Ecological and adaptive physiological responses of seagrasses to heavy metal pollution in highly urbanized areas

Abstract

Seagrasses are important primary producers in coastal ecosystems around the globe. However, due to rapid changes in habitat quality, these organisms are declining globally at an unprecedented rate. One of the main drivers behind such trends is heavy metal pollution. This type of chemical contamination impacts the physiology and survival of seagrasses, leading to population declines and local extirpation. In Hong Kong, despite the significant record of heavy metal pollution in the waters and sediments of coastal areas, little is known about the influence of this chemical threat on the ecology and resilience of local seagrasses. This thesis aims to fill this knowledge gap, establishing a fundamental understanding of the effects of heavy metals on the ecological dynamics and resilience of seagrass ecosystems in Hong Kong. Findings of this work reveal spatial and temporal variation in heavy metal pollution (including copper, chromium, manganese and zinc), that has a significant influence on the taxonomic profile of seagrass-associated microbial communities. Seagrass sites with higher ecological risk were also identified in this study, providing evidence for future conservation needs. To further understand the effect of heavy metal pollution, this study assessed the physiological and molecular responses of the vulnerable seagrass Halophila beccarii to elevated concentrations of copper and lead. The results have indicated a potential hormetic response in populations of H. beccarii in Hong Kong. Such novel findings can provide insights for conservation planning in seagrass transplantation. Overall, using two different omics studies, this thesis can establish the fundamental understanding of seagrass in Hong Kong and contribute to the effort of seagrass conservation.