Since 2009, a number of inventories specific to alien species have been done in the Dutch and German parts of the Wadden Sea, which could form the basis for a future long-term monitoring programme. In addition, a number of long-term monitoring programmes exist, which have objectives other than the monitoring of alien species, but which can also provide data on alien species for use in the trilateral long-term monitoring of alien species. Brief descriptions of all explicit alien species inventories and, for the Netherlands, other relevant long-term monitoring programmes are given below.
Up to the end of 2014, three inventories of the alien macroflora and macrofauna of the Dutch Wadden Sea had been performed. In 2009 and 2011, only hard substrates were surveyed, whereas in 2014, both hard substrates and soft sediments were investigated. In addition, experiments with settlement plates and a unique inventory in the military harbour of Den Helder were carried out.
Inventories of alien macroflora and -fauna in the Dutch Wadden Sea (2009 and 2011)
In 2009, the inventory for alien species was carried out within the framework of the ‘Covenant transition mussel sector and nature restoration’ (‘Convenant transitie mosselsector en natuurherstel Waddenzee’) and was commissioned by the Team Invasive Alien Species of the Dutch Ministry of Agriculture, Nature and Food Quality (since 2012 Ministry of Economic Affairs). The inventory of alien species in 2011 was commissioned by the Dutch Mussel Culture Producers’ Organisation (Producentenorganisatie van de Nederlandse Mosselcultuur) as part of a risk assessment of the South-North transport of mussel seeds from the Oosterschelde to mussel farming plots in the Wadden Sea. Both inventories were primarily aimed at finding new alien species in the Wadden Sea.
In July and August 2009, GiMaRIS investigated the hard substrate of 83 locations with a variable salinity, ranging from 10 ppt (brackish) to 32 ppt (marine) (Gittenberger et al. 2009). Attention was paid to study as many different habitats as possible, e.g. mussel banks, marinas, and dikes, with various methods such as observation during snorkelling, the use of an underwater ROV (remotely operated vehicle) and fishing nets, and turning over of rocks at low tide. Of the 129 species recorded, 28 were either alien or unknown to the region, of which 12 species and one subspecies had never before been registered in the Dutch part of the Wadden Sea. These findings increased the number of alien species or species with an unknown origin recorded in the literature in the Dutch Wadden Sea from about 50 to 62 species.
The inventory as performed in 2009 was repeated in July – September 2011, and expanded by 13 locations to total 96 sampling sites (Gittenberger et al. 2012). The salinity range was somewhat larger than in 2009, ranging from 8 to 33.5 ppt. Additionally, published and unpublished data on alien species in the Dutch Wadden Sea were included in the overview. Of the 159 species of macroflora and -fauna recorded, 34 species discovered in 2011 were either alien or of unknown origin. Eight of these were new discoveries for the Dutch Wadden Sea, and thus the total number of alien species for this subregion increased to 72 (article in Levende Natuur by Gittenberger & Rensing).
Baseline study of non-native macroflora and -fauna of soft sediments and hard substrates in the Dutch Wadden Sea, including seed mussel plots (2014)
In the autumn of 2014, the inventory as performed in 2009 and 2011 was repeated, but this time extended to soft sediments in addition to hard substrates (Gittenberger et al. 2015). The inventory was commissioned by the Team Invasive Alien Species of the Ministry of Economic Affairs and carried out by GiMaRIS for hard substrates and by NIOZ for soft sediments. The focus of the inventory was on new alien species, previously not described for the Dutch part of the Wadden Sea. The purpose of this inventory was to create a baseline of alien macroflora and macrofauna related to hard as well as soft sediments in the Dutch part of the Wadden Sea. The information will be used in the decision-making of the South-North transport of mussel spat and the trilateral discussions on alien species monitoring.
