Combining historical and citizen science jellyfish records to inform marine biodiversity management Open Access

Abstract

Effective management of ecosystems requires knowledge of biodiversity and how it is changing. There are, however, some species and regions for which such data are missing. Combining historical records with those added using non-traditional monitoring methods such as citizen science can fill this gap. Jellyfish are one group for which such an approach is advantageous as jellyfish are difficult to observe, with records particularly lacking for understudied regions outside of Europe and North America. Using Hong Kong as an example, we combine historical jellyfish observation records obtained using traditional methods (published from 1910 to current day) with recent records facilitated by citizen science under the Hong Kong Jellyfish Project (published since 2022). The published literature documenting jellyfish records captured using traditional methods for monitoring jellyfish in Hong Kong had recorded 80 species, while contemporary citizen science observations added 25 more jellyfish species, for a new total of 105 jellyfish species in Hong Kong waters. Given these species records, and the regional context, we suggest marine biodiversity in Hong Kong is likely still underestimated and further monitoring—including via citizen science approaches—is required. As recognition of biodiversity improves, the corresponding data will be better able to inform management, such as outlined in the Hong Kong Biodiversity Strategy and Action Plan. While focused here on the example of jellyfish in Hong Kong, we advocate for similar approaches to improve understanding of diverse taxa in other regions which would facilitate the development of more broadly effective and holistic management approaches.

Introduction

Management to protect and enhance biodiversity requires an understanding of the species present (Wilson 2000) and their roles in ecosystem functioning (Brodie et al. 2018), along with if and how these characteristics are changing over time. Effective biodiversity monitoring will, therefore, be able to inform management decision-making about impending or long-term problems, as well as how to make management more effective (Lindenmayer et al. 2011, McQuatters-Gollop et al. 2015). Despite this importance, the biodiversity of some groups and regions remains under-reported in the existing academic literature. This absence of data can result from a range of factors including, e.g. a lack of time to conduct periodic, detailed surveying, paucity of funding, and a limited number of scientists with taxonomic expertise (Kallimanis et al. 2012, McQuatters-Gollop et al. 2017). Moreover, it can be difficult to access and monitor marine environments using traditional approaches, so species level information is often fragmented, and many marine models focus on species with data (e.g. commercially important fish species) to the detriment of understanding other less well-documented species (Reiss et al. 2011). Promisingly, however, many of these limitations to traditional approaches can be overcome where monitoring projects incorporate emerging approaches such as inclusion of citizen scientists and their observations (Hyder et al. 2015). Therefore, where biodiversity estimates incorporate both historical records made using established methods, as well as those recently reported by citizen scientists (Gueroun et al. 2022), we move closer to having a complete record to inform decision-making.

Citizen science data are being included in an increasing number of scientific publications across a range of disciplines and taxa, indicating growing acceptance by the broader scientific community of this monitoring approach that can inform management (Follett and Strezov 2015). It is important to note, however, that there is a bias of citizen science projects being completed in North America and Europe, and using the English language (Chandler et al. 2016). This focus can result in limitation of data sharing as a consequence of language and cultural differences (Amano et al. 2016). Within the context of these projects, citizen scientists themselves can exhibit taxonomic biases towards birds or large, charismatic species, as well as biases in temporal and geographic coverage (McKinley et al. 2017). Consequently, citizen science projects benefit from project design (Callaghan et al. 2023), volunteer training, and data authentication practices (McKinley et al. 2017). As these projects expand and address their biases; however, they can provide an important complement to historical monitoring projects.

Synthesising historical records and contemporary records obtained with citizen science could facilitate improved understanding of biodiversity and inform subsequent management. Notably, citizen science techniques in combination with historical datasets have been used to study jellyfishes (Gravili et al. 2015, Gueroun et al. 2022) and sharks (Giovos et al. 2019) in the Mediterranean Sea, reef fish assemblages in the Florida Keys, USA (Greenberg et al. 2024), and birds in CO, USA (Walker et al. 2024). The wide diversity of taxa and regions to which combining historical and citizen science records can be applied demonstrates the utility of this approach to inform biodiversity monitoring. Such monitoring has benefit to a range of management programmes. For example, data from citizen science projects is contributing towards the monitoring of indicators for the United Nations Sustainable Development Goals (Fraisl et al. 2020), with the United Nations declaring 2021–2030 to be the Ocean Decade and encouraging the use of citizen science to build society’s relationship with the ocean (UN 2021).

