Abstract
In the present work, we analysed time series data on the introduction of new non-indigenous species (NIS) in the Mediterranean between 1970 and 2017, aiming to arrive at recommendations concerning the reference period and provisional threshold values for the NIS trend indicator. We employed regression analysis and breakpoint structural analysis. Our results confirm earlier findings that the reference conditions differ for the four Mediterranean subregions, and support a shortening of the reporting cycle from six to three years, with a two-year time lag for the ensuing assessment. Excluding Lessepsian fishes and parasites, the reference period, defined as the most recent time segment with stable mean new NIS values, was estimated as 1997–2017 for the eastern Mediterranean, 2012–2017 for the central Mediterranean, 2000–2017 for the Adriatic and 1970–2017 for the western Mediterranean. These findings are interpreted primarily on the basis of a basin scale temperature regime shift in the late 1990s, shifts in driving forces such as shellfish culture, and as a result of intensified research efforts and citizen scientist initiatives targeting NIS in the last decade. The threshold values, i.e., the three-year average new NIS values during the reference period, are indicative and will ultimately depend on the choice of species and pathways to be used in the calculations. This is discussed through the prism of target setting in alignment with specific management objectives.
Highlights
The role of biological invasions as a pressure that threatens ecosystems is investigated in the framework of numerous policies and strategies worldwide
Distribution data on marine non-indigenous species (NIS) in the Mediterranean Sea were retrieved from the European Environment Agency/Hellenic Centre for Marine Research (EEA/HCMR) offline database stored in the European Alien Species Information Network (EASIN) (https://easin.jrc.ec.europa.eu/easin), which is continuously updated based on emerging literature regarding new occurrence/records, nomenclatural or taxonomic changes, and updates in the establishment success and alien status of species
All data was compiled at the pan-Mediterranean level as well as at the level of MSFDdefined marine subregions [20], i.e., the Western Mediterranean Sea (WMED), the Adriatic Sea (ADRIA), the Ionian Sea and the Central Mediterranean Sea (CMED) and the AegeanLevantine Sea (EMED), and data analysis was performed on these separate datasets
Summary
The role of biological invasions as a pressure that threatens ecosystems is investigated in the framework of numerous policies and strategies worldwide. In the Mediterranean Sea, besides the MSFD and the WFD, which apply only to EU countries, the issue is included in the Integrated Monitoring and Assessment Programme (IMAP) of the Mediterranean Action Plan at the pan-Mediterranean level (Ecological Objective 2: Trends in abundance, temporal occurrence, and spatial distribution of non-indigenous species) Within these descriptors, different aspects of species introductions are addressed with different “criteria”, aiming to break down policy implementation into manageable steps. In the latest MSFD update [2], among the criteria/indicators for assessing descriptor D2, criterion D2C1 concerning new NIS introductions states that: “The number of nonindigenous species which are newly introduced via human activity into the wild, per assessment period (6 years), measured from the reference year (2011) as reported for the initial assessment under Article 8(1) of Directive 2008/56/EC, is minimised and where possible reduced to zero.” While this is not, in itself, a quantitative target that allows for a GES assessment, the regulation further asks Member States to establish a threshold value for the number of new introductions of non-indigenous species, through regional or subregional cooperation. The definition of what Good Environmental Status is in the context of NIS management, as well as a number of methodological issues, are still pending [3]
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