Harnessing genetic tools for monitoring, understanding and conserving seagrasses in highly urbanized coastal areas

Abstract

Seagrasses are important marine primary producers that provide a variety of ecological functions and services for the health and dynamics of coastal ecosystems. Despite their key ecological roles, seagrass ecosystems are rapidly declining globally. The appearance and abundance of these species are highly seasonal, modulated by changes in environmental conditions. The decline of seagrasses makes their conservation one of the highest priorities for local biodiversity. In order to provide an effective intervention for seagrass management, it is essential to assess their population dynamics. However, traditional approaches, such as ecological surveys for assessing temporal and spatial trends in seagrasses are known to be logistically challenging and limiting, which constraining our capacity to plan effective conservation management. Environmental DNA (eDNA), offers an alternative approach to conventional methods, allowing rapid, accurate, and deeper temporal and spatial resolution of the presence and abundance of seagrasses. This thesis aims to understand the capacity and efficiency of eDNA approaches to monitor and assess seagrass population dynamics (availability, distribution, and abundance) in Hong Kong. In Chapter 1, field and aquarium experiments investigate the utility of eDNA study on the presented seagrass population. The findings elucidate the efficacy of eDNA techniques, as seagrass DNA was able to be detected successfully in both mediums (water and sediment). The results showed that DNA concentration decreased with further distance from the seagrass patch in both water and sediment, while sediment tend to have higher DNA concentration results compared to water. These indicated that the presence of DNA dispersal effect is impacted by tidal events and sedimentary deposition, and sediment has greater preservability of DNA and fewer disturbance events than the source of water. In Chapter 2, the focus shifted to the application of eDNA in ancient environments to investigate past populations. The results presented the positive detectability of the genetic information under a certain depth at the sediment layer of the year 1980, but with a decreasing trend of detected DNA with depth of sediment. The results of this thesis in both chapters have provided insight into applying eDNA in spatial and temporal monitoring in present or past seagrass populations. The molecular survey study approach can reflect changes in seagrass occurrence and abundance across spatial-temporal scales in Hong Kong, but these characteristics would differ when comparing seawater and sediment sources. Ultimately, this study provided an understanding of the application of the genetic tools that promote and support long-term ecological and genetic monitoring programs for seagrasses.