SUSTAINING SEAGRASS: A THESIS ON STRESS FACTORS AND RESTORATION TECHNIQUES

Abstract
Seagrass meadows provide essential ecosystem services. However, seagrass cover has decreased the past decades, due to climate change and other disturbing factors. To ascertain coastal stability, biodiversity and ecological well-faring, seagrass meadows need to be restored. In this thesis, we unfold complex interactions that need to be taken into account during such restoration projects.

In particular, this study explores the spatial distribution and factors influencing seagrass cover in Lac Bay, Bonaire, with a focus on the interactions between turtle grazing, bioturbation, invasive seagrass (Halophila stipulacea), and native seagrass (Thalassia testudinum). The observational study reveals competition between the two seagrass species, as well as the negative impact of high grazing pressure and bioturbation on T. testudinum. A linear mixed model identifies significant predictors for T. testudinum cover, including macroalgae cover, turtle grazing pressure, H. stipulacea cover, and mound cover. Additionally, a negative influence between H. stipulacea and T. testudinum is observed. Bioturbation is found to negatively affect T. testudinum but does not significantly impact H. stipulacea. The experimental study investigates the effect of bioturbation on seagrass growth using different planting techniques, indicating that transplanting T. testudinum fragments can be successful for restoration. However, no significant differences are found between lattice and mesh treatments. The study concludes that the complex interactions between these factors contribute to the decline of T. testudinum and the proliferation of H. stipulacea. Future research is suggested to further investigate these interactions and evaluate the long-term effects of bioturbation and planting techniques on seagrass growth. The findings emphasize the importance of considering multiple variables when studying seagrass ecosystems and propose transplanting as a potential restoration measure in areas with high bioturbation.