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Crayfish patterns in lakes and streams
The role of predatory fish, productivity and substratum
Per Nyström et al
Ecology Building
Lund University
Background
The abundance and production of crayfish could
be determined by several interacting factors:
-
Predation (fish) and cannibalism
Productivity (food supply)
Substrate availability
(water quality: pH, temperature)
(physical disturbance in streams)
Tot-P
Background
The signal crayfish has established populations in
many lakes (> 1000) and streams (> 400) in Sweden
- We know, however, very little about the factors
affecting its abundance and production. We know
even less about its role as an energy source for its
potential predators
?
Background
Crayfish are important consumers and prey in many
ecosystems
In Swedish streams most native crayfish populations
have been replaced by signal crayfish...crayfish plague
• The native noble crayfish has declined by 97% during
the 20th century (CR)
• What are the roles of these omnivores in the
streams - the same? What are the limiting factors for
signal and noble crayfish populations - the same?
Objectives, Lakes
Investigate the influence of predatory fish,
substratum grain size and resource supply for:
- The abundance (CPUE) and size-distribution of
signal crayfish
• Determine the importance of crayfish as an
energy source for predatory fish (stable isotopes)
Methods
General (July-August, 2001-2003):
- Established populations of signals (but harvested)
- CPUE of crayfish (100 traps)
- CPUE (gillnets), to capture fish
- 100 crayfish measured from each site
- Stable isotopes of crayfish and fish
- Gut contents of fish
- Phytoplankton biomass as indicator of productivity
(Tot-P:8-130 µg/l)
- Substratum grain sizes (30 at each site)
My name is Per
I count cobbles
My name is Patrik
I count fish
• 10 Lakes dominated
by Perch (57%) and
Cyprinids (35%)
Perch eat (large) crayfish!
…and so do pike
Who else eat crayfish?
Perch > 15 cm
47% (102)
Perch < 15 cm
0% (21)
Pike > 15 cm
60% (5)
Pike perch > 15 cm
0% (8)
Roach > 15 cm
0% (23)
Bream > 15 cm
0% (2)
Tench > 15 cm
0% (3)
Humans > 15 cm
100% (2)
Any size-refuges?
9.5 cm
N=28
Crayfish size (cm)
10
7.5
5
2.5
0
10
20
30
40
Perch size (cm)
50
Fewer crayfish when lots of predators?
12.5
10
r = 0.74
CPUE
7.5
p = 0.015
5
2.5
0
0
1000
2000
3000
CPUE Perch (g)
4000
5000
Proportionally more perch
12.5
CPUE
10
7.5
r = 0.69
p = 0.026
5
2.5
0
0
1
2
3
4
5
Perch/Cyprinids
6
d15N (- 3.4 ‰) in large Perch
Perch: one trophic level above crayfish?
20
3.4 ‰
15
10
5
5
10
15
20
d15N (‰) in adult crayfish
Perch and crayfish: same carbon source?
d13C (‰) in large Perch
-22
-24
N +C reveals:
80% from crayfish
20% from fish
-26
-28
-30
-30
-28
-26
-24
d13C (‰) in Crayfish
-22
More crayfish when lots of cobbles?
12.5
CPUE
10
7.5
Lake Bunn!
5
r = 0.69
2.5
p = 0.027
0
0
0.25
0.5
0.75
Proportion of cobbles
1
More crayfish in productive lakes?
12.5
CPUE
10
7.5
5
2.5
0
0
10
20
30
40
Chl a (mg/m3)
50
Nae!
Larger crayfish in productive lakes?
11.5
Mean size (cm)
11.0
10.5
r = 0.82
p = 0.003
10.0
No patterns
with CPUE or
fish biomass !
9.5
9.0
8.5
0
10
20
30
Chl a (mg/m3)
40
50
Conclusions Lakes
The abundance of signal crayfish seems to be
influenced mainly by cobbles
In lakes, signal crayfish may have positive effects
on its predators and could be an important energy
source
The size distribution of signal crayfish seems to be
related mainly to algal biomass (productivity)
Native and exotic crayfish in Swedish streams:
How many, how big and what are they doing?
Not much…
Per Nyström
Karin Olsson
Patrik Stenroth
Erika Nilsson
Are we the same?
=
Pacifastacus leniusculus
Illustrations: Linda Nyman
Astacus astacus
Background
Previous work suggests that the abundance and
individual size of crayfish could be determined by several
interacting factors:
-
Predation (trout) and cannibalism
-
Productivity (periphyton biomass)
-
Substrate availability
Background
The signal crayfish is a fast growing and aggressive
species with a strong impact on its food sources
(experiments)
In nature? Not in experiments!
Here I am!
Objectives, Streams
Investigate the influence of predatory fish,
substratum grain size and resource supply for:
- The abundance and size-distribution of signal and
noble crayfish in streams
• Determine their trophic position and (feeding) niche
width (stable isotopes) and the factors affecting the
niche width of these omnivores
Nitrogen signature
Niche width…
Carbon signature
Methods and sites
• July-August:
- 2002-2003 signals (13)
- 2005 noble crayfish (14)
Summer in Finland….
Methods
- Established populations of crayfish (but harvested ≈ 10 cm)
- CPUE of crayfish (30 traps)
- 100 crayfish measured at each site
Methods
- Biomass of predatory fish (predominantly trout)
estimated by electrofishing (three runs)
- Invertebrate biomass (surber samples, five at each site)
- Substratum grain size
(30 at each site)
Methods
Stable isotopes of crayfish
(n=10-14), Hydropsychidae
and mayflies (baseline corrections,
primary consumers)
-
- Periphyton biomass on cobbles
- Physico-chemical parameters
A mayfly for
Stable isotopes
Supervision….
