Thesis Defense - Zostera marina in times of Climate Change
In the coming weeks, UW master's students will defend their theses. The subjects are varied and the students are from both master's programs, Coastal Marine Management and Coastal Communities and Regional Development. The defenses are accessible to everyone through zoom links but they are also open to the public, at the University Centre of the Westfjords in Ísafjörður.
Student: Riitta Chorfi
Thesis title: Multiple stressor effect study on Zostera marina's morphological properties, erosion mitigation capacity and shoot dislodgement in the Turku Archipelago, Finland.
Program: Coastal and Marine Management
Abstract:
One of the biggest threats that our marine systems are currently facing is temperature variability. This is directly consequential of increasing marine heatwaves (MHWs) and heightened wave activity due to stronger and more frequent storms poses a threat to coastal systems. Seagrass, Zostera marina, in the Baltic Sea serves as a coastal protection mechanism against erosion. Vast research exists in the field of single stressor effects on coastal vegetation, but coherent empirical support is yet lacking in multiple stressor effects. In this research, I studied the effects of temperature and hydrodynamic forcing as treatment stressors on Z. marina’s morphological properties, erosion mitigation capacity and shoot dislodgement in the Turku Archipelago in Finland. In a mesocosm facility, half of seagrass samples were exposed to ambient temperatures and the other half to a MHW. Through the comparison of control treatments to the MHW treatment, I considered the differences in seagrass’ morphology. Samples were then subjected to continuous oscillatory flow for an hour in wave flumes under minimal orbital velocities of 8 cm s−1 - 29 cm s−1. Eroded sediment was collected for the test area the grams of sediment eroded per hour compared between samples and the dislodged shoots were collected. I found no significant differences in Z. marina’s morphological structure when comparing samples from the ambient to the MHW treatment. Similarly, no statistically notable distinctions were found in roots, rhizomes, leaves and overall belowground- and aboveground-biomass. For sediment erodibility, 86% was explained by wave velocities as predictors, but no effect was detected for the MHW treatment. A significant quadratic relationship was observed between velocity and dislodgement (57% of the variation explained). MHW treatment showed no significant effect. It is possible that the simulated MHW was not strong enough to hinder the state of homeostasis of seagrass. Alternatively, it is possible that this is an indication of stronger resilience of the organisms to thermal stress.