Checklist of alien species in the Scheldt estuary in Flanders, Belgium

Study Extent

Within the Belgian part of the Schelde estuary, benthos has been monitored by INBO since 1996. Most of the alien species were found since then.

Sampling

Prior to 2008, sampling was conducted every third year at fixed intertidal and subtidal stations in an increasing quantity of sites: from 51 sampling sites in 1999 up to 75 in 2005. At each sampling site, 3 core samples (diameter: 3.5 cm; depth: 10 cm) were collected. In case of subtidal samples, these were obtained from a Reineck boxcorer (diameter: 15 cm; depth: 10 cm). Sampler size was chosen to reduce highly laborious sorting effort of samples with high densities of oligochaetes (occasionally more than 1 106 individuals m-²). Sediment samples were stored in 4% formaldehyde. In the laboratory, samples were sieved in two steps over mesh sizes of 250 μm and 1000 μm. Benthic invertebrates were sorted, identified to species level, and counted. Since 2008, samples have been collected each year, following a stratified random sampling design; 212 stations are stratified by salinity zone, subtidal depth, and intertidal elevation. Two core samples (diameter: 4.5 cm; depth: 15cm) were collected at each station, fixed in 4% formaldehyde, and taken to the laboratory. These were sieved over mesh sizes of 500 μm and 1000 μm and subsequently treated as described for the samples collected prior to 2008. Since 2013 hyperbenthic monitoring occurs at 6 fixed stations; five locations along the Scheldt and one along its major tributary the Rupel. Other locations are sporadically sampled. For regular monitoring a bongonet (diameter, mesh 1mm) is pulled back and forth by 2 persons at low tide over 100m (total distance 200m). As part of projects, occasional samplings occur with the bongo net or less frequent using a benthic sledge (width 1m, heigh 50cm). Samples are always taken along the shoreline at low tide, with the exception of a series of bongo net samples taken from a boat near the surface in the navigation channel. All samples were fully sorted and all species identified to the lowest level possible. Very large samples (1000s of specimens) were subsampled (usually 1/8).

Quality Control

All records are individually validated by species experts (resource creators of this dataset).

Method steps

1. The source data for this standardized checklist is a Google Spreadsheet and re-uploaded regularly at https://docs.google.com/spreadsheets/d/1V_rQhyz_AjszobCMxBe-xFWI3kUNLrYzMeqyUNt3Vc4/edit#gid=0
2. This raw data file was uploaded to a GitHub repository (https://github.com/trias-project/alien-scheldt-checklist).
3. We developed a RMarkdown script to document and perform the transformation of the data to Darwin Core, which includes the following steps:
4. Perform some basic data cleaning of the raw data.
5. Generate stable and unique identifiers for each taxon (taxonID).
6. Create a taxon core file (http://rs.gbif.org/core/dwc_taxon.xml).
7. Create a distribution extension file (http://rs.gbif.org/extension/gbif/1.0/distribution.xml), including standardization of the distribution date range and event dates.
8. Create a species profile extension file (http://rs.gbif.org/extension/gbif/1.0/speciesprofile.xml), with coarse habitat information.
9. Create a description extension file (http://rs.gbif.org/extension/gbif/1.0/description.xml), with standardized pathway of introduction (using the pathway vocabulary from the Convention on Biological Diversity (2014)), native range, and degree of establishment (based on Blackburn et al. (2011)).
10. The resulting Darwin Core data files are uploaded to the INBO IPT and documented with metadata.
11. The dataset is published and registered with GBIF.

This checklist includes over 62 alien invertebrate species present in Flanders, Belgium

1. Animalia
   rank: kingdom
2. Annelida
   rank: phylum
3. Arthropoda
   rank: phylum
4. Cnidaria
   rank: phylum
5. Mollusca
   rank: phylum
6. Platyhelminthes
   rank: phylum

The dataset includes information on the presence of alien invertebrate species in Flanders, Belgium