The influence of environmental parameters on the growth of Thalassia testudinum in a field setting.

The seagrass Thalassia testudinum is ecologically valuable serving as habitat and food for many organisms. There has been a documented decline in seagrass communities over the past decades and aspects of climate change are predicted to negatively impact seagrass growth. This study sought to understand how environmental variables influence T. testudinum communities in Jobos Bay, Puerto Rico. Forty 1 m² quadrats within transects in Jobos Bay were sampled. For each quadrat, percent cover (Braun-Blanquet (BB) score), density, and blade length of T, testudinum were recorded along with environmental parameters (depth, temperature, pH, DO, turbidity, and salinity). Additionally, growth rates of T. testudinum plants were measured within 12 (25 cm²) quadrats placed at different locations (less turbid and more turbid) and depths (1m and 2m). A Principle Component Analysis (PCA) characterized variation in environmental parameters and community structure for each quadrat. The PCA scores, along with site location and season were used to develop models to predict T. testudinum, BB score, blade length and density. The best explanatory models for predicting BB scores included depth, community structure, and location. As depth increased there was a marked decrease in BB score. The best performing models for blade length included the interaction between location and seagrass community structure, with length increasing as the prominence of the invasive seagrass, Halophila stipulaceae, increased. The global model (all variables included) was best at modeling density. For the growth study an ANOVA indicated significant differences in growth rate for depth and a significant interaction between location and depth. At the clearer location growth rates were greatest at 2 m but for the turbid location greater at 1 m. This research depicts the importance of understanding location variability on assessing the health and vitality of T. testudinum beds when considering estuary conservation strategies and seagrass loss mitigation. [ABSTRACT FROM AUTHOR]