1. Water Motion and Sediment Grain Size Effects on Benthic Microalgae Adrian Jones, Andrew Watkinson, Joelle Prange & William Dennison Botany Department, The University of Queensland, Brisbane, QLD, Australia Marine Botany T HE U NIVERSITY O F Q UEENSLAND

2. Benthic Microalgae Diatoms, dinoflagellates and cyanobacteriaDiatoms, dinoflagellates and cyanobacteria Ubiquitous distributionUbiquitous distribution Can tolerate low light (<1% I o )Can tolerate low light (<1% I o ) Capable of small scale migrationCapable of small scale migration Large contribution to primary productivity in marine systemsLarge contribution to primary productivity in marine systems

3. Aims Determine biomass and photosynthetic capacity of benthic microalgae in relation to sediment grain size and water motionDetermine biomass and photosynthetic capacity of benthic microalgae in relation to sediment grain size and water motion Determine the changes in photosynthetic capacity of benthic microalgae under different water flow regimesDetermine the changes in photosynthetic capacity of benthic microalgae under different water flow regimes Examine the photosynthetic viability of BMA at different sediment depths within fine and coarse grain sedimentsExamine the photosynthetic viability of BMA at different sediment depths within fine and coarse grain sediments

4. Study Sites 10 sites on Heron Reef from areas of different water motion and sediment grain sizes10 sites on Heron Reef from areas of different water motion and sediment grain sizes Sites near the reef crest experience greater water motion than those in the lagoonSites near the reef crest experience greater water motion than those in the lagoon

5. Sediment Grain Size Coarse grained sediments Sediment ridges due to high water motionSediment ridges due to high water motion High water flow prevents smaller particles from accumulatingHigh water flow prevents smaller particles from accumulating Occurs near reef crestOccurs near reef crest Fine grained sediments Even, “undisturbed” sediment surface due to lack of water motionEven, “undisturbed” sediment surface due to lack of water motion Low water flow allows fine particles to settle out of suspensionLow water flow allows fine particles to settle out of suspension Occurs in middle of the lagoonOccurs in middle of the lagoon

6. Wentworth’s Grade Scale Granule > 4.0 - 2.0 µmGranule > 4.0 - 2.0 µm Very Coarse Sand1.69 - 1.0 µmVery Coarse Sand1.69 - 1.0 µm Coarse Sand0.84 - 0.5 µmCoarse Sand0.84 - 0.5 µm Medium Sand0.42 - 0.25 µmMedium Sand0.42 - 0.25 µm Fine Sand0.21 - 0.125 µmFine Sand0.21 - 0.125 µm Very Fine Sand0.105 - 0.0625 µmVery Fine Sand0.105 - 0.0625 µm Silt< 0.053 µmSilt< 0.053 µm

7. Sand Grain Size Very FineFineMediumCoarse

8. PAM Fluorescence (Pulse Amplitude Modulated) 0 5 10 15 20 25 30 35 40 02004006008001000120014001600 Photosynthetically Active Radiation (PAR) (µE m -2 s -1 ) Electron Transport Rate (ETR) (µmol e - m -2 s -1 )Photoinhibition Generates rapid light curvesGenerates rapid light curves Maximum ETR can be used as a measure of potential photosynthetic capacityMaximum ETR can be used as a measure of potential photosynthetic capacity Maximum ETR

9. Grain Size & BMA Concentration

10. Grain Size & Fluorescence (F o )

11. Grain Size & Photosynthetic Capacity

12. Water Motion Experiments Fine grain sand Coarse grain sand Fast water flow regime Slow water flow regime No disturbance of sediment surfaceNo disturbance of sediment surface Fast water flow regime Significant disturbance of sediment surface and exposure of lower layersSignificant disturbance of sediment surface and exposure of lower layers

13. Fast Slow Fast Slow Fine Grain Sand Coarse Grain Sand Water Flow & Photosynthetic Capacity

14. Effects of boundary layer on BMA vary between coarse and fine sediments Fine grained compacted sediment Coarse grained loose sediment Irregular flowIrregular flow Boundary layer brokenBoundary layer broken Increased gas and nutrient diffusionIncreased gas and nutrient diffusion Higher photosynthesisHigher photosynthesis Greater BMA biomassGreater BMA biomass Slow water flow regime Laminar flowLaminar flow Thick boundary layerThick boundary layer Reduced gas and nutrient exchangeReduced gas and nutrient exchange Reduced photosynthesisReduced photosynthesis Lower BMA biomassLower BMA biomass

15. Effects of boundary layer on BMA vary between coarse and fine sediments Coarse grained loose sediment Irregular flowIrregular flow Boundary layer brokenBoundary layer broken Increased gas and nutrient diffusionIncreased gas and nutrient diffusion Higher photosynthesisHigher photosynthesis Greater BMA biomassGreater BMA biomass Fast water flow regime Mixed flowMixed flow Reduced boundary layerReduced boundary layer Increased gas and nutrient exchangeIncreased gas and nutrient exchange Increased photosynthesisIncreased photosynthesis Fine grained compacted sediment

16. Vertical Distribution Experiments

17. Vertical distribution of BMA Fine Grain Sand Coarse Grain Sand 30 mins Initial 30 mins Initial

18. Conclusions BMA abundance is highest in sites of intermediate grain sizeBMA abundance is highest in sites of intermediate grain size Water motion over the coarse grain substrate does not affect BMA photosynthetic capacityWater motion over the coarse grain substrate does not affect BMA photosynthetic capacity Photosynthetic capacity within fine grained substrate is enhanced by water motionPhotosynthetic capacity within fine grained substrate is enhanced by water motion Vertical distribution of BMA is variable between coarse and fine grain sedimentsVertical distribution of BMA is variable between coarse and fine grain sediments