Photo: Esther Leong

Citizen science is expanding our knowledge of Hong Kong’s jellyfish

By John Terenzini 18 January 2022

Citizen science is a growing movement in Hong Kong, with members of the public making contributions to water monitoring, light pollution, and biodiversity, while one prominent campaign is focused on documenting and learning about Hong Kong’s jellyfish.

Jellyfish are not considered economically important or of conservation concern locally, and Hong Kong’s Agriculture Fisheries and Conservation Department does not study them. There is limited local institutional research being done on jellyfish. As a result, the available information for jellyfish in Hong Kong is incomplete or outdated. Citizen science is helping to fill the gap, with the Hong Kong Jellyfish Project (HKJP) studying the presence, abundance, and distribution of jellyfish in Hong Kong waters. The project’s goals are to increase understanding of jellyfish, their impacts in local waters, and potentially enhance water sports safety by determining what causes jellyfish to bloom locally.

This often feared animal is frequently overlooked by scientists who incorrectly believe jellyfish are a trophic dead-end and of limited importance to marine ecosystems. In fact, jellyfish are major marine predators found in every ocean and are part of the diet of over 160 species of fish, including economically important ones. Hu-mans use jellyfish for food and a green fluorescent protein derived from a jellyfish is used in biomedical research. Their importance is only just starting to be appreciated, but they can be difficult to detect due to unpredictable appearances across large ocean areas, making them an ideal candidate for study by citizen scientists.

A role for citizen science

Citizen science is increasingly seen as a complement to traditional science where-in members of the public collaborate with scientists to research questions that can impact the public good. Public participation improves data gathering by increasing manpower at a lower cost. Even untrained members of the public can be effective contributors when simple protocols are used to gather data across long time periods or large geographical areas beyond the abilities of a single scientist.

Members of the public are contributing to citizen science from project creation to execution, data gathering, data analysis, and communication of findings. The United Nations has declared this the Decade of Ocean Science for Sustainable Development, encouraging the involvement of citizens in collecting data about the world’s oceans.

The Hong Kong Jellyfish Project uses an internationally recognised methodology applied to local circumstances to study local jellyfish. The public submit simple data and photographs of their observations of jellyfish in local waters through a website, social media or the iNaturalist app. iNaturalist is a citizen science platform that allows individuals to submit photos and data of species observations via their smartphones, and makes this information available to scientists and other users internationally.

As new information about jellyfish is discovered it is shared through media, public presentations, and journal articles, creating a community of amateur jellyfish re-searchers. Launched in February 2021, HKJP has recorded three new species records for Hong Kong, accumulated over 400 sightings of jellyfish from over 200 observers, and shared this growing body of knowledge with watersports groups, The Royal Geographical Society (Hong Kong), and the Hong Kong Natural History Society.

Cyanea nozakii is one of the most common jellyfish in Hong Kong and packs a powerful sting. Photo: Casey Chu

Project data is also shared with institutional scientists. Samples of live or stranded jellyfish are collected and genetically analysed in the laboratory of Dr Jerome Hui, Associate Professor and Programme Director of the Biology unit at the School of Life Sciences at The Chinese University of Hong Kong (CUHK). Sightings records and overall project results are now in review for publication in collaboration with Dr Laura Falkenberg, Assistant Professor of the Falkenberg Lab, also at CUHK. Dr Falkenberg studies changing marine ecosystems and their socio-economic consequences for human societies. Proliferation of jellyfish can be a symptom of a changing marine ecosystem because they are able to thrive in conditions that would be harmful to other marine creatures.

“Working with the HKJP has enabled me to be involved with work that I wouldn’t have the opportunity to do otherwise,” said Dr Falkenberg. “Moreover, projects such as this harness the time, energy, and enthusiasm of citizen scientists to carry out widespread documentation of species’ occurrences at a scale which would be difficult (if not impossible) for a single research laboratory to complete.”

Rhopilema hispidum is known to bloom in Chinese waters and travels ocean currents to Hong Kong. Photo: Edie Hu

The HKJP is also conducting survey research to examine the motivations for public participation researching jellyfish. The results may inform other practitioners of ways to engage citizen scientists and build upon this research.

Common local species

In Hong Kong many people consider summer to be the “jellyfish season”. However, the public likely sees more jellyfish in summer because that’s when more people are active in or near the water. Jellyfish populations are also known to be episodic, appearing and disappearing without a confirmed cause.

One of the most common jellyfish reported in Hong Kong waters is Cyanea nozakii, locally known as the Lion’s Mane. This jellyfish has tentacles that are several meters in length and it packs a powerful sting. They were reported in small size as early as February and increased in size and number through May, only to reduce in number this summer.

The second most common stinging species is Rhopilema hispidum, the flower or sand jellyfish. The HKJP discovered that this species increased in number throughout spring, then disappeared in early summer, only to return in later summer. Understanding how environmental variables and ocean currents affect jellyfish populations across the different seasons will be important to understanding jellyfish.

Acromitus flagellatus blooms as a local population. Photo: Harriet (Bugs) Harpley

Whereas Cyanea nozakii is likely to bloom in Hong Kong, it is possible Rhopilema hispidum is coming from elsewhere, via ocean currents. Another species that forms a local population is the river jellyfish Acromitus flagellatus. This species bloomed in Sai Kung bay, near Pak Nai, and near Tai Mei Tuk in Tolo Harbour. Jellyfish polyps are known to settle on hard surfaces like rocks or the plastic floats of docks or fish farms before blooming under the right environmental conditions. Further research is needed to determine the source of these populations.

The HKJP demonstrates the ability of citizen science to complement institutional science to provide baseline data about local jellyfish. The general public, alongside and in partnership with academic researchers, can add to the knowledge and appreciation of Hong Kong’s unique biodiversity. 

John Terenzini is a recent graduate of The University of Hong Kong’s master’s program in Environmental Management and the founder of the Hong Kong Jellyfish Project. His scientific curiosity is inspired by his years of experience as an outdoor educator and wilderness guide.