Advancing improvement in riverine water quality caused a non-native fish species invasion and native fish fauna recovery

Abstract

The knowledge of biotic and abiotic drivers that put non-native invasive fishes at a disadvantage to native ones is necessary for suppressing invasions, but the knowledge is scarce, particularly when abiotic changes are fast. In this study, we increased this knowledge by an analysis of the biomass of most harmful Prussian carp Carassius gibelio in a river reviving from biological degradation. The species' invasion followed by the invasion's reversal occurred over only two decades and were documented by frequent monitoring of fish biomass and water quality. An initial moderate improvement in water quality was an environmental filter that enabled Prussian carp's invasion but prevented the expansion of other species. A later substantial improvement stimulated native species' colonization of the river, and made one rheophil, ide Leuciscus idus, a significant Prussian carp's replacer. The redundancy analysis (RDA) of the dependence of changes in the biomass of fish species on water quality factors indicated that Prussian carp and ide responded in a significantly opposite way to changes in water quality in the river over the study period. However, the dependence of Prussian carp biomass on ide biomass, as indicated by regression analysis and analysis of species traits, suggests that the ecomorphological similarity of both species might have produced interference competition that contributed to Prussian carp's decline.

Figure 1

Ner River, Poland, and its location in Europe. Red dots situated along the Ner are fish sampling sites in the recovered course. The left asterisk is the Dąbie water quality monitoring station, the right asterisk is the Podłęże water quality monitoring station. Dashed blue line is the Ner catchment limit. River degradation gradient extended from the Łódź City (worst condition) to the downstream end of the recovered course (best condition). Map of this figure was drawn by the present Authors using Microsoft PowerPoint v. 2010 software on the basis of other maps of the study area.

Figure 2

Total biomass of all fish species in the recovered course of the Ner River, Poland, in subsequent sampling surveys over the period of 2000–2012.

Figure 3

Prussian carp biomass decline in the recovered course of the Ner River, Poland, over the fish sampling period of 2000–2012. Green dots are Hellinger transformed values of Carassius gibelio—Prussian carp biomass in each of the sampling surveys. Red line is linear regression of the values.

Figure 4

RDA biplot of water quality variables presented in Table 1 (after deleting collinear variables) and fish species’ biomass values obtained from samples collected in the recovered course of the Ner River, Poland, in 2000–2012. Abbreviations of water quality variables: DO dissolved oxygen, BOD₅ biological oxygen demand, NO₃ nitrates; T. Phosph. total phosphorus, Conduct. conductivity, Ca calcium. Abbreviations of fish species’ names: Blbjo—Blicca bjoerkna (silver bream); Cacar—Carassius carassius (crucian carp); Cagib—Carassius gibelio (Prussian carp); Cotae—Cobitis taenia (spined loach); Esluc—Esox lucius (pike); Gaacu—Gasterosteus aculeatus (stickleback); Gogob—Gobio gobio (gudgeon); Gycer—Gymnocephalus cernua (ruffe); Leidu—Leuciscus idus (ide); Lolot—Lota lota (burbot); Mifos—Misgurnus fossilis (weatherfish); Peflu—Perca fluviatilis (perch); Rurut—Rutilus rutilus (roach); Saluc—Sander lucioperca (pikeperch); Titin—Tinca tinca (tench).

Figure 5

GLM model of the dependence of Carassius gibelio—Prussian carp (Cagib) and Leuciscus idus—ide (Leidu) biomass on dissolved oxygen in the recovered section of the Ner River, Poland in 2000–2012. Red and green dots are characteristic points of the GLM model. Dissolved oxygen (DO) was measured in mg O₂/l.

Figure 6

Carassius gibelio—Prussian carp biomass as a function of Leuciscus idus—ide biomass (both Hellinger transformed) in the recovered course of the Ner River, Poland, in subsequent sampling surveys over the period of 2000–2012. Green dots are biomass values in given surveys, while green numbers in brackets are years of the surveys. Red solid line is the major axis (of the bivariate distribution and of the ellipse). Red dashed lines are 95% confidence limits of the major axis. Black dotted line is the minor axis. The blue ellipse is 95% confidence region of the mean of both variables. Blue dots (marked by blue letters, ‘A…H’), are characteristic points of the ellipse. The coordinates of the points (e.g. ‘A (x, y) =’) are also indicated, x being the abscissa, y the ordinate axis location.