Twelve new human-mediated introductions to the Baltic Sea were observed from 2011 to 2016. These species are: Antithamnionella ternifolia, Beroe ovata, Tharyx killariensis, Chaetoceros concavicornis, Diadumene lineata, Echinogammarus trichiatus, Grandidierella japonica, Haminoea solitaria, Hemigrapsus takanoi, Laonome sp., Proasellus coxalis and Sinelobus c.f.vanhaareni. In three sub-basins only one new NIS was observed (Kattegat, Arkona Basin, Gulf of Riga), in three areas two new NIS were observed (Great Belt, Bay of Mecklenburg, Bornholm Basin) and in one area (Kiel bay) three new NIS were observed for the first time in the Baltic Sea. These areas are considered to fail the established threshold value. As the uncertainty related to vectors and pathways concerning many new introductions inside the Baltic Sea is high we cannot say the other sub-basins are in good status although there are no known new Baltic Sea-first observations recorded in them. There are however several human-mediated introductions (e.g. for bivalve species) from one Baltic country or sub-basin to another during the assessment period, indicating failed threshold value conditions elsewhere. Therefore we are not assessing the sub-basins without Baltic Sea-first observations with the present level of knowledge.
The current results are based on AquaNIS data that has been verified by national experts. The indicator results could be significantly improved if dedicated monitoring program for NIS would be launched in all HELCOM countries. Current evaluations are strongly biased towards better investigated groups (molluscs, crustaceans, fish), whereas almost no information on micro/meio taxa and pathogens is available for consideration.
The number of new NIS increased steadily until the mid-20th century (Results figure 1). Results figure 1 illustrates the temporal development of numbers of new NIS and CS observed in the Baltic Sea until 2016. The number of arrivals has increased over time and there seems to be a shift in the time series in the 1960s.
Results figure 1. Number of new NIS in Baltic Sea until 2016. The bars indicate the number of invasions per time period.
The trend of new NIS has increased sharply and has not shown signs of decline in 1990s and 2000s (Results figure 2). Shipping and cultural activities (includes crustaceans, bivalves, fish and other taxa, which have been intentionally stocked) have been responsible for the majority of the introductions (Zaiko et al. 2011).
The confidence for areas where detections of new NIS have been made is high. The detections have been verified by regional experts, and the observations are considered to be correct.
In assessment units where no detections have been made, the confidence may be low if no regular monitoring is conducted. This however varies between assessment units.
Regular monitoring dedicated to NIS is not available in most countries and areas and thus data is not considered to sufficiently cover all areas of the Baltic Sea to ensure that all new introductions are detected, thus a zero result for an assessment unit may be a false negative.