One taxonomic group whose diversity, abundance, and distribution have the potential to be impacted by the consequences of human activities, including overfishing (Boero 2013), nutrient enrichment, and ocean warming (Lee et al. 2023b)—and whose monitoring and management is important—is jellyfish (Lucas et al. 2014). Jellyfish are frequently considered in relation to their negative impacts on humans through stings (Mulyadi and Sianturi 2021) and economic impacts on fisheries (Lee et al. 2023a). However, they are increasingly also understood as important to marine ecosystems and the services they provide, whether as a predator influencing food webs (Suchman et al. 2008) or as prey for economically important fish (Pauly et al. 2008), warranting their inclusion in ecosystem models (Lamb et al. 2019). Additionally, jellyfish have a long history of consumption by humans, particularly in Asia (Hsieh et al. 2001), where jellyfish fisheries are a multimillion dollar (US$) business (Duarte et al. 2022). The ecosystem role of jellyfish may currently be undergoing alteration as there are suggestions that jellyfish populations are increasing globally as a consequence of human activities (Gibbons and Richardson 2013, Boero et al. 2016), although there should be caution taken when attributing the change in populations solely to anthropogenic drivers (Pitt et al. 2018). The relative lack of historical data compared to other taxonomic groups and limited knowledge of jellyfish populations globally inhibits understanding of how jellyfish populations are changing (Brotz et al. 2012). Therefore, given the lack of basic information about jellyfishes, a requirement exists for increased understanding of their occurrence and distribution globally (Brodeur et al. 2016). Where such knowledge is developed, it can be used to inform relevant management strategies specific to the diverse regions where jellyfish are found (Dobson et al. 2024).

There is a need to fill in the geographical gaps of global biodiversity monitoring, especially in biodiversity-rich regions outside of Europe and North America (Schmeller et al. 2017). In addressing these gaps for jellyfish specifically, the incorporation of citizen science approaches will likely be advantageous as they have been effectively used to monitor jellyfish at broad temporal and geographical scales (Marambio et al. 2021), supplementing traditional marine monitoring where sufficient attention is paid to citizen science data quality (Hyder et al. 2015). Notably, there are a number of regions that are potentially home to large undocumented jellyfish biodiversity, such as Indonesia (Fitriani et al. 2020), Malaysia (Syazwan et al. 2020), and Hong Kong (Terenzini et al. 2023a), where citizen science approaches could be particularly useful.

Hong Kong is associated with high tropical and subtropical marine biodiversity (Liu 2013), yet the true biodiversity of this region is still likely not yet fully documented. Even with relatively limited exploration of Hong Kong’s biodiversity, ∼26% of the total number of marine species in China are recorded in Hong Kong despite the region representing just 0.03% of China’s marine area (Ng et al. 2017). In this region, some taxonomic groups remain particularly poorly studied, including crabs (Liang et al. 2023) and cephalopods (Xu et al. 2022). The historical reports of jellyfishes in Hong Kong are largely from research in the 1980s and 1990s (e.g. Chen 1982, Chan 1995), though some earlier records exist (e.g. Mayer 1910 and Kramp 1961). It is worth noting that there have been more recent publications of jellyfish species reports based on citizen science methods (Terenzini and Falkenberg 2022, Terenzini et al. 2023a, 2023c), and these records are detailed in public databases (database detailed in Terenzini et al. 2024). It is likely, therefore, that the reported biodiversity of jellyfish in Hong Kong represents an underestimation. Moreover, the records that do exist for Hong Kong may not be accurate given current understanding, with some jellyfishes reported in the 1980s and 1990s likely representing outdated nomenclature and taxonomy.