Yes! Put the herbes
in the ethanol…..
will be great with
crayfish…tonight
Analyses
1) Test for physico-chemical differences between
signal and noble crayfish streams
2) Use stepwise regression to evaluate the importance
of predatory fish, substratum and periphyton biomass
for abundance and size distribution of crayfish
3) Use best predictors as covariates to test for
differences between crayfish species with respect to
their abundance and size (ANCOVA)
4) Compare trophic position and niche area
(convex Hull) of the two species when correcting
for site specific nitrogen and carbon ranges
(baseline invertebrates)
Carbon range
13
Nitrogen range
11
9
7
-16
-14
-12
Unfragmented
Partially fragmented
Highly fragmented
-10
δ 13 C
Polygon area = TA
•Layman et al. 2007 showed that niche width in top predatory fishes decreased with increasing habitat fragmentation
Results from this observational study…
Physico-chemical properties
pH
Ca (mg/l)
Tot-P (µg/l)
Oxygen (%)
6.8 (6.1-7.6)
11.6 (2.3-56)
28 (5-130)
92 (72-101)
Canopy cover (%)
Depth (cm)
Width (m)
Current velocity (m/s)
50 (0-99)
30 (12-86)
6.3 (1.8-13.4)
0.26 (0.02-0.92)
• Four extracted PCA-axes explained 78% of the variation
• Scores did not differ between signal and noble crayfish streams!
Signal crayfish
Noble crayfish
Crayfish abundance
- Dependent variable: CPUE of crayfish
- Predictors: Biomass of predatory fish, periphyton biomass
and substratum grain size
Stepwise regression
- Model 1: Biomass of predatory fish (r2=0.37)
- Model 2: Biomass of predatory fish
+ substratum grain size (r2=0.44)
”Few crayfish when fish biomass is high and substratum grain size is large”
Do trout eat crayfish?
One signal stream only!
Coleoptera (terrestrial)
Crayfish
Asellus aquaticus
Gammarus pulex
Gerridae
Chironomidae
Corixidae
Myriapoda (terrestrial
Seeds (terrestrial)
Fish
Trichoptera
Lymnaea peregra
Gyraulus
Pisidium
Colembola (terrestrial)
N=15 (12.6 - 29.0 cm)
0
20
40
60
Frequency of occurrence
80
Crayfish abundance and fish
20
Signal crayfish
Noble crayfish
CPUE
15
ANCOVA results
10
Crayfish
p > 0.97
Fish
p = 0.001
(Interaction NS, omitted)
5
0
0
2.5
5
7.5
10
12.5
Biomass of predatory fish (g/m2)
Crayfish abundance and fish
20
Signal crayfish
Noble crayfish
CPUE
15
< 2.0 g/m2
10
5
0
0
2.5
5
7.5
10
12.5
Biomass of predatory fish (g/m2)
Crayfish abundance and substrate
20
Signal crayfish
Noble crayfish
CPUE
15
Quadratic regression
10
5
0
0
5
10
15
20
25
Median substrate size (cm)
Signal crayfish
p = 0.013
Noble crayfish
p = 0.79
Crayfish abundance and substrate
Cannibalism!
Signal crayfish
Noble crayfish (?)
”A particularly unsocial behaviour”
Elgar and Crespi 1992
Crayfish mean size
- Dependent variable: Mean size of crayfish
- Predictors: Biomass of predatory fish, periphyton biomass
and substratum grain size
Stepwise regression
- Model 1: Periphyton biomass (r2=0.35)
”Larger crayfish when periphyton biomass is high”
Mean size (cm)
Crayfish size and periphyton
11.0
Signal crayfish
10.5
Noble crayfish
ANCOVA results
10.0
Crayfish
p > 0.52
Periphyton
p = 0.001
9.5
(Interaction NS, omitted)
9.0
8.5
8.0
0
1
2
3
4
Periphyton (Chl a /cm2)
5
d15N in crayfish - mayflies
Same trophic position (t-test, p > 0.31)!
S ig n a l c ra yfis h
8
No b le c ra y fis h
6
4
Predator 1
2
3.4 ‰
0
-32
-30
-28
-26
-24
-22
d13C (‰) in adult crayfish
Grazer
Niche width (TA)-species
S ig n a l c ra yfis h (6.5)
No b le c ra y fis h (2.7)
Trophic position
Niche width (TA)-populations
(t-test, p > 0,36)
Carbon signature
Niche width (TA)- affected by?
Niche width (TA)
0.5
ANCOVA results
Crayfish
p > 0.10
Invertebrates
p = 0.014
(Interaction NS, omitted)
Not by:
H´(inv.diversity, p=0.08)
Crayfish density
Periphyton biomass
Canopy cover
Conclusions
The abundance of signal and noble crayfish seems to be
influenced mainly by predatory fish in streams
Substratum grain size is important only for signal crayfish
and only when predators are few (interactive effects)
The size distribution of signal and noble crayfish is similar
and seems to be related to algal biomass (invertebrate
biomass)
Conclusions
Signal and noble crayfish are at the same trophic levels:
In many streams they are predators
Niche width is affected by prey availability. Signal crayfish
has a larger niche width at the species level
but not at the population level
We are almost the same
≈
Pacifastacus leniusculus
Astacus astacus
Thank you!
A signal crayfish on the rocks…please!