study area: the okavango delta - ucl geography blog
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Hydrological and habitat controls of algal biodiver sity and biomass in a subtropical flood-pulsed wetland
Luca Marazzi, MScPh.D. Candidate
Department of GeographyUniversity College London
INTECOL 2013 – 19 th August 2013
Study area: the Okavango Delta
1. Introduction
Flooded area: 2,500–4,000 km2 (Feb-Mar) to 6,000–12,000 km2 (Aug-Sep)
Ramsar and UNESCO Heritage site
Source: MODIS satellite image.
Microalgae, base of aquatic food webs
Ecosystem services. Provisioning: food, fiber and fuel. Regulating: climate regulation; water purification. Supporting: primary production; nutrient cycling; production of atmospheric oxygen
1. Introduction
Acknowledgements
� Anson Mackay, Viv Jones, Sophie des Clers, Lars Ramberg; Brian Whitton, David John, David Williamson and Chris Carter, Gina Clarke, Tom Davidson, Barbara Leoni, Letizia Garibaldi
� Royal Geographical Society, UCL Geography Department & Graduate School, UK DEFRA Darwin Initiative (funding forfieldwork and other expenses)
� Nqobizitha Siziba, Ponde Kauheva, Richard Mazebedi and Okavango Research Institute staff
� Responding to Climate Change, Campbell Harris Tutors, Greater London Tutors, Mouseion Limited (employers 2009-2013)
Main aims and key questions
A1)Present first ever estimate of algal biodiversity in the Okavango Delta
A2)Explain biomass and diversity patterns in relation to macrohabitats and environmental variables
Q1) Does algal biomass grow with increasing speciesrichness?
Q2) What is the shape of the diversity-biomass curve inthe different macrohabitats?
1. Introduction
The Okavando Delta: sampling campaigns
= Algal sampling
R
H
LE
Campaign 1 : I. Sep. 2006 (Flood Recession ); II. Apr.-May 2007 (Flood Expansion ); III. Jul.-Aug. 2007 (High Water )
Campaign 2 : I. May 2009 (Flood Expansion ); II. Jul-Aug. 2009 (High Water ); III. Oct. 2009 (Flood Recession ); IV. Feb. 2010 (Low Water )
Upper Panhandle (UPH); Lower Panhandle (LPH); Xakanaxa (XAK ); Boro (BOR); Santantandibe (SAN). [Ngami Lake (NGA), Thamalakane (THA)]
2. Methods
Macrohabitats sampled
Open Water (main channel) & Marginal Vegetation (e.g.:Typha, Phragmites, Vossia) Floodplain
Open Water, Sedgeland and Grassland
1)Delta-scale
2)Within-floodplain
For comparisons across all samples
For investigation of floodplain dynamics
2. Methods
Water samples for algae + limnological variables
Algal counts – 132 samples (49,975 algal units)
Regions Bac Chl Chr Cry Cya Eug Pra Pyr Uni Xan
UPH (N) 4,407 1,095 14 133 214 36 0 12 13 7
LPH (N) 2,560 839 30 281 132 34 0 9 8 6
XAK (E) 2,196 1,108 230 365 192 102 0 67 1 11
BOR (S) 6,190 14,068 81 1,404 2,277 762 0 115 182 95
SAN (S) 3,918 4,311 21 617 605 647 1 72 60 28
(NGA - SW) 179 217 0 0 17 0 0 0 0 1
Total 19,450 21,638 376 2,800 3,437 1,581 1 275 264 148
•About 400 algal units (cells, colonies, filaments, coenobia) counted in each sample
•Biovolumes estimated using cell measurements and geometric formulas
[Bac= Bacillariophyta; Chl=Chlorophyta; Chr=Chrysophyt a; Cry=Cryptophyta; Eug= Euglenophyta; Pra= Prasinophyta; Pyr=Pyrrophyta; Uni=Unid entified; Xan=Xanthophyta]
2/3. Methods / Results
Species richness per algal phylum
Phylum N Species N Genera
Bacillariophyta (B) 113 37
Chlorophyta (Chl) 283 88
Chrysophyta 7 6
Cryptophyta (Cr) 11 3
Cyanophyta (Cy) 28 22
Euglenophyta (Eu) 37 6
Prasinophyta 1 1
Pyrrophyta (Py) 8 7
Xanthophyta 7 4
Total 495 174
Cryptomonas sp. (Cr)
10 µm
Phacus longicauda (Eu)
Micrasterias pinnatifida (Chl) (© Chris Carter )
Anabaena sp. (Cy)
20 µm
3. Results
20 µm
Stauroneis phoenicenteron (B)
30 µm
20 µm
Peridinium sp. (Py)
10 µm
New variety: Cosmarium pseudosulcatum var okavangicum
Williamson D.B. and Marazzi L.. 2013. A new Cosmarium (Chlorophyta, Desmidiaceae) variety from the Okavango Delta, Botswana. Quekett Journal of Microscopy 42, 35:37.
