Project - Coral Sea Mapping 2021-2024 (AIMS, Parks Australia)

Research Project

Researchers: Lawrey, Eric (Principal investigator) ,  Lawrey, Eric, Dr. (Point of contact) ,  Wolfe, Kennedy (Dr) (Point of contact) ,  eAtlas Data Manager (Point of contact) ,  mailto:b.robson@aims.gov.au (Point of contact)

Brief description This project developed a set of high quality GIS datasets of the emergent and shallow marine features (reef boundaries, reef tops, islands, and cays) of the Coral Sea Marine Park (CSMP). The goal of this mapping was to improve the precision and spatial detail of existing reef maps. Features mapped: - Coral atoll platform boundary - outer visible extent combined with available multi-beam bathymetry (100 m depth) - Coral reef boundary - coral substrate, plus connected sand, raised off atoll platform, mapped to 30 - 50 m depth. - Reef tops (5 m and 10 m depth) - Coral cays regions (above mean high water over time) This project mapped reef boundaries features in a manner similar to the existing reef mapping of the Great Barrier Reef Marine Park (GBRMP) and Torres Strait (Lawrey, et al. 2016). The key characteristics of this mapping is the focus on determining the outer most boundary of coral reefs, where they rise up off the surrounding sea floor. In the Coral Sea the coral atoll platform was considered the sea floor and any solid coral structure raised up off the atoll platform by more than 5 m was considered a coral reef. The reef boundaries also include sandy areas that connect close reef patches and surrounding sand that is highly connected to the coral substrate, as evidenced by halos (sand cleared of algae by fish around the coral patches). Patches of coral closer than 50 - 300 m were merged together to make fewer, but larger coral reef boundaries. The merge distance depended on slope, depth, structural uncertainty and visual uncertainty. The accuracy of the reef boundaries was checked by comparing digitisation of a subset of the features by independent team members. The mapped reef outlines were compared, verified and adjusted in areas (Flinders reefs, Holmes reefs) where there was high quality high resolution bathymetry (Beaman, 2017). Digitised features were reviewed and refined by a second team member using additional imagery. Reef boundaries were linked with historic names based on nautical charts and historic maps, then assigned a permanent identifier that can be used instead of the reef name. Large reef features were cut into multiple segments where different sections are known by different names. In addition to reef boundary mapping the structure of the reef tops was mapped using satellite derived bathymetry to estimate a 5 and 10 metre depth boundary. The 5 m depth reef top aligns with the existing 'Dry reefs' mapping performed in the Great Barrier Reef. Shallow features were also mapped, including coral cays. As cays move over time their boundaries were repeatedly mapped over a period of 8 - 10 years to estimate their stability and region extent. The features were digitised using Sentinel 2 (10 m resolution) and Landsat 8 (30 m resolution) satellite imagery that was optimised for observing deep marine features. To obtain the very clearest imagery the entire catalogue of historic images available from each satellite was manually reviewed and sorted. The final composite images for each scene were statistically combined, to lower noise, from the collection of images with very low cloud cover, low noise from clouds, low sun glint and high water clarity. The Sentinel 2 and Landsat 8 imagery were processed into cloud free composite images using the Google Earth Engine. The imagery along with the processing scripts and mapped features are openly available. References: Beaman, R. J. (2017). High-resolution depth model for the Great Barrier Reef - 30 m. [Dataset]. Geoscience Australia, Canberra. http://dx.doi.org/10.4225/25/5a207b36022d2 Lawrey, E. P., and Stewart, M. (2016) Mapping the Torres Strait Reef and Island Features: Extending the GBR Features (GBRMPA) dataset. Report to the National Environmental Science Programme. Reef and Rainforest Research Centre Limited, Cairns (103pp.).

Notes Credit
This project was co-funded by Parks Australia and the Australian Institute of Marine Science

Notes Purpose
This project aims to provide a more detailed spatial map of reef features to improve planning and management of the Coral Sea Marine Park

Data time period: 2022-01-01 to 2024-12-31

-24.4984,86 -9.65558,86

-17.07698609615,90