An overview of non-native marine species in Hong Kong


Being one of the largest marine ports world-wide, our knowledge about marine non-native speceis in Hong Kong is scarce. In order to manage non-native species and to protect local marine communities, it is crucial to identify these species and to monitor their establishment and distribution. However, very little documentation exists. This study aims to assess the current distribution, abundance and population status of the previously reported non-native species in Hong Kong.


Non-native species are species that exist outside their natural range distribution and could potentially threaten biological diversity. They have been introduced to new regions through human mediated means of dispersal such as hull fouling and ballast water of shipping vessels, aquaculture, aquarium trade, etc. The rapid increase of new introductions in the last decades through global transport and commerce represent a major threat to the conservation of native marine ecosystem.


Non-native species are a major threat to the conservation of marine ecosystems with a constant increase of biological invasions through vectors such as ballast water, hull fouling, aquaculture, and aquarium trade. Non-native species can cause negative impacts on biodiversity, economy and human health (Van Dolah 2000). These non-native species can cause an impact on local biodiversity through predation, competition, parasites, habitat modifications and genetic effects. Although, in some cases biodiversity could increase with the introduction of non-native species, negative impacts in biodiversity are more frequently reported. The impact of non-native species is clearly observed when commercial species or commercial activities are affected by them.


In 2014, there were 189 thousands of vessel arrivals, carrying 297 million tonnes of cargos and 26 million passengers.


The major record of marine non-native species in Hong Kong was compiled about 30 years ago, with six marine invertebrate described as non-native (Morton 1987).

These species are the solitary ascidian, Ciona intestinalis (Linnaeus, 1767), native to the North Atlantic and Mediterranean Sea;; the slipper limpet, Crepidula onyx (G.B Sowerby I, 1824), from the Pacific coast of North America; the bryozoan, Bugula californica (Robertson, 1905), from the Pacific coast of North and Central America; the Caribbean bivalve, Mytilopsis sallei (Récluz, 1849), from the Caribbean and Atlantic coast of Central America; the Mediterranean mussel, Mytilus galloprovincialis (Lamarck, 1819), from the Mediterranean Sea; and the isopod, Sphaeroma walkeri (Stebbing 1905), native to the Indian Ocean.

Based on these previous studies, the non-native species in Hong Kong were mainly distributed in fouling communities in semi-enclosed areas with high human disturbances, such as piers in Victoria, Tolo and Tsing Yi Harbors (Huang and Morton 1983, Morton 1987), except for the isopod Sphaeroma walkeri that had a widespread distribution (Mak et al. 1985). Posterior surveys on fouling communities found Crepidula onyx, Ciona intestinalis, and Mytilopsis sallei in other areas in Hong Kong (Huang et al. 1992, Huang et al. 1999), indicating that their distribution has been expanding. However, their current distribution and impact have been largely unknown.


Bugula californica
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Ciona intestinalis
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Crepidula onyx
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Sphaeroma walkeri
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Mytilopsis sallei
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Mytilus galloprovincialis
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Jacques-Yves Cousteau improved the aqua-lung design in the 1940s into today's open circuit scuba technology, allowing divers and researchers to explore the underwater world.



Field surveys were conducted at 31 locations included fouling communities (organism attached to human facilities) on piers and mariculture zones from the estuarine to oceanic zones in Hong Kong. These facilities were sampled because are considered the main entrance for non-native species in new environments. Three depths including intertidal, shallow subtidal (1–3 m), and deep subtidal (3–6 m) were sampled.


Seasonal fluctuations between dry and wet seasons strongly affect seawater characteristics such as temperature and salinity, which can fluctuate between 15 and 31°C, and between 11 and 34 ppt, respectively (EPD 2010). The surveys were done during the summer (2011) and winter (2012) seasons. In order to detect temporal changes in the abundance and recruitment of the sedentary non-native species, three piers were monitored with permanent photo-quadrats and recruitment panels for one year period. The relationship between seawater quality data available for Hong Kong and the abundance of fouling and non-native species was investigated.


Visual observation

Each site was visually explored for at least 15 minutes by SCUBA divers to check for the target non-native species.


All piers were sampled by photo-quadrats (15 x 15 cm) at both intertidal and subtidal depths, whenever possible. Floating facilities, such as open-sea-cage farms in mariculture zones and pontoon facilities, were sampled only at shallow subtidal depth.

Destructive sampling

Destructive quadrats (15 x 15 cm) were randomly taken at intertidal, shallow subtidal, and deep subtidal depths by SCUBA divers. The whole community within each of the destructive quadrats was scraped using a metal scraper and saved in plastic bags.


