Water Motion and Sediment Grain Size Water Motion and Sediment Grain Size Effects on Benthic MicroalgaeEffects on Benthic Microalgae

Adrian Jones, Andrew Watkinson, Joelle Prange & William DennisonAdrian Jones, Andrew Watkinson, Joelle Prange & William DennisonBotany Department, The University of Queensland, Brisbane, QLD, AustraliaBotany Department, The University of Queensland, Brisbane, QLD, Australia

Marine BotanyMarine Botany

THE UNIVERSITY

OF QUEENSLAND

Benthic MicroalgaeBenthic Microalgae• Diatoms, dinoflagellates and cyanobacteriaDiatoms, dinoflagellates and cyanobacteria• Ubiquitous distribution Ubiquitous distribution

• Can tolerate low light (<1% ICan tolerate low light (<1% Ioo))

• Capable of small scale migrationCapable of small scale migration• Large contribution to primary productivity in marine Large contribution to primary productivity in marine

systemssystems

AimsAims

• Determine biomass and photosynthetic capacity of Determine biomass and photosynthetic capacity of benthic microalgae in relation to sediment grain size benthic microalgae in relation to sediment grain size and water motionand water motion

• Determine the changes in photosynthetic capacity of Determine the changes in photosynthetic capacity of benthic microalgae under different water flow regimesbenthic microalgae under different water flow regimes

• Examine the photosynthetic viability of BMA at different Examine the photosynthetic viability of BMA at different sediment depths within fine and coarse grain sedimentssediment depths within fine and coarse grain sediments

Study SitesStudy Sites• 10 sites on Heron Reef from areas of different water motion and sediment grain 10 sites on Heron Reef from areas of different water motion and sediment grain

sizessizes• 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

Sediment Grain SizeSediment Grain SizeCoarse grained sedimentsCoarse grained sediments• Sediment ridges due to high water motionSediment ridges due to high water motion• High water flow prevents smaller particles from High water flow prevents smaller particles from

accumulatingaccumulating• Occurs near reef crestOccurs near reef crest

Fine grained sedimentsFine grained sediments• Even, “undisturbed” sediment surface due to lack of water Even, “undisturbed” sediment surface due to lack of water

motionmotion• 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

Wentworth’s Grade ScaleWentworth’s Grade Scale• Granule Granule > 4.0 - 2.0 µm> 4.0 - 2.0 µm

• Very Coarse SandVery Coarse Sand 1.69 - 1.0 µm 1.69 - 1.0 µm

• Coarse SandCoarse Sand 0.84 - 0.5 µm 0.84 - 0.5 µm

• Medium SandMedium Sand 0.42 - 0.25 µm 0.42 - 0.25 µm

• Fine SandFine Sand 0.21 - 0.125 µm 0.21 - 0.125 µm

• Very Fine SandVery Fine Sand 0.105 - 0.0625 µm 0.105 - 0.0625 µm

• SiltSilt < 0.053 µm< 0.053 µm

Sand Grain SizeSand Grain Size

Very Fine Fine Medium Coarse

PAM Fluorescence PAM Fluorescence (Pulse Amplitude Modulated)(Pulse Amplitude Modulated)

05

10152025303540

0 200 400 600 800 1000 1200 1400 1600

Photosynthetically Active Radiation (PAR)(µE m-2 s-1)

Ele

ctro

n T

ran

spo

rt R

ate

(ET

R)

(µm

ol e

- m-2 s

-1 ) PhotoinhibitionPhotoinhibition

• Generates rapid light curvesGenerates rapid light curves

• Maximum ETR can be used as a Maximum ETR can be used as a measure of potential photosynthetic measure of potential photosynthetic capacitycapacity

Maximum ETRMaximum ETR

Grain Size & BMA ConcentrationGrain Size & BMA Concentration

0

100

200

300

400

Fine Medium Coarse

Sediment Grain Size

Ch

loro

ph

yll a

(m

g m

-2)

Grain Size & Fluorescence (FGrain Size & Fluorescence (Foo))

0

50

100

150

200

Fine Medium CoarseGrain Size

Init

ial

Flu

ore

sce

nce

(F

o)

Grain Size & Photosynthetic CapacityGrain Size & Photosynthetic Capacity

0

20

40

60

Fine Medium Coarse

Grain Size

Ma

xim

um E

TR

(µm

ol e

- m

-2 s

-1)

Water Motion ExperimentsWater Motion Experiments

Fine grainsand

Coarse grainsand

Fast water flow regime Slow water flow regime

Slow water flow regimeSlow water flow regime• No disturbance of sediment No disturbance of sediment

surfacesurface

Fast water flow regimeFast water flow regime• Significant disturbance of sediment Significant disturbance of sediment

surface and exposure of lower layerssurface and exposure of lower layers

FastSlow

Fast

Slow0

10

20

30

40

50

60

0 500 1000 1500 2000

PAR (µE m-2 s-1)

ET

R (

µmol

e- m

-2 s

-1)

FineGrain Sand

0

20

40

60

80

100

120

0 500 1000 1500 2000

PAR (µE m-2 s-1)

ET

R (

µmol

e- m

-2 s

-1)

CoarseGrainSand

Water Flow & Photosynthetic Capacity Water Flow & Photosynthetic Capacity

Effects of boundary layer on BMA vary Effects of boundary layer on BMA vary between coarse and fine sedimentsbetween coarse and fine sediments

Fine grained compacted sedimentFine grained compacted sedimentCoarse grained loose sedimentCoarse 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 regimeSlow water flow regime• Laminar flow Laminar flow • Thick boundary layerThick boundary layer• Reduced gas and nutrient exchangeReduced gas and nutrient exchange• Reduced photosynthesisReduced photosynthesis• Lower BMA biomassLower BMA biomass

Effects of boundary layer on BMA vary Effects of boundary layer on BMA vary between coarse and fine sedimentsbetween coarse and fine sediments

Coarse grained loose sedimentCoarse 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 regimeFast water flow regime• Mixed flow Mixed flow • Reduced boundary layerReduced boundary layer• Increased gas and nutrient exchangeIncreased gas and nutrient exchange• Increased photosynthesisIncreased photosynthesis

Fine grained compacted sedimentFine grained compacted sediment

Vertical Distribution ExperimentsVertical Distribution Experiments

Vertical distribution of BMAVertical distribution of BMA

0

10

20

30

40

0 500 1000 1500 2000 2500

PAR (µE m-2 s-1)

ET

R (

µm

ol e

- m-2

s-1

)

0

10

20

30

40

0 500 1000 1500 2000 2500

PAR (µE m-2 s-1)

ET

R (

µm

ol e

- m-2

s-1

)

FineGrain Sand

CoarseGrainSand

30 minsInitial

30 mins

Initial

ConclusionsConclusions

• 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 Water motion over the coarse grain substrate does not affect BMA photosynthetic capacityphotosynthetic capacity

• Photosynthetic capacity within fine grained substrate is enhanced Photosynthetic capacity within fine grained substrate is enhanced by water motionby water motion

• Vertical distribution of BMA is variable between coarse and fine Vertical distribution of BMA is variable between coarse and fine grain sedimentsgrain sediments