Longitudinal variation in fish prey utilization, trophic guilds, and indicator species along a large subtropical river, China

Abstract

Due to the heterogeneous distribution of resources along large rivers, understanding prey utilization by basin‐scale fish assemblages remains a challenge, and thus, recognizing regional fish trophic guilds and indicator species is important. We analyzed the stomach contents of 96 fish species along the subtropical East River in China and identified 8 prey items (29 subcategories). Site‐specific differences in fish diet composition (DC) revealed longitudinal shifts in utilized prey taxa, from upstream lotic to downstream semi‐lentic items, and these were characterized by a decrease in the proportions of epilithic diatoms and aquatic insect larvae (Ephemeroptera and Chironomidae) accompanied by an increase in bivalves (Corbicula and Limnoperna), shrimps and fishes, and organic sediments. The relative prey consumption weighted by fish abundance and biomass indicated that decreasing insect consumption and increasing detritus consumption were two fundamental vectors governing fish‐centered feeding pathways. Seventeen prey‐oriented fish guilds that were clustered based on DC matrix determined the spatial variation in the fish trophic structure. The cumulative presence of (a) upstream guilds reliant on insects and epiphytes, (b) midstream guilds reliant on hydrophytes, molluscs, and nekton, and (c) downstream guilds reliant on detritus, annelids, and plankton resulted in a longitudinal increase in guild richness, but this continuity was interrupted near the industrialized estuary. The most abundant 28 fish species across the guilds were selected as trophic indicator species; their spatial distribution significantly (p < 0.05) explained >80% of the environmental and prey variables identified. These species signified the availability of predator–prey links in distinct habitats and the key environmental factors supporting these links. With a high contribution (>51%) of exotic species, an increase in detritivores downstream distinguishes the subtropical East River from temperate rivers. Particularly, in the disturbed lower reaches, the dominance of detritivores prevailed over the predicted increase in other feeding groups (e.g., omnivores and carnivores).

Longitudinal pattern of resource utilization by aquatic consumers along a disturbed subtropical urban river: Estimating the relative contribution of resources with stable isotope analysis

“…Diatom‐dominated periphyton (epilithic biofilm) appeared to be the main autochthonous carbon source driving secondary production in the upper wadable stream (sites 1–3) of this subtropical urban river in the Northern Hemisphere. Previous investigations in tropical systems also reported that periphyton, despite forming an inconspicuous component of the total carbon biomass, is largely responsible for metazoan biomass (Bunn et al, 2003; Thorp & Delong, 2002; Wang et al, 2018b), whereas detritus from terrestrial vascular C 3 and C 4 plants plays only a minor role (Lau et al, 2009; Lewis et al, 2001).…”

“…Moreover, the longitudinal pattern of resource utilization by consumer FFGs in the Liuxi River was almost the same as that reported in the Waikato River of New Zealand (Pingram et al, 2012b), where the morphological features of hydrophytes and feeding habitats of fish/invertebrates in the two regions were similar. By comparing the habitat features provided in these studies, we speculated that, regardless of climate zone, the open canopy cover, pristine riffle habitats and cobble/gravel substrates, as well as the undisturbed hydrologic conditions (e.g., shallow depth and high flow velocity in the upper stream), were the determinants influencing the region‐specific carbon flows (Figure 6, also see Wang et al, 2018b; 2020c). Given that aquatic vegetation serves as a key substrate for biofilms as well as a habitat and refugium for aquatic organisms, riverine invertebrates prefer to dwell and hide in submerged hydrophytes, and thus, they often scrape the periphyton attached to the blade surface (Wu, 2016).…”

Partitioning fish communities into guilds for ecological analyses: an overview of current approaches and future directions

“…In this case, guild classification is generally qualitative and requires minimal data beyond general natural history, with each group likely encompassing large variation in feeding ecology, again, typically focused on the adults of the species. In contrast, trophic guilds can be created at a much finer resolution by defining more specific resources (e.g., Auster and Link 2009;Wang et al 2018). This latter approach typically leads to a larger number of guilds and is more data-intensive.…”

Consumer‐diet discrimination of δ13C and δ15N: Source‐ and feeding‐oriented patterns based on gut content analysis in a large subtropical river of China

“…These results indicated that the δ 13 C of high-quality food sources (e.g., epilithic diatom-rich biofilms) may first determine the δ 13 C baseline of local food webs and then influence trophic discrimination factors through predator-prey interactions. In this context, it is better to select regionally specific discrimination values rather than a rough value, particularly in the upstream food webs with periphyton as the basic resource supply (Jardine & Bunn, 2012;Wang et al, 2018b). (Post, 2002a).…”

“…Better estimates of diet-tissue discrimination for riverine consumers are needed because of the implications of Δ 15 N variation for mixing model outputs and TL calculations (Caut et al, 2008). In large river systems, where complex geographic and hydrological factors determine the region-specific resource supply, species distributions, and predator-prey interactions (Woodward & Hildrew, 2002;Wang et al, 2018b), spatial variation in trophic discrimination may lead to unstable results and large errors in quantitative stable isotope model outputs (di Lascio et al, 2013;Mccutchan, Lewis, Kendall, & Mcgrath, 2003).…”