Alien macroinvertebrates in Flanders, Belgium

Study Extent

Different sources of data available: (1) Data collected by the Flemish Environment Agency (VMM) of over 4,600 sampling locations situated in inland waters (fresh and brackish water). Biological samples were taken yearly and each sampling location was sampled on average every three years resulting in a large dataset of more than 11,000 biological samples collected between 1989 and 2012. The samples are stored at the Royal Belgian Institute of Natural Sciences (RBINS). Since samples of the VMM are identified to genus or family level, information about alien macrocrustacean species, such as Dikerogammarus villosus (Sowinsky, 1894) or Gammarus tigrinus Sexton, 1939 was not available since both species belong to the same family Gammaridae as the indigenous species G. pulex (Linnaeus, 1758). Although we try to give a complete overview of all alien macroinvertebrates encountered in Flanders, we mainly focused on aquatic macrocrustaceans in Flanders. Consequently, we identified all crustaceans of over 2,500 samples to species level. (2) Data collected during the four years of this study (2008-2012) at different sampling locations where alien macroinvertebrate species were expected based on historical records, information retrieved from databases or observations made by colleague zoologists. In addition, data were collected in the scope of a study that was performed in the Belgian coastal harbours to assess the diversity and abundance of alien macro-Crustacea (Malacostraca). (3) Data retrieved from the collections of the RBINS and from literature reporting on the occurrence of alien macroinvertebrates.

Sampling

The standard method used for biological monitoring of aquatic macroinvertebrates is the one used by the VMM and described by Gabriels et al. (2010). Depending on the depth of the watercourses, macroinvertebrates were sampled by means of a standard handnet or artificial substrates (Gabriels et al., 2010). The handnet consists of a metal frame of approximately 0.2 m by 0.3 m to which a conical net is attached with a mesh size of 300 μm. With the handnet, a stretch of approximately 10-20 m was sampled during three minutes for watercourses less than 2 m wide or five minutes for larger rivers. Sampling effort was proportionally distributed over all accessible aquatic habitats. In addition to the handnet sampling, macroinvertebrates were manually picked from stones, leaves, or branches along the same stretch (Gabriels et al. 2010). Artificial substrates were used for deep waters like canals where handnet sampling was not possible (Gabriels et al., 2010). Three replicates of artificial substrates, which consist of polypropylene bags (5L) filled with bricks of different sizes, were left in the water for a period of at least three weeks before they were retrieved. In this way, species had the time to colonise the substrates. Both sampling methods are standardised semi-quantitative methods (Gabriels et al., 2010). When investigating the macroinvertebrate fauna of the Belgian coastal harbours we used, besides the abovementioned sampling techniques, a trawl net with a circular diameter of 100 cm, a length of 3 m and a mesh size of 200 μm. This sampling method was used for qualitative analysis only and the samples were used to assess the species present in the water column between 0.2 m and 1.2 m above the bottom. This sampling technique was used to catch mobile species, such as Mysida, since these are often missed when using a handnet or artificial substrates. The trawl net was with a long rope attached to a zodiac and left into the water to the appropriate depth for sampling. Samples were taken by sailing within a radius of 100 m from a predetermined fixed sampling location (GPS determined) within the harbour for 10 minutes at an average ship speed (4 km hour-1 relative to the bottom). All samples were taken during day time when hyperbenthic organisms are known to be concentrated near the bottom. In order to be able to give a representative overview of the distribution of crayfish in Flanders we did not only use the standard sampling techniques as described by Gabriels et al. (2010), but we also used fyke nets (0.25 m diameter and a length of 0.50 m) specifically designed to catch crayfish and bait (cat food). Historical records as well as recent observations of crayfish were checked from October 2010 to May 2011.

Quality Control

The occurrence data from the original alien macroinvertebrate dataset were pre-processed using open.refine (http://www.openrefine.org/) and cartoDB (www.cartoDB.com) before being imported in Recorder6 (http://www.recorder6.info/) at the Research Institute for Nature and Forest (INBO). By creating a custom SQL view, the data were standardized to Darwin Core (Wieczorek et al. 2012) and were published as open data through the GBIF Integrated Publishing Toolkit (Robertson et al. 2014) at INBO (http://data.inbo.be/ipt) (for the terms of use see Appendix 1).

Method steps

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In total, 73 alien macroinvertebrate species have been collected in Flanders of which 52 are regularly encountered in fresh and/or slightly brackish waters. The remaining 21 species are restricted to the marine environment for at least a considerable share of their lifetime. Most alien macroinvertebrate species are crustaceans (51%), followed by Mollusca (27%), Annelida (19%) and Platyhelminthes (3%) (Figure 3). Most alien macroinvertebrates originate from North America (37%) or the Ponto-Caspian region (21%). The main vector of introduction is probably passive transport via the hull of ships (biofouling) and ballast water (71%). The transport via canals is the second main vector (28%) and promoted the dispersion of alien macroinvertebrates. Also, some species were introduced through aquaculture (17%) and hobbyists (6%)

1. Ampharetidae
   rank: family
2. Asellidae
   rank: family
3. Astacidae
   rank: family
4. Atyidae
   rank: family
5. Cambaridae
   rank: family
6. Caprellidae
   rank: family
7. Corophiidae
   rank: family
8. Crangonyctidae
   rank: family
9. Dendrocoelidae
   rank: family
10. Dreissenidae
    rank: family
11. Gammaridae
    rank: family
12. Grapsidae
    rank: family
13. Hydrobiidae
    rank: family
14. Janiridae
    rank: family
15. Mactridae
    rank: family
16. Melitidae
    rank: family
17. Mysidae
    rank: family
18. Ostreidae
    rank: family
19. Palaemonidae
    rank: family
20. Panopeidae
    rank: family
21. Physidae
    rank: family
22. Planorbidae
    rank: family
23. Pleustidae
    rank: family
24. Serpulidae
    rank: family
25. Talitridae
    rank: family
26. Varunidae
    rank: family

Biological invasions of aquatic macroinvertebrates are gaining interest because of their potentially significant ecological and socio-economic impacts. During the present study an inventory was made of the alien macroinvertebrates occurring in Flanders (northern Belgium). Extensive existing collections of biological samples were investigated and supplemented with our own sampling campaigns. Fresh and brackish waters as well as the Belgian coastal harbours, situated at the interface of the marine environment, were investigated. Over 2,500 samples containing alien macroinvertebrates were identified to species level, which allowed us to accurately map their distribution in Flanders. Four new macroinvertebrate species for Flanders were discovered. In total, 52 alien macroinvertebrates were encountered in fresh and slightly brackish surface waters.