Irish Freshwater Biologists Meeting 2012
Macroinvertebrate Resource Utilisation in Upland Streams:
Riparian Management Impacts
C. Barry & Y. McElarney
Agri-Environment Branch
Newforge Lane, Belfast
Riparian Management Impacts
RCC – interpretative paradigm for resource utilisation /
carbon flow in river food webs
High terrestrial inputs
Low nutrient inputs
Low PP
low P:R
But,
● Variation of riparian
vegetation at low
stream orders
– alters resource
availability and quality
● Resource utilisation
by functional feeding
group
Increasing light and
nutrients
greater PP
P:R increasing
High light & nutrients
& C inputs from
upstream processing
P:R decreasing
-feeding mechanisms
to determine resource
use
-opportunism and
generalist feeding
frequent
●To eat is to
assimilate?
How to assess macroinvertebrate resource utilisation?
Natural abundance Carbon and Nitrogen Stable Isotope Analysis
13C:12C
15N:14N
Consumer isotopic ratios reflect the isotopic ratios of their diet in a consistent way
► You are what you eat, less what you excrete
Fractionation: stuff happens to lighter isotopes more readily
●Physical: evaporation
●Chemical: respiration
Ratios unwieldy; reported as signatures-
12
deviation from standards (δ13C, δ15N)
Fox
8
15
(d N)
Nitrogen isotopic signature
10
Measure stable isotope signatures for
Geese
6
Rabbit
● Macroinvertebrates
Seagrass
4
● Potential dietary sources
2
Grass
Some consumers use several different
resources…. Mixing models
0
-30
-28
-26
-24
-22
-20
Carbon isotopic signature
13
(d C)
-18
-16
SIAR in R … Bayesian mixing model
Methods
25 streams sampled once in summer (50m reach)
No Buffer
(n=6)
Natural Upland
catchments (n=5)
Unplanted Buffer
(n=4)
Recently Harvested
(n=6)
Broadleaved Buffer
(n=4)
Quantitative estimates of biomass and C & N isotopic analysis for
●macroinvertebrates
●benthic organic matter
●biofilm
●biofilm chl a
●riparian vegetation
Physico-chemistry sampled seasonally on 3 occasions
●macrophytes
●seston
●macroalgae
●Light penetration
Methods: deriving macroinvertebrate dietary reliance
Stream with an unplanted riparian buffer
5 potential resources / end members
4
Leuctra fusca
3
Simulium
Ecdyonurus insignis
Seston
2
Gammarus duebeni
celticus
Baetis rhodani
δ15N 1
(‰)
Elmis aenea
Biofilm
Seratella ignita
0
-1
River conditioned
detritus
Ulothrix tenuissima
-2
Scapania undulata
-3
-34
-33
-32
-31
-30
-29
δ13C (‰)
-28
-27
-26
Methods: deriving macroinvertebrate dietary reliance
1.0
Resource: River conditioned detritus
Dietary reliance (%)
0.8
0.6
0.4
0.2
0.0
1. Baetis 2. Ecdyonurus 3. Elmis
4. Simulium 5. Leuctra 6. Gammarus
7. Seratella
Methods: deriving macroinvertebrate dietary reliance
1.0
Resource: Biofilm
Dietary reliance (%)
0.8
0.6
0.4
0.2
0.0
1. Baetis 2. Ecdyonurus 3. Elmis
4. Simulium 5. Leuctra 6. Gammarus
7. Seratella
Methods: deriving macroinvertebrate dietary reliance
1.0
Resource: Ulothrix tenuissima
(filamentous green alga)
Dietary reliance (%)
0.8
0.6
0.4
0.2
0.0
1. Baetis 2. Ecdyonurus 3. Elmis
4. Simulium 5. Leuctra 6. Gammarus
7. Seratella
Methods: deriving macroinvertebrate dietary reliance
1.0
Resource: Seston
(suspended fine particulate organic matter)
Dietary reliance (%)
0.8
0.6
0.4
0.2
0.0
1. Baetis 2. Ecdyonurus 3. Elmis
4. Simulium 5. Leuctra 6. Gammarus
7. Seratella
Methods: deriving macroinvertebrate dietary reliance
1.0
Resource: Scapania undulata
(bryophyte)
Dietary reliance (%)
0.8
0.6
0.4
0.2
0.0
1. Baetis 2. Ecdyonurus 3. Elmis
4. Simulium 5. Leuctra 6. Gammarus
7. Seratella
Methods: Apportioning macroinvertebrate biomass
Terrestrial vs. Aquatic
Allochthonous
(Terrestrial)%
Autochthonous
(in situ PP) %
Total Invertebrate mass
mg m-2
Allochthonous mass
mg m-2
Autochthonous mass
mg m-2
Baetis
15
85
174
26
148
Simulium
61
39
35
21
14
Ecdyonurus
10
90
180
18
162
Elmis
20
80
3
1
2
Gammarus
83
16
342
283
55
Leuctra
89
11
38
34
4
Seratella
47
53
91
43
48
Plectrocnemia
69
31
57
39
18
465
450
Total mg m-2
C & N stable isotope analysis
Functional feeding groups
Predator
Shredder
Collector
Allochthonous
Grazer/Scraper
Autochthonous
Macroinvertebrate Biomass Apportionment by site
900
Invertebrate Biomass (mg m2 Dwt.)
