Aquatic invasive species - Seawater - Data Information

Figure 1

Settlement collectors are used to detect and followed the dispersal of sessile AIS, particularly invasive tunicates (sea squirts).


From 2006-2016, collectors were made of three PVC plates (10 x 10 cm) and a plastic plate to which three petri dishes were attached, all of which were threaded onto a rope (Figure 1). From June to October, in collaboration with Merinov and aquaculture farmers, a minimum of six collectors was installed at various sampling sites, attached to port infrastructures or anchorages, about one meter below the water surface.

Monitoring was carried out for three different periods:

  • Spring-summer: collectors installed in June and removed in August;
  • Spring-autumn: collectors installed in June and removed in October;
  • Summer-autumn: collectors installed in August and removed in October.


The sampling protocol was modified in 2017. Collectors are now made of only one PVC plate and one plate to which three petri dishes are attached (Figure 2). The number of collectors installed at each site has been increased to ten collectors per site (where possible) and there is only one sampling period (spring-autumn).

Note that only data from the spring-autumn period are presented in the Biodiversity application, but data from all periods are available in the catalogue.

Figure 2

When possible, temperature and salinity are measured during collector installation and recovery. At each collector recovery date, the percent cover of each AIS present on collectors is evaluated and assigned into one of six coverage categories:

Coverage class used for data collectionPercent cover
(plate and petri dish)
Quantitative value retained for display
(median of class)
00 %0 %
10-25 %12,5 %
225-50 %37,5 %
350-75 %62,5 %
475-100 %87,5 %
5100 %100 %

Each cell or point on the map represents the average value of all the data contained therein. For example, if for a given station there are 12 records, the mapped value will be equal to the average of these 12 values.