Supporting data for “Coastal urbanization: impacts on cryptobenthic fishes and food safety”

Next, I examined cryptobenthic fish community composition in Hong Kong, by coupling invasive collection with environmental DNA (eDNA) metabarcoding, to determine which abiotic factors drive their distribution along a pollution gradient. Cryptobenthic fishes emerged as valuable bioindicators of environmental pollution, exhibiting varying degrees of sensitivity to environmental degradation for both sampling techniques. Although their overall species richness is comparable to that observed in pristine reef sites, the urban community is dominated by a limited number of species, signalling intense anthropogenic impact.

Their abundance was higher at highly urbanized sites and significantly driven by nutrients, as tolerant species like <i>T. trigonocephalus</i> were associated with higher total inorganic nitrogen and total inorganic phosphorus. Crucially, environmental DNA proved to be a reliable tool for species detection in turbid waters, detecting 57 species compared to just 17 species via conventional invasive sampling. I then examined the biotic factors shaping their distribution, by integrating eDNA and collection data with benthic community surveys and gut content analysis of the most abundant cryptobenthic fishes.

I have uncovered that their distribution is not constrained by bottom-up resource limitations, instead, it is regulated by a top-down effect, where diminished predation pressure allows these small fishes to proliferate at highly urbanized sites. Furthermore, gut content analysis demonstrated that high dietary adaptability and a generalist feeding strategy enable these species to prosper in urban environments. Finally, adopting a One Health framework, I evaluated the potential public health risks associated with live seafood sold at local wet markets in Hong Kong.

Through bacterial metabarcoding of live fish skin tissue, eDNA analysis of holding tank water, and PCR screening for seven antimicrobial resistance (AMR) genes, I detected several potentially zoonotic or opportunistic pathogens, including the genera <i>Vibrio</i>, <i>Campylobacter</i>, and <i>Shewanella</i>. Moreover, all fish specimens harboured AMR genes on their skin, including the multidrug efflux pump gene <i>mexB</i> and the anthropogenic pollution proxy <i>intI1</i>.

Collectively, these findings advance our understanding of how coastal urbanization reshapes marine communities and fuels public health risks, providing insights for integrated management of urbanized coastal ecosystems.</p>