Student Presentation

International Conference on Conservation and Sustainable Development of Coastal Wetland Programme Student Presentation

Student Presentation

Mr. Yuet-tung TSE

School of Science and Technology, Hong Kong Metropolitan University

Title: Full Size Microplastics Pollution Survey to the Costal Marine Waters of Hong Kong

Microplastics (MPs) are defined as plastic particles with sizes ranging from 1 μm to 5 mm, which are considered as a severe concern to the pollution of marine environment. Traditional practices by the collecting of MPs through trawling a net and quantification by microscopy limited the range of MPs down to around 50 µm. In this study, the abundance of full-size MPs in Hong Kong marine water at twelve locations was investigated using fluorescence microscopy (50 µm – 5 mm) and flow cytometry (1 – 50 µm) respectively, during the wet (September 2021) and dry (March 2022) seasons. The average abundance of MPs with size ranges of 50 μm – 5 mm and 1 – 50 μm from twelve sampling locations marine surface waters were found ranging from 27– 104 particles L-1 and 43,675 – 387,901 particles L-1 in the wet season respectively, and 13 – 36 particles L-1 and 23,178 – 338,604 particles L-1 in the dry season respectively. Significant temporal and spatial variations of small MPs abundance were observed at the sampling locations, which might be contributed by the influences of the estuary of Pearl River, sewage discharge points, land structure, and other anthropogenic influences. Ecological risk assessment was conducted and revealed that the small MPs (< 10 μm) in coastal marine surface waters may pose potential health risks to aquatic organisms.

Mr. Jialin ZHANG

Xiamen University

Title: : The Surface Elevation Changes of Salt Marshes and Vulnerability to Sea-level Rise

Salt marshes, as an essential part of coastal wetlands, not only play a critical role in maintaining biodiversity, but are also significant for climate change mitigation and adaptation. Sea-level rise has become a climate change factor that seriously threatens the survival of salt marshes. Although the surface elevation change of salt marshes could keep peace with the sea-level rise through vertical and longitudinal biomorphic processes within normal limits, most of the landward successional paths of salt marshes are blocked by human facilities in China. Therefore, accurate quantification of the relationship between surface elevation changes of salt marshes and sea-level rise rate becomes the key to scientifically assess the vulnerability of salt marshes to sea level rise in the future. The interannual change of surface elevation and sea level rise rate in coastal wetlands are both on millimeter scale, and the tidal and vegetation disturbances greatly limit the study of surface elevation response to sea level rise in coastal wetlands. The surface elevation table-marker horizon (SET-MH) monitoring system enables high-precision monitoring of surface elevation changes, vertical accretion and shallow subsidence in coastal wetlands. We established a unified standard SET-MH monitoring system in salt marshes in China, clarify the range of surface elevation change rates in China's salt marshes, also explore the relationship between different processes of surface elevation change. It will provide a scientific basis and support for accurate assessment of the vulnerability of salt marshes to sea-level rise and the management of climate change response.

Mr. Zhaobin LI

School of Science and Technology, Hong Kong Metropolitan University

Title: The Impact of Urban Development on Wetland Conservation

Wetland is an integrated ecosystem which includes ecosystems such as hydrology, soil, vegetation, and biological environments. At present, the urbanization rate of China's national economic development process is rapidly increasing, and by the end of 2021, the urbanization rate of China's resident population will be 64.72%. This paper analyzes the hydrological effects of urbanization, the impact of water resources, climate change, and biodiversity on wetland ecosystems, and also analyzes the role of wetlands on the ecological environment, especially in terms of ecological and cultural values. The economic and social benefits of the whole society are also analyzed. The ecological and social benefits of urban wetlands have made their conservation and sustainable development increasingly important worldwide. Based on the current situation of China's urban wetland protection and restoration, we put forward countermeasures and suggestions for China's urban wetland protection. This is conducive to promoting the sustainable development of the urban wetland ecosystem, promoting the operation of the market, realizing the optimal allocation of ecological resources, improving the benefits of ecological environmental protection, and promoting the coordinated development of the ecological environment. This paper provides a reference for the better development of wetland conservation under urbanization development conditions.

Ms. Ho Tun NG

School of Biological Sciences, The University of Hong Kong

Title: Assessing the Effect of Heavy Metal Pollution on Seagrass Microbiomes in Highly Urbanized Areas: Tools for Monitoring and Restoring Seagrasses in Hong Kong

