Monitoring programmes must be tailored to the specific objective of the monitoring type (Figure 2) and will sometimes need to involve close cooperation with research. Listed below are some general recommendations that apply to the monitoring of alien species in the Wadden Sea in general, and more specifically, for a monitoring approach with the objective of early detection of alien species, a desired objective in the Strategic Framework for Alien Species.
The recommendations in the following paragraphs are of a general nature. Specific recommendations for a monitoring of alien species in the trilateral Wadden Sea area are currently under discussion in the trilateral groups (e.g. Task Group-Management, Working Group Alien Species). The recent report by Bureau Waardenburg, which this WaLTER thematic report also fed into, is a contribution to this discussion.
Emphasis should be put on the coordination between responsible authorities with the aim of harmonising methodologies, data management and data assessment. It is recommended that each country has its own alien species task group consisting of scientists, policy makers and other stakeholders (similar to German FAG Neobiota), that can address all aspects of the national alien species management to assess potential threats and impacts associated with these organisms in a timely manner, and react accordingly. Beyond that, representatives of these national groups should come together regularly to ensure good communication and implementation of a trilaterally concerted IAS management.
Network of experts
A solid, comprehensive network of experts is needed to ensure that species identification is done reliably and in the fastest possible way. The DAISIE Project created an Expertise Registry, which is currently no longer being updated. It is recommended to update and expand this registry or to substitute it with a similar one.
Prevention as priority
Prevention should continue to be the cornerstone of management efforts, as eradication or control of IAS populations in the marine environment is near to impossible. In their paper on monitoring of marine alien species to serve legislative requirements, Lehtiniemi et al. (2015) also come to the conclusion that the management potential is the greatest during the ‘pre-border’ stage, i.e. before alien species are being introduced into a new environment. With regard to the various relevant vectors, prevention of alien species transported by mussel transplants is most promising, as monitoring of mussel transplants has already successfully been done in the past and can be achieved with relatively low effort.
IAS alert or watch list
Monitoring may need to focus on specific taxonomic groups to optimise the probability of detection. In order to devise or advance an alert list of high-risk species, horizon scanning should be (further) pursued for the trilateral region and the neighbouring countries to determine the most likely points of introduction of high-risk species.
Spatial and temporal scale of monitoring
The whole of the Wadden Sea with all relevant habitats needs to be monitored in a standardised and regular manner, whereby special attention must be given to all anticipated or known hotspots, e.g. marinas, harbours and aquaculture operations. Depending on the methods chosen, the point in time in the course of a year will vary. Rapid assessments based on expert searches in the field will take place in summer/early autumn as this ensures that species can be detected and identified more easily (settlement of many species completed and individuals have reached a discernible size).
Online alien species database
It is recommended to set up an easy-to-understand online database on detected alien species in the trilateral Wadden Sea, which includes the visualisation of findings of alien species, e.g. similar to the one by the US Geological Survey or MITIS Marine Invader Tracking and Information System. Another suitable option is AquaNIS, the ‘Information system on aquatic non-indigenous and cryptogenic species’, although the (interactive) display of findings is not (yet) possible on this site. Online databases serve two functions. They can be used by scientists and managers for e.g. reporting purposes with regard to the MSFD subregional approach, and as information for the public to stimulate involvement via citizen science. Preferably, an online database will collect all data on alien species in the wider Wadden Sea area, irrespective of the vectors involved. Thus data collected through e.g. monitoring in aquaculture, ballast water management and basic monitoring, but also chance findings of alien species would all be stored in such a database, indicating any possible uncertainties related to the specific monitoring type taken. The database could then be part of the centralised information system collating all existing information on alien species in the Union, as proposed by the EU in its Regulation on the Prevention and Management of the Introduction and Spread of Invasive Alien Species (European Commission 2014).
Experience has shown that public outreach can have a positive effect on alien species management, if people are aware that their behaviour (e.g. recreational boating) can have an effect on the spreading of alien species (example of effective IAS management in New Zealand). A strong and long-lasting communications initiative could help to increase acceptance and participation in alien species management. The development of public outreach material has also been mentioned in the Strategic Framework for Dealing with Alien Species in the Trilateral Wadden Sea (2014), and could include a travelling exhibition on alien species, thereby joining forces with organisations with a marine educational mission.
