Development of a Seamless, High-Resolution Bathymetric Model to Compare Reef Morphology around the Subtropical Island Shelves of Lord Howe Island and Balls Pyramid, Southwest Pacific Ocean

Abstract

Lord Howe Island and Balls Pyramid are located approximately 600 km offshore of the southeastern Australian mainland, in the subtropical waters of the northern Tasman Sea. Lord Howe Island hosts the most southern coral reef in the Pacific Ocean, and the shelves surrounding both islands feature fossil coral reefs. This study creates a seamless, high-resolution (5 m cell size) bathymetry model of the two shelves to compare and contrast the extent of reef development and shelf morphology. This was produced by integrating satellite-derived depth data (derived to 35 m depth) and multibeam echosounder (MBES) data. Image partitioning and filtering improved the accuracy of the bathymetry estimates and the suitability for integration with MBES data. Diverse accretionary and erosional geomorphic features were mapped on both shelves, with fossil reefs dominating the shelves in 25-50 m depth. Similar patterns of shelf morphology were observed for the middle and outer shelves, while the inner shelf regions were most dissimilar, with reef development greater around Lord Howe Island compared to the more restricted inner shelf reefs around Balls Pyramid. Understanding the relative extent and morphology of shelf features provides insights into the geological and ecological processes that have influenced the formation of the shelves.

Ecological speciation in sympatric palms: 4. Demographic analyses support speciation of Howea in the face of high gene flow

“…Our results are consistent with the idea that initial local adaptation and postzygotic isolation were supplemented by the rapid completion of prezygotic isolation through flowering time differences (Papadopulos et al 2013b(Papadopulos et al , 2014. Furthermore, given the supporting evidence these results allow us to rule out continuous absence of gene flow, even though LHI was larger at the time of speciation (Papadopulos et al, 2011(Papadopulos et al, , 2013aLinklater et al 2018). Unlike recent genomic reanalyses of classic cases of speciation in sympatry, our results support the proposition that Howea palms must have diverged with continuous gene flow.…”

“…, ). Furthermore, given the supporting evidence these results allow us to rule out continuous absence of gene flow, even though LHI was larger at the time of speciation (Papadopulos et al., , ; Linklater et al ). Unlike recent genomic reanalyses of classic cases of speciation in sympatry, our results support the proposition that Howea palms must have diverged with continuous gene flow.…”

Towards Routine Mapping of Shallow Bathymetry in Environments with Variable Turbidity: Contribution of Sentinel-2A/B Satellites Mission

“…Some depth errors may also be due to the differences in resolution, i.e., 10 m from the satellite, and the 1 m spot size for lidar-a consideration in areas with steep gradients, such as channel edges. Using a median filter on the SDB reduced other artifacts that typically lead to random noise [49]. One potential error factor that needs to be considered in the future is tide range.…”

“…The final step for a corrected bathymetry mapping (SDB) corresponded to a switching model implementation between SDBred and SDBgreen due to the sensitivity of each model: while SDBred performs better over shallow regions [48], SDBgreen performs better over deeper regions [21,31,44,49]. Moreover, SDBgreen frequently yields severe overestimation in shallow regions [22,44,50], especially with dense seagrass, highly undesirable for navigational purposes.…”

Charting the Course for Future Developments in Marine Geomorphometry: An Introduction to the Special Issue

“…For instance, Walbridge et al [14] used a 3 m resolution lidar dataset of the Buck Island Reef National Monument, in the U.S. Virgin Islands, to classify the seafloor into nine geomorphic classes. Linklater et al [15] empirically derived depth estimates from 2-m resolution WorldView-2 and 2.4-m resolution Quickbird satellite images that were corrected for atmospheric effects and sun glint. Those depth estimates were then combined with existing acoustic data from deeper waters to develop a seamless, high-resolution DBM of the shelf around Lord Howe Island (Southwest Pacific Ocean), from which geomorphometric analyses were performed.…”