Food web structure and trophic diversity for the fishes of four islands in the Pearl River Estuary, China

The Wanshan Archipelago, situated in the Pearl River Estuary, stood as a key fishing ground in China, boasting abundant fishery resources. To investigate variations in trophic niches and food sources among different islands within the Wanshan Archipelago, and to advance research on fish food webs and energy flow in the Pearl River Estuary, this study conducted a survey of fish communities in nearshore islands (Guishan Island, Dongao Island) and offshore islands (Wailingding Island, Wanshan Island) using triple gill nets during the autumn of 2021. The trophic niche characteristics of fishery organisms in these islands were analyzed utilizing carbon and nitrogen stable isotope technology. The results indicated that trophic niche width and biodiversity of fish communities in the nearshore islands surpassed those in the offshore islands, and the food chain length exhibited a trend of Guishan Island (4.04) > Dongao Island (3.98) > Wanshan Island (3.91) > Wailingding Island (3.86). The trophic niche indexes (CR, NR, CD, and SEAc) of fish communities in nearshore islands were higher compared to those on offshore islands, while MNND and SDNND suggested that fish communities in offshore islands were at a lower trophic level. Zooplankton emerged as the primary food source for fishery organisms in the Wanshan Archipelago. Feeding rates on zooplankton were 68.8 % and 70.4 % in Guishan Island and Dongao Island, and 53.7 % and 58.0 % in Wailingding Island and Wanshan Island, respectively. The proportion of benthic organisms fed near offshore islands was higher than nearshore islands. This study speculated that the fish in nearshore islands may shift from zooplankton food chain to benthic food chain. In addition, this study compared the trophic niche differences among the four islands in the Pearl River Estuary, clarified the diversity of feeding sources and trophic structure within fish communities, and revealed significant distinctions in fish food webs between the islands inside and outside the Pearl River Estuary. It will provide new information on the trophic interactions of fish in the Pearl River Estuary, and help to promote the ecological development and sustainable use of fishery resources.