Information

Definitions

Non-native species (alien species)
A non-native species is an organism that has established itself outside its original distribution range in an area where it does not naturally occur.

Introduced non-native species
Introduced non-native species form a subcategory within non-native species. An introduced non-native species is an organism that has established itself outside its original distribution range in an area where it does not naturally occur, with the crossing of a (natural) barrier (e.g., an ocean) only being possible with the help of human activities (such as shipping, aquaculture, etc.). The main policy frameworks for monitoring and taking measures regarding (invasive) non-native species primarily focus on this subcategory (e.g., Marine Strategy Framework Directive 2008/56/EC – Descriptor 2; EU Invasive Alien Species Regulation (EU) No 1143/2014; United Nations Convention on the Law of the Sea Article 196.1). Within the present initiative, only introduced non-native marine species are considered, with the emphasis on the 'primary' introduction method. For example, an organism originally found in the Pacific region and introduced to Northern France via shipping (primary), then spreading naturally towards Belgium (secondary), would still be included.

Species that expand their habitat naturally without a human distribution vector, thereby colonising new areas, are not part of this inventory exercise. Changes in the biogeographic distribution of organisms due to climate change are considered part of this latter category within the context of the present initiative.

Watchlist species
A Watchlist species is a non-native marine species introduced to Western Europe that has already been observed near the Belgian border in the Dutch Western Scheldt and Eastern Scheldt, as well as along the French Opal Coast, but has not yet been observed on Belgian territory. Therefore, increased vigilance is warranted for these species, which are considered within the scope of the current inventory.

Invasive species
If a non-native species proves harmful to its new environment or to the local economy, it is considered an invasive species. However, the level of impact justifying the label 'invasive' is not clearly defined, which often leads to debate.

Cryptogenic species
For some species, the origin is not clearly identifiable and/or it is difficult to determine whether they are native to a particular region. This uncertainty may arise in cases of (i) cosmopolitan organisms, (ii) species with a cryptic lifestyle that are thus hard to observe, and (iii) species that were not well-known in the past because the techniques of the time were not sufficiently developed to study the organisms in question.

Primary and secondary introduction pathways
The primary introduction pathway refers to the human activity responsible for the (intentional or unintentional) introduction of a non-native species 'directly' from the source area. Secondary distribution pertains to the subsequent further spread of the organism within the new area

Introduced alien species: impact and overarching policy framework

Introduced alien species are often associated with negative effects on local biodiversity and ecosystem functions. However, not all alien species have a demonstrable impact on other species or habitats in their new environment. For a minority, however, the invasive nature is such that they pose a threat to local biodiversity, the economy, public health, or jeopardize ecosystem services. It is estimated that about 10 to 15% pose a risk to European biodiversity (cf. Regulation (EU) No 1143/2014). These invasive alien species (IAS) are globally considered the second most significant cause of biodiversity loss (after direct habitat destruction) (Kettunen et al. 2008). It is important for policy to prioritise attention on these IAS and implement concrete management measures where urgent and necessary. In this way, management efforts and (limited) resources can be optimally utilised. Additionally, it is important to continue focusing on existing general preventive measures to avoid the harmful effects of IAS.

At the European Union level, Regulation (EU) No. 1143/2014 on the prevention and management of the introduction and spread of invasive alien species was established. This regulation sets out rules to prevent, minimise, and mitigate the adverse impacts on biodiversity from both the intentional and unintentional introduction and spread of introduced IAS within the Union. The so-called ‘Union List’ of priority species is compiled by the European Commission (in consultation with member states) and has been revised three times (in 2017, 2019, and 2022, with a fourth revision ongoing in 2024). Currently, the list includes 88 species. For these species, there is a ban on the intentional import, possession, breeding, transport, trade, and release. However, member states are required to establish a permit system to allow for certain exceptions. Furthermore, member states must develop action plans for the pathways of introduction, set up a surveillance system and official controls to enable early detection and rapid eradication, and determine effective management measures for controlling widely spread introduced IAS. However, the required criteria (Article 4.3a-e) complicate the inclusion of marine IAS in the Union List. For instance, the adverse impacts on biodiversity (and on human health and the economy) are not always straightforward to demonstrate (Article 4.3c). Additionally, the successful eradication of marine introduced IAS in an open system is challenging, and it is often uncertain that coordinated action at the Union level will effectively prevent the introduction, establishment, or spread of a species, or mitigate the adverse impacts associated with the presence of an invasive species (Articles 4.3d-e). Due to the limited availability of practical and cost-effective methods to eradicate or control alien species in the marine environment without harming the local ecosystem, preventing the introduction of alien species is currently regarded as the only feasible management option for the marine environment. As a result, only two marine introduced IAS are currently on the list: Rugulopteryx okamurae (algae) and Plotosus lineatus (Striped eel catfish). Neither of these species is present in Belgian territory. However, two species on the Union List do occur in the study area (primarily in brackish environments) and are therefore included in this publication: Pseudorasbora parva (Stone moroko) and Eriocheir sinensis (Chinese mitten crab).

