Reports

Assessment of deep-water habitat for crown-of-thorns starfish (COTS) in the Great Barrier Reef

Authors: Beaman, R.J.

Year: 2018

Publication: Assessment of deep-water habitat for crown-of-thorns starfish (COTS) in the Great Barrier Reef. Report to the National Environmental Science Program, Reef and Rainforest Research Centre Limited, Cairns, Australia, pp. 45.

Abstract

(1) This project integrated all the available source bathymetry data currently used within the
latest gbr100 grid and generated a much higher-resolution gbr30 bathymetry grid (~30 m pixel
spacing) over the GBR shelf area. The gbr30 grid is publically available for download on the
Geoscience Australia website at: http://pid.geoscience.gov.au/dataset/115066

The gbr30 grid is recommended for use as a spatial dataset to feed into the Local and Regional
Decision Support Tool (DST) being developed by CSIRO for Integrated Pest Management.
Other uses of the grid may extend beyond COTS control efforts to include hydrodynamic
modelling, natural hazard assessment, to plan and build offshore infrastructure, and to benefit
tourism and fishing.

(2) The gbr30 grid was used to generate spatial datasets and descriptive statistics of the 22
‘super spreader’ and tourism reefs, to better understand the extent of deep-water habitat at
these sites. Output files included Fledermaus 3D visualisation files, Google Earth kmz, ESRI
raster grids, hillshade geotifs, ESRI shapefiles, Excel spreadsheets and histograms, xyz files.

These spatial datasets are recommended for operational use in helping with COTS control at
these 22 ‘super spreader’ and tourism sites by understanding the topographic variability and
overall depth distribution of each reef. Benthic Terrain Modeler was used to extract the crest
and slope areas deeper than 15 m, which are likely to be potential deep-water coral habitats.

(3) An assessment was conducted on whether submerged banks or deeper reefs may provide
deep-water coral habitat for COTS, and the implications for the design of the control program.
Extensive mesophotic (twilight zone) coral ecosystems have been described on these banks
and deeper reefs with zooxanthellate corals found to ~60 m. However, the scientific literature
does not record any evidence of COTS outbreaks being found in depths significantly below the
zone of highest coral cover on emergent reefs, which generally peak at ~10-15 m.

The assessment concluded there is a low risk of adult COTS outbreaks in deep-water habitats
below the zone of highest coral cover. The assessment also discounted the deep-water
recruitment hypothesis for larvae settling in deep-water on the basis of observations of COTS
movements over their lifecycle. The assessment concluded there is low risk of larval COTS to
be found in deep-water habitats on emergent reefs below the zone of highest coral cover.

The recommendation is that COTS control efforts should continue in the relatively shallow
waters of emergent reefs, and to not expend resources searching for COTS outbreaks in
deeper waters significantly below the zone of highest coral cover.

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