[A-HW18] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW18-P03] EVALUATION OF FISH SPECIES STRUCTURE IN THE COASTAL WATERS USING ENVIRONMENTAL DNA ON AN ISLAND SCALE

*Nhat Hong Nguyen¹, Mayuko Hamada², Mitsuyo Saito³, Shin-ichi Onodera³, Takuya Akinaga¹, Hideaki Nagare¹ (1.Graduate School of Environmental and Life Science, Okayama University, 2.Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, 3.Graduate School of Advanced Science and Engineering, Hiroshima University)

Keywords:environmental DNA, fish species, environmental factors, island scale

Due to their isolated position, coastal islands have some unique marine ecosystems and associated fish assemblages. Besides, coastal habitats are essential for providing a feeding ground, nursery areas, and reproductive habitats for fish diversity. It is important to understand the interaction between environmental factors and fish communities, but the information on fish communities that are structured by biogeographical and anthropogenic factors remains scarce. To date, most methods that have been used to investigate fish diversity were capture surveys (e.g., tow nets and beam trawls), however, traditional surveys potentially influence island ecosystems, and large-scale surveys are challenging. Thus, a rational method for surveying fish biodiversity is urgently needed. Environmental DNA (eDNA) metabarcoding uses DNA shed from organisms (e.g., skin cells, feces, etc.) that are present in water, air, soil, or sediment samples to assess community composition. This study examined coastal fish faunas around an island, using environmental DNA (eDNA) analysis, and aimed to detect the most relevant factor on fish species around a coastal island. Ikuchijima Island, located in the Seto Inland Sea, this small island has sandy beaches as well as rocky reefs and clusters of seagrasses and seaweed beds in the surrounding waters. The results showed that a total of fifty-four species of fish belonging to twenty-nine families were detected in the coastal seawaters of Ikuchijima Island. The dominant species in this area were Acanthopagrus schlegelii, Mugil cephalus, Pagrus major. Besides, temperature water and elevated dissolved silica (DSi) levels cause significant differences in the structure of local fish assemblages. Planktivore fish species have a significant positive correlation with DSi concentrations (r = 0.64, p-value = 0.02) and water temperature (r = 0.56, p-value = 0.05). The mean number of fish species was higher on the sites of the ‘seagrass bed’ and ‘sandy bottom’ than in both the ‘seaweed bed’ and ‘rocky-reef’ sites. These findings demonstrated that eDNA metabarcoding can be applied as an efficient method to conduct surveys on fish species in coastal waters and highlight the potential effect of DSi and water temperature on fish species composition and structure.

Acknowledgments
This research was supported by JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito) and Fostering Joint International Research (A) (No. 20KK0262, PI: Mitsuyo Saito).