The SETL-project is a fouling community study monitoring the diversity of hard substratum related organisms with a focus on non-native species in harbours. It has started in 2006 in the Netherlands and is run since then by GiMaRIS continuously in The Netherlands, locally in the USA by the Salem Sound Coastwatch
, and project based in other European countries
and throughout the Ponto-caspian region
. In 2006 the SEtTLement-project (SETL) was started by GiMaRIS in cooperation with the ANEMOON foundation
promoting volunteer monitoring in the marine environment and in close contact with the Smithsonian Marine Invasions Laboratory. Their plate design was used as the basis of the SETL-project to ease worldwide comparisons to be made as they have been deploying plates along both coastlines of northern America and in Hawaii (Ruiz et al., 2006
). In 2006 and 2007 a few thousand SETL plates were delivered to various European marine institutes to be deployed from the Mediterranean up to Scandinavian waters within the MarPace project
(Marine Propagation Along the Coasts of Europe) undertaken within the MarBEF EU Network of excellence
. MarPace aimed at studying the settlement of pelagic propagules of benthic plants and animals along large-scale Pan-European transects representing spatial gradients in environmental conditions such as seawater temperature, insolation and seasonality. Using molecular techniques for assessing the presence of larvae in water this project resulted in a detailed overview of the spatial synchronies in the seasonal occurrence of larvae of Pacific oysters (Crassostrea gigas
) and mussels (Mytilus edulis/galloprovincialis
) in European coastal waters. In 2007-2008 SETL plates were deployed in the six main ports of The Netherlands to assess the ecological quality of the water with a special focus on non-native species for the Dutch Ministry of Infrastructure and the Environment (RWS) and Deltares in the frame of the implementation of the EU Water Framework Directive and its pertinent monitoring. These projects form the basis of the SETL-project as it is described for sampling the marine realm in the international manual on field recording techniques and protocols for all taxa biodiversity inventories by Templado et al. (2010) and has been conducted in The Netherlands since 2006 at a total of 35 sites.
Annually about 150 plates are being deployed in The Netherlands at about 12-15 sites, mostly in pleasure craft harbours and ports. A SETL-plate consists of a 14x14x0.5 cm grey PVC plate attached to a brick to keep it horizontal, hanging from a plastic line with a metal core in the water column. It is deployed at a depth of 1 meter under the water line if it is attached to a floating object and 1 meter under the low water line in tidal areas if it is fastened to non-floating structures. The downward facing side of the smooth PVC-plate was roughened with sand paper (roughness K60) to ease the attachment of fouling species. Three monthly at least three new plates per site are deployed. The already deployed plates are then taken out of the water and directly placed upside down in a tile of water showing the roughened side of the plate just submerged under the waterline. After photographing the unique label that indicates the deployment date, the plate surface is then photographed in overview and in detail. Most plates are then taken back to the lab for further analyses after three months of deployment, but some are redeployed after photographing them in the field, enabling the monitoring of the succession of fouling communities over time periods up to eight years. After dividing each plate on an overview photo into 25 grids, the presence of species, recognisable from the photos, was scored for each grid. The monitoring data from 2006 to 2017 thereby includes about 21.945.000 presence/absence records of species, i.e. 150 plates x 4 seasons x 11 years x 133 species x 25 grids.
Using SETL data
In the Netherlands the presence of 133 species, of which 38 non-native, was scored on SETL plates over the years. Immediately after the start in 2006, a species was recorded as new to the Netherlands in the Wadden Sea (Gittenberger & Schipper, 2008). Further illustrating the potential as an early detection method of non-native species, in the same year the westernmost sighting was done of the invasive ponto-caspian quagga mussel Dreissena rostriformis bugensis within the Haringvliet a few months after its first sighting in The Netherlands (Schonenberg & Gittenberger, 2008). Samples from SETL plates were furthermore used for the extended genome analyses of the invasive carpet sea squirt Didemnum vexillum (Velandia-Huerto et al., 2016), the quantification of the competition for space between non-native and native fouling species (Gittenberger & Moons, 2011), and the study of dominance and presence of non-natives in species communities in their pioneer stages in comparison to later succession stages (Lindeyer & Gittenberger, 2011). In 2009 the SETL-dataset was used for the first non-native species focussed survey of the Wadden Sea (Gittenberger et al., 2010), which was subsequently used for a risk analysis of hull fouling on small to medium sized boats as an import vector of non-native species in the Wadden Sea (Gittenberger et al., 2011).