Where understanding of plankton biodiversity is developed, including the contribution made by jellyfish, it can be used to inform management approaches (McQuatters-Gollop et al. 2015, 2017, 2019a). Such work is particularly timely for Hong Kong given the current development of the next iteration of the Hong Kong Biodiversity Strategy and Action Plan (BSAP) which shapes its biodiversity management and is set to be released in 2025. China ratified the United Nations Convention on Biological Diversity (CBD) in early 1993 and applied the obligations of the CBD to Hong Kong in 2011 (Government of Hong Kong Advisory Council on the Environment 2023). Hong Kong, as a Special Administrative Region of the People’s Republic of China, then implemented the region-level BSAP in 2016 to increase biodiversity conservation efforts and support sustainable development to contribute to China’s national plan (Government of Hong Kong Environment Bureau 2016). The next iteration of the Hong Kong BSAP is to be based on the Kunming-Montreal Global Biodiversity Framework (KMGBF) as stated in the Chief Executive’s Policy address in October 2023 (The Government of Hong Kong SAR 2023). The BSAP will, therefore, likely focus on enhancing biodiversity conservation, building capacities, partnering with neighbouring cities, and integrating biodiversity conservation or sustainable use across all parts of society (Government of Hong Kong Advisory Council on the Environment 2023). Consequently, an improved recognition of biodiversity, including that of jellyfish (Xu et al. 2014), will be important in the development of the Hong Kong BSAP, as well as other management approaches.

Information regarding biodiversity needs to be presented clearly and simply to enable effective incorporation by policymakers and managers (McQuatters-Gollop et al. 2019a). Currently, the disparate nature of records of Hong Kong’s jellyfish diversity complicates understanding and could drive underestimation of diversity. The aim of this paper is to synthesize widely dispersed historical records gathered by traditional methods with more contemporary observations obtained using citizen science methods. Using the aggregated biodiversity information from these two disparate sources, we present a framework for how additional monitoring data could be collected and used to inform the development of jellyfish management approaches.

Materials and methods

The current study aggregates widely dispersed historical records of jellyfishes in Hong Kong by traditional methods with contemporary citizen science-derived records from the Hong Kong Jellyfish Project (HKJP). For the purposes of this study, ‘jellyfish’ are the medusae of scyphomedusae, hydromedusae, cubomedusae, siphonophores, and planktonic ctenophores, following the definition in Brotz et al. (2012).

Literature synthesis

Published records of Hong Kong’s jellyfishes were identified through a review of the English language literature carried out in 2024, using Google Scholar with the search terms: ‘Hong Kong’ combined with either ‘jellyfish,’ ‘gelatinous plankton,’ ‘scyphozoan,’ ‘ctenophora,’ ‘hydrozoan,’ or ‘siphonophore.’ Results returned in the first 200 entries from Google Scholar for each search combination (or all search results returned if there were <200) were examined for observations of jellyfish combined with explicit mention of Hong Kong as the study location in the Title, Abstract, or Methods. Literature results that mentioned more ambiguous locations in these sections, such as the ‘northern South China Sea,’ were read in greater detail to clarify the study location. Papers were subsequently included if they explicitly referenced jellyfish species observed in Hong Kong waters. Literature on jellyfish species that were studied in a laboratory or as a food product were not included. Only English language literature was reviewed due to the language limitations of the authors of this study.

These results were augmented with records from other sources of records of which the authors were aware. Specifically, we conducted a systematic review of the context sources of jellyfish records on the Hong Kong Register of Marine Species (HKRMS), a node on the World Register of Marine Species (https://www.marinespecies.org/). Jellyfish records were also obtained from seminal jellyfish literature, such as Mayer (1910) and Kramp (1961), that were known to the authors. Species records from these two literature sources were included if there was an explicit mention of the species being found in Hong Kong waters. For example, Mayer (1910) notes Chrysaora chinensis as ‘Found near Hongkong [sic], China, in October,’ so C. chinensis was included in the literature review results. For the identified records (Table 1), we then extracted the number of species and taxonomic composition of jellyfish to as fine resolution as possible.

