10.5061/DRYAD.M37PVMD1V
Guo, Fen
0000-0002-4976-5456
Wasser Cluster Lunz
Bunn, Stuart
0000-0002-6540-3586
Griffith University
Brett, Michael
University of Washington
Hager, Hannes
Wasser Cluster Lunz
Kainz, Martin
0000-0002-2388-1504
Wasser Cluster Lunz
The dark side of rocks: an underestimated high-quality food resource in
river ecosystems
Dryad
dataset
2021
FOS: Earth and related environmental sciences
FWF Austrian Science Fund
https://ror.org/013tf3c58
P 28902-B25
2021-03-25T00:00:00Z
2021-03-25T00:00:00Z
en
63874 bytes
4
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
This dataset contains data of fatty acid profiles described in the paper:
“Guo et al. (2021) The dark side of rocks: an underestimated high-quality
food resource in river ecosystems. Journal of Ecology,
https://doi.org/10.1111/1365-2745.13647”. This study was a field
investigation conducted along a subalpine river continuum in Austria and
aimed to identify the nutritional role of a “hidden” food resource for
aquatic consumers; the biofilms growing on the underside of rocks (dark
biofilms). Dark and light (i.e., upper surface of rocks) biofilms, and
invertebrates were collected, and their fatty acid (FA) composition was
analyzed. Main results were: (1) compared with light biofilms, dark
biofilms contained greater proportions of bacterial FA, long-chain
saturated FA (biomarkers of terrestrial plants), and oleic acid (18:1ω9; a
fungal biomarker), but a lower proportion of algal FA, especially omega-3
polyunsaturated FA (ω3 PUFA). (2) The ω3 PUFA composition in dark biofilms
was strongly correlated with that in light biofilms. (3) the overall FA
profiles of dark biofilms were significantly associated with invertebrate
FA profiles. (4) Strong correlations were also observed between
invertebrates and dark biofilms for bacterial FA and the ω3 PUFA
eicosapentaenoic acid (EPA, 20:5ω3).
Sample collection Biofilms and macroinvertebrates were sampled at 8
riffles from upstream to downstream in the subalpine River Ybbs catchment,
Austria, across three seasons, i.e., summer (July), fall (October) and
winter (November) in 2017. Three paired samples of light and dark biofilms
were collected for FA analyses along a 20-m reach from each riffle. Each
paired sample was collected using a quadrat (1.5 m * 1.5 m), and five
cobbles (diameters ranging from 8 to 16 cm) within the quadrat were
randomly picked. Light and dark biofilms were scraped from the substrate
with a toothbrush and kept separate. Macroinvertebrates clinging to the
above cobbles within each quadrat were washed into white trays. Ecdyonurus
sp. (Heptageniidae, Ephemeroptera), which is the most abundant algal
grazer in the study streams (Kühmayer et al., 2020), was selected for
analysis. Although there are four Ecdyonurus species from our study
streams, including E. helveticus (Eaton, 1885), E. venosus (Fabricius,
1775), E. dispar (Curtis, 1834) and E. picteti (Meyer-Dur, 1864), more
than 95% of the larvae were late instars of E. helveticus (Moog, 2002).
All four species have identical feeding habits and are assigned to the
same functional feeding groups: 50% grazer and 50%
detritivore/gatherer/collector (Moog, 2002). One replicate with at least
10 individuals of Ecdyonurus sp was collected from each riffle. All
samples were immediately placed in zip-lock plastic bags, stored on ice
and kept in the dark in a portable freezer. Samples were brought to the
laboratory within 4 hours and placed in a -80°C freezer until further
processing. Due to the heavy snow in early November, there was no access
to one of the upstream sites (WO), where biofilms and invertebrates were
not collected. There was limited access to the sites FB, TB and WO during
winter and invertebrates were not collected. Sample processing All biofilm
and macroinvertebrate samples were freeze-dried (Virtis Genesis Freeze
Dryer). Dry mass from each biofilm sample (~10 mg) and from each
invertebrate sample (5-7 mg) was used for the lipid extractions. Lipids
were extracted and methylated according to the methods reported in Guo et
al (2016c), with nonadecanoic acid (19:0) used as an internal standard.
Fatty acid methyl esters (FAME) were analysed using a gas chromatograph
(THERMO Trace; FID 260°C, Carrier gas: He: 1 ml/min, Detector gases: H2:
40 ml/min, N2: 45 ml/min, air: 450 ml/min, temperature ramp: 140°C (5
min)– 4°C/min–240°C (20 min) = 50 min) equipped with a
temperature-programmable injector and an autosampler. FAME were separated
by a SupelcoTM SP-2560 column (100 m, 25 mm i.d., 0.2 mm film thickness),
and FA peaks were identified by comparison of their retention times with
known standards, i.e., 37-component FAME mix (Supelco 47885-U) and
Bacterial Acid Methyl Ester Mix (Supelco 47080-U), and quantified with
reference to seven-point calibration curves based on known standard
concentrations. FA compositions were expressed as percentages relative to
the total FA (FA%).