As in 2009 and 2011, the inventory focused on hard-substrate locations with a high chance of alien species’ presence. The soft sediment sampling carried out by NIOZ made use of 100 of the random sample locations of the SIBES project (see below). Samples were sorted for all macroflora and -fauna and were not limited to certain species (groups). On the basis of species accumulation curves for the hard and soft substrate inventories respectively, rough indications of the total number of species that could have been found with the methods used were generated.
SETL-project (since 2006)
Since 2006, experiments with PVC settlement plates have been performed by GiMaRIS in the harbours of Den Helder and Eemshaven. These experiments are part of the larger, long-term SETL-project which investigates the fouling communities at 13 localities along the Dutch coast. With the help of the settlement plates, alien fouling species can be detected and the succession of marine fouling communities studied (e.g. Gittenberger & Moons 2011, Gittenberger & van der Stelt 2011, Lindeyer & Gittenberger 2011). Alien species that can be recorded with settlement plates mainly include ascidians, bryozoans, barnacles and, in more brackish waters, dreissenid bivalves (pers. comm. A. Gittenberger, GiMaRIS).
The design of this study is based on Ruiz et al. (2006). In the SETL-project, 125-150 grey, 14×14 cm large PVC plates are deployed horizontally at a depth of 1 m to observe which fouling communities grow on the underside of the plates over time. Every three months the settlement plates are checked for new growth, photographed and species identified, and partly replaced with new ones. Salinity of the surface water is recorded for all locations.
In the first instance, the SETL-project is used in the training of biology students who examine the settlement plates and analyse the data (pers. comm. A. Gittenberger, GiMaRIS). However, part of the project’s data have also been used in policy, e.g. part of the data were collected for Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and the Environment) in the frame of the implementation of the WFD and its pertinent monitoring, and have also been used in a report on risk assessments of hull-fouling for the Dutch Ministry of Agriculture, Nature and Food Quality (pers. comm. A. Gittenberger, GiMaRIS).
Inventory of alien species in the military harbour of Den Helder (2014)
In the autumn of 2014, an inventory of non-native macrofauna and -flora was performed by GiMaRIS in the military harbour of Den Helder. The inventory was commissioned by the Team Invasive Alien Species of the Ministry of Economic Affairs with the objective to gain knowledge on alien species in this specific location. This inventory may give an idea of alien species transported by this different category of ships between (military) harbours that are not necessarily located along the common trading routes, thus possibly pointing to (groups of) alien species previously not appropriately accounted for in assessments of vectors and invasion pathways. No results are publicly available yet (status: February 2015).
In a number of monitoring programmes with other objectives than the specific monitoring of alien species, taxonomic experts have been collecting detailed information on populations of species for sometimes several decades. These programmes can also offer valuable information on alien species.
Balgzand intertidal transect programme (since 1973)
On the tidal flat area ‘Balgzand’ in the westernmost part of the Dutch Wadden Sea, the macrozoobenthos community has been monitored at 15 fixed sampling sites (12 transects 1 km long, and 3 squares 30 × 30 m) since the early 1970s (SEED maps portal and factsheet B8). The monitoring programme comprises biannual (late winter: February-March, late summer: August-September) estimates of numbers (n m–2) and biomass (g AFDW m-2) of all macrobenthic animal species (those retained on 1 mm sieves). The sampling sites cover the entire intertidal depth range and have a wide range of sediment compositions. Along each of the transects, 50 cores are taken at equal intervals of 20 m, covering a total of 0.45 m2 (summer) or 0.95 m2 (winter) per transect. In winter, larger samples are taken compared to summer as numerical densities are generally lower in winter than in summer. In addition, 18 – 32 samples are taken per square, covering 0.95 to 1.7 m². Sampling depth is 35 cm. Samples are taken to the laboratory, live animals identified up to species level and counted, and bivalves are measured and allotted to year-class level.
