Abstract: To characterize the food web structure of tropical marine, we analyzed the carbon and nitrogen isotope signatures, trophic levels, sources of basal organic matter, and isotopic niches of major consumers in the Wuzhizhou Island marine ranching, Sanya. Isotope analysis was conducted on 42 fish species and 21 invertebrate species from trawl net sampling. The δ¹³C values of fish ranged from -17.95‰ to -14.74‰ (-16.92‰±0.79‰), δ¹⁵N ranged from 10.94‰ to 15.44‰ (12.80‰±1.05‰), and trophic levels ranged from 2.98 to 4.33 (3.54±0.31). For invertebrates, δ¹³C values ranged from -17.77‰ to -13.35‰ (-15.82‰±1.24‰), δ¹⁵N from 7.08‰ to 12.08‰ (10.59‰±1.36‰), and trophic levels from 1.85 to 3.71 (2.89±0.40). Using the SIMMR model, we estimated the contribution of six basal organic matter sources, revealing that fish primarily relied on sedimentary organic matter (43.2%), while invertebrates mainly utilized benthic microalgae (47.6%). Isotopic niche metrics calculated via the SIBER model indicated that nitrogen range was 4.43‰, carbon range was 7.86‰, the total area of the convex hull was 20.39‰², the mean distance to centroid was 1.54‰, the mean nearest neighbor distance was 0.27‰, the standard deviation of nearest neighbor distance was 0.26‰, and the corrected standard ellipse area was 4.76‰². Compared with food webs in other marine, the food web of the Wuzhizhou Island marine ranching exhibited a broader trophic span and larger isotopic niche space, along with more diverse basal organic matter sources, indicating a complex nutritional structure, high biodiversity, strong ecological stability, and an overall healthy state.

Key words: tropical marine ranching, food web, stable isotope, Wuzhizhou Island