Disentangling long-term responses of

crustacean zooplankton to multiple

stressors

Stephen J. Thackeray (sjtr@ceh.ac.uk),

Peter Smyntek, Heidrun Feuchtmayr, Ian J. Winfield, Ian D. Jones &

Stephen C. Maberly

Lake Ecosystems Group, Centre for Ecology & Hydrology

Multiple stressors

• Lake ecosystems are affected

by many internal and external

factors

• External factors:

climate change

eutrophication

acidification

species introduction

• Operate at different (local –

regional) scales and may

interact.

Top-down and bottom-up effects

Maberly & Elliott (2012) Freshwater Biology, 57, 233-243

• Stressors may act upon:

physical properties and basal

resources – “bottom up”.

predator/consumer populations –

“top down”.

• Relative importance of these pathways

and associated stressors will vary among

ecosystems, and over time.

Windermere, as a model system

Mean winter SRP (mg m-3

)

0

5

10

15

20

25

30

1950 1960 1970 1980 1990 2000 2010

Year

North Basin

South Basin

6

8

10

12

1950 1970 1990 2010Year

Mean surface temperature (oC)

North Basin

South Basin

Nutrient enrichment Warming

Windermere, as a model system

0

1000

2000

3000

4000

5000

6000

1990 1995 2000 2005 2010

Ab

un

dan

ce (

fish

ha

-1)

Year

Expansion of non-native species

Focus on crustacean zooplankton

Pre

dat

ors

G

raze

rs

Foo

d/T

emp

erat

ure

• Effects on grazers of long-term

changes in:

Temperature

Food (algae)

Predators (invertebrate)

Predators (fish)

• Is it possible to detect these

effects on the long-term

dynamics of grazer populations?

Drivers of zooplankton change

• Fortnightly data,1991-2010

• Response data:

• Crustacean zooplankton abundance

• Driving data:

• Water temperature • Phytoplankton biomass,

(Chlorophyll a) • Predatory zooplankton

(Bythotrephes, Leptodora, Cyclops)

• Fish abundance (monthly)

A proxy for zooplanktivory

0

1000

2000

3000

4000

5000

6000

1990 1995 2000 2005 2010

Ab

un

dan

ce (

fish

ha

-1)

Year

6

8

10

12

1950 1970 1990 2010Year

Mean surface temperature (oC)

North Basin

South BasinMe

an

su

rfac

e t

em

pe

ratu

re (

˚C)

Maximum consumption rate (Cmax) = 0.016 x Weight (g)-0.16 x e0.133 x Temperature (˚C)

Hölker & Haertel (2004) Journal of Applied Icthyology, 20, 548-550

Statistical methods • Seasonality:

Focus on long-term (not seasonal)

change.

Induces correlation among driving

variables.

Therefore, removed smooth seasonal

“trend” from original data using generalised

additive models (GAMs).

• Lagged effects:

Response at time t related to drivers at

time t-1.

• Seasonal shifts in drivers:

Drivers can vary (interact) with month-of-

year.

• Linear models with different predictor

combinations compared by AIC.

°C Food

Fish

Patterns of change: Eudiaptomus

Correlates of change: Eudiaptomus

• “Top” model (by AIC): “effects” of chlorophyll (food) and planktivory by fish

Correlates of change: Eudiaptomus

November -

March data

1991 1994 1997 2000 2003 2006 2009

-0.2

0.0

0.2

Seasonally-detrended log chlorophyll concentration

Year

1991 1994 1997 2000 2003 2006 2009

-0.5

0.0

0.5

Seasonally-detrended log fish consumption

Year

1991 1994 1997 2000 2003 2006 2009

-1.5

-1.0

-0.5

0.0

0.5

1.0

Seasonally-detrended log Eudiaptomus abundance

Year

1991 1994 1997 2000 2003 2006 2009

-1.5

-1.0

-0.5

0.0

0.5

1.0

Model prediction

Year

Summary and next steps

• Can detect a likely effect of increased

planktivory upon Eudiaptomus, though

much unexplained variation.

• Further exploration of the zooplanktivory

“effect”

sensitivity to parameter choice

can we apportion planktivory

among fish species?

is magnitude sufficient to cause

observed population change?

• What about other species?

• Can we see a cascade to the

phytoplankton?

• Independent process modelling studies.

Acknowledgements

• This work was funded by NERC

Grant NE/H000208/1: “Whole lake

responses to species invasion

mediated by climate change”

(http://www.windermere-

science.org.uk/).

• Many thanks to everyone involved

in maintaining the Cumbrian

Lakes long-term monitoring

programme, past and present.

• Thank you for your attention!