Page 36 - GIS for Science, Volume 3 Preview

(continued from page 19)
as a preliminary set of 16 macroscale global coastal ecosystems based on integrated information about the coastline and adjacent land and water environments. The ECUs are composed of many different coastal segment units (CSUs), and it is important to note that there is no hierarchical relationship or perfect spatial nesting between CSUs and ECUs.
One aspect in evaluating the accuracy and potential use of the ECUs relates to how well they line up with existing coastline segmentation and coastal ecosystem delineation efforts. This map of Australia shows the ECUs distributed along the Australian coast compared with the locations of Primary Coastal Compartments from a national sediment compartments assessment.66 Five ECUs occur in mainland Australia, Tasmania, and territorial islands (a sixth ECU is found on an Australian island south of New Zealand not shown in the map). The distribution of the Primary Coastal Compartments is based on “major, usually distinctive structural features such as rocky headlands or major changes in orientation.”66
The ECUs do not contain any information on rocky headlands or coastal orientation, and as such would not necessarily be expected to predict the Primary Coastal Compartment geographies. Importantly, however, many of the locations along the coast where ECUs change are at or near a coastal compartment boundary. This may indicate that, as expected,7 changes in the macro-level geology and orientation are associated with changes in other features of the general ecological setting that in turn are “captured” by ECUs.
Although ECUs often change at coastal compartment boundaries, they do not predict them. For example, one ECU in particular (ECU 2) has an extensive distribution along the Australian mainland, occurring on all four (eastern, western, northern, and southern) coasts. ECU 2 is subdivided into numerous coastal compartments. It would be interesting to see whether the much finer resolution CSUs would have stronger predictive value in identifying the coastal compartment locations.
A visual comparison of the distribution of ECUs along the Australian coast and the set of Primary Coastal Compartments from an Australian sediment compartments assessment.66 The coastal compartments, bounded by black markers, were approximated from figure 1 in Thom et al.66 and used with permission. The data for the interior represent the Australian distributions of World Terrestrial Ecosystems.45 Bathymetry data are from Esri’s Ocean Basemap®.
The ECUs are globally distributed and are relatively few in number. They were developed to explore coastal variation at the global scale, and using them to attempt to explain local phenomena is not advised, in a “scale-inappropriate” sense. For example, it is common knowledge that Hawaiian islands have sandy beaches, rocky coasts, mangroves, and steep coastal cliffs, so an ECU user might ask, “Why are all Hawaiian islands just one ECU?” It would appear that the aggregate coastal variation among Hawaiian islands is less than the aggregate coastal variation between Hawaii and other locations. The CSU data, not the ECU data, should be considered the go-to resource for addressing these types of questions dealing with local and regional variation in coastal environments. But for global scale comparisons of similarity in coastal ecological setting, the ECU data are likely appropriate. Moreover, the ECU data might be used to frame new research collaborations between, say, Norwegians, Chileans, and Alaskans seeking to better understand their common ECU.
24
GIS for Science