Phenology, sexual reproduction, and the factors affecting sexual reproduction of the marine angiosperm, Thalassia testudinum, in the Florida Keys National Marine Sanctuary (FKNMS)

This study investigated phenology and the factors affecting sexual reproduction of Thalassia testudinum in the FKNMS. Flowering was assessed at 30 permanent monitoring sites via direct observation and age reconstruction techniques of seagrass cores in 2002. The mean flowering frequency was 1.49%, was spatially variable, and exhibited sex-specific timing in floral anthesis. Historical flowering reconstruction demonstrated that flowering frequencies are not temporally variable. Floral sex ratios were female-biased, spatially variable, and likely temporally variable. Relative nitrogen availability was most important in influencing flowering and was negatively correlated with flowering. Higher flowering occurred with low N availability and lower flowering occurred with high N availability. A 15 month in situ nutrient addition experiment conducted at 10 sites in the upper Florida Keys, where N + P were added at ecologically significant loading rates, significantly reduced flowering in the N + P treatment plots at all 10 sites.