Analysis of pathways of alien species
Managing the pathways and vectors of movement of alien species is of major importance, as different pathways pose different risks for a given area and/or taxonomic groups (Pearce et al. 2012). For the Dutch Wadden Sea with its many marinas and relevance for the mussel industry, the presumed main pathways are recreational boating, aquaculture, natural drifting and, to a lesser degree, ballast water. Aside from the mapping of cluster areas of alien species (further described below) it would be advisable to analyse major travel routes of recreational boats in the Wadden Sea, hereby identifying the pathways that should be targeted in order of priority for early detection but also control purposes (as described in the EU Regulation 2014 for example). Information could be collected with the help of instruments such as Real Life AIS, and via associations concerned with recreational boating (e.g. for NL: De Wadvaarders, ANWB, HISWA).
Use of new methods
If eradication of an alien species is the objective of a management programme, then focus must be laid on the still rare (and thus most likely hard-to-detect) alien species, as chances for eradication are then highest. Consideration should be given to the use of eDNA in harbours or other semi-enclosed locations. There are a number of advantages to new methods such as eDNA, as for example taking frequent eDNA samples can ensure that various life stages of a species are being found. However, there are also a number of disadvantages (see ‘DNA techniques’, chapter 4 WaLTER analysis).
Priority areas for monitoring
Monitoring programmes should prioritise the areas with high likelihoods of both introduction and establishment. These can be based on past accounts of alien species that have become established, e.g. by mapping all locations of first detections of alien species for the whole trilateral Wadden Sea and thereby visualising ‘alien species cluster areas’. Although detection probabilities are highly correlated with search effort in a specific area and hence do not allow for the conclusion that there are no other relevant (unsearched) cluster areas, this approach could be useful in narrowing monitoring efforts should this be necessary. The alien species overview reports by Lackschewitz et al. (2015) for the German part of the Wadden Sea and the report by Gittenberger et al. (2015) for the Dutch part of the Wadden Sea can serve as knowledge bases for such a map, expanded by the results of alien species inventories and other (chance) reports. Such a map could have an additional layer of habitats, thereby serving as background information to lay out (future) alien species findings and to further assist in selecting the most suitable monitoring locations.
The monitoring of impacts of alien species forms an important part in EU regulations and guidelines. Impact monitoring is the systematic identification and evaluation of the potential effects an alien species may have on its environment, and generally requires scientific experiments to precede the monitoring. Close cooperation with researchers studying the alien species in question is therefore obligatory to enable reliable statements about impacts. Past research on impacts of alien species in the Wadden Sea (e.g. research by Diederich 2005, 2006, Eschweiler & Christensen 2011 on Crassostrea gigas) was commonly initiated because researchers surmised that a specific invasive alien species could have an effect on native species or habitats. These research endeavours were usually not motivated by policy makers’ needs for information for IAS management. This indicates the importance of scientists, policy makers and other stakeholders forming alien species task groups, to enable direct interaction with regard to research needs (see above ‘Coordination’). The quantification and mapping of alien species’ impacts is further complicated by ‘(1) the lack of coverage and resolution in the available natural and socioeconomic data (e.g. habitat mapping, spatial distribution of native and alien species), (2) gaps in assessments of marine ecosystem services […], which naturally precedes the assessment of any impact on them, and (3) the inherent complexity of the problem’ (Katsanevakis et al. 2014).
Create a Wadden Sea DNA collection
DNA information collected by Lise Klunder during her PhD research at NIOZ could provide a start for a Wadden Sea-wide DNA collection. The collection could be expanded by filling it with DNA information of all new (alien and native) species found in the Wadden Sea. This DNA collection could serve as a reference for future monitoring.
Map future risk areas for further bioinvasions
Special attention should be paid to developments in the Wadden Sea or North Sea areas bordering the Wadden Sea. This includes offshore blue energy projects (e.g. wind farming, or ocean farming), as the pertinent structures will likely function as stepping stones for new species (see Buschbaum et al. 2012).
Stimulate further research on alien species in the Wadden Sea
Current IAS management involves a number of assumptions, including those about vectors or connectivity. Further research can help improve IAS management, e.g. is it possible to identify hotspots for alien species in soft sediments possibly related to local currents for example? What is the importance of anthropogenic vectors such as boating or aquaculture in comparison to natural drifting of larvae for population connectivity? What percentage of alien species related to anthropogenic hard substrates such as the various habitats in marinas, can be found on natural hard substrates such as mussel beds, and are there differences with regard to the taxa that can be found on these anthropogenic and natural hard substrates? Bluntly said: should alien species that find a suitable habitat in man-made environments, such as marinas, not be managed if natural hard substrate habitats such as mussel beds are not prone to their colonisation and thus impacts on natural habitats are not to be expected?