Mapping, Classification, and Spatial Variation of Hardbottom Habitats in the Northeastern Gulf of Mexico

• Other Authors: Kingon, Kelly (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Geography
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-7449

This dissertation starts by evaluating the applicability of using a commercially available, cost-effective, sidescan sonar system to detect benthic habitats, in particular hardbottom habitats, in the nearshore northeastern Gulf of Mexico. Hardbottom habitats are likely to function as essential fish habitat for several important fisheries species. Identifying and mapping these habitats is a crucial first step to learn more about their roles in sustaining the associated fisheries species and their ecological importance in harboring biodiversity. The locations of nearshore hardbottom habitats in the Gulf of Mexico are largely unknown in part because mapping the seafloor is generally an expensive and time-consuming process. To illustrate the capability of low-cost devices in mapping benthic habitats, I tested the Humminbird 997c SI unit marketed to fishermen at a cost of approximately $2,000. Methodological approaches to effectively capture and process the Humminbird sidescan imagery were developed. Humminbird sidescan data from three sites were compared to overlapping sidescan imagery acquired by the National Marine Fisheries Service using a standard, much more expensive (~$20,000) Marine Sonic system. This analysis verified that the classification results of sand and hardbottom habitats based on data collected using the Humminbird sidescan system were similar to those produced using the traditional and more expensive Marine Sonic sidescan equipment. The similarity of the hardbottom and sand classes extracted from both datasets was large for all three sites with overall accuracies of 86.2%, 78.5%, and 81.5%. The results indicate that the Humminbird system can be used independently to create valid benthic imagery of nearshore marine habitats. Thirty-three sites in total were then mapped with the Humminbird system and sampled using dive surveys. Seascape pattern metrics were calculated from the classified Humminbird sidescan maps. The dive survey data included measurements of the geomorphology, physical attributes of the water column (e.g. temperature, depth, and visibility), and coverage and heights of the benthic biota. The coverage and heights of the biota were compared to the geomorphology, seascape, and water column variables to identify patterns in the distribution and community composition of the sessile organisms. Sponges and red algae were dominant at the western sites while hard corals and brown algae dominated the eastern sites. A cluster analysis revealed four communities, each with unique species indicators: group 1 - bivalves and bryozoans, group 2 - sea urchins and sponges, group 3 - red algae, group 4 - brown algae. Groups 1 and 4 in the east were higher in diversity than groups 2 and 3 in the west. The cluster analysis results also showed the longitudinal pattern of sponge and red algae communities (groups 2 and 3) to the west and brown algae (group 4) to the east. Within the study area, visibility was found to vary with longitude. Sites in the east showed higher visibility than sites in the west and this may be driving the community patterns that were identified. Relationships were identified between the four most abundant taxa (sponges, hard corals, brown algae, and red algae) and the geomorphology, physical, and seascape variables. However, the relationships were often complicated and the biota did not strictly follow gradients or boundaries in substrate or geoform (physical feature or landform), even though these features are often used to classify habitats and biotopes. The percent cover of rock was a significant geomorphology variable for red algae and hard coral coverage while geoforms were related to the heights of sponges and brown algae. Seascape metrics also had significant effects on the sessile biota particularly related to patch edges, heterogeneity, core areas, nearest neighbor distances, and the percent cover of hardbottom. Despite the fact that sessile organisms do not move much, if at all following their planktonic larval stage, the surrounding seascape contributes to the patterns we see in their distribution, coverage, and heights. The third chapter focuses on applying a new classification standard to the benthic habitats in the nearshore northeastern Gulf of Mexico. The United States Geological Survey (USGS) has a standardized system for classifying terrestrial and aquatic habitats found across the U.S. which has been in place for almost 40 years. This classification standard does not include marine and most coastal habitats. Therefore, marine researchers developed a number of classification systems for coastal and marine habitats relevant to their local or regional studies in U.S. waters. A national standardized method for classifying marine and coastal habitats was not adopted until recently. The Coastal and Marine Ecological Classification Standard (CMECS) developed by the Federal Geographic Data Committee was approved last year and is intended to fill the gap in U.S. marine habitat classification standards. Since the classification standard is in its infancy, it has not been applied in many geographic areas. My third chapter is the first study to apply the CMECS to the benthic habitats in the nearshore northeastern Gulf of Mexico off the coast of northwest Florida. Hardbottom and sand habitats are characteristic of this area. In the previous chapter, the underwater surveys revealed that the dominant taxa at the sites within the study area were hard corals, sponges, and macroalgae. I used CMECS to broadly classify the sites where the surveys were completed. I found that habitat heterogeneity and a wide variety of environmental characteristics influenced the distribution of taxa at the local scale. This made applying CMECS at scales finer than the composite study area unfeasible without major modifications. CMECS worked well for classifying the broad scale in this region but was not appropriate for classifying complex fine-scale biotopes. === A Dissertation submitted to the Department of Geography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Summer Semester, 2013. === June 14, 2013. === classification systems, Gulf of Mexico, hardbottom, sessile biota, sidescan sonar, spatial analysis === Includes bibliographical references. === Tingting Zhao, Professor Directing Dissertation; Markus Huettel, University Representative; Xiaojun Yang, Committee Member; Christopher Uejio, Committee Member.