To supplement the literature searches and examination of previously-identified information sources, we also contacted local Hong Kong experts and conducted a web search to identify records that may not have been included in the academic literature. Specifically, the Agriculture Fisheries and Conservation Department (AFCD) of the Government of Hong Kong SAR was contacted for jellyfish information. Feedback received was that the AFCD does not research jellyfish and relies upon the HKRMS and universities for knowledge of marine species. The World Wild Fund’s Hoi Ha Marine Life Centre was also contacted for jellyfish information but did not provide any additional records. Researchers at the Swire Institute of Marine Science and the Hong Kong Biodiversity Museum at the University of Hong Kong, the Simon F.S. Li Marine Science Laboratory at The Chinese University of Hong Kong, and the Department of Ocean Science at The Hong Kong University of Science and Technology were contacted for further sources of information about Hong Kong’s jellyfish but were not able to provide any additional sources. In addition, generalized searches using the Google search engine for jellyfish in Hong Kong identified a mention of a freshwater jellyfish in Hong Kong in 1940 from a Hong Kong Naturalist journal and a jellyfish stranding in 2005 from The University of Hong Kong’s biodiversity newsletter, neither of which meet our inclusion criteria. Consequently, no contacts to these researchers or additional searches of the literature provided records beyond those obtained through our original academic literature search or consideration of the HKRMS (as such, they are not included in Table 1).

Citizen science records

Citizen science records were obtained through the HKJP (www.hkjellyfish.com), a citizen science project studying the presence and distribution of jellyfish in Hong Kong. The HKJP was launched in early 2021 to encourage anyone in Hong Kong (‘citizen scientists’) who opportunistically encounter jellyfish during water activities (e.g. kayaking, diving) or their daily activities (e.g. taking a ferry, walking on a beach) to take photographs or videos of jellyfish and record simple information such as time, date, and location. This information is submitted through the bilingual (English and Traditional Chinese) website (www.hkjellyfish.com) using a simple online form or through a collection project on the citizen science biodiversity application iNaturalist. Records made with citizen science methods are hereafter referred to as ‘HKJP.’ Outreach to the public was conducted through a bilingual (English and Traditional Chinese) poster, website, and iNaturalist project, as well as English language public presentations, social media posts, and traditional media articles, and through academic publications.

Recorded between 2021 and 2023, 1020 usable citizen science observations from over 400 observers made under the HKJP are publicly available and discoverable in the Global Biodiversity Information Facility (GBIF, DOI: 10.15468/s4qwyk; database described in Terenzini et al. 2024). In compiling the database, the observations were identified by an HKJP researcher to the lowest taxonomic level (genus or species) with reference to the literature, primarily Mayer (1910), Kramp (1961), Jarms and Morandini (2019), Schuchert (2024), and taxonomic experts. This identification was largely done using photographs, although some sightings were verified through in-field observations, beach surveys, and specimen collections (Terenzini et al. 2023a, 2024). In this verification process, observations of non-medusa taxa, those taken of organisms in captivity, or those of poor quality which prevented identification were excluded.

Identification of nomenclatural and taxonomic inconsistencies of previously published records

In combining observations from the historical literature and contemporary citizen science records, we identified some issues around nomenclatural and taxonomic reporting from earlier studies. These concerns may mean previously published species records, e.g. of Stomolophus meleagris, Mastigias papua, and Aurlia aurita in Morton and Morton (1983), need to be revised given updated, contemporary understanding (Omori and Kitamura 2004, Souza and Dawson 2018, Lawley et al. 2021). We indicate the key apparent inconsistencies and our interpretation of what the species records represent in the Supplementary Material.

