Biofilm community structure and loading effect of netted cages for offshore aquaculture in the Western Yellow Sea

Biofouling on the netting limits the exchange of water flow within the net cage. This deteriorates the aquatic environment, increases the net cage load, and threatens the health of the farmed fish and the safety of the cage structure. In this study, we utilized net panels at offshore cage sites to continuously monitor the community succession of fouling organisms on netting at different water depths (0.5, 2.5, and 4.5 m), exploring the relationships between biofouling communities and environmental factors. The collected fouled nets were then subjected to hydrodynamic tests. In total, 22 taxa were identified, with motile species being predominant (54 %). Significant temporal and spatial variations in offshore cage cultures were observed in the succession of biofouling communities. The average abundance (∼6.22 × 10⁵ individuals m⁻²), average biomass (∼985 g m⁻²), and average percentage net aperture occlusion (∼0.99). Caprella aino (Caprellid), Jassa mormorata (Gammaridea), and Tubularia mesembryanthemum (Hydroid) were the most dominant species, and their abundances were closely related to the concentration of SiO₃^2--Si. Community changes in the fouling organisms were influenced by temperature (T), dissolved oxygen (DO), salinity (S), SiO₃^2--Si, PO₄^3--P, and NO₂^--N, with T and SiO₃^2--Si having the greatest influence. Hydroids significantly altered the hydrodynamic properties of the net panels in terms of current, increasing the maximum drag on the net panels by 6.09 times and the maximum lift by 15 times. These results have significant reference value for preventing and removing fouling organisms in offshore aquaculture cages and for the safety assessment of cage structures.