Synoptic Intertidal Benthic Surveys (SIBES) (since 2008)
Macrozoobenthos and sediment particle sizes have been investigated throughout the entire Dutch Wadden Sea by the SIBES project at NIOZ since 2008 (SEED maps portal and factsheet B27). The goal of the project is to describe the species composition of the macrozoobenthic infauna (worms, crustaceans, bivalves) as well as the particle size distribution of tidal flats in relation to natural gas extraction in the Dutch Wadden Sea. With this information, long-term changes of the Wadden Sea macrobenthic fauna and the consequences for the carrying capacity of the Wadden Sea shall be investigated and described. Furthermore, SIBES aims to monitor the introduction of alien species.
Information about alien macrozoobenthos can be retrieved from the WaLTER Data portal. The SIBES database is limited to specific macrozoobenthic taxa and does not contain information on e.g. barnacles, hydrozoa and bryozoa. In the autumn of 2014, 100 of the SIBES random locations were specifically surveyed for alien species. This survey included all macrozoobenthos as well as macrophytobenthos (see also above Baseline Study 2014 GiMaRIS and NIOZ).
MWTL programme in the Wadden Sea and the Eems-Dollard (since 1991)
As part of the environmental monitoring network ‘Monitoring Waterstaatkundige Toestand des Lands’ (MWTL) by Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and the Environment; see Bogaart-Scholte et al. 2014), macrozoobenthos and sediment have been sampled as part of the biological sampling network ‘Research Wadden Sea and Eems-Dollard’ (factsheet B9). Sampling of macrozoobenthos takes place at 17 locations along transects, spread over the Dutch Wadden Sea area (Groninger Wad, Eems-Dollard, Balgzand, Piet-Scheve-Plaat and three more sites in Wadden Sea West). Between 10 and 20 samples were taken at each of these locations in February/March and August/September of each year until 2011. Since then, sampling has only taken place every three years.
NIOZ fyke net monitoring (since 1960)
Since 1960, fish have been monitored (factsheet F2) near the southern part of Texel, de Hors, at the Western entrance of the Dutch Wadden Sea in spring (April–June) and autumn (September–October). A sampling description can be found in Van der Veer et al. (2011). Fishing is done with a passive trap, which consists of a pound net and a fyke supported by wooden poles and with a leader of 200 m running from above the high water mark into the subtidal. At the end, two chambers catch and retain fish and other species. The stretched mesh size of the leader and the two chambers is 20 mm. The fyke net is emptied every morning from Monday to Friday, irrespective of tidal phase, except on occasions of bad weather. When catches are low, the net is emptied every other morning. All catches are sorted immediately down to species level and total length of individuals are measured to the nearest cm.
Long-term phytoplankton monitoring at the NIOZ Jetty (since 1974)
Since 1974, the Wadden Sea phytoplankton species composition has been determined as part of the long-term field observation programme carried out at the NIOZ Jetty (factsheet P3). A sampling description can be found in Ly et al. (2014). The NIOZ Jetty is located in the Marsdiep basin near the inlet between the North Sea and the Wadden Sea. Surface water samples have been collected using a bucket at a sampling frequency of once a month in midwinter and twice per week during spring blooms. Phytoplankton samples are preserved and then counted with a microscope. Most algae are identified to species level; some are clustered into coarser taxonomic and size groups (e.g. small flagellates).
In the late 90’s, the first comprehensive literature overviews of neozoa in the German Wadden Sea were done (Gollasch 1996, Nehring & Leuchs 1999). This information was used as background data for assessments that followed.
