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Intertidal and SubtidalMicrobialites in the Shark Bay
World Heritage areaLindsay Collins
Jahnert & Collins 2011, 2012 Marine Geology
Acknowledgements: Ricardo Jahnert, Therese Morris, Alex Stevens, Giada Bufarale
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Outstanding examples representing the major stages of the
earth's evolutionary history
• Shark Bay contains the most diverse and abundant examples of stromatolitic microbialities in the world. The living cyanobacteria (Scytonema) still building stromatolites at Hamelin Pool are similar to the earliest Cyanobacterial life forms which dominated the earth for 3000 million years (3 giga years).
Walker, 2011
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Outstanding examples representing significant ongoing geological processes,
biological evolution and human interaction with the natural environment
• Shark Bay's enormous seagrassbeds (>4000 km2)
• an impressive example of the role seagrasses play in modifying a whole marine ecosystem.
• directly influence the physics, chemistry, biology and geology of the Bay
Walker, 2011
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Shark Bay at present• Semi-arid to arid climate - hot dry summers
and mild winters• Evaporation used to exceed rainfall by a factor
of 10 – Mean annual precipitation ranges from
200 mm in the east to 400 mm in the far southwest
– Mean annual evaporation ranges from 2000 mm in the west to 3000 mm in the east
• As a result, Shark Bay has a strong salinity gradient from marine (35 ppt) to hypersaline(70 ppt) in Hamelin Pool
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Research focused on the Shark Bay Marine Park Holocene sedimentary
deposits.
RESEARCH THEMES:
• Microbial mats facies and fabrics, chemistry, organic composition and microbial communities,
• Subtidal microbial structures origin, occurrence, distribution and growth history,
• Coquina ridge morphology, facies, structures, chronology and depositional evolution,
• Analogy with ancient carbonate systems.
SHARK BAY RESEARCH PROJECT
NilemahGardenPoint
Rocky Point
HAMELINPOOL
Hutchinson
Telegraph
Carbla
SHARK BAY MARINE PARK
HENRY FREYCINET
L’HARIDONBIGHT
Hamelin PoolFlooding
Predicted SL Rise
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Shark Bay microbialites are organo-sedimentary deposits that trap and bind sediment,
induce mineralization by bacteria and have aragonite
cement to form solid structures.
Shark BayMicrobialDeposits
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NSHARK BAY
MARINE PARK
3 Km
Rocky Point
1400 Km2
Hamelin Basin
Embayment Plain6‐10 m
Sublittoral Platform1‐6 m
IntertidalSupratidalPlatform0‐1 m
L’HARINDONBIGHT
SEAGRASSES
CARBONATE BANKSTIDAL
CHANNEL
HENRIFREYCINETHARBOR
TidalFlats
ImageDept. Environment &
Conservation
Hutchinson
Nilemah
Garden Point
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Microbial Mats
11 Km2
Garden Point
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Smooth Mat Pustular MatGarden Point
Smooth MatTufted Mat
50.00 60.00 70.00 80.00 90.00 100.00
Gas Chromatography17
15
16
DMC17?
18
Ph
18:1
19?? 20 21
29
22 23
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W E
Rocky PointRocky Point
Distance (m) 0
W E
Elevation
Sea Level
1800
Rocky Point
L’HaridonBight
L’HaridonBight
IntertidalIntertidal
SublittoralPlatform
SublittoralPlatform
SeagrassBanks
SeagrassBanks
Embayment PlainEmbayment Plain
8 Km2
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Intertidal PustularMat
Intertidal PustularMat
Subtidal SmoothMat
Subtidal SmoothMat
Subtidal Colloform
Mat
Subtidal Colloform
Mat
Subtidal Microbial Mud over
Biocl. Qtz Sand
Subtidal Microbial Mud over
Biocl. Qtz Sand
SubtidalMicrobial Carbonate Pavement
SubtidalMicrobial Carbonate Pavement
E
IntertidalBlisterMat
IntertidalBlisterMat
Supratidal ShellRidges
Supratidal ShellRidges
100 m
HamelinPool
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Nilemah
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Strontium
LACUSTRINE
HYPERSALINE
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SUBTIDAL RESEARCH
Characterization of Microbial Deposits in the Subtidal Zone at Hamelin
Pool, Shark Bay
Based on High Resolution
Orthophotos, Limited ground truth, Multi‐
beam data and Submarine Videos
Cerebroid Heads
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Colloform build-ups
Cerebroid build-ups
Shells and Bio SS
Pustular heads
Pustular Mat
Breccia and Sand
Shell Ridges
Tabular Pavement
Blocky Pavement
DEC Orthophoto
1 Km
Aerial View
Hamelin Pool
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Submarine Investigation Hamelin Bathymetry
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1235 467
89
Regional Cross-section + Microbial build-ups (projected)
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Schematic microbial head
• Idealised sequence of internal fabrics and relative water depths.
