| Ten transects (A-J) oriented perpendicular to shore were evenly spaced between the St. Petersburg/Clearwater airport and the Gandy Bridge. Five transects were located north of the Howard Frankland bridge, and five were located between the Howard Frankland and Gandy bridges.
Each transect extended from shore to a depth of approximately 3 meters. A series of 200 m x 200 m quadrats were centered along each transect, and each quadrat was subdivided into one hundred 20 m x 20 m grid cells. These transects were overlain on the geo-referenced image so that they occupied the same location for each photo. Each cell had a unique geo-referenced position that could be used to compare the same point throughout the time series.
SAV cover in each quadrat cell was assigned a value between 1 and 5: cells completely filled with dense seagrass received a value of 5, while bare cells received a value of 1.
SAV cover data were merged with bathymetry data. Cover class data were found to be approximately normally distributed. Analysis of variance was conducted on the main effects of location, depth, and distance from shore, and on their interactions.
Data was analyzed for the entire study period, each decade, and the 1942-1965 (pre-development) and 1965-1999 (post-development) time periods (_= 0.05). The rates of change for the main effects and their interactions were tested for differences using Duncan’s Multiple Range Test (_=0.05) (SAS Institute 1990).
The study site was divided into two locations: north (N: transects A-E) and south (S: transects F-J). Depths were divided into four groups: very shallow (VSH: <0.5 m), shallow (SHL: 0.5 m-1.0 m), moderate (MOD: 1.0 m-1.5 m), and deep (DEP: >1.5 m). Distances from shore were divided into three groups: close (CLO: <500 m), middle (MID: 500 m–1000 m), and far (FAR: >1000 m).
|