Seagrasses, the only flowering plants that have adapted to live in marine environments, are unique primary producers that play an important role in coastal habitats. They provide various ecosystem services such as carbon sequestration, nursery ground for numerous marine species, water quality improvement and sediment stabilization. Unfortunately, habitat fragmentation and the enhanced pressure of chemical pollution are driving a global decline in seagrass populations, ultimately affecting the services provided and the well-being of our communities. Hong Kong is not the exception to this trend. The five local species of seagrass are evidencing drastic reductions and local extinctions during the last 10 years, following the global trend. However, there is a limited understanding of the drivers behind such declines and the resilience capacity of the seagrasses to withstand further anthropogenic pressures. Heavy metal pollution has been identified as one of the main drivers of seagrass decline and extinction. Metal pollutants such as cadmium (Cd), arsenic (As), chromium (Cr), and lead (Pb) impose detrimental physiological and demographic effects on seagrasses. Nevertheless, as with other plants, the effects of these pollutants on the health and resilience of seagrasses are not only determined by the plant, but also by the functional interplay with their associated microbial communities. Here, we examined the seagrass-associated microbial communities across gradients of metal pollution in Hong Kong aiming to unveil the drivers underpinning local declines of seagrasses. Our study aimed to 1) characterize the levels of metal pollution in seagrasses and their habitats and 2) understand the ecological condition of seagrasses and their habitats through the structure and diversity of seagrass-associated microbiome. We have identified spatial differences of metal pollutions across different seagrass habitats with some of them exceeding standard ranges. By further looking into their correlations with microbiome, we can provide a baseline record of seagrass habitats in Hong Kong with identification of pollution problems, which is a novel information valuable for the planning of seagrass conservation in the future.

Ms. Kit-ling LAM

School of Science and Technology, Hong Kong Metropolitan University

Title: The Distribution and Abundance of Antibiotics and Heavy Metals in Mangrove Sediments and Their Effect on Sediment Microbial Composition and Diversity

Little is known about the effect of environmental antibiotics and heavy metals on mangrove sediment’s microbial composition and diversity. Here, I characterized the distribution and abundance of twenty antibiotics and eight heavy metals and the microbial community profiles in the sediments collected from the three habitats of the Mai Po RAMSAR, namely the mudflat, mangrove, and gei wai, and I also delineated the correlation between all tested environmental factors and microbial community profiles. The results showed that the concentrations of almost all tested antibiotics and heavy metals in the sediments of mangrove and mudflat were higher than that in the gei wai. Proteobacteria was the dominant phylum in the sediment. Shannon indices and microbial composition in the mangrove sediments were higher than in the sediments of the other two habitats. Moreover, the results of canonical correspondence and variance partitioning analyses revealed that pH, macrolides antibiotics (MLs), and manganese (Mn) were the major factors correlated with the variation in microbial composition at the phylum level. Also, the effect of MLs and Mn collectively explained more variation of the microbial composition than pH alone, suggesting that the co-occurrence of MLs, and Mn might play more influential roles among all measured factors in the microbial communities in wetland sediments. This study sheds light on the possible effect of the co-occurrence of antibiotics and heavy metals at low concentrations in shaping microbial composition in wetland sediments.

Mr. Hewei ZHAO

The Chinese University of Hong Kong

Title: Magnitude and Controls of Stem Methane Fluxes in a Subtropical Mangrove Ecosystem in Hong Kong

Methane is a potent greenhouse gas that contributes toabout 25% radiative forcing and has a global warming potential that is 34 times greater than CO2 over a 100-year time scale. While detailed investigations of wetland methane emissions have been made from soil and water surfaces, the contribution of trees has largely been overlooked. Coarse woody debris (CWD) and dead standing trees (snags) are important components in forest ecosystems, but their role in ecosystem methane fluxes is poorly known. In this study, we measured methane fluxes at the ecosystem scale and from tree stems in a mangrove ecosystem dominated by Kandelia obovata in Hong Kong using eddy covariance and chamber methods, respectively. Our results show that mean methane fluxes from CWD, snags, live trees and ecosystem were 68.10, 58.78, 46.72 and 122.59 μmol m-2 h-1, respectively. Results of Pearson correlation analysis suggest that the most important controls for average monthly methane fluxes from CWD, snags, live trees and the whole ecosystem were photosynthetic photon flux density, dissolved oxygen, sap flow density and soil temperature, respectively.

Mr. Ian Dale RIOS

University of San Carlos

Title: Through the Lens of Ecodevelopment: Institutional Mangrove Conservation at the Local Government Level in the Camotes Islands, Cebu, Philippines

This is a qualitative study on the prevailing coastal conservation approach in the Camotes Islands, Cebu, the Philippines ‒ a proclaimed Mangrove Swamp Forest Reserve. Through the lens of ecodevelopment and the new ecological anthropology, this study particularly looks into the sustainability and efficacy of mangrove conservation in the Camotes Islands; and how local political institutions regard the socioeconomic welfare of the local communities that live around it. The main part of this study documents the knowledge, practices, perspectives, experiences, and narratives of key local government actors as embedded in implemented programs, initiatives, ordinances, implementation management strategies, and challenges in conservation. As it presents, the prevailing mangrove conservation in the Camotes Islands is a state-led institutional approach predominated by the scientific ecological values which center on the preservation and rehabilitation of the biophysical aspects of natural resources. This top-down conservation has little regard for the cultural and socioeconomic values of the local people who apparently value mangroves quite differently from the institutionalized values. This study also presents that key local government actors are crucial instruments in negotiating the conflicting values that surround the institutional mangrove conservation. Moreover, although numerous mangrove-related initiatives, programs, and policies have already been implemented in the Camotes Islands, non-compliance among the local people still persist up to this day. In addition, a combination of challenges ‒ such as the unsteady political integrity and unsustainable programs ‒ devitalize mangrove conservation on the ground. Furthermore, this study hopes to illuminate the incongruous chasm that detaches the biophysical aspect of coastal ecosystems from the local communities in the context of conservation. Lastly, this study emphasizes the importance of a holistic and integrated approach to conservation that regards both the biophysical integrity of the natural world and the welfare of humankind as a foundational whole.