Results

Jellyfish diversity in Hong Kong

A synthesis of the historical academic literature and contemporary citizen science records from the HKJP indicates the documented presence of 105 jellyfish species in Hong Kong; 19 scyphozoans, 6 ctenophores, 3 cubozoans, and 77 species of hydrozoans, (Fig. 1), with this number increasing over time (Fig. 2). Of the scyphozoans, 12 species are in the order Rhizostomeae, 6 are in the order Semaeostomeae, and 1 is in the order Coronatae. For the ctenophores, 3 species are in the order Lobata, 2 are in the order Beroida, 1 is in the order Clydippida. All of the cubozoans are in the order Carybdeida. For the hydrozoans, 27 species are in the order Leptothecata, 21 species are in the order Anthoathecata, 17 are in the order Siphonophorae, 6 are in the order Narcomedusae, 3 are in the order Trachymedusae, and 3 are in the order Limnomedusae (full systematics in Supplementary Material).

Of the jellyfishes documented here, 80 jellyfish species records were gathered with traditional monitoring methods and recorded in the historical literature (the majority of which were published before 2000); 9 scyphozoans, 3 ctenophores, 1 cubozoan, and 67 hydrozoans. Of the scyphozoans, 5 species are in the order Rhizostomeae and 4 species are in the order Semaeostomeae. For the ctenophores, there is one species in each of the orders Lobata, Beroida, and Clydippida. There is one cubozoan species in the order Carybdeida. For the hydrozoans, 26 species are in the order Leptothecata, 18 are in the order Anthoathecata, 13 are in the order Siphonophorae, 6 are in the order Narcomedusae, 2 are in the order Trachymedusae, and 2 are in the order Limnomedusae. Of these 80 species, 61 were found only in the historical literature (i.e. not also identified with citizen science methods); 2 scyphozoans in the order Rhizostomeae and 59 hydrozoans of which one species is in the order Limnomedusae, 16 in Anthoathecata, 12 in Siphonophorae, 5 in Narcomedusae, 1 in Trachymedusae, and 23 in Leptothecata.

Contemporary citizen science efforts through the HKJP recorded a total of 45 jellyfish species (17 scyphozoans, 6 ctenophores, 3 cubozoans, and 19 hydrozoans) (Table 2). Citizen science contributed 25 species that were recorded only using these methods and therefore represent new species records (i.e. the first occurrence in the published literature of the species in Hong Kong) (Terenzini and Falkenberg 2022, Terenzini et al. 2023a, 2023c, 2024). The species included 10 scyphozoans, 3 ctenophores, 2 cubozoans, and 10 hydrozoans.

While there were some species recorded only in either historical or citizen science methods, many overlapped. That is, 20 species of jellyfish were found in both the historical literature and by citizen science methods; 7 scyphozoans, 3 ctenophores, 1 cubozoan, and 9 hydrozoans. Of those found using both methods, 3 of the scyphozoans are in the order Rhizostomeae and 4 of the scyphozoans are in the order Semaeostomeae. Each of the three ctenophores is in a difference order; 1 in Lobata, 1 in Beroida, and 1 in Cydippida. The 1 cubozoan is in the order Carybdeida. For the hydrozoans, 1 species is in the order Limnomedusae, 2 are in Anthoathecata, 1 is in Siphonophorae, 1 is in Narcomedusae, 1 is in Trachymedusae, and 3 are in Leptothecata. Details of the literature sources for each species identified from the historical literature and identified with citizen science methods can be found in the Supplementary Material.

Discussion

Marine biodiversity observations are critical to inform management and address issues stemming from changing ecosystems (Miloslavich et al. 2018). Although the importance of a comprehensive dataset is recognized, in many instances records remain disparate. By bringing these records together, we can better inform management. Here, we synthesize historical and contemporary citizen science records of jellyfishes in Hong Kong to reveal a greater diversity than previously recognized. That is, there are 80 jellyfish species recorded in historical literature, with contemporary citizen science methods adding 25 new species, for a total of 105 species (an increase of 31%). Overall, however, our knowledge of the biodiversity of jellyfish in Hong Kong is still likely underdeveloped. As we continue to develop longer-term records of jellyfish, this information will be useful for predicting changes in their occurrences and, consequently, managing their impacts. Our results show that the jellyfish species recorded by contemporary citizen science continue to increase the total number of species records for Hong Kong (Fig. 2), and therefore ongoing research effort into monitoring jellyfish is necessary for more complete understanding and effective management.