Marine introduced alien species are specifically addressed in Directive 2008/56/EC, establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive - MSFD). The MSFD defines Good Environmental Status (GES) through eleven descriptors, with ‘descriptor 2’ stating that species introduced by human activities should be at a level that does not alter the ecosystem. The following national MSFD measures specifically contribute to achieving the GES for descriptor 2, although this GES was not yet achieved in the latest evaluation (2022) (Belgian State, 2022):

Since 2016 (first MSFD cycle):
- Environmental impact assessment and appropriate assessment (with attention to fouling);
- Permit condition (e.g., wind farms): maximum restriction on the introduction of hard substrates;
- Permit condition: monitoring during construction and operation – fouling macrobenthos;
- Prohibition on the intentional (unless permitted) and unintentional introduction of alien organisms through ballast water, regulated by the Marine Environment Act of December 11, 2022;
- Anti-fouling measures (2011 IMO guidelines for the control of biofouling on ships).

Since 2022 (second MSFD cycle):
- Development of a classification system for alien species (categorised by threat level);
- Enforcement of IMO biofouling guidelines: cleaning of ship hulls before entering Belgian waters;
- Stricter adherence to and implementation of the Ballast Water Convention, with increased attention to ballast water exchange monitoring.

Monitoring within the framework of the MSFD focuses on detecting the arrival of new introduced alien species. Alongside information obtained from systematic monitoring, observations of new introduced alien species from projects or ad-hoc sightings are also recorded. The systematic monitoring, as outlined in the updated monitoring program for Belgian marine waters, includes the following activities (Belgian State, 2020):

- ‘ANSBE-P6-Benthos-1-soft-sediment’: Monitoring of soft-sediment benthos as part of the environmental impact assessment for dredge disposal sites and sand extraction areas in the Belgian part of the North Sea (Conducted by the Research Institute for Agriculture, Fisheries and Food - ILVO);
- ‘ANSBE-P7-Benthos-2-epi-fish’: Monitoring of epibenthos and demersal fish as part of the environmental impact assessment for dredge disposal sites and sand extraction areas in the Belgian part of the North Sea (Conducted by ILVO);
- ‘ANSBE-P8-Benthos-3-windfarm’: Monitoring of macrobenthos and sediment in offshore wind farms (Conducted by Ghent University - UGent);
- ‘ANSBE-P9-Benthos-4-hard-substrate’: Monitoring of alien species on hard substrates (such as groynes, buoys, wind turbines, monitoring stations, and other offshore artificial structures like artificial islands and reefs as they become available) (Conducted by the Institute of Natural Sciences - RBINS).

Since 2014 and 2017, Flanders Marine Institute (VLIZ) has generated long-term data series for zooplankton and phytoplankton in Belgian coastal waters and sandbank systems as part of LifeWatch Belgium (Belgian State, 2020). These monitoring programs, ‘ANSBE-P13-Plankton-2-phyto’ and ‘ANSBE-P14-Plankton-3-zoo,’ are integral parts of the updated monitoring program for Belgian marine waters, enhancing insights for descriptor 1 ‘Biodiversity’—specifically for the three indicators PH1, PH2, and PH3 (McQuatters-Gollop et al., 2022) assessing pelagic habitats. These time series include publicly accessible biodiversity data on zooplankton and phytoplankton from the pelagic zone (also accessible through LifeWatch Species Information Backbone (LW-SIBb), the World Register for Marine Species (WoRMS), and the World Register for Introduced Marine Species (WRiMS)), collected via high-throughput imaging sensors (ZooScan, FlowCam). The phytoplankton data (FlowCam data and genetic LifeWatch data) may also offer insights relevant to descriptor 2, though this potential pathway has not yet been actively explored. A physical sample library for zooplankton is also maintained, allowing for retrospective analyses to track the presence of potential alien species and invasive taxa over time. In addition, analysis tools for IAS are being developed within the LifeWatch Alien Species Virtual Research Environment (Alien Species VRE). Applications are also being created through the Digital Twin of the Ocean (DTO)-BioFlow project (coordinated by VLIZ with a focus on integrating biodiversity data into the DTO) and the MARCO-BOLO project (Marine Coastal Biodiversity Long-term Observations, aimed at enhancing biodiversity monitoring to support policy).

In Belgium, the Harmonia+ protocol was developed in 2014 under the ‘Alien Alert project’ (D'hondt et al., 2015). This tool provides a first-line risk assessment of potentially IAS and is applicable internationally. It stems from a revision of the former ISEIA protocol (Invasive Species Environmental Impact Assessment) (Branquart, 2009; Vanderhoeven et.al., 2015), now encompassing all stages of invasion and a variety of impact types.

