THE ECOSYSTEMIC APPROACH IN LIMNOLOGY THE SCIENTIFIC APPROACH

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Lindsay Rose
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THE ECOSYSTEMIC APPROACH IN LIMNOLOGY Fashion? Some pecularities of South American research groups Very few researchers consider that topdown control exists also in South American lakes.

1 THE ECOSYSTEMIC APPROACH IN LIMNOLOGY Fashion? Some pecularities of South American research groups Very few researchers consider that topdown control exists also in South American lakes. There are exceptional cases where specialists in phytoplankton, zooplankton, aquatic plants, fish, benthos, and aquaculture work on the SAME ECOSYSTEM, focused on critical questions and hypotheses that demand a multidisciplinary approach. THE SCIENTIFIC APPROACH EVENTS CONTROLLED BY OBSERVER REPLICATED EXPERIMENTS UNREPLICATED EXPERIMENTS DISTINT PERTURBATION OCCURS INTERVENTION ANALYSIS STUDY OF UNCONTROLLED EVENTS OBSERVATIONAL STUDIES NO DISTINT PERTURBATION EVIDENT 1

2 ENHANCEMENT OF TOP-DOWN CONTROL Algal biomass Oligotrophication Eutrophication BIOLOGICAL RESISTANCE CAUSE: HIGH PLANKTIVOROUS AND BENTHIVOROUS FISH ABUNDANCE. STRATEGY: PLANKTIVORE REMOVAL AND PISCIVORE INTRODUCTION (BIOMANIPULATION). Nutrient load Daphnia obtusa size (mm) T value=25.9 p<.1 Degrees of Freedom= 196 Maximum mean Cladocera body size (mm) Latitude 65 Mean Cladocera body length for latitude 35 EVENTS CONTROLLED BY OBSERVER STUDY OF UNCONTROLLED EVENTS In (sub)tropical areas only a strong reduction of small omnivorous-planktivorous fish promote the occurrence of medium and high-size cladocerans..6.4 RODO RIVERA NUMBER OF OBSERVATIONS BODY LENGTH (mm) BODY LENGTH (mm) Expected Normal 2

3 EVENTS CONTROLLED BY OBSERVER BIOMASS (kg ha -1 ) Cd Jm Gr Cf Chi Hm Rh Chl Hr Shrimps EVENTS CONTROLLED BY OBSERVER 7 NEKTON STOCK (kg ha -1 ) CD JM GR AS CHI PA 3

PHYTO+ZOO+J. multidentata PHYTO+ZOO+J.multidentata+H.

4 Replicated experiments (mesocosms) with Daphnia obtusa, Jenynsia multidentata and different sizes of Hoplias malabaricus PHYTO+ ZOO PHYTO+ZOO+J. multidentata PHYTO+ZOO+J.multidentata+H.malabaricus (small) PHYTO+ZOO+J.multidentata+H.malabaricus F(36,96)=1.93, p<.1 Chl a in vivo TIME (days) 4

Replicated experiments (microcosms) with Daphnia obtusa,

Salvinia auriculata and Eichhornia crassipes.

5 Replicated experiments (microcosms) with Daphnia obtusa, Cnesterodon decemmaculatus (different diets) and different free-floating plants species. PORCENTAJE 8 6 Daphnia obtusa avoids Pistia stratiotes, Salvinia auriculata and Eichhornia crassipes TIEMPO (min) Pistia stratiotes Tubo lado estímulo Centro Tubo lado sin estímulo Sin estímulo 5

6 PORCENTAJE TIEMPO (min) Macerado Daphnia obtusa Tubo lado estímulo Centro Tubo lado sin estímulo Sin estímulo D. obtusa avoids the signal generated by the fragmentation of Daphnia specimens, but it is indifferent to C. decemmaculatus presence (independently of its diet). PORCENTAJE 8 6 The repellence effect of free-floating plants is higher than the predation risks. In other words, freefloating plants don t offer refuge to D. obtusa TIEMPO (min) Macerado Daphnia obtusa Tubo lado estímulo Centro Tubo lado Pistia stratiotes Pistia stratiotes 6

7 15 5 CYCLOPOIDS MICROFILTRATORS MESOFILTRATORS INTERVENTION ANALYSIS WINTER SPRING SUMMER AUTUMN J. multidentata NEKTON ABUNDANCE CPUE 8 6 Shrimps 15 5 Chaoborus (ind m -3 ) WINTER SPRING SUMMER AUTUMN 8 6 INTERVENTION ANALYSIS 1..5 OW OW EP EP SP SP. CPUE 7

8 15 5 INTERVENTION ANALYSIS OW OW EP EP SP SP CPUE 8

Vancouver Lake Biotic Assessment

Vancouver Lake Biotic Assessment Washington State University Vancouver Aquatic Ecology Laboratory Dr. Stephen M. Bollens Dr. Gretchen Rollwagen-Bollens Co-Directors Problem: Noxious cyanobacteria blooms