Citizen science methods represent a complement to traditional surveying, with both approaches having inherent strengths and biases that influence the species documented. These differences mean that, when used in combination, such complementary approaches allow for detection of a greater diversity of jellyfish. That is, here, the jellyfishes recorded using only citizen science bias towards the larger scyphozoans when compared to the records from only the historical literature. Such patterns typically result as citizen scientists are more likely to record large scyphozoans as their observations can bias towards large, visible species (Thiel et al. 2014). In contrast, the two studies published in the historical literature with the largest species counts (Chen 1982, Chan 1995), used vertical haul nets which favour the capture of smaller hydrozoans (Hosia et al. 2017). Thus, we advocate that these complementary approaches be used together, with recognition of their strengths and biases, to gain a comprehensive understanding of the species present at any given time and how this is changing. We caution, however, that as the recording biases of citizen scientists will be different from the biases in biodiversity recording in the past (Isaac and Pocock 2015), attention will have to be paid when combining or updating past records.

While already contributing new species records, there is the potential for citizen science methods to be even more effective in the future if current limitations are overcome. One notable limitation of many current citizen science observations is their ad-hoc nature. Coordinating citizen science projects across government agencies and non-governmental institutions increases the utility of biodiversity observations for policy making (McKinley et al. 2017). Therefore, to enhance jellyfish monitoring in Hong Kong, an inter-agency group could be formed. Relevant agencies that could be incorporated include the AFCD, the Tourism Board, the Leisure and Cultural Services Department which manages Hong Kong’s beaches, and the Hong Kong Hospital Authority (Fig. 3). Academic institutions such as the University of Hong Kong’s Swire Institute of Marine Science or The Chinese University of Hong Kong’s Simon F.S. Li Marine Science Laboratory could be enlisted to conduct jellyfish research into their impacts on fisheries and marine ecosystems in general. Public engagement and data collection could continue through efforts of citizen science projects like the HKJP. Also incorporated into the network could be frontline workers such as lifeguards on beaches, fishers on the water, or recreational users as they could provide information to government departments, NGOs, healthcare workers, and researchers. In turn, these groups could provide more detailed information to workers and water recreation users about conditions that affect them, an effective policy to mitigate human health impacts (Nunes et al. 2015). The research done by this proposed inter-agency group would provide a baseline of species presence from which further jellyfish research could be conducted into life history traits, seasonality, and distribution. This information could then be fed into the existing Biodiversity Information Hub, as mandated by the Hong Kong BSAP, providing a richer picture of Hong Kong’s biodiversity. While we have used Hong Kong and its stakeholder groups to illustrate the specific linkages that are possible, in other regions, similar coordination and collaborations would also be advantageous.

Knowledge about which species are present in marine environments and their roles in ecosystem functioning is necessary for effective management and conservation of marine biodiversity (McQuatters-Gollop et al. 2017). In Hong Kong specifically, biodiversity management approaches are currently being developed for the Hong Kong BSAP, so there is a need to understand the diversity of jellyfish, and how they can impact sustainable development (and vice versa), a key goal of the KMGBF. Understanding jellyfish populations, how they are changing, and ultimately the socio-economic effects of such alterations, would provide a basis for adaptive management strategies to prevent or mitigate their impacts (Aubert et al. 2018). Such management is, however, currently compromised by a lack of studies into jellyfish populations that has led to a gap in knowledge of how jellyfish populations are changing over time across different geographic scales and variable local and regional environments (Dawson et al. 2015). Subsequently, losses to ecosystem services such as fisheries or impact on public health through medical costs or lost productivity (Gershwin et al. 2010) go unexamined and are not addressed by preventative or mitigating action. Hong Kong risks falling into the ‘measurement trap,’ in which a lack of data can suppress the political will to engage resources (human, technological, etc.) to combat an issue threatening sustainability (Pirkle and Yanagihara 2019). Consequently, where jellyfish are better monitored, there may be a move towards having enough data to engage the needed resources to address potential issues.

