Rapid assessments of Cyclone Yasi's impact on nearshore coral reefs and resultant sediment records of the event.

Lead Research Organisation: University of Exeter
Department Name: Geography

Abstract

Cyclones and hurricanes exert a major influence on the structure and ecology of shallow water coral reefs. This occurs through the physical destruction of corals (especially branching coral species), with the resultant rubble being a major source of detrital reef framework carbonate. Ecologically, these high magnitude physical disturbance events also exert a profound influence on benthic habitat composition and diversity, and drive the remobilisation and distribution of reef-derived sediments - transporting such materials either shorewards into lagoons or onto beaches, or flushing sediment offshore into deeper water. Many future climate models predict an increasing frequency and intensity of such tropical storms, and thus data on the physical and ecological resilience of shallow water coral reefs is of significant scientific and management interest.

Various studies have examined the impact of such physical disturbance events on coral reefs, in many cases basing their findings only on post-impact assessments. In only a few cases have high quality pre- and post-impact data been available, and in most cases this has only been sufficient to consider the (albeit critically important) ecological transitions. It is extremely rare to have the opportunity to undertake multi-proxy assessments of physical disturbance events that can draw on pre-impact data covering not only the reef ecology, but also geomorphology (structure, elevation), contemporary sedimentology, and the late Holocene history of reef development (as preserved in core records). To be able to do this at a range of sites both immediately proximal to a cyclone track and at more distal sites, represents an unprecedented opportunity, especially where data is available from a range of nearshore to offshore depositional settings.

Here we have such an opportunity, and one that will allow us to undertake multi-proxy assessments (geomorphical, ecological and sedimentological) of the changes induced by an especially high magnitude recent cyclone. The event in question, Severe Tropical Cyclone Yasi, was a Category 5 cyclone (the highest category on a scale of 1-5) that made landfall on the Queensland coast of Australia, in the vicinity of Mission Beach and Tully, on 3rd Feb 2011. The eye of the storm was ~35 km wide, with a front stretching across ~650 km. Evidence from instrumentation that survived the event shows a central pressure of around 929hPa, with winds gusting up to 285 km/h, and with storm surge heights reaching at least 5 m. Yasi was thus one of the most powerful cyclones to have affected Queensland since records commenced. Previous cyclones of a comparable measured intensity include Cyclone Mahina (1899) in Princess Charlotte Bay ~350 km to the north, and the 1918 cyclones at Mackay and Innisfail.

Specifically, we are in a position, having undertaken detailed studies of the structure and ecology of a wide range of reefs in the immediate vicinity of the storm track and its landfall point, to be able to undertake a rapid post-impact assessment, and to compare this data with that collected (between 2006-2009) at the same sites. We are submitting this as an Urgency application because of the need to undertake such post-impact studies as soon as logistically possible. This is of critical importance in marine environments to ensure that as much of the evidence (both ecological and geomorphological) of the event is preserved. We are planning to undertake this study in August 2011, giving a 6 month lead in from this application (this is probably as soon as logistically possible given the need for the review process and subsequent travel planning). The timing will be such, so as to coincide with one of the winter low spring tide periods when site access is far easier. Based on existing post-storm recovery trajectories in other tropical regions we would anticipate such evidence being well preserved within the 6 month lead in time we are working to.

Planned Impact

The main 'user communities' of the data this study will generate will be marine ecologists, geomorphologists and geologists interested in past and present environmental change, along with coastal and marine managers.

Specifically we would see these groups benefitting from the resultant data as follows:

Marine Ecologists - because the study will provide novel datasets on the impacts of very high magnitude physical disturbance events, and specifically for the often poorly studied inner-shelf reefs where the negative effects of high sediment loading and high turbidity are already considered threatening to reef 'health'.

Marine Geomorphologists - 1) because the study will provide an insight into the physical resilience of these inner-shelf reef structures. This has particular relevance because, in contrast to their clear-water, offshore counterparts, these muddy inner-shelf reefs are typically poorly lithified (weakly cemented and unbound depositional structures) and have thus been the subject of much academic speculation regarding their long-term preservation potential. In a recent regional scale assessment, we identified a clear break in reef-building on the inner-shelf of the GBR between about 4,500 to 2000 years BP. One hypothesis is that many of the reef structures that may have existed through this mid-Holocene interval were actually reworked during high energy events - this research on the impacts of such a high magnitude event as Cyclone Yasi will allow us to test such ideas; 2) because the study will allow us to examine whether distinct storm depositional horizons form and are preserved in the sediment record under such extreme conditions. If so, the potential to develop diagnostic indicator tools for such events, and which could be applied to other core records, will be of consider interest to this 'user' group.

Marine managers - because the data will provide unprecedented knowledge on the resilience and vulnerability of the reefs that exist within what has typically been a very poorly studied area of the Great Barrier Reef Shelf. We have a unique, pre-existing dataset that will allow us to provide information on this issue for a range of cyclone influenced sites.

The PI on the project will gain further invaluable and applied research experience and continue to foster research links with the international research community - especially those in Australia.

The RA to be employed on the project will gain invaluable experience that will provide a solid and wide-ranging basis for subsequent doctoral research, or for field/laboratory-based employment in the environmental sector.

Publications

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Related Projects

Project Reference Relationship Related To Start End Award Value
NE/J005398/1 01/08/2011 11/09/2011 £50,887
NE/J005398/2 Transfer NE/J005398/1 11/09/2011 10/08/2012 £48,230
 
Description This Urgent project examined the impacts of Tropical Cyclone Yasi on a number of nearshore, turbid-zone coral reefs within the inner-shelf areas of Australia's Great Barrier Reef. Data were collected from four reefs that were the focus of recent (between 2006 to 2009) pre-Yasi studies into their geomorphology, sedimentology and community structure. This provided a unique opportunity to identify and describe the impacts of an intense tropical cyclone on nearshore reefs, which are often assumed to be vulnerable to physical disturbance and reworking due to their poorly lithified framework. Observed impacts of TC Yasi were site specific and spatially highly heterogeneous, but appear to have been strongly influenced by the contemporary evolutionary stage and ecological make-up of the individual reefs. Exposure regime also appears to have been more important than proximity to the landfall path. The most significant ecological impacts were observed at King Reef (interpreted to be a result of freshwater bleaching) and at Paluma Shoals, where widespread physical destruction of branched Acropora occurred. New coral recruits are, however, common on all of the reefs examined and colony re-growth clearly evident at King Reef. Only localised geomorphic change was evident, mainly in the form of coral fracturing, rubble deposition, and sediment movement, but again these impacts were highly site specific. The dominant impact at Paluma Shoals was localised storm ridge/shingle sheet deposition, at Lugger Shoal major offshore fine sediment flushing, and at Dunk Island major onshore coarse sand deposition. There was little geomorphic change evident at King Reef. Thus whilst small-scale and taxa specific impacts from Cyclone Yasi are clearly evident, geomorphological changes appear minor and ecological impacts highly variable between sites, and there is no observed evidence for major reef structural change.
Exploitation Route Most relevant for a marine management perspective No commercial applications, but relevant for reef managers in relation to understanding ecosystem vulnerability to disturbance
Sectors Environment

 
Description Finding from this research have been diseminated via jnl publications (see outputs) and through conference talks - namely at the 12th ICRS meeting in Cairns. This led to media coverage in Australia - both in the newspapers and on local television.
First Year Of Impact 2012
Sector Environment
Impact Types Policy & public services