The results of our project not only detail the current situation of the occurrence of the non- native species in our marine environment, but it provides information on the most abundant and potentially invasive species. The list of these invasive species will be highly useful for us to manage these species in order to protecting and conserving the local marine biodiversity. It will also provide useful information for marine ecological studies.

Field assessment conducted in fouling communities on pier and mariculture facilities revealed that four of the six previously reported non-native species are still present in Hong Kong, including the solitary ascidian, Ciona intestinalis; the slipper limpet, Crepidula onyx; the Caribbean bivalve, Mytilopsis sallei; and the isopod Sphaeroma walkeri. The bryozoan Bugula californica and the mussel Mytilus galloprovincialis were not found and likely failed to establish. During the course of this study, the recently established non-native bivalve Xenostrobus securis was also found. The spatial distribution and abundance of the non-native species were closely related to seawater quality and habitat disturbance. The abundance of S. walkeri increased with low seawater quality. The sedentary non-native species were abundant in disturbed environments in Victoria and Tolo Harbors. Typhoon shelters with low seawater quality (due to estuarine conditions, pollution and/or habitat alteration) were the most invaded.

The field assessment indicated that seawater quality could explain the fouling community assemblages at the sampled piers. A gradient of decreasing seawater quality from the east of Hong Kong and within marine parks (oceanic conditions) to western sites (and some sites in Victoria Harbor) was related with the community assemblage measured. Typhoon shelters host more non-native species (number of species and/or abundance) than semi-enclosed bays. Kwun Tong typhoon shelter, with the lowest seawater quality among the sites of this study, has the most dissimilar fouling community assemblage in comparison to the other sites (Chapter 2) and it was the only site where all the five non-native species (including Xenostrobus securis) were recorded.

The overall distribution and abundance of the reported non-native species remains similar to that in 1980’s, suggesting that they are not highly invasive in Hong Kong. However, the presence and fast spread of the recently introduced bivalve Xenostrobus securis, which is highly invasive in other regions, could represent a threat for the local biodiversity.

A map of the distribution of the marine non-native species recorded in the literature (black symbols) and in the present study (white symbols) in Hong Kong. The recent introduced bivalve Xenostrobus securis is included.(Astudillo et al. 2014)


Astudillo, J.C., Wong, J.C.Y, Dumont, C.P., Bonebrake, T.C., Leung, K.M.Y. (2014) Status of six non-native marine species in the coastal environment of Hong Kong, 30 years after their first record. BioInvasions Records. 3(3):123-37. (PDF)


About 340 species have been reported in fouling communities for Hong Kong, however, the origin of those species is still unclear.


Juan-Carlos Astudillos

Juan did his bachelor degree in Marine Sciences and he graduated with a professional degree in Marine Biology from the University Católica del Norte, Chile. He has been part of the Laboratory of Biology, Ecology and Diversity of Marine Invertebrates (BEDIM), where he was involved in marine ecology research, related to marine debris, dispersion of marine organisms, fouling communities and non-native species. In his PhD research, in the Swire Institute of Marine Sciences (SWIMS) at The University of Hong Kong, he worked on the distribution and abundance of non-native marine invertebrates and fouling communities. In his PhD study he also explored the role of the antagonistic subtropical conditions and human disturbances (such as pollution) on the abundance of the non-native species and the biotic resistance of local communities to avoid invasion.

Juan is currently working on his first post-doctoral research at SWIMS. This research project aims to determine the biodiversity of Tolo Harbor in Hong Kong and develop a sampling protocol for Hong Kong marine communities in order to be used as criteria for future environmental impact assessments in Hong Kong.

Jane Wong

Research assistant. Jane is helping in undertaking underwater surveys and species identifications in the lab. She started diving after her undergrad and this was her first project as a research diver. Jane is now a postgraduate student at SWIMS, exploring the unique relationship on coral-algal symbiosis, and its implication on reef resilience under the threats from rapid population growth and global climate change.

Clément Dumont

Principal Investigator. Dr. Dumont has been conducting research on benthic communities for the last 10 years in different countries and more importantly obtained funding between 2007 and 2008 to conduct research on the invasion processes of marine communities. He is the mastermind of SWIMS benthic lab.

Kenneth Mei Yee Leung

Co-Investigator. Prof. Leung is a Professor of School of Biological Sciences and a Resident Scientist at SWIMS, HKU. He is an expert in aquatic toxicology and ecological risk assessment with a research focus on studying the effect of anthropogenic activities on local marine organisms and benthic communities. In 2006/2007, he was invited by Food and Agriculture Organisation (FAO) of the United Nations to develop an ecological risk assessment protocol as a preventive tool for minimizing biological invasion through aquaculture and mariculture activities.


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last update: Feb 2016