Mr. Kaze LAI

School of Science and Technology, Hong Kong Metropolitan University

Title: Establishment of Sample Preparation Workflow for Metataxonomic Analysis of Epiphytic Bacteria on Pneumatophores

The highly dynamic microhabitat on pneumatophores of mangrove species harbors unique assemblages of microorganisms that are largely unexplored. Today next-generation sequencing (NGS) is widely used to characterize complex microbial communities in the environment. While often being overlooked, poor sample preparation could introduce significant biases and lead to inconsistent results. However, reference methods for collecting epiphytic microorganisms from pneumatophores are highly lacking. It is believed that some epiphytic microorganisms might attach strongly on pneumatophore surface to withstand tidal flushing so the detachment method is critical. We tested the effectiveness of several approaches to detach epiphytic bacteria from pneumatophores and found that vortex agitation at 2000 rpm detached approximately 1.5X and 2.5X more viable bacteria than bath sonication at 40kHz and vortex agitation at 3000 rpm respectively. Extending the detachment time from 5 min to 10 min not only did not improve effectiveness but led to reduced number of viable bacteria, while the effect of 0.05% Tween 80 depended on other conditions. The results revealed that the balance between detachment efficiency and cell damage has to be well considered. To harvest as much detached cells as possible from the suspension, membrane filtration with pore size 0.2 μm should be used over centrifugation. One DNA extraction kit, under the optimized lysis condition, outperformed the other two kits in terms of yield and purity, mainly due to the flexibility to choose between lysis buffers. As demonstrated by amplicon sequencing of 16S rRNA gene, our suggested workflow was able to produce high-quality NGS data for reliable metataxonomic analysis.

Ms. Mingdang LI

Shenzhen University

Title: Effects of Different Sea Level Height on the Growth of Rhizophora Stylosa Seedlings

Mangrove vegetation is typically found in intertidal zones, where they exhibit exceptional resilience to wave impacts and waterlogging. However, rising sea levels have increased the risk of tidal flooding, and the effects of different flooding heights on the growth of Rhizophora stylosa, a typical mangrove species, have yet to be explored. In this study, artificial semi-diurnal tides were created to simulate tidal flooding at different heights. R. stylosa seedlings were grown for 90 days in incubators at simulated sea water heights of 0 cm, 10 cm, and 30 cm, and morphological and physiological indices were measured every 30 days. The results indicate that R. stylosa seedlings may experience optimal growth at a water height of 10 cm during the first 60 days, followed by 30 cm for better growth. Morphological indexes and physiological indices of the roots and buds were positively correlated, and there were no significant differences in superoxide dismutase (SOD) and malondialdehyde (MDA) in the root tissues among all groups. According to the study findings, R. stylosa is a type of mangrove plant that exhibits good resilience to flooding stress. As a result, it has the potential to become a significant tree species for the purpose of restoring mangroves in face of rising sea levels. These findings provide insights into the growth conditions of R. stylosa and offer a strategy for managing mangrove ecosystems.

Ms. Ka Wai CHAN

School of Science and Technology, Hong Kong Metropolitan University

Title: Comparison of Pneumatophore Characteristics and Epiphytic Microalgae between Two Distinct Mangrove Wetlands in Hong Kong

Avicenna marina is mangrove species found in Hong Kong which grow vertical roots from root system, called pneumatophores to facilitate the gaseous exchange in root system during low tide. However, the function of pneumatophores cease when immersed into seawater. Hence, epiphytic microalgae is found on pneumatophores and revealed that it may contribute to pneumatophores by photosynthesis during high tide. In this study, pneumatophores characteristics and microalgal species in two distinct mangrove wetland in Hong Kong, Ting Kok and Tai O, were compared. The means of pneumatophore height and density were higher in Tai O than that of Ting Kok. Among the measured environmental variables, strong positive correlation between sediment moisture content and pneumatophore characteristics was found. All the environmental variables and pneumatophore characteristics measured in two sites were summarised using principal component analysis (PCA). It suggested that the features of Ting Kok and Tai O were different, thus the appearance of mangrove habitats in Ting Kok and Tai O was different. Epiphytic microalgal density on pneumatophores in two sites was estimated by counting under microscope with no significant difference was found. Microalgal diversity and relative abundance were compared by 18S amplicon sequencing. The result of sequencing showed that the microalgal communities in seawater and on pneumatophores were different, especially in Tai O. The potential cause of difference in epiphytic microalgae communities has to be further study.

* Presenters are arranged according to their presentation order.