3.4.1 Reef Morphology and Growth History

Description

Preliminary growth history studies have revealed two stages of reef growth; a “Tantabiddi phase” during which a large fringing reef grew in an active stage of Leeuwin Current flow (ca 125 ky U/Th ago), and a “Holocene phase” during which today’s reef recolonised the earlier reef (active reef growth during the last 7ky U/Th; Collins et al, 2003).  During habitat mapping of Sanctuary Zones in 2004 (Cassata & Collins, 2008) it was recognised that much of the lagoon substrate and geomorphology is inherited from the earlier stage of reef growth.

This research mapped this relationship through extended habitat mapping (an adjunct to the benthic biodiversity assessment project), regional geomorphic mapping and selected shallow coring and dating in the lagoon and near the reef crest. This helps predictions of reef response to sea-level change which is linked to potential changes in energy flux across the lagoon and at the shoreline, which is aligned to the climate change assessments.

The growth history objective of this project used shallow coring of the western reef flat to reef crest and eastern marina site test cores to investigate:

• The relationship between the Last Interglacial and Holocene reefs
• The sea-level and growth history of the Holocene (last 10,000 years) as determined from U-series dating
• The chronology of reef growth onset, duration and termination

The response of the reef system to past Holocene sea-level rise, and the likely response to future sea-level change

Aims

• Determine the geomorphological and sedimentary characteristics (biological and physical) of the Ningaloo Reef and shelf
• Identify evolutionary characteristics relevant to the maintenance of marine biodiversity and likely climate change impacts
• Characterise reef growth history, coastal and seabed geomorphology, surficial sediment facies and their influence on the distribution of benthic habitats

Methods

• Core sampling; transects of reef flat
• High precision U-series thermal ionization mass spectrometry (TIMS) used for core dating
• Vertical accretion rates analysed
• hyperspectral remote sensing; geomorphology investigation

Outcomes

• Analysis of the internal structure of the eastern Ningaloo Reef has provided a clear insight into Holocene reef growth during environmental change.
•  The last Interglacial reef provided the substrate for Holocene reef initiation and further influenced reef accretion rates, facies development and reef morphology.
• The effect of environmental disturbance on coral reefs due to climate change and other anthropogenic stresses may depend on which growth type a particular reef represents.
• Local activities that may increase disturbances such as increased sedimentation and turbidity from dredging, coastal development and overfishing, must be considered particularly at a time when increased global challenges to coral reef environments may reduce reef resilience.

Reports

Cassata L,  Collins  LB,  2008.  Coral  reef  communities,  habitats,  and  substrates  in  and  near  Sanctuary Zones of Ningaloo Marine Park. Journal of Coastal Research: Vol. 24, No. 1 pp. 139–151. https://doi.org/10.2112/05-0623.1

Twiggs  EJ,  and  Collins  LB  2010.  Development  and  demise  of  a  fringing  coral  reef  during  Holocene environmental change. Marine Geology 275, 20-36. doi.org/10.1016/j.margeo.2010.04.004

Collins, Lindsay B. 2010. Controls on Morphology and Growth History of Coral Reefs of Australia’s Western Margin, in Morgan, W.A. et al (ed), SEPM Special Publication 95: Cenozoic Carbonate Systems of Australasia. pp. 195-217. USA: Society for Sedimentary Geology (SEPM).  ISBN 9781565763029

Collins,  L.B.  2011:  Reef  Structure.  In:  David  Hopley  (ed.)  Encyclopedia  of  Modern  Coral  Reefs,  Springer.

Collins,  L.B.  2011:  Western  Australian  Reefs.  In:  David  Hopley  (ed.)  Encyclopedia  of  Modern  Coral Reefs, Springer.