Jiao Qin

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, the authors investigated trophic niche patterns within and between two ontogenetic groups (juveniles and sub‐adults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). The authors hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to sub‐adult stages. The results revealed that both δ¹³C and δ¹⁵N values varied greatly across populations and between ontogenetic groups, and complex spatio‐ontogenetic variations were expressed by Layman's metrics. They also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. In addition, trophic niche position increased consistently from juveniles to sub‐adults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial‐ontogenetic variation, which is consistent with optimal foraging theory. The findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems.

Knowledge of large‐scale dispersal processes and their associated genetic diversity patterns is significant for managing invasive species. These patterns remain unclear for invasive species that colonise new habitats through inter‐basin water transfer projects. A worm goby Taenioides cirratus colonised several large inland lakes in China, thereby expanding its distribution through the East Route of the South‐to‐North Water Transfer Project (ESNT). Here, we used nuclear microsatellites to analyse patterns of genetic diversity, population structure, gene flow and, invasion history across its native and invasive ranges in China. Our objectives were to: (a) reveal contemporary genetic diversity patterns of T. cirratus in two native and four invasive populations in China; and (b) identify its main model of dispersal in the ESNT. Invasive populations experienced significant loss of genetic diversity because of bottlenecks and low levels of gene flow, and strong population genetic structure due to founder effects that occurred during expansions. Significant genetic isolation‐by‐distance patterns were largely influenced by landscape connectivity and the reduced active dispersal ability of T. cirratus. The one‐way stepping‐stone dispersal model was identified as being most likely for T. cirratus in the ESNT, influenced by the long distance of upstream dispersal and downstream water transfer events. Our results highlight that T. cirratus could overcome low genetic diversity in founding populations, allowing for invasive spread. For management, we suggest physical removal of invasive populations and installation of deterrents near the pump intake area and the lake outflow to reduce further spread in the system. We provided a general paradigm for understanding dispersal patterns involved in inter‐basin water transfers.

Understanding long-term changes in life-history traits is central to assessing and managing freshwater fisheries. In this study, we explored how life-history traits have shifted in association with long-term change in population status for a native fish species (freshwater sleeper, Odontobutis sinensis, a by-catch species of shrimp traps) in the middle Yangtze lakes, China. We assessed the life-history traits of the species from Honghu Lake in 2016, where abundance had been dramatically lower following about 60 years of high fishing pressure, and made comparisons to similar data from Liangzi Lake (1957), when fishing intensity was low and abundance was high, and Bao’an Lake (1993–1994), when about 10 years of intense exploitation had occurred and abundance had greatly declined. Modern Honghu Lake sleeper exhibit life-history traits that are substantially more opportunistic compared to both of the historical populations. Modern fish were larger at age-1 and had significantly faster growth rates, a higher prevalence of sexually mature individuals and increased fecundities. Fish from the historical samples were larger and had higher age class diversity and delayed sexual maturation. Combined, the data suggest that faster growth towards early sexual maturation and reduced body sizes are associated with destabilized populations and ecosystems. Similar life-history patterns are common in other declined fish populations under exploitation. Recovering historic fish life-history dynamics requires conservation management policies aimed at reducing harvest and improving floodplain habitats.

Genetic patterns observed among populations by neutral molecular markers is a major method used to reconstruct the invasion history of invasive species. The Shimofuri goby (Tridentiger bifasciatus) has invaded several lakes along the East Route of the South‐to‐North Water Transfer Project, China (ENST). However, neutral molecular markers for this goby are not currently available. In this study, fourteen novel polymorphic microsatellite loci were developed through next generation sequencing technology. These markers were also tested in an invasive population (Nansi Lake, a storage lake of ENST) consisting of 54 individuals. The average number of alleles per locus was 7.6 and ranged from 4 to 13. The average H_o was 0.587 and ranged from 0.404 to 0.852, and the average H_e was 0.733 and ranged from 0.564 to 0.851. The average PIC per locus was 0.689 and ranged from 0.521 to 0.824. Four markers (TB4, TB65, TB66 and TB26) were found to deviate from HWE after correction following the False Discovery Rate method. Null alleles were found in four loci (TB11, TB65, TB66 and TB26). These highly polymorphic microsatellite markers are useful for further study to reconstruct invasion history of Shimofuri goby.

The diet composition of an invasive population of Shimofuri goby (Tridentiger bifasciatus) was investigated bimonthly during the period from September 2015 through August 2016 in Nansi Lake, a storage lake of the East Route of the South-to-North Water Transfer Project, China. The diet consists of a broad spectrum of prey items, including mollusca (Bellamya sp. and Physa sp.), aquatic insects (Odonata sp., Chironomidae sp., and Cirolanidae sp.), other macroinvertebrates (Nematoda sp. and Rhynchobdellida sp.), shrimp (Palaemon modestus and Gammarus sp.), fish (Rhinogobius giurinus and Tridentiger bifasciatus), fish eggs, and detritus. Dominant diets shifted from Rhynchobdellida sp. and unidentified digested food in July to P. modestus during September and November, and then shifted to both P. modestus and R. giurinus. Additionally, cannibalism was observed in March before spawning season of the goby, during which large males (SL > 70.0 mm) predated on small-sized ones. We suggest that broad spectrum of prey items and apparent seasonal shifting of dominant diets in the invasive goby fish, which might be an important mechanism favoring its successful invasion in water transfer system.

Inter‐basin water transfers create new pathways between previously disjunct systems and communities. If fish movement occurs, it can lead to invasion or altered regional connectivity patterns, which could induce biotic/genetic homogenisation or synchronisation. Understanding ecological factors promoting movement is critical for predicting potential impacts during project planning, to assess ongoing effects, and to develop mediation strategies. Potential characteristics influencing movement rates were reviewed, including intrinsic traits that increase passive entrainment or active dispersal rates, extrinsic traits of the connected environments and their interactions. In order to examine patterns among these potentially influencing characteristics, a trait‐based screening method for movement and invasion risk was developed to analyse linked communities in a database from a large‐scale inter‐basin water diversion in China. Groups of fishes that scored high in the risk assessment were compared with worldwide examples of entrainment in inter‐basin water transfer systems or smaller‐scale diversions to examine emergent patterns of shared ecological characteristics. Specific traits that were most often shared in these groups, indicating a higher likelihood of movement in water diversions, include the following: a smaller body size, high adult or larval abundance, migratory behaviour, generalist and pelagic habitat preferences, and a high reproductive output. The synthesis of factors identified in this research can be used to guide future empirical studies to fill knowledge gaps regarding ecological impacts of inter‐basin water transfers or other smaller‐scale diversions on local communities and ecosystems.