Date of Award
4-3-2024
Degree Type
Thesis
Degree Name
Master of Philosophy (MPHIL)
Discipline
Environmental Science
First Advisor
Prof. FONG Jonathan
Second Advisor
Prof. LAU Yin Kun Anthony
Abstract
Different organisms have been introduced worldwide both intentionally and unintentionally by humans. Some of the introduced species can establish populations outside their native geographic range and invade the environment, causing negative ecological impacts to the ecosystem. Freshwater ecosystems are prone to species invasion due to the aquatic linkage between freshwater habitats, thus facilitating the dispersal of introduced species. To minimise the potential negative impacts of introduced species, early detection and rapid response is vital. Compared to traditional survey methods (e.g., hand nets and cast nets), environmental DNA (eDNA) survey is a sensitive method for species detection by extracting the species’ DNA from environmental samples (e.g., water, soil, and faeces). eDNA surveys can account for the limitation of the traditional survey methods to detect rare and elusive species, which are usually hard to capture.
In this study, I conducted eDNA surveys to detect the introduced Australian redclaw crayfish (Cherax quadricarinatus) and introduced freshwater fish in Hong Kong. I collected water samples from 17 reservoirs and 12 streams. Quantitative polymerase chain reaction (qPCR) was used for species-specific crayfish detection, while eDNA metabarcoding detection was used to assess introduced freshwater fish biodiversity. This study aims to obtain baseline information on the introduced C. quadricarinatus and freshwater fish in Hong Kong to facilitate the establishment of introduced species management programmes.
In Chapter 1, I give a general introduction to introduced species and eDNA surveys, and further explain the objectives of this study. In Chapter 2, I use qPCR techniques and species-specific primers to investigate the distribution of C. quadricarinatus. Also, occupancy models were used to estimate the occupancy and detection probability of C. quadricarinatus in the field sites. A total of six reservoirs tested positive for the presence of C. quadricarinatus DNA, and no amplification was found in the water samples from all 20 streams. The study also detected this crayfish in four new reservoirs, which indicates that C. quadricarinatus is more widespread than previously known and possibly spreading in Hong Kong.
In Chapter 3, I use eDNA metabarcoding techniques to investigate the diversity and distribution of introduced freshwater fish. I used a universal primer set that targeted the 12S rRNA gene of fishes in this study. A total of 58 families, 117 genera, and 177 species were detected. In addition to introduced species, 21 native species were detected in this study, including seven species with conservation status. These results suggest that introduced species are widely distributed in Hong Kong, and can pose threats to native species.
In Chapter 4, I summarise the major findings of Chapters 2 and 3 and discuss further the application of eDNA surveys to freshwater species conservation. I recommend long-term species monitoring using eDNA surveys in hotspots of introduced species. Also, I suggest developing species-specific primers for species of special concern to improve our baseline information on presence-absence, and hence prioritise the important habitats for protection.
Introduced species may cause harm to the local environment. This study found that introduced species are extremely widespread and abundant in Hong Kong, however, their ecological impacts on the local environment are largely unknown. I hope this baseline information on introduced species obtained in this study can promote species protection by establishing management plans using the eDNA technique for long-term species monitoring. Further development of the eDNA technique to improve the accuracy of qPCR results and establish local referencing databases are necessary in order to improve species detection results for future eDNA studies in Hong Kong.
Language
English
Copyright
The copyright of this thesis is owned by its author. Any reproduction, adaptation, distribution or dissemination of this thesis without express authorization is strictly prohibited.
Recommended Citation
Yau, S. M. (2024). Environmental DNA (eDNA) survey of introduced freshwater species in reservoirs and streams in Hong Kong (Master's thesis, Lingnan University, Hong Kong). Retrieved from https://commons.ln.edu.hk/otd/230/