Geoscience Reference
In-Depth Information
Between 1984 and 1985, eight benthic samples were taken in each season
within each river, giving a total of 96 sample-units for the whole sampling
period (
Campos et al., 1985
). Invertebrates were collected using a Surber
sampler (sampling area: 0.09 m
2
; mesh aperture 250
m) and preserved in
70% ethanol before being transported to the laboratory for species identifi-
cation and food web analyses.
All individuals were measured and identified to the highest level of taxo-
nomic resolution (i.e. species, wherever possible). Invertebrates were identi-
fied using available taxonomic keys and species descriptions (
Fern
´
ndez and
Dom´nguez, 2001; McCafferty, 1983; Peters and Edmunds, 1972
). Chirono-
midae larvae were measured before being mounted on slides with Euparal
medium and identified under oil
m
immersion microscopy at 400
magnification.
The feeding links were established by gut contents analysis of all indivi-
duals found in each sample. The guts of large invertebrates were removed
and mounted in Euparal, while small specimens were mounted whole and
examined at 400
magnification. Species prey items found on each gut were
identified from previously mounted reference slides, after Schmid (1993) and
Schmid-Araya et al. (2002)
. All linear dimensions were then converted to
body mass estimates using published regression equations (listed in
Baumg¨rtner and Rothhaupt, 2003; Miserendino, 2001; Reiss and Schmid-
Araya, 2008; Woodward et al., 2010
).
5. Tadnoll Brook
The Tadnoll Brook is a tributary (mean annual discharge 0.35 m
3
s
1
,pH
6.9-7.7) of the River Frome, in Southern England, UK (
Edwards et al.,
2009b
).
Between February and December 2005, a 240-m reach was sampled every
2 months to construct the summary food web. Invertebrates were sampled
every 2 months using a Surber sampler (0.06 m
2
; mesh aperture 300
m). On
each occasion, 20 random samples were collected, preserved in the field in 4%
(w/v) formalin and subsequently sorted for invertebrates, which were identi-
fied to the lowest possible taxonomic level (usually species).
On each occasion, fish were caught with an electrofisher, anaesthetised
using 2-phenoxyethanol, identified to species, measured and weighed
(
Woodward et al., 2010
). The guts of trout (Salmo trutta L.)
m
70 mm fork
length were then flushed using a small manual water pump, and the contents
immediately preserved in 4% formalin. For smaller trout and other fish
species (bullhead, Cottus gobio L. (n
>
¼
126), European eel Anguilla anguilla
(L.) (n
¼
37), minnow Phoxinus phoxinus (L.) (n
¼
17), stone loach Barbatula
