA preservation and release The seabed of coral reefs is usually covered with a large amount of calcium carbonate sand particles, coral debris and other sediments. Studies have shown that a considerable portion of the eDNA in water bodies settles into benthic sediments in the form of particles, thereby reducing the DNA concentration in columnar water samples. Stoeckle et al. (2020) compared the eDNA attenuation under sediment conditions in the experimental environment, and found that the DNA concentration in the water sample was significantly reduced in the presence of sediment, while delayed release of DNA was detected in the sediment: even after the source organism was removed, the sediment still slowly released previously adsorbed DNA, resulting in the continued appearance of target DNA signals in the water. This phenomenon may be manifested in the wild as the target species has actually disappeared or distanced, but its DNA is lagging due to sediment storage and resuspended effects (Wu et al., 2024). Further quantitative comparisons found that the degradation rate of eDNA in sediments is more than one order of magnitude lower than that in water, and the concentration of DNA accumulated in unit mass sediments can be dozens or even thousands of times higher than that of water samples, indicating that coral reef substrates can serve as an important reservoir of eDNA. At the same time, the species composition reflected by the sediment and water bodies is slightly different in quality and quantity: water body eDNA is more representative of the current active species, while sediment eDNA is superimposed on species information over the past period (Sakata et al., 2020). Therefore, in the coral reef environment of Hainan Island, seabed sediments will prolong the tail of eDNA signals in time, which is not only conducive to detecting the historical existence of rare species, but also may bring the risk of "false positive". 6 Challenges and Solutions For the Application of eDNA Technology 6.1 Technical sensitivity and environmental interference issues Although the advantages of eDNA technology are obvious, it also faces challenges in sensitivity and reliability in practical applications. The eDNA test results may be affected by environmental conditions and there are false
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