Turtle Grass, Thalassia testudinum, is a species of seagrass native to bays and estuaries of the tropical Atlantic. It is ecologically valuable acting as a sediment stabilizer, carbon sink, and habitat and food source for many marine organisms. These plants are often found in association other seagrass species, creating seagrass beds. There has been documented global decline in seagrass communities over the last few decades due to human activities and some aspects of climate change are predicted threaten seagrasses in the future. Two broad goals of this study are to document longitudinal changes occurring in seagrass populations in Jobos Bay, PR and characterize environmental parameters which may be driving these changes. To address these goals, in January 2019, previously established (2017) transects within Thalassia beds in Jobos Bay National Estuarian Research Reserve (JBNERR) were resampled. Percent cover, density, and blade height were compared to environmental parameters (such as pH, depth, temperature). A principal component analysis (PCA) was utilized to explore the variation in the dataset and visualize the relationships between the transects and years. Secondarily, a multivariate analysis of variance (MANOVA) was performed to compare whether the linear combinations of dependent variables differed by year and to access their effect.
Results/Conclusions
Since 2017, a decrease in T. testudinum and macroalgae cover was observed in the resampled transects. Preliminary PCA results indicated that the first two principal components account for 76.2% of the variation in the dataset (60.1% and 16.1%, respectively). Seagrass density and total cover weighed heaviest on the positive PC1 axis, opposite macroalgae coverage. On the PC2 axis, pH and total vegetation coverage weighed heaviest (negative and positive scores, respectively). The PCA graph depicted considerable overlap on PC1 axis between years. However, PC2 axis depicted separation between years, with a decrease in total vegetation coverage and an increase in water pH for 2019. The initial MANOVA indicated a significant difference in linear combinations of the environmental parameters between years (Wilk’s λ= 0.087, df = 9,6, P = 0.014). Post-hoc tests revealed that pH was the environmental parameter showing significant difference between years (F = 105.36, df = 1, 14, P < 0.001). Additional data will be collected to investigate whether these trends hold and which environmental variable influences the vegetational characteristics of seagrass communities most. Understanding the influence of various environmental parameters on these impacted communities may yield a better understanding of how to manage future populations and reintroduction/mitigation projects.