Rapid assessments of alien macrobenthos in the German Wadden Sea (since 2009)
Rapid assessments of the occurrence and distribution of alien macrobenthic species in the German Wadden Sea have been performed on a yearly basis since 2009. Initially, they were financed by the State Agency for Agriculture, Environment and Rural Areas in Schleswig-Holstein and the Lower Saxony Water Management, Coastal Defence and Nature Conservation Agency, and were meant to advance the knowledge on ecological effects of alien species on native communities and to develop an evaluation system in the framework of the WFD. Since 2011, they have been financed by the Federal Agency for Nature Conservation and contribute to the alien species baseline, which will be used to compare and evaluate any future monitoring and control measures implemented to fulfil the MSFD requirements in the German Wadden Sea. Sampling has been carried out by researchers of the Alfred Wegener Institute for Polar and Marine Research, Sylt. The assessments have been done within, or in the vicinity of, eight harbours and marinas of the German North Sea Coast between July and October of each year (Buschbaum et al. 2012, Lackschewitz et al. 2015; (SEED maps portal). Sample locations were selected based on their accessibility and thus do not include major harbours such as Bremerhaven (pers. comm. C. Buschbaum, Alfred Wegener Institute). These assessments particularly focus on artificial structures in harbours and marinas, as these are known to be gateways for alien newcomers with suitable habitats for establishment (e.g. Ashton et al. 2006, Minchin 2007, Gittenberger et al. 2009). At each location three different habitat types, including hard and soft substrates are examined, resulting in a total of 24 sites.
In addition, an extensive literature study on recent records of alien species in the Wadden Sea and at the Baltic Sea coast has been carried out to achieve a valid and comprehensive list of alien and cryptogenic species currently distributed in German coastal waters (Lackschewitz et al. 2015).
Inventory of alien macrobenthos in the Schleswig-Holstein Wadden Sea (2012 and 2013)
In 2012 and 2013, GiMaRIS conducted an inventory focused on alien species, commissioned by the shellfish industry, as part of a risk assessment for shellfish translocations, throughout the Schleswig-Holstein Wadden Sea (unpublished report by Gittenberger et al., status March 2015). The methodology was similar to the one used in the Dutch inventories by GiMaRIS (2009, 2011, 2014).
Survey of alien marine species in two harbours of Schleswig-Holstein (2014)
On behalf of the State Agency for Agriculture, Environment and Rural Areas in Flintbek, Schleswig-Holstein, an inventory of alien species was conducted by researchers of GEOMAR, Helmholtz Centre for Ocean Research Kiel, in two harbours in Schleswig-Holstein, Husum and Büsum, in autumn 2014 (pers. comm. G. Bock and C. Lieberum, GEOMAR). This semi-quantitative inventory was performed according to the methods described in the Joint HELCOM/OSPAR Guidelines (HELCOM 2013). The results are being used by HELCOM and also contribute to a baseline of alien marine species for the management of the Wadden Sea under the MSFD. The final report of this project will likely be available at the end of April 2015 (status 29 March 2015).
Inventory of alien marine species in Lower Saxony (2014)
In autumn 2014, an inventory of alien marine species was carried out by researchers of the Institute for Chemistry and Biology of the Marine Environment at the University of Oldenburg in the Lower Saxon part of the Wadden Sea (pers. comm. G. Scheiffarth, National Park Wadden Sea of Lower Saxony). This inventory contributes to a baseline of alien marine species for the management of the German Wadden Sea under the MSFD and also included investigations in harbours, performed according to the Joint HELCOM/OSPAR Guidelines. No information about this inventory is publicly available to date (status 29 March 2015).
To date, no organised monitoring of alien species in Danish marine waters has taken place (Andersen et al. 2014). However, the MONIS (Monitoring of Non-Indigenous Species in Danish Marine Waters) project identified two long-term monitoring programmes that are of interest to the future monitoring of alien species in Danish marine waters, namely the NOVANA programme, coordinated and primarily carried out by the Danish Nature Agency, and the fish monitoring programme carried out by the National Institute of Aquatic Resources (Andersen et al. 2014). The NOVANA programme has two monitoring stations for phytoplankton and Zostera (eelgrass) species (and drifting macroalgae), respectively, in the Danish Wadden Sea, but monitoring stations for zooplankton, macroalgae and benthic macroinvertebrates are missing in this area (Andersen et al. 2014, p.12). Likewise, the surveys that are incorporated into the fish monitoring programme do not investigate the Danish Wadden Sea.
In order to visualize the published inventories of alien species in the trilateral Wadden Sea area (status: April 2015) go to the Maps portal. Inventories of single alien species have not been included in the Maps portal.