Seagrass, bioindicator, light, water quality, Zostera marina, Zostera noltii, Halodule wrightii, monitoring, Chlorophyll fluorescence, stable isotope, nutrients.

This thesis aims to investigate the effect of environmental drivers on seagrasses by studying shoot-scale and meadow-scale responses, focussing on Zostera marina, Zostera noltii and Halodule wrightii. Seagrasses are plants that have evolved from being terrestrial to living in an entirely marine environment which means they have become highly adapted. The conditions that effect seagrass growth can also be described as drivers as they have the ability to modify seagrass meadows in a variety of ways. These drivers can either be natural environmental factors or anthropogenic processes directly or indirectly affecting the marine environment in which seagrasses are found. These responses environmental conditions allow seagrasses to be used as indicators of the health of our coastal waters with poor water quality causing substantial impacts on seagrasses. Better knowledge of seagrass responses to local environmental conditions will help the identification of stressors which can then be managed. It will also help to comprehend the degree of risk to be expected from the threat of climate change including increased storm events, rises in sea level and sea temperature, and ocean acidification. Mitigating existing or potential impacts that lead to a reduction in water quality will improve the overall health and resilience of the seagrass to future threats from climate change.