Resource use of crucian carp along a lake productivity gradient is related to body size, predation risk, and resource competition

Generalist fish species can feed on a wide resource spectrum and across trophic levels depending on resource availability and trophic interactions. Crucian carp (Carassius carassius) represents a good candidate species to investigate variation in the trophic ecology of generalist fish as it can be found in highly variable fish communities and its resource use is well documented. In this study, we explored the trophic ecology of crucian carp at the individual and population levels using stable isotope and gut content analysis. We tested if trophic resource use varied according to lake productivity, predation risk, intra- and interspecific competition, or individual fish size. We found that crucian carp resource preference was highly variable among and within lakes. In predator-free lakes, small crucian carp occurred in high densities, showed increased interindividual specialisation, and relied mainly on pelagic zooplankton. In presence of predators, large crucian carp occurred in low densities and included greater proportions of benthic macroinvertebrates in their diet. This shift in resource use was further favoured in productive, shallow lakes where littoral prey was probably abundant. Resource partitioning was an important factor determining crucian carp niche use, as fish had higher trophic position in absence of other cyprinids. Crucian carp showed highly dynamic resource use and food preferences in response to variable environmental conditions. Overlooking complex diet preferences of generalist fish may lead to an oversimplification of freshwater community dynamics.publishedVersio

Tannins, phenolics, carbon, nitrogen, and C/N in bilberry annual shoots after simulated herbivory.

Mean concentration (mg/g ± se (standard error of the sample mean), dry weight) of tannins, 22 phenolics (see text), carbon (C) and nitrogen (N) and mean C/N ratio (± standard error), per treatment (see text). For all treatments together (All) also the sd (standard deviation of the sample) is given. Number of observations between parentheses.</p

HPLC chromatogram of phenolics in bilberry annual shoots.

The chromatograms shown here (A wavelength 280 nm, B wavelength 320 nm; retention time (x-axis) in minutes (min), response (y-axis) in mAU (AU = absorption units)) are from the subsample which was used to identify the peaks with mass spectrometry. Phenolics identified (for footnotes, see S1 Table): 1. protocatechuic acid derivative, 2. arbutin derivative7, 3. gallocatechin derivative, 4. procyanidin 1, 5. procyanidin 2, 6. epicatechin (formerly called: (-)-epicatechin), 7. procyanidin 3, 8. procyanidin 4, 9. procyanidin 5, 10. procyanidin 6, 11. chlorogenic acid, 12. para-hydroxycinnamic acid derivative 1, 13. cinnamic acid derivative, 14. para-hydroxycinnamic acid derivative 2, 15. hyperin1, 16. quercetin 3-glucuronide5, 17. quercetin 3-arabinoside4, 18. kaempferol 3-glucoside2, 19. quercitrin6, 20. isorhamnetin 3-glucoside, 21. para-hydroxycinnamic acid derivative 3, 22. monocoumaroyl-isoquercitrin3,8.</p

Study design.

Schematic bilberry ramet, eight treatments (see text): C (control), three leaf treatments (L), three shoot treatments (S), one ramet treatment (R). 21 annual shoots are visible (1 at the top of the stem, 10 at each side of the stem). AGE: the stem and all shoots (same schematic bilberry as in the treatments) are depicted with numbers: the stem is at least four years old and indicated with 4, shoots at least three years old are indicated with 3, shoots at least two years old are indicated with 2, annual shoots (with leaves) are indicated with 1. NOTE: the upper three-year-old shoot at the right side of the stem and the middle three-year-old shoot at the left side of the stem may also be two years old. LOCATION: at four lines, 34 (upper three lines) and 33 (lower line) ramets are selected: 30 control ramets and 15 ramets for every one of the other 7 treatments, randomly appointed. Approximately 2 m between each ramet and 10 m between each line. This location is one of six locations (namely: “Imsdalen 1”). Drawing: Marcel Schrijvers-Gonlag.</p

Differences in individual phenolic concentration in bilberry annual shoots between simulated herbivory treatments.

The number of differences (#) between treatments (P < 0.05) is given for 22 phenolics separately, and for all 22 phenolics analyzed together (n = 200, every treatment n = 25).</p

The high tolerance to aluminium in crucian carp (<i>Carassius carassius</i>) is associated with its ability to avoid hypoxia - Fig 3

<p><b>Scanning electron micrographs</b> of gill filaments from the apical right side of crucian carp, exposed to acidic Al-rich water (a), acidic Al-poor water (b), and untreated department water (c).</p

Total phenolic concentration in bilberry annual shoots after simulated herbivory.

Boxplot with total phenolic concentration (mg/g, dry weight), n = 200, every treatment n = 25. Treatments: see text. The bottom and top of each box indicate the first and third quartiles. Bold horizontal lines within each box indicate median values. The plot whiskers extend to the most extreme data point which is no more than 1.5 times the interquartile range away from the box; extreme data points more than 1.5 times the interquartile range away from the box are indicated with black points. Treatments with the same letter above the box are not different from each other (P > 0.05).</p

A schematic presentation of the experimental set-ups used in the experiments.

<p>A schematic presentation of the experimental set-ups used in the experiments.</p

Phenolic concentrations after simulated herbivory.

Phenolic concentrations after simulated herbivory.</p