(© David Williamson )
3. Results
Diversity-biomass relationship
Floodplain sites: higher species richness, biovolumes and Chl a
130 samples 2009-2010 samples
3. Results
Biovolumes: Mean=8.103 mg/L(0.176 - 90.41 mg/L)
Temperature and habitat vs species richness
R2adj=0.286; p=0.000
3. Results
Key factors for species richness:
1.Temperature (+)
2.DO (-)
3.TN (-)
4.depth (-)
Facilitation
3. Results
Higher biomass
Factors driving diversity and biomass
Competition
Key factors for biovolume:
1.Cations (+), 2.temperature (+),3.species richness (+)
Algal cell length across regions / habitats
3. Results
•On average smaller algae in Southern Delta
•In some floodplains (Bororegion) larger algae than in other habitats
Diversity-biomass across macrohabitats
MV=Marginal Vegetation
F=Floodplain
OW=Open Water
Plankton: Competitive displacement
Benthos: FacilitationSee: Passy, S. I. and P. Legendre (2006). "Are algal communities driven toward maximum biomass?“
3. Results
“Facilitation in the benthos delays the negative effect of competition , which, together with the
weaker response to top-down controls, permits more species to coexist and produce maximum biomass”
Macrohabitats for algae (Northern Delta)
Upper and Lower Panhandle: Open Water and Marginal Vegetation
Upper Panhandle with Papyrus
Eunotia pectinalis
20 µm
Eunotia sp.
20 µm
Synedra sp.
30 µm
Cryptomonas sp.
10 µm
Here water velocity is higher, high profile diatomsare very abundant
Eunotia rhomboidea
20-30 µm
3. Results
Floodplains (Boro, Santantandibe): Open Water and Floodplain habitats (Sedgelands and Grasslands)
Floodplain with sedges and grasses (e.g. Schoenoplectus and Cynodon)
5 µm
Cosmarium haynaldii
25 µm
Micrasterias tropica Mougeotia sp.
20 µm
Macrohabitats for algae (Southern Delta)
Scenedesmusfalcatus
Both planktonic and benthic algae attached to sand / sediments or plants
15 µm
Euastrum bidentatum(© Chris Carter )
3. Results
Conclusions
1. 495 species of algae + epiphytic diatoms found by Mackay et al. (2012) = total 610 species (Pantanal: 337 spp.; Kakadu National Park: >700 spp.)
2. Habitat diversity generated by the slow periodic flood-pulse creates more heterogeneous conditions in the floodplains; thus the higher algal species richness (whichdrives algal biomass) .
3. Mechanisms: Facilitation / niche overlap occurs in the Floodplains (greater habitat diversity, e.g. in 3D biofilms); competition / niche complementarity prevail in the Open Water (less habitat diversity)
Ongoing and possible future work
• Multivariate analyses to interpret relative roles of all environmental variables (e.g. conductivity, DO, TN, TP) in shaping algal communities (cluster analysis / ordination & response curves for key taxa).
• Exploring synergies with other projects, e.g. “The Future Okavango” ; funding applications for raising awarenesswork on algae with local communities.
• Post-PhD : Further taxonomic analyses? Study of food-webs ? Comparative biogeographic research acrosstropical wetlands? Distribution of desmids via birdmigration ?