Monitoring is resource-intensive and resources are limited even where inter-agency groups such as those proposed above are formed, so there is a need to have cost-effective methods of monitoring jellyfish (Aubert et al. 2018). Citizen science has been shown to be effective for monitoring jellyfish at broad temporal and geographical scales (Marambio et al. 2021), supplementing traditional marine monitoring where sufficient attention is paid to citizen science data quality (Hyder et al. 2015). Combining traditional monitoring with citizen science can result in longer-term data sets, enabling jellyfish forecasting tools to be developed (Marambio et al. 2021). There are, however, currently limitations to the effectiveness of these tools, mostly through lack of data on the distribution and life histories of jellyfish species (Record et al. 2018). Where effective, forecasting can be used to inform management actions, such as those taken by beach managers to better allocate lifeguard and medical resources during high jellyfish activity.

While citizen science techniques have proved valuable in Hong Kong (Terenzini et al. 2023a), and are a facet of the proposed monitoring scheme (Fig. 3), there are additional complementary approaches that can be implemented in future studies to better understand jellyfish biodiversity. For example, there are a number of techniques used in nearby countries in Southeast Asia to discover more about their gelatinous biodiversity that could also be implemented in Hong Kong. Such approaches include, e.g. examining the diversity and distribution of jellyfish polyps in Thailand (Punnarak et al. 2023), using DNA analysis to identify species in Malaysia (Rizman-Idid et al. 2016), and leveraging opportunistic sampling in Singapore (Yap and Ong 2012). Additionally, jellyfish monitoring can also use data collected from fisheries sources (Aubert et al. 2018). Together, these different approaches will be useful in understanding jellyfish community biodiversity, and, eventually, informing management.

Conclusion

In recognition of the increased diversity of jellyfishes recorded in this synthesis, we propose more attention needs to be paid to the impact that jellyfish have upon human activities and ecosystems and highlight the importance of their monitoring and management. Here, we aggregate historical records with contemporary citizen science records to increase the number of species of jellyfish recognized in Hong Kong and propose updates in taxonomy. It is likely, however, that our understanding of the true biodiversity of Hong Kong’s jellyfish is still incomplete, and further research into the presence and distribution of jellyfish using citizen science as a complement to specimen collection and DNA analysis will continue to increase our understanding of jellyfish biodiversity. By developing information collection and sharing networks throughout relevant government departments and other stakeholders, the information gap can be further addressed. While we outline the approaches that could be used for jellyfish in Hong Kong, similar methods would be beneficial where there are disparate historical and contemporary citizen science records of other species. Once gaps in our understanding of biodiversity are addressed, effective monitoring and management policies can be developed.

Acknowledgements

The authors would like to thank all of the citizen scientists who contributed their sightings to the HKJP. We would like to thank Alejandro Damian Serrano for his identification of siphonophores.

Author contributions

John Terenzini (Conceptualization [equal], Data curation [lead], Formal analysis [lead], Investigation [lead], Methodology [lead], Visualization [equal], Writing – original draft [lead]), Abigail McQuatters-Gollop (Supervision [equal], Writing – review & editing [equal]), and Laura J. Falkenberg (Conceptualization [equal], Supervision [equal], Visualization [equal], Writing – review & editing [equal])

Conflict of interest

None declared.

Funding

The authors did not receive support from any organization for the submitted work.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper, its supplementary material files, and on the Global Biodiversity Information Facility (GBIF). Terenzini J, Fan Y, Liu M J, Falkenberg L J (2024). Jellyfish in Hong Kong: a citizen science dataset. Version 1.3. GigaScience Press. Occurrence dataset https://doi.org/10.15468/s4qwyk accessed via GBIF.org on 2024-05-24.

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