shallow lakes trophic web in contrasting climates iglesias cbl xiii

Widespread omnivory in warmer shallow lakes determines different food web structures than

observed in temperate ones

Carlos Iglesias , Mariana Meerhoff, Liselotte S. Johansson, Mariana Vianna, Néstor Mazzeo, Juan Pablo Pacheco, Franco Teixeira de Mello, Guillermo Goyenola, Iván González-Bergonzoni, Torben L. Lauridsen, Martin Søndergaard, Thomas A. Davidson & Erik Jeppesen

XIII Congresso Brasilero de Limnologia

4-8 de Setembro 2011, Natal, RN

SUMMARY:

Framework

Objectives

Methodology

Results

Conclusions


What is a Shallow lake ?

• Light can reach bottom

• Medium depht ca. 3 m

• No or very short-term stratifications

Very well studied in cold temperate areas

Theoreticalframework

• Wide distributed, very important tohumans

ALTERNATIVE STATES(Scheffer et al., 1993)

PPP

• Strong water-sediments link


Transparency and plant -associated mechanisms scarce

plantssubmerged plants

phytoplankton

dominanceTurbid water-associated mechanisms

phytoplankton

higher probability of phytoplankton OR free-floating plants

higher probability of submerged plants dominance

only

submerged

plants

25 50 100 1000

Total P(g L-1) concentration

turbid water

clear water

Alternative (stable) states hypotheses

Forward switches Biomanipulation


Modified from Scheffer et al. 1993

+

-

+

+

phytoplankton

nutrients

allelopathy-

+submerged plants

turbidity

- periphyton

+

BOTTOM-UPNutrients/LightSedimentation rate

Role of submerged plants in temperate lakes


Role of submerged plants in temperate lakes

piscivorous fish

+

zooplankton

planktivorous fish

submerged plants

REFUGEDiel migrations (Timms & Moss, 1984)

Behavioural cascades (Romare & Hansson 2002)

TOP DOWNDirect trophic InteractionsCascading effects (Carpenter & Kitchell 1986)



Temperate lakes

high submerged plant cover with low phytoplankton

high phytoplankton biomass with low plant %PVI

Subtropical lakes

loss of clear patterns

high plant %PVI simultaneous with phytoplankton biomass

Jeppesen et al in 2007

Role of submerged plants in warmer lakes


Subtropical lakes

Effects of macrophytes on trophic interactions more complex and water clarity less improved

This is apparently a consequence of markedly different trophic web interactions (zooplankton & fish)

Role of submerged plants in warmer lakes


High diversity (TdeM 2009)

High density (specialy in plants)

Small-sized species with high abundances (Meerhoff et al., 2007)

Few large-sized strict piscivores

(Quiros, 1998)

Dominance of omnivorous species

(Lazzaro, 1997)

Several reproduction events. No window of opportunity for zooplankton (Van Leeuwen et al.,

2007)

Changes on fish community structure


Denmark Uruguay

Large-bodied zooplankters infrequent or absent.

5.5x lower density in subtropical lakes

11x higher density in the subtropical lakes

temperate fish more “pelagic” subtropical fish more “littoral”

8x lower density of macroinvertebrates

4x lower periphyton biomass, despite better growing conditions of light & temperature

(Meerhof et al GChB 2008)

Food webs changes among climatic regions


More complex and less hierarchically structured

More fish co-ocurred with fewer cladocerans and invertebrates

Lower biomass of periphyton than expected (less grazing high light and temp)

(Meerhof et al GChB 2008)



Are the food webs more truncated in subtropical lakes?

and fuelled by periphyton to a larger extent?

Objectives and Methodological approach

From Hugie & Dill 1994


Uruguay 30-35 。 S

Denmark 55-57 。N

dN indicates trophic position and dC carbon sources

Objectives and Methodological approach

Stable isotopes analysis + Community-wide measures of trophic structure (Vander Zanden & Vadeboncouer, 2002/Post, 2002/Layman et al., 2007)



Stable isotopes analysis + Community-wide measures of trophic structure

• Trophic position

• Trophic web length (Max TP)

• % Littoral Contribution

• Carbon range (amplitude of C sources)

• Total area (niche space ocupied)

• Mean nearest neighbour distance

(redundancy)

CR= max –min carbon

CR3

CR2

TA

TWL


Lake FR* TLW* CR CR 2 CR 3* %CONT

LITT TA NND*

CISNE 13 4.0 7.7 4.5 3.5 53.5 10.1 0.4

DIARIO 11 3.4 9.7 9.7 5.9 54.7 9.2 0.4

GARCIA 11 3.9 9.9 9.4 7.6 64.5 15.5 0.6

CLOTILDE 9 4.1 8.5 7.7 5.1 50.7 16.0 0.6

BLANCA 4 4.4 7 7 3.4 46.1 10.7 0.7

UY Median 11 4.0 8.5 7.7 5.1 53.5 10.7 0.6

Range 4-13 3.4-4.4 7.0-9.9 4.5-9.7 3.4-7.6 46.1-64.5 9.2-16.0 0.4-0.7

VAENG 8 5.1 4.9 4.3 2.6 52.7 8.6 0.6

TRANEVIG 6 5.8 10.5 7.3 0.6 58.3 16.1 0.9

GAMMELMOSE 4 4.6 4.6 4.4 3.0 98.2 10.2 1.2

DENDERUP 3 4.4 9.9 9.9 4.1 31.6 15.4 0.6

DK Median 5 4.8 7.4 5.9 2.8 55.5 12.8 0.8

Range 3-8 4.4-5.8 4.6-10.5 4.3-9.9 0.6-4.1 31.6-98.2 8.6-16.1 0.6-1.2

Zvalue 1.85 2.2 0.1 0.7 1.96 0.25 0.0 1.98

p 0.06 0.02 0.9 0.5 0.05 0.6 0.99 0.05


In warmer lakes

2X Fish richness

-1 Trophic Levels

2x CR3

More redundant species

Temperate = Subtropical lakes

Reliance in Littoral (ca. 50%)

Carbon range

Total extent of trophic diversity



Implicances on Trophic webs architecture

-1 Trophic Levels

2x CR3


Temperate = Subtropical lakes

Reliance in Littoral (ca. 50%)

Carbon range

Total extent of trophic diversity



(Meerhoff et al,2007)

XII Congresso Brasilero de Limnologia

3 Structural mechanisms (Post & Takimoto,2007)


Implicances on Trophic webs architecture

-1 Trophic Levels

2x CR3



Omnivory may explain the observed architecture (Post & Takimoto,2007)



Gonzalez-Bergonzoni subbmited

Different structure of trophic webs (and probably also functioning). Omnivory appears as the most plausible explanation

Strong effects to whole system functioning.

Asymmetries in some important feed backs probably weak alternative states to occur

Conclusions


piscivorous fish

+

zooplankton

OMNIVOROUSfish

submerged plants


piscivorous fish

+

zooplankton

planktivorous fish

submerged plants

ONE FINAL REMARK: We do have plant dominated clear water systems, even with quite high nutrient levels that seems to be persistent in time.

Conclusions


Thanks!!

Thanks for finantial support to AU, NERI and the Ministry of Science, Technology and Innovation in DK. PDT, ANII, CSIC –Udelar in Uruguay


Methods

shallow lakes trophic web in contrasting climates iglesias cbl xiii

Education

role of submerged plants

limnologia periphyton

low plant

warmer shallow lakes

high density

lower periphyton biomass

pvihigh plant

water clarity