• Upward shallowing arrangement of fabrics
• Truncated fabric sequences
• Depends on environmental setting and growth history
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Microbial Development and Colonization
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Thrombolite Stromatolite
Stromatolite Cryptomicrobialite
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Stage 1Cyanobacteria
Stage 2Endolithic Bact.
Microbial Constructional Mechanism
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Stage 3Sulphate‐reducers
Stage 4Aragonite Cement
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Hamelin Pool Substrate Habitat Map
From Digital Orthophotos, Aero-photos,Ground Truth, Submarine Videos,
and Multi-beam
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HAMELIN POOL MICROBIAL DEPOSITS MODEL
• Extensive Microbial colonization at subtidal zone (84 % of microbial deposits) • Distinct topographic zonation of mat types and heads • Deeper build‐ups have distinctive external Cerebroid morphology/internal fabric
Jahnert and Collins, 2011 Marine Geology
• Proteobacteria the dominant group in Shark Bay > 60% of bacteria (16S rRNA)• Subtidal build‐ups a domain of Coccoid bacteria• Filamentous bacteria only in shallow subtidal Smooth.
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• Based on Haigh & Pattiaractchi (this project)
• Highly likely:+ 0.5m SL Rise– IPCC 2007 Mid‐range
• Likely: +1m SL Rise– WA coastal planning policy – IPCC & CSIRO
• Unlikely but possible: +1.5m SL Rise– IPCC potentially underestimates SL rise
Future Scenarios ‐ SL change predictions by 2100
Global averaged projections of SL rise to 2100 with respect to 1990 from IPCC 2007. Bars at right show projections range for various emission scenarios. Horizontal lines/diamonds represent central values without & with rapid ice sheet contribution.
Church et al 2011
WAMSI Caring for our Country Project, 2012
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Shoreline migration on low slope tidal flat
WAMSI Caring for our Country Project, 2012
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Risk ‐ Future SL rise scenariosNilemah, Open tidal flat
Approximate Intertidal Zone position under different SL scenarios
Scenario Area
1
2
3
• Landward shift of intertidal zone (tufted, pustular mats).
• Former intertidal mats may become permanently subtidal.
• May re-establish if change within tolerance range.
• Sediment influx, increased flushing, falling salinity, reduced evaporative efficiency may prevent re-establishment of mats.
• Erosion of coquina ridges.• Slope change, drowning new
landscape.WAMSI Caring for our Country Project, 2012
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Hutchison, Barred tidal flatApproximate Intertidal Zone position under different SL scenarios
Scenario Area
1
2
3
• Landward shift & reduction of intertidal zone (tufted, pustularmats affected).
• Former intertidal mats may become permanently subtidal.
• May re-establish if changes within tolerance range.
• Seaward barrier breach/destruction likely.
• Sediment influx, increased flushing, falling salinity, reduced evaporative efficiency may prevent re-establishment of mats.
• Slope change, drowning new landscape.WAMSI Caring for our Country Project, 2012
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Conclusions: +1m rise SL by 2100 Scenario 2 (“Likely”)• Tidal flat ecosystems developed during falling SL (4 cm/100 yrs) / last
6,000 years; likely future SL rise is up to 100 cm/100 years• Salinity fall in hypersaline HP is unlikely alone to cause significant change
to microbial mat communities• New subtidal stromatolites mapped in HP/ incr. conservation significance• Stromatolite heads relatively robust (age of heads is up to 2000 yrs).• Low gradient tidal embayments marginal to HP are “likely” to be subject
to breaching of protective coastal coquina barriers, more landward shoreline positions, incr. water exchange (falling salinities), incr. storm surge impact, increased sediment mobility and influx
• High change rates not previously experienced by the microbial mat habitats/ tidal embayments more vulnerable
• IN GENERAL, LOSS OF PRESENT STABLE MICROBIAL HABITAT IS PREDICTED, BUT ADAPTIVE CAPACITY TO HABITAT CHANGE AND CHANGE RATES FOR NEXT 100 YEARS IS UNKNOWN.
WAMSI Caring for our Country Project, 2012
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Acknowledgements
• WAMSI
• CSIRO
• DEC
• UWA
• Shark Bay Community