Development of planted seagrass beds in Tampa Bay, Florida, USA .1. Plant components

In this study we evaluated the floral attributes of planted seagrass beds as they developed over time. The seagrasses Halodule wrightii and Syringodium filiforme were planted on 0.5 m centers at several sites within Tampa Bay, Florida, USA. Planting unit (PU) survival, change in areal shoot density, plant morphometrics and associated macroalgae were monitored over a 3 yr period. These parameters were compared with nearby, natural beds as a reference. Comparisons were not limited to the same species, but included Thalassia testudinum in order to address management issues regarding the substitution of one habitat type for another. Despite use of experienced personnel, in some plantings, an average 47% loss of PU was sustained, apparently due to seasonal bioturbation. Depending on the spatial distribution of loss, persistent cover at equivalent densities was still attained within 1.8 yr (for plantings on 0.5 m centers) over portions of some planted sites. Seagrass recovery rate and recommended monitoring times have a positive, linear relationship to spacing of plantings. Although moderately variable, areal shoot density clearly defined trends in bed development over time. Many plantings exhibited little spread in the first year after planting, and then expanded rapidly in the second year. Seagrass surface area, length or biomass, as well as macroalgal biomass, proved to be weak indicators of system development for most seagrass species. Although substantial PU losses were experienced, the subsequent survival, spread and persistence of seagrasses indicate that large areas of Tampa Bay, which historically had supported seagrass, are now suitable for restoration. For remaining seagrass habitat however, conservation provides a more certain basis for maintaining the resource than attempting to mitigate through planting.