800
A
Autochthonous
Allochthonous
700
600
500
400
300
200
CE = No buffer: Conifers to stream edge
CF = Clear felled
B = broadleaved buffer
B207
OB0
CF6
OB74
CE44
CM2
B126
OB41
B209
CF5
CF3
CF2
CF8
B208
CM1
CM6
CE56
CM15
CF4
CM14
CE133
OB13
CE148
CE0
0
CE185
100
OB = Open buffer (unplanted)
CM = Natural upland (control)
Consumer frequency distributions of reliance on terrestrial C
Un-skewed distributions
- consumers exploiting a wide variety of resources
- greater niche availability / utilisation
► Clear felled sites, Natural upland sites (control), no
buffer sites*
Skewed distributions
-consumers exploiting resources of similar origin
-Suggests high abundance of such resources and/or
resources of the same origin present in different
forms…. FPOM, CPOM
► Broadleaved buffer & Open buffer sites
Caveat
*Depleted consumer δ13C indicative of methane C
►while terrestrial in origin, the approach regards
consumers as utilising an autochthonous resource
100% terrestrial
100% aquatic
id
ae
Error bars = 1SD
at
us
Co
nu
l
n = 20
an
ae
Co
s
Gr
bi
id
Gr
ru
su
Sh
n=4
hl
e
n = 13
D
n = 13
ae
n = 14
Le
pt
op
Co = Collector
Ba
et
id
Sh
en
i
e
Co
n = 23
ep
ta
g
Gr
rid
a
ae
n = 23
em
ou
n=4
N
tri
d
Co
Le
uc
Sh
ul
id
ae
Sh
n=4
Si
m
Co
es
Sh
llip
n = 18
pa
n=2
lo
ae
n=7
Si
yc
hi
d
ps
s
de
r
at
um
sh
re
d
yd
ro
ae
on
ilis
gr
ac
us
tic
n = 25
H
H
lid
pe
rs
en
a
el
Sh = shredder
El
Ep
m
he
id
ae
m
er
el
la
ig
ni
ta
ph
i
st
om
a
yd
ra
.c
Mean proportional deviation from terrestrial diet
0.8
Li
m
ne
ico
Se
r
H
G
.d
Species Specific Resource utilisation
Gr = Grazer
1.0
n=3
n=1
Co
0.6
0.4
0.2
0.0
Gr
Conclusions
• Light reduction, slope & organic biofilm mass most
important variables driving resource utilisation among
sites
• Biomass and species richness greater at buffered
compared to un-buffered sites
• Invertebrate community structure and resource use
at buffered sites show little similarity to unimpacted
control sites
• Broadleaved buffer sites show high invertebrate
biomass but a community largely specialised for an
allochthonous diet
Acknowledgements
AFBI Staff
Lesley Gregg, Rachel Patterson, Alex Higgins
Colm McKenna, Kirsty McConnell,
Louise Davis, Elaine Hamill,
Phil Dinsmore, Brian Stewart
Forest Service, NI
Ian Irwin, Colin Riley
EPA (Strive) for part funding study (project 2007-W-MS-3-S10):
An Effective Framework For assessing aquatic ECosysTem
responses to implementation of the Phosphorus Regulations
(EFFECT)
Department of Agriculture and Rural Development (DARD) for
remainder of project funding.
Results: Isotopic overview
60
Carbon:Nitrogen (molar)
50
Coniferous
Coniferous
Deciduous
Deciduous
Bryophyta
40
Grasses
Grasses
River conditioned
detritus
Macro-algae
River conditioned detritus
30
Macro-algae
Bryophyta
Biofilm
20
Biofilm
Macro-Invertebrates
Macro-Invertebrates
10
0
-10
-50
-5-45
0
-40
5
15
δ13 N
(‰) )
δ C (‰
-35 10
-3015
20
-25