MULTIVARIATE ANALYSIS OF GEOLOGIC FEATURES SHEDS LIGHT ON BIOTIC ZONATION OF THE SOUTH TEXAS BANKS

The broad, flat continental shelf of the northwestern Gulf of Mexico has several bathymetric highs that provide rare hard-bottom habitat on the otherwise soft substrate. The rare bathymetric highs occur in areas of different origins. The area generally to the east of Matagorda Bay in the northwestern Gulf of Mexico has underlying allochthonous salt sheets, the movement of which often forms salt diapirs that protrude from the seafloor. Organisms colonized the hard-substrate protrusions forming biodiverse hotspots with several biotic zones. In a region where the continental shelf is terrigenous generally south of Matagorda Bay, the South Texas Banks are bathymetric highs formed by relict barrier islands on the present-day mid shelf and relict coralgal reefs on the present-day outer shelf. A recent expedition to explore several of the South Texas Banks allowed collection of bathymetric data and biological data from a few video transects. In this study, we use physiographic data to examine a sample of the South Texas Banks using multivariate statistical tests as was done in a previous study for banks in the salt diapir region. Analysis of multibeam bathymetry data produced statistical input variables such as distance to nearest neighbor, regional depth, relief, area of the site, number of terraces, and rugosity. After detecting patterns based on geophysical data, we compared results with known ecological data, namely the number of biotic zones present at previously explored sites. The comparison elucidated similar patterns as with the salt diapir study, and we submit that the multivariate results can be utilized as a model to predict the number of biotic zones at a site. Results from the predictive model can benefit scientists by: 1) expediting justification and prioritization of ecological explorations of additional sites in the region, and 2) providing a scientific basis for proposing place-based protection for some South Texas Banks as important sites within the existing ecological network in the face of climate change.