Brian Walker
I run the GIS and Spatial Ecology lab at the Nova Southeastern University Halmos College of Natural Science and Oceanography. http://www.nova.edu/ocean/overview/faculty-staff-profiles/brian_walker.html
http://cnso.nova.edu/research/labs/walker.html
My primary research has centered on coral reef ecology and geology, reef fish ecology, and landscape/seascape ecology. I am presently active in researching the following aspects of marine science:
Spatial Ecology-
Seascape/landscape ecology, spatial dynamics of coral reef communities, latitudinal coral reef biogeography, marine faunal relationships to topography
Seafloor Characterization-
Benthic habitat mapping (Shallow and Deep water), accuracy assessment, mapping techniques and technologies
Marine Spatial Planning and Decision Support Tool Design-
http://ofr.marineplanner.io/
Scientific research study design-
Optimize research study design using GIS spatial data, developing and evaluating assessment and monitoring methodologies
Management applications of scientific research-
Coral habitat impact assessment (Shallow and Deep), marine spatial planning, Acropora monitoring and mapping, anchorage placement/modification, special event impact minimization planning
Coral Reef Geology-
Historical perspectives gained from present-day morphology and community dynamics
My research has taken place in the tropical Atlantic and Caribbean including Florida, Mexico, the Bahamas, Puerto Rico, and the U.S. Virgin Islands. I have held grants and contracts from NOAA, FFWCC, and FL DEP, and have authored numerous publications including technical reports, book chapters, and scientific peer-reviewed publications.
Phone: 954-262-3675
Address: 8000 N Ocean Drive
Dania Beach, FL 33004
http://cnso.nova.edu/research/labs/walker.html
My primary research has centered on coral reef ecology and geology, reef fish ecology, and landscape/seascape ecology. I am presently active in researching the following aspects of marine science:
Spatial Ecology-
Seascape/landscape ecology, spatial dynamics of coral reef communities, latitudinal coral reef biogeography, marine faunal relationships to topography
Seafloor Characterization-
Benthic habitat mapping (Shallow and Deep water), accuracy assessment, mapping techniques and technologies
Marine Spatial Planning and Decision Support Tool Design-
http://ofr.marineplanner.io/
Scientific research study design-
Optimize research study design using GIS spatial data, developing and evaluating assessment and monitoring methodologies
Management applications of scientific research-
Coral habitat impact assessment (Shallow and Deep), marine spatial planning, Acropora monitoring and mapping, anchorage placement/modification, special event impact minimization planning
Coral Reef Geology-
Historical perspectives gained from present-day morphology and community dynamics
My research has taken place in the tropical Atlantic and Caribbean including Florida, Mexico, the Bahamas, Puerto Rico, and the U.S. Virgin Islands. I have held grants and contracts from NOAA, FFWCC, and FL DEP, and have authored numerous publications including technical reports, book chapters, and scientific peer-reviewed publications.
Phone: 954-262-3675
Address: 8000 N Ocean Drive
Dania Beach, FL 33004
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Papers by Brian Walker
Data were collected in January 2009 at ROI 1 (eastern Lower Keys), in June 2009 at ROI 2 (western Lower Keys), in September 2012 and February, March, and May 2013 at ROI 3 (back country), and in May 2013 at ROI 4 (Key Largo) (Figure 1). A total of 2029 sampling stations were visited, of which 1969 were used in the accuracy assessment. The sites were selected using a stratified random sampling protocol that equally distributed sampling points amongst the detailed structure categories. Most sites were sampled by deploying a weighted drop camera with the vessel drifting in idle and recording 30-120 seconds of dGPS-referenced video. The shallowest sites were sampled by snorkel, waverunner, or kayak, using a hand-held dGPS for navigation and a housed camera to record video. Each sampling station was given a Detailed Structure, Biological, and Coral Cover assignment in the field. These field classifications were reevaluated post-survey during a systematic review of video and photographic data, designed to ensure consistency within classifications. The efficacy of the benthic habitat map was assessed by a number of classification metrics derived from error matrices of the Major and Detailed levels of Geomorphological Structure and Biological Cover.
