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

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

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

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

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

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

Filtered versus water sample

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

filtered samples Présentation: Yves water samples

Lake Challa – July 2010 – filtered sample Présentation: Yves

Lake Challa – January 2011 – water sample Présentation: Yves

Species diversity

Species diversity Diatoms 44 Chlorophyta 40 Cyanobacteria 15 Euglenophyta 2 Dinophyta 2 Chrysophyta 3 Total 106

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.

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

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

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

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

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

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

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

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

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

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