Morphometric variability and allometric relationships in the seagrass Thalassia testudinum in Florida Bay

Morphometric variability and allometric relationships were investigated in the seagrass Thalassia testudinum in Florida Bay in 1998 and 1999. Thalassia testudinum is the dominant seagrass in this perturbed estuary and is important to its ecology. In this study I describe the trends and patterns of the morphometric characteristics of T. testudinum in ten basins in Florida Bay at two spatial scales in two sampling seasons. At the larger scale examined, only mean leaf number showed a significant interannual difference. Distributions of shoot-specific variables were more sensitive to interannual variation; however, both shoot-specific and area-specific characteristics have a high degree of variability at both levels examined. Certain morphometric parameters grouped together consistently and led me to define four ecological zones, similar to ecological zones defined in other studies based upon physical and other characteristics. The results of this study confirm that spatial heterogeneity in the distribution, abundance, and physical characteristics of T. testudinum support the concept of these ecologically distinct regions. Also, the results demonstrate the plasticity of T. testudinum morphology and the significant control that the physical and chemical environment of Florida Bay exert on this morphology. Density had little effect on the morphology of T. testudinum, which is similar to results reported for other clonal plants. However, density had a slight but significant negative correlation with leaf number; this was the only evidence of selfthinning seen. Age and water depth also had little effect on T. testudinum morphology. The results demonstrate that leaf area index can be used to estimate standing crop (and by extension productivity) and total shoot biomass of T. testudinum in Florida Bay. Leaf area index explained 97% of the variance in standing crop. The data compiled here show that some of the shoot-specific and area-specific characteristics of T. testudinum in Florida Bay are strongly related and may prove to be useful descriptors of the architecture of this important seagrass.