The overall, producer’s, and user’s accuracies were computed directly from the error matrices. The analyses of the combined ROIs 1 – 4 gave an overall accuracy of the benthic habitat map of 90.4% and 84.6% at the Major and Detailed levels of Structure respectively, and 85.1% and 76.5% at the Major and Detailed levels of cover. The known map proportions, i.e. relative areas of mapped classes, were used to remove the bias introduced to the producer’s and user’s accuracies by differential sampling intensity (points per unit area). The overall accuracy at the Major and Detailed levels of Structure changed to 92.3% and 85.9%. The overall accuracy at the Major and Detailed levels of cover changed to 84.3% and 79%. The overall accuracies were also adjusted to the number of map categories using the Tau coefficient. Tau is a measure of the improvement of the classification scheme over a random assignment of polygons to categories, bounded between -1 (0% overall accuracy for 2 map categories) and 1 (100% accuracy for any number of categories). The Tau coefficients were 0.807 ± 0.026 and 0.829 ± 0.018 at the Major and Detailed levels of Structure, and 0.814 ± 0.020 and 0.745 ± 0.020 at the Major and Detailed levels of cover.
Percent coral cover was classified for every polygon, thus coral cover was evaluated separately. Total accuracy for Coral in all habitats for all ROIs was 89.6% and 93.4% after adjusting for map marginal proportions. This calculation, however, was not realistic because it evaluated coral cover in non-coral habitat which inflated the number of correct sites. To account for this, coral cover was also evaluated at only those sites found to be Coral Reef and Hardbottom habitats. Total map accuracy for mapping coral cover on Coral Reef and Hardbottom habitats was 79.8%, and 82.7% after adjusting for habitat proportions. The accuracy varied greatly between the two coral categories present. User’s and Producer’s accuracies for Coral 0% - <10% were near or equal to 90%. Conversely, Coral 10% - <50% user’s and producer’s accuracies were 54.3% and 66.5% respectively. Adjusted producer’s accuracy was reduced to 55.2%. The adjustment for map proportions was very relevant here due to the large disparity of area between the two classes. The map contained 658.5 km² of Coral 0% - <10% and 39.8 km² of Coral 10% - <50%. Further 583 of AA points on Coral Reef and Hardbottom habitat were in Coral 0% - <10% and 219 were in Coral 10% - <50%. Interestingly, there were no mapped polygons of Coral 50% - <90% and 90% - 100%. There was confusion between coral classes where 88 locations mapped as Coral 10% - <50% were actually Coral 0% - <10% and 60 locations mapped as Coral 0% - <10% were found to be Coral 10% - <50%. Confusion between 11 locations that were mapped as Coral 10% - <50% were actually Coral 50% - <90% and 1 location mapped as Coral 10% - <50% was found to be Coral 90% -100%. These sites were all located in the patch reefs of Hawk Channel. It is unknown if these sites met the minimum mapping unit criteria, but the field data indicated high coral cover at these locations. The relatively low adjusted producer’s accuracy for Coral 10% - <50% (55.2%) suggests that not all higher coral cover areas were captured in the map. Furthermore the relatively low user’s accuracy (54.3%) indicates that the areas of Coral 10% - <50% portrayed in the map are highly variable.
Combining all the results into a total map accuracy assessment gave a sense of how the overall map portrays the seascape. However, it should be noted that large gaps in map coverage exist, especially between Marathon and Key Largo, a 137 km stretch. The results given in the appendices are more representative of their specific regions. ROIs 1 and 2 covered most of the lower Keys and their results are a good representation of map accuracy for that region. ROI 3 covered the Backcountry which had higher accuracies, presumably due to a reduced diversity of habitats and lack of coral cover. ROI 4 is a good representation of the upper Keys map accuracy. It is difficult to know which assessment best represents the middle Keys. The landscape is more similar to the upper Keys, but Hawk Channel becomes deeper and more turbid.
focused on higher-latitude coral communities is warranted to investigate possible range expansions and ecosystem shifts
due to global warming. As the northern extension of the Florida Reef Tract (FRT), the third-largest barrier reef ecosystem in
the world, southeast Florida (25–27u N latitude) is a prime region to study such effects. Most of the shallow-water FRT
benthic habitats have been mapped, however minimal data and limited knowledge exist about the coral reef communities
of its northernmost reaches off Martin County. First benthic habitat mapping was conducted using newly acquired high
resolution LIDAR bathymetry and aerial photography where possible to map the spatial extent of coral reef habitats.
