Environment and Conservation Fund - Assessing and monitoring ecological dynamics of seagrass ecosystems in Hong Kong: Tools for management and restoration efforts

Professor Gaitan Espitia, Juan Diego   (Principal Investigator (PI))

Professor Russell Bayden Dwight   (Co-Investigator)

Amrit Mishra   (Co-Investigator)

36

2023-09-01

2307296

Environment and Conservation Fund - Assessing and monitoring ecological dynamics of seagrass ecosystems in Hong Kong: Tools for management and restoration efforts

ecological dynamics; seagrass ecosystems; management and restoration

Ecology

ECF Project 107/2022

Environment and Conservation Fund 2022

2022

On-going

Seagrasses in Hong KongFive species of seagrasses inhabit the coastal waters of Hong Kong (i.e., Zostera japonica, Ruppia maritime, Halophila ovalis, H. minor and H. beccarii)1. Their populations are under major threat from local extinction as result of the interplay between rapid coastal development, drastic changes in the water quality driven by pollution, and the direct conflict with some human activities in seagrass habitats (e.g., clam digging, recreational kayaking)1–3. Despite the immense threats faced by seagrasses, there is a significant lack of information on their biology and ecology1. Our research group at the University of Hong Kong has made some progress regarding this major conservation problem by developing baseline information on local seagrass populations. We have learned that Halophila ovalis is the most widely distributed species (commonly found in various areas of both the eastern and western territories), while Ruppia maritima is the most locally rare. In addition, we have identified a strong decline in the abundance of local species, particularly in Eastern waters of Hong Kong. The local extinction of seagrasses represents a great impact for marine biodiversity and the loss of ecosystem services provided by these species in our coastal waters. Under the Environmental Impact Assessment Ordinance (EIAO), all established seagrass beds in Hong Kong have been considered as important habitats where ecological assessments are highly needed4. Since the establishment of the EIAO, all proposed developments that have the potential to affect seagrass habitats should undergo ecological assessment so that the threat to local seagrass communities caused by urban development can be minimized. However, there is limited information about the implementation of this ordinance and its effectiveness to maintain healthy seagrass habitats around Hong Kong. Furthermore, this ordinance is also affected by lack of baseline data on various ecological parameters that indicate the health and population trends of seagrass ecosystems. Therefore, our proposed project aims to develop fundamental information and tools aimed to: i) understand the zonation and distribution patterns of seagrasses; ii) assess the current health status and population trends; iii) identify the impacts of various human activities (land reclamation, eutrophication/pollution) on local seagrass beds; iv) characterise the associated biodiversity and ecosystem services; and v) determine the adaptive capacity and potential for seagrass habitat restoration and enhancement in Hong Kong.Why seagrasses are importantSeagrasses play important ecological roles as ecosystem engineers. They provide shelter and food to many animals, and they also improve water quality by filtering out nutrients and by controlling pathogens5. These ecosystem services contribute with numerous socio-economic benefits to the coastal communities, sustaining for instance many commercial fisheries worth as much as $3500 ha-1 yr-1 6,7. Despite of this, seagrass populations are declining globally mainly as result of Anthropogenic activities. Hong Kong is not the exception to this trend1–3. Currently, there are only five species described for Hong Kong, all of them are patchily distributed along the coast (Fig.1).  This diversity of species is very low compared to the 25 species described for the South China coast6, making urgent the conservation of unique seagrasses in Hong Kong before their local extirpation. The risk of their loss implies profound ecological consequences as these seagrasses are hotspots of biodiversity, they help to stabilize the coastlines and sediments, and serve as shelters, feeding grounds and food sources for a variety of animals such as fishes, crabs, gastropods, horseshoe crabs and turtles8. The disappearance of seagrasses in Hong Kong could transform mudflats and other coastal habitats in deserts for marine life as the sediments inhabited by seagrasses are typically anoxic and highly reduced due to the presence of sulfide (a strong phytotoxin). Seagrasses buffer this environmental stress to other marine organisms by developing strategic ecological interactions (e.g., mussels, oysters and the sediment associated microbes). Through these interactions, seagrasses are able to reduce sulfide stress and to improve the water/sediment quality of these areas5. Seagrasses also play an important role in coastal primary productivity, nutrient and trace metal cycling. The roots of seagrasses are able to utilize abundant nutrients in the sediments, which generally cannot be utilized by other primary producers in this ecosystem. Being primary producers, seagrasses are able to sequester organic carbon and act as carbon storehouse, thus they play an important role in climate change mitigation and adaptation. Considering that seagrass meadows are among the most threatened ecosystems on earth (with loss rates comparable to those reported for mangroves, coral reefs, and tropical rainforests7), it is urgent to prioritise novel and more integrative strategies for their conservation, management and restoration in Hong Kong. Our group will build upon the gained experience on seagrass ecology in Hong Kong, aiming to provide high resolution ecological information as well as the tools and guidelines for effective conservation, management and restoration of our valuable local seagrasses.