Unveiling the trophic dynamics and ecological roles of demersal fish in Hong Kong: A metabarcoding and isotope analysis approach

Abstract

This study provides a comprehensive examination of the trophic ecology and feeding dynamics of 16 demersal fish species inhabiting the southern and southwestern waters of Hong Kong, utilizing advanced 12S and COI gut content metabarcoding alongside stable isotope analysis. Dietary dissimilarities, primarily driven by Decapoda and fish, are significant among species. Network plots further highlight unique predator-prey interactions. Eight species, including horn dragonet Callionymus curvicornis and Japanese butterflyray Gymnura japonica, are identified as piscivores, primarily preying on demersal fish, while six species such as rough flathead Grammoplites scaber and Japanese flathead Inegocia japonica are classified as crustacean feeders, focusing on Decapoda. Notably, spotted sicklefish Drepane punctata and goatee croaker Dendrophysa russelii exhibit unique feeding behaviors, relying on brittle star and Bivalvia, respectively, and demonstrate non-selective feeding patterns that do not prioritize dominant environmental species. This diverse range of prey consumption highlights the critical roles these fish play in regulating demersal fish and benthic invertebrate communities. The study also reveals clear trophic niche partitioning with low isotope niche overlap, predominantly below 55.30%, except for a notable overlap of 72.91% between bartail flathead Platycephalus indicus and goatee croaker D. russelii. Our results established essential baseline data on trophic niche diversification and resource partitioning through varied dietary preferences, facilitating coexistence and resilience within the ecosystem. This research serves as a foundational assessment of the trophic dynamics and ecological stability in Hong Kong's marine ecosystems, offering valuable insights into anthropogenic pressures and guiding the development of specific conservation strategies aimed at preserving fish biodiversity and sustaining global fisheries.

Fig 1. Map of Hong Kong showing the sampling location of fish specimens and potential prey items.

Fig 2. Workflows of stable isotope analysis and gut content analysis.

Created with BioRender.com, under a CC BY license, with permission from BioRender, original copyright 2025.

Fig 3. Bivariate isotope plots for 16 fish species illustrating (A) δ¹³C and δ¹⁵N values, and (B) the mean and standard deviation (± S.D.) of these values.

(C) Biplot of corrected standard ellipse area (SEAc) and (D) density box plot of Bayesian standard ellipse area (SEAb) depicting the isotopic niche sizes for different fish species. Solid lines show standard ellipse area (40% of the data) and dashed lines show total convex hull area (100% of the data). Coloured boxes represent 50%, 75%, and 95% credible intervals, while central black dots and white ‘X’s represent modes and the SEAc point, respectively.

Fig 4. Bivariate isotope plot of δ¹³C and δ¹⁵N (mean ± S.D.) values for 16 fish species and other smaller fish and invertebrates as potential prey items.

Fig 5. Cluster dendrogram of diet dissimilarity (Bray-Curtis index) (A) and stacked bar charts showing dietary compositions based on prey frequency of occurrence (B) and relative read abundance (C).

Prey frequency of occurrence is calculated as (Number of samples with a specific prey group detected ÷ Total number of samples with prey detected) × 100. Relative read abundance is calculated as (Number of reads of a specific prey group ÷ Total number of reads of all prey groups) × 100.

Fig 6. Bipartite network plots showing the trophic interactions between the (A) epibenthic fish community, (B) hyperbenthic fish community, and their prey items.

The upper boxes represent the epibenthic and hyperbenthic fish species, and the lower boxes represent the prey items. The line thickness connecting prey to fish species represents the relative read abundance.

Fig 7. Two-dimensional non-metric multi-dimensional scaling (NMDS) ordination plots representing Bray-Curtis distances among prey items.

Fig 8. Bubble plot showing the relative abundance of prey items in gut content DNA.