Quantitative data were collected to characterize benthic cover and stony coral demographics and a comprehensive
accuracy assessment was performed. The data were then analyzed in a habitat biogeography context to determine if a new
coral reef ecosystem region designation was warranted. Of the 374 km2 seafloor mapped, 95.2% was Sand, 4.1% was Coral
Reef and Colonized Pavement, and 0.7% was Other Delineations. Map accuracy assessment yielded an overall accuracy of
94.9% once adjusted for known map marginal proportions. Cluster analysis of cross-shelf habitat type and widths indicated
that the benthic habitats were different than those further south and warranted designation of a new coral reef ecosystem
region. Unlike the FRT further south, coral communities were dominated by cold-water tolerant species and LIDAR
morphology indicated no evidence of historic reef growth during warmer climates. Present-day hydrographic conditions
may be inhibiting poleward expansion of coral communities along Florida. This study provides new information on the
benthic community composition of the northern FRT, serving as a baseline for future community shift and range expansion
investigations.
Data were collected in January 2009 at ROI 1 (eastern Lower Keys), in June 2009 at ROI 2 (western Lower Keys), in September 2012 and February, March, and May 2013 at ROI 3 (back country), and in May 2013 at ROI 4 (Key Largo) (Figure 1). A total of 2029 sampling stations were visited, of which 1969 were used in the accuracy assessment. The sites were selected using a stratified random sampling protocol that equally distributed sampling points amongst the detailed structure categories. Most sites were sampled by deploying a weighted drop camera with the vessel drifting in idle and recording 30-120 seconds of dGPS-referenced video. The shallowest sites were sampled by snorkel, waverunner, or kayak, using a hand-held dGPS for navigation and a housed camera to record video. Each sampling station was given a Detailed Structure, Biological, and Coral Cover assignment in the field. These field classifications were reevaluated post-survey during a systematic review of video and photographic data, designed to ensure consistency within classifications. The efficacy of the benthic habitat map was assessed by a number of classification metrics derived from error matrices of the Major and Detailed levels of Geomorphological Structure and Biological Cover.
The overall, producer’s, and user’s accuracies were computed directly from the error matrices. The analyses of the combined ROIs 1 – 4 gave an overall accuracy of the benthic habitat map of 90.4% and 84.6% at the Major and Detailed levels of Structure respectively, and 85.1% and 76.5% at the Major and Detailed levels of cover. The known map proportions, i.e. relative areas of mapped classes, were used to remove the bias introduced to the producer’s and user’s accuracies by differential sampling intensity (points per unit area). The overall accuracy at the Major and Detailed levels of Structure changed to 92.3% and 85.9%. The overall accuracy at the Major and Detailed levels of cover changed to 84.3% and 79%. The overall accuracies were also adjusted to the number of map categories using the Tau coefficient. Tau is a measure of the improvement of the classification scheme over a random assignment of polygons to categories, bounded between -1 (0% overall accuracy for 2 map categories) and 1 (100% accuracy for any number of categories). The Tau coefficients were 0.807 ± 0.026 and 0.829 ± 0.018 at the Major and Detailed levels of Structure, and 0.814 ± 0.020 and 0.745 ± 0.020 at the Major and Detailed levels of cover.
