10.5061/DRYAD.R2280GBBQ
Symons, Celia C.
0000-0003-4120-0327
University of California, Irvine
Schulhof, Marika A.
University of California, San Diego
Cavalheri, Hamanda B.
University of California, San Diego
Shurin, Jonathan B.
University of California, San Diego
Antagonistic effects of temperature and dissolved organic carbon on fish
growth in California mountain lakes
Dryad
dataset
2020
TN
TP
DOC
otolith growth
C and N stable isotopes
δ13C
δ15N
Salvelinus fontinalis
Oncorhynchus mykiss
National Science Foundation
https://ror.org/021nxhr62
1457737
2020-11-18T00:00:00Z
2020-11-18T00:00:00Z
en
https://doi.org/10.1007/s00442-018-4298-9
20740 bytes
2
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Resources and temperature play major roles in determining biological
production in lake ecosystems. Lakes have been warming and ‘browning’ over
recent decades due to climate change and increased loading of terrestrial
organic matter. Conflicting hypotheses and evidence have been presented
about whether these changes will increase or decrease fish growth within
lakes. Most studies have been conducted in low-elevation lakes where
terrestrially derived carbon tends to dominate over carbon produced within
lakes. Understanding how fish in high-elevation mountain lakes will
respond to warming and browning is particularly needed as warming effects
are magnified for mountain lakes and treeline is advancing to higher
elevations. We sampled 21 trout populations in the Sierra Nevada Mountains
of California to examine how body condition and individual growth rates,
measured by otolith analysis, varied across independent elevational
gradients in temperature and dissolved organic carbon (DOC). We found that
fish grew faster at warmer temperatures and higher nitrogen (TN), but
slower in high DOC lakes. Additionally, fish showed better body condition
in lakes with higher TN, higher elevation and when they exhibited a more
terrestrial δ13C isotopic signature. The future warming and browning of
lakes will likely have antagonistic impacts on fish growth, reducing the
predicted independent impact of warming and browning alone.
Lake sampling At the deepest point in each lake, in situ measurements of
temperature was taken using a YSI probe (YSI Incorporated, Yellow Springs,
Ohio, USA). Surface water samples were filtered through 63-μm mesh to
remove zooplankton and processed for chlorophyll-a (chl-a), particulate
organic matter (POM), total nitrogen (TN), total phosphorus (TP) and
dissolved organic carbon (DOC). For chl-a quantification, a known volume
of water was filtered through 0.7 μm glass fiber filters (GF/F Fisher
Scientific) and frozen. Chl-a, a proxy for phytoplankton biomass, was
measured using a fluorometer after a 24 h cold methanol extraction. For
POM isotope analysis, a known volume of water was filtered through
pre-weighed pre-combusted (7 h, 500 °C) 0.7 μm glass fiber filters. Upon
returning to the laboratory, filters were dried for 24 h at 60 °C, weighed
and packaged in tin capsules for 13C and 15N isotope analysis. Total
nitrogen and total phosphorus samples were collected in HDPE vials and
preserved with H2SO4 to a pH < 2 and stored at ~ 4 °C until
analysis. TN and TP were measured using an auto analyzer (LaChat QuikChem
8500, persulfate digestions). Leaves of several common plant species were
collected from shoreline and frozen until processing for isotopic
analysis. Leaves were sorted into broad functional groups (grasses,
shrubs, pine) and dried at 60 °C for 2 days. A mortar and pestle was used
to grind the leaf samples before packaging in tin capsules for isotope
analysis. Based on a subset (10 lakes) of the plant data, we chose to
process a grass and pine sample to capture the maximum variation in
isotopes within the terrestrial organic matter entering lakes. To quantify
DOC, water samples were filtered through pre-combusted glass fiber filters
(Whatman GF/F, pore size 0.7 μm) into triple-rinsed 20 mL glass vials and
preserved with HCl to a pH < 2. DOC was measured using a total
organic carbon analyzer (TOC-V CSN, Shimadzu Scientific Instruments,
Japan). To characterize DOC quality, we used UV–Vis absorbance,
spectrofluorometry and spectrophotometry, which reflect several aspects of
the molecules comprising the light-absorbing and fluorescing DOM pool,
respectively. We used excitation-emission matrices (EEMs) as a
three-dimensional representation of fluorescence intensities scanned over
a range of excitation/emission wavelengths (Coble 1996; Chen et al. 2003).
EEMs were collected with a JY-Horiba Spex Fluoromax-3 spectrofluorometer
(HORIBA, Japan) at room temperature using 5 nm excitation and emission
slit widths and an integration time of 1.0 s. The Aqualog
spectrophotometer simultaneously collects both fluorescence and absorbance
spectra on a sample. All fluorescence spectra were collected in
signal-to-reference (S:R) mode with instrumental bias correction.
Instrument-specific corrections, Raman area normalization and Milli-Q
blank subtraction were conducted with Matlab (2009). From the UV–Vis
absorbance and EEMs data, we calculated two indices of DOC quality: the
freshness index (FI) and specific UV absorption (SUVA). FI (β:α) is a
ratio of emission intensity at 380 nm to that of the region between 420
and 435 nm at an excitation of 310 nm and is reflective of recently
produced algal organic matter (Parlanti et al. 2000). SUVA is a
DOC-normalized index of aromaticity calculated as UV absorbance at 254
nm/[(DOC (mg L−1) × path length (0.01 m)] (Weishaar et al. 2003). FI
increases with autochthonous carbon production, whereas SUVA increases
with allochthonous carbon production. All isotope samples were analyzed by
the University of California, Davis Stable Isotope Facility for 13C and
15N, using an elemental analyzer interfaced to a continuous flow isotope
ratio mass spectrometer. Fish sampling At each of the 21 lakes, we caught
fish by angling. Each fish was identified to species, weighed,
photographed and measured (TL; maximum length). We collected a dorsal
muscle sample from each individual which was frozen until processing for
stable isotope analysis. Upon returning to the laboratory, muscle samples
were freeze dried for 24 h, ground with a mortar and pestle and packaged
for 13C and 15N analysis. Otoliths were removed, cleaned, dried and stored
in vials for age determination and growth rate analysis. We calculated
catch per unit effort (CPUE) as the total catch divided by the number of
person-hours spent angling at each lake. All applicable institutional
guidelines for the use of animals were followed and approved by the
Institutional Animal Care and Use Committee at the University of
California, San Diego (Protocol #S14140). Fish sample processing Fish in
temperate regions can be aged by examining calcified structures called
otoliths, which form annuli—rings that correspond to low winter growth.
The width of the annuli is an indicator of annual growth (Casselman 1990).
To determine age and annual growth, the sagittal otoliths were mounted on
the edge of a microscope slide with the core positioned just within the
microscope slide’s edge and polished to section the otolith. The otolith
was then flipped onto the transverse cross-section and polished again
until the core was exposed in the transverse section similar to Taylor and
McIlwain (2010). Annuli were counted by two independent readers in the
absence of information about fish size or lake. Ages were in agreement for
84% of the otoliths, and never differed by more than 1 year. For otoliths
where the age determinations disagreed, the two readers examined the
otoliths together and were able to reach a consensus. The width of each
annuli was measured using imaging software (Image J).
Please see ReadMe files for units.