To date, the total number of invasive alien species (IAS) has reached an estimated record of 17,000 species worldwide, causing billions of dollars in losses each year [1]. For example, in South-East Asia alone, IAS are estimated to cause 33.5 billion USD worth of damages. IAS can cause financial loss through several different ways, but one factor is through the loss of local biodiversity, largely through direct or indirect competition. This loss represents a serious problem internationally, negatively affecting not only biodiversity, but also human and animal health, as well as agricultural and/or fisheries production. Although there are many policies and regulations focusing on some of the worst IAS, the management practices and implementation must still be improved. Additionally, while there is ample evidence for the direct detrimental and often irreversible effects that IAS have on terrestrial, freshwater, and marine ecosystems, there lacks sufficient knowledge regarding the impact IAS have on ecosystem services. This lack of knowledge hinders the conservation and sustainable use of biodiversity.
Previous studies found that IAS and climate change constitute two global threats to biodiversity that may act synergistically [2, 3] but also may interact in other ways [4]. Impacts associated with climate change, such as increased carbon dioxide (CO2) concentration, heavy precipitation [5], or elevated temperatures [6] may facilitate biological invasion. This will likely lead to an increase in frequency and abundance of IAS across the globe, necessitating international and national efforts to mitigate issues related to invasive alien species. Some such groups include the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), International Union for Conservation of Nature’s (IUCN), Invasive Species Specialist Group (ISSG), Invasive Species Compendium (ISC), and the National Committee on IAS of Malaysia (as well as national committees in other countries). There also already exist many examples of international policy related to invasive species such as the Aichi Target (Target 9), Convention on Biological Diversity (Nagoya Protocol), United Nations Sustainable Development Goals (SDG)—Goal 15.8 (Life on Land), and various national policies in different countries (e.g. Action Plan for Aquatic Invasive Alien Species in Malaysia) [7]. All these different organizations and policies demonstrate the importance of managing IAS and their impacts.
Management of IAS can be improved in many ways [7,8,9]. First, improving the education and public awareness about IAS would facilitate local prevention. Such education would include research on all aspects of the management, pathways of introduction, ecological impacts, containment technologies, future threats and problems, prevention or control, and mitigation efforts. Second, conducting a risk assessment on all potential IAS before they are introduced would help to set a formal and rigorous response plan, as well as ensuring there is the capacity to contain and eradicate any potential IAS. Finally, strengthening quarantine inspection and enforcement at entry points as well as international borders would help reduce risk of introduction. Such measures could include enforcement legislation, the implementation of safeguards against water-based IAS, establishment of quarantine facilities, and an effective monitoring/implementation action plan. A systematic study could help better understanding on the goal of supporting evidence-informed decision making in conservation and environmental management for various stakeholders in the future [10,11,12,13,14].
One global initiative to improve awareness of IAS was established in 2000 by the IUCN working group of ISSG, which established the “One Hundred of the World’s Worst Invasive Alien Species” list [15]. Here, a species is listed based on two main criteria: (i) the severity of their impact on biological diversity and/or human activities, and (ii) their ability to illustrate important issues surrounding biological invasion [16]. Focusing on species of fish and shellfish, there are nine and four species, respectively, listed in the worldwide Global Invasive Species Database (GISD). These species include the following:
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A.
Green crab, Carcinus maenas
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B.
Walking catfish, Clarias batrachus
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C.
Common Carp, Cyprinus carpio
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D.
Zebra mussel, Dreissena polymorpha
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E.
Chinese mitten crab, Eriocheir sinensis
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F.
Western mosquito fish, Gambusia affinis
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G.
Nile perch, Lates niloticus
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H.
Largemouth bass, Micropterus salmoides
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I.
Mediterranean mussel, Mytilus galloprovincialis
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J.
Rainbow trout, Oncorhynchus mykiss
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K.
Mozambique tilapia, Oreochromis mossambicus
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L.
Marine clam, Potamocorbula amurensis
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M.
Brown trout, Salmo trutta
Stakeholder engagement
Because our systematic map will inform a climate change related program and project undertaken by Universiti Malaysia Terengganu (UMT), we worked with project partners (i.e. researchers, government agencies, and NGOs in Malaysia) to develop our methodological strategies and objectives. The aim of the Malaysian research program is to increase climate resilience for flora and fauna, especially invasive species in freshwater and marine areas impacted by the climate change while supporting community livelihoods, food security, health, and well-being. In our discussions, stakeholders provided topic-relevant input by refining the scope of the map question, suggesting search terms for the search strategy, and suggested relevant studies and sources of grey literature. Stakeholders will also provide comment on other parts of the systematic map as it progresses, for example, the appropriateness of the meta-data extraction.
Objective of the systematic map
The primary objective for our systematic map is to identify, collate and categorise how climate change impacts on some of the worst invasive fish and shellfish in the world. We focus on the 13 species listed above and how different elements of climate change will impact the type of invasiveness (e.g. spread, establishment, etc.) of said species. We aim to demonstrate global trends in the literature and identify areas in research that could be improved.
Primary question
What evidence exists on the impact of climate change on some of the worst invasive fish and shellfish.
Definitions of the questions
For simplicity, we broke our research objective down into a “Population–Exposure–Outcome” structure, where “Population” represents any of the 13 world’s worst fish and shellfish IAS, “Exposure” represents aspects of climate change and “Outcome: represent the type of invasiveness.