1. PHYTOPLANKTON DYNAMICS IN LAKE CHALLA AS DERIVED
FROM SEDIMENT TRAP ANALYSES
Christine Cocquyt
National Botanic Garden of Belgium
Limnology Unit, Ghent University
Présentation: Yves
National Botanic Garden of Belgium

2. Quantitative phytoplankton analyses
Uthermöhl method:
- “sedimentation chamber” of 10 ml
- inverted microscope
- counts of organisms and colonies (known surface area)
Calculation
- number of cells/ml
- conversion to biovolumes

3. Major algal groups - percentages derived from biovolumes
Lake Challa
2007
2008
2010
2011
Présentation: Yves
Major algal groups - percentages derived from biovolumes

4. Gomphocymbella Synedra/Ulnaria Nitzschia “long” 2007 2008 2010 2011
Présentation: Yves
percentages derived from biovolumes
2007
2008
2010
2011

5. Staurosira/ Staurosirella spp.
Encyonema/
Cymbella spp.
Staurosira/ Staurosirella spp.
Rhopalodia spp.
Présentation: Yves
percentages derived from biovolumes
2007
2008
2010
2011

6. Closteriopsis acicularis
Cosmarium spp.
Closteriopsis acicularis
Oocystis sp.
Présentation: Yves
percentages derived from biovolumes
2007
2008
2010
2011

7. Filtered versus water sample

8. Challa phytoplankton productivity
filtered sample
water sample
flux (cell volume/day cm2)
Présentation: Yves
2007
2008
2010
2011

9. filtered samples
Présentation: Yves
water samples

10. Lake Challa – July 2010 – filtered sample
Présentation: Yves

11. Lake Challa – January 2011 – water sample
Présentation: Yves

12. Species diversity

13. Species diversity
Diatoms
Chlorophyta
Cyanobacteria
Euglenophyta
Dinophyta
Chrysophyta
Total

14. Bacillariophyta
Achnanthidum exiguum
Achnanthidum sp.
Amphora copulata
Amphora pediculus
Cymatopleura clavata
Cymbella sp.
Diploneis sp.
Encyonema meulleri
Encyonema minutum
Gomphocymbella sp. Gomphonema affine
Gomphonema parvulum
Gomphonema sp.
Hantzschia amphioxys
Navicula sp. 1
Navicula sp. 2
Navicula sp. 3
Navicula sp. 4
Nitzschia bacata
Nitzschoa epiphyticoides
Nitzschia fonticola
Nitzschia lancettula
Nitzschia palea
Nitzschia palea var. tropica
Nitzschia vanoyei
Nitzschia sp. 1
Nitzschia sp. 2
Nitzschia sp. 3
Nitzschia sp. 4
Placoneis gastrum
Rhopalodia gibba
Rhopalodia gibberula
Rhopalodia gracilis
Rhopalodia hirudiniformis
Sellaphora nyassensis
Sellaphora pupula
Stauroneis sp.
Staurosira construens
Staurosirella pinnata
Surirella sp.
Ulnaria acus
Ulnaria danica
Ulnaria ulna
Urosolenia sp.

15. Chlorophyta
Ankistrodesmus sp.
Chlorococcus sp.
Chlorella sp.
Closteriopsis acicularis
Closteriopsis acicularis var. africana
Crucigeniella quadrata
Crucigeniella sp.
Dictyosphaerium pulchellum
Dictyosphaerium tetrachotomum
Didymosphenia sp.
Eremosphaeria sp.
Kirchneriella arcuata
Kirchneriella contorta var. elongata
Kirchneriella microscopica
Kirchneriella obesa
cf. Kirchneriella sp.
Lagerheimia chodatii
Lagerheimia ciliata
Lagerheimia citriformis
Lagerheimia subsalsa
Lobocystis planctonica
Monoraphidium arcuatum
Monoraphidium irregulare
Monoraphidium mirabile
Monoraphidium minutum
Oocystis sp.
Oonephris sp.
cf. Oonephris sp.
Podohedra falcata
Schroederia planctonica
Tetraedron triangulare
Tetraedron minimum
Treubaria setigera
Tetrastrum komareckii
sp. 1
sp. 2
sp. 3
Cosmarium sp. 1
Cosmarium sp. 2
Staurastrum

16. Cyanobacteria
Chroococcus limneticus
Chroococcus dispersus
Chroococcus sp.
Chroococalles sp.
cf. Aphanocapsa microscopica
cf. Gloeotrichia sp.
Gomphosphaeria cf. natans
Synechococcus elongatus
Planktolyngbya sp.
Microcrocis sp.
Microcystis sp.
Snowella sp.
sp. 1
sp. 2
sp. 3

17. Euglenophyta
Trachelomonas volvocina
Trachelomonas volvocinopsis
Dinophyta
Peridinium sp.
Gymnodinium sp.
Chryso/Cryptophyta
Chrysomonas sp.
cf. Chrysomonas sp.
sp.

18. Bacillariophyta - Diatoms
Gomphonema
Diploneis
Encyonema minutum
Staurosira construens
Gomphocymbella
Nitzschia “small”
Présentation: Yves
Nitzschia “long”
Rhopalodia gibba
Sellaphora nyassensis

19. Chlorophyta – green algae
Tetraedron minimum
Oocystis
cf. Eremosphaera
Closteriopsis acicularis
Cosmarium
Tetrastrum
Présentation: Yves
sp.
Lagerheimia
Treubaria setigera
Kirchneriella
Staurodesmus

20. Chlorophyta – green algae
Tetraedron minimum
Oocystis
cf. Eremosphaera
Closteriopsis acicularis
Cosmarium
Tetrastrum
Présentation: Yves
sp.
Lagerheimia
Treubaria setigera
Kirchneriella
Staurodesmus

21. Peridinium cf. africanum
Euglenophyta
Dinophyta
Trachelomonas
Peridinium cf. africanum
Présentation: Yves

22. National Botanic Garden of Belgium
Conclusions
- phytoplankton dominated by a Diatom-Chlorophytes community
seasonal and interannual variability in major algal groups
interannual variability in diatom composition, e.g. Synedra/Ulnaria spp. and “long” Nitzschia spp.
“small” Nitzschia not important in the actual phytoplankton, probably benthic species
water samples more reliable than filtered samples
non-diatoms probably underestimated – disintegration during sedimentation
- need of actual phytoplankton samples (taken during the monthly sampling of the sediment trap)
Présentation: Yves
National Botanic Garden of Belgium

23. National Botanic Garden of Belgium
Acknowledgement
Dirk Verschuren
all persons involved in the sampling of the sediment trap and in the proceeding of the samples
Présentation: Yves
National Botanic Garden of Belgium

24. Thank you for your attention
Présentation: Yves
National Botanic Garden of Belgium