Percent coral cover was classified for every polygon, thus coral cover was evaluated separately. Total accuracy for Coral in all habitats for all ROIs was 89.6% and 93.4% after adjusting for map marginal proportions. This calculation, however, was not realistic because it evaluated coral cover in non-coral habitat which inflated the number of correct sites. To account for this, coral cover was also evaluated at only those sites found to be Coral Reef and Hardbottom habitats. Total map accuracy for mapping coral cover on Coral Reef and Hardbottom habitats was 79.8%, and 82.7% after adjusting for habitat proportions. The accuracy varied greatly between the two coral categories present. User’s and Producer’s accuracies for Coral 0% - <10% were near or equal to 90%. Conversely, Coral 10% - <50% user’s and producer’s accuracies were 54.3% and 66.5% respectively. Adjusted producer’s accuracy was reduced to 55.2%. The adjustment for map proportions was very relevant here due to the large disparity of area between the two classes. The map contained 658.5 km² of Coral 0% - <10% and 39.8 km² of Coral 10% - <50%. Further 583 of AA points on Coral Reef and Hardbottom habitat were in Coral 0% - <10% and 219 were in Coral 10% - <50%. Interestingly, there were no mapped polygons of Coral 50% - <90% and 90% - 100%. There was confusion between coral classes where 88 locations mapped as Coral 10% - <50% were actually Coral 0% - <10% and 60 locations mapped as Coral 0% - <10% were found to be Coral 10% - <50%. Confusion between 11 locations that were mapped as Coral 10% - <50% were actually Coral 50% - <90% and 1 location mapped as Coral 10% - <50% was found to be Coral 90% -100%. These sites were all located in the patch reefs of Hawk Channel. It is unknown if these sites met the minimum mapping unit criteria, but the field data indicated high coral cover at these locations. The relatively low adjusted producer’s accuracy for Coral 10% - <50% (55.2%) suggests that not all higher coral cover areas were captured in the map. Furthermore the relatively low user’s accuracy (54.3%) indicates that the areas of Coral 10% - <50% portrayed in the map are highly variable.
Combining all the results into a total map accuracy assessment gave a sense of how the overall map portrays the seascape. However, it should be noted that large gaps in map coverage exist, especially between Marathon and Key Largo, a 137 km stretch. The results given in the appendices are more representative of their specific regions. ROIs 1 and 2 covered most of the lower Keys and their results are a good representation of map accuracy for that region. ROI 3 covered the Backcountry which had higher accuracies, presumably due to a reduced diversity of habitats and lack of coral cover. ROI 4 is a good representation of the upper Keys map accuracy. It is difficult to know which assessment best represents the middle Keys. The landscape is more similar to the upper Keys, but Hawk Channel becomes deeper and more turbid.
focused on higher-latitude coral communities is warranted to investigate possible range expansions and ecosystem shifts
due to global warming. As the northern extension of the Florida Reef Tract (FRT), the third-largest barrier reef ecosystem in
the world, southeast Florida (25–27u N latitude) is a prime region to study such effects. Most of the shallow-water FRT
benthic habitats have been mapped, however minimal data and limited knowledge exist about the coral reef communities
of its northernmost reaches off Martin County. First benthic habitat mapping was conducted using newly acquired high
resolution LIDAR bathymetry and aerial photography where possible to map the spatial extent of coral reef habitats.
Quantitative data were collected to characterize benthic cover and stony coral demographics and a comprehensive
accuracy assessment was performed. The data were then analyzed in a habitat biogeography context to determine if a new
coral reef ecosystem region designation was warranted. Of the 374 km2 seafloor mapped, 95.2% was Sand, 4.1% was Coral
Reef and Colonized Pavement, and 0.7% was Other Delineations. Map accuracy assessment yielded an overall accuracy of
94.9% once adjusted for known map marginal proportions. Cluster analysis of cross-shelf habitat type and widths indicated
that the benthic habitats were different than those further south and warranted designation of a new coral reef ecosystem
region. Unlike the FRT further south, coral communities were dominated by cold-water tolerant species and LIDAR
morphology indicated no evidence of historic reef growth during warmer climates. Present-day hydrographic conditions
may be inhibiting poleward expansion of coral communities along Florida. This study provides new information on the
benthic community composition of the northern FRT, serving as a baseline for future community shift and range expansion
investigations.