Scope and spatial delimitation

Globally, numerous plant and animal species have successfully colonised new habitats, including marine environments. The issue of introduced alien species is not new; historical records note early introductions. However, for some species, it is challenging to determine whether they are truly native, given our limited historical knowledge of certain marine organisms (see also Definitions – Cryptogenic Species).

This website provides a concise overview of knowledge regarding marine and coastal introduced alien species in the Belgian part of the North Sea and adjacent estuaries (see Figure 1). Specifically, this scope includes the Belgian part of the North Sea, beaches, port areas, estuaries, mudflats, salt marshes, and brackish inland waters. For inland waters, the requirement is that the habitat must have some seawater influence (mesohaline or polyhaline).

This website and the related book reflect the current state as of October 2024. Compared to the 2020 edition (Verleye et al. 2020, 79 species), 32 new species were identified, with six being ‘Watchlist’ species (see also Definitions – Watchlist species). Most species fact sheets from 2020 remain unchanged, except for a few species where significant new insights or substantial distribution changes have occurred, such as Ammothea hilgendorfi, Bugulina stolonifera, the Striped sea anemone Diadumene lineata, Diplosoma listerianum, Fenestrulina delicia, the Australian tubeworm Ficopomatus enigmaticus, and Incisocalliope aestuarius.

Efforts are made to keep the species list up to date. This is challenging because marine introduced alien species are often discovered accidentally, and certain groups, such as plankton, are less well-known. Furthermore, these species can sometimes be difficult to distinguish from native ones, occasionally leading to misidentification of an introduced alien species.

This website provides information on the lifecycle and ecology of each species, introduction pathways and spread, potential or measurable impact on the environment, and possible mitigation measures. However, since uncertainties remain about the precise origins or primary introduction pathways for some species, multiple potential origin regions or transport vectors may be assigned to a single species. Therefore, it is recommended to exercise caution before drawing conclusions based on the summarised fact and figures and to consult the detailed species pages and corresponding sources for further information.

Figure 1: Overview of the study area. Blue: Belgian territory (marine or influenced by seawater). Yellow: regions where present non-native species, not yet detected in Belgium, have been included in the Watchlist (see Definitions). Source: EMODnet Bathymetry, Eurostat, NGI, Vlaamse Hydrografie, INBO, Agentschap voor Natuur en Bos, Agentschap Digitaal Vlaanderen, OpenStreetMap contributors.

Which species can be found on our website?

- Alien species introduced by human activities (whether intentional or unintentional) that occur in salty and brackish environments in Belgium.
- Non-native species that occur in salty and brackish environments in neighboring countries near the Belgian border but have not yet been found in Belgium (so-called 'Watchlist species'). Specifically, this includes species that have already been reported in the Dutch Western Scheldt and Eastern Scheldt, or along the French Opal Coast.
- Cryptogenic species for which there is a strong suspicion that they have been introduced.

Which species will NOT be found on our website:

- Strictly freshwater species;
- Marine species that have naturally found their way into Belgian waters ('eco shifters' or 'climate shifters'). The reasons for excluding (alien) organisms that have expanded their habitat naturally in this overview are both legal and practical. According to the European Marine Strategy Framework Directive (2008/56/EC), the overarching European policy framework for the protection of the marine environment, alien species introduced by human activities must be at a level where the ecosystem is not altered. This automatically means that (alien) species that have naturally spread to our waters do not fall under this policy framework. Despite the fact that climate change is largely influenced by anthropogenic processes, it does not constitute a human activity in itself. Moreover, for some 'new' species, it is uncertain whether they were already present in low concentrations and may therefore be native, with environmental changes having positively affected the occurrence of certain organisms. Furthermore, it is expected that climate warming will result in the northward shift of the biogeographic distribution of numerous species in the future, leading to a list of alien species that will no longer be manageable. As a result, the following alien species present in Belgium have not been listed under the introduced alien species on this website: the cymothoid Anilocra frontalis, the varunid crab Asthenognathus atlanticus, the crab Atelecyclus undecimdentatus, the fish parasite Ceratothoa steindachneri, the Angular crab Goneplax rhomboides, the polychaete Loimia ramzega, the cymothoid Nerocila cf. bivittata, the rhizocephalan parasite Septosaccus cuenoti and the opossum shrimp Neomysis americana.
 

VLIZ Alien Species Consortium

The provided scientific information was gathered and compiled under the umbrella of the 'VLIZ Alien Species Consortium,' a collaboration between VLIZ and researchers from various national and international knowledge institutions. The following experts (32), working within 17 different institutions and from four different countries, contributed to the creation and update of species information (2020-2024):