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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Crayfish are important consumers and prey in many ecosystems In Swedish streams most native crayfish populations have been replaced by signal crayfish...crayfish plague • The native noble crayfish has declined by 97% during the 20th century (CR) • What are the roles of these omnivores in the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!