A national crowdsourcing-based tick collection campaign was organized in 2015 with the objective of producing novel data on tick distribution and tick-borne pathogens in Finland. Nearly 20 000 Ixodes ticks were collected. The collected material revealed the nationwide distribution of I. persulcatus for the first time and a shift northwards in the distribution of I. ricinus in Finland. A subset of 2038 tick samples containing both species was screened for Borrelia burgdorferi sensu lato (the prevalence was 14.2% for I. ricinus and 19.8% for I. persulcatus), B. miyamotoi (0.2% and 0.4%, respectively) and tick-borne encephalitis virus (TBEV; 0.2% and 3.0%, respectively). We also report new risk areas for TBEV in Finland and, for the first time, the presence of B. miyamotoi in ticks from mainland Finland. Most importantly, our study demonstrates the overwhelming power of citizen science in accomplishing a collection effort that would have been impossible with the scientific community alone.

HighlightsWe modelled the surface water salinity in the Baltic from the 1960s to 2100.We studied possible changes in distribution areas of predominant plant, invertebrate and fish species.The results suggest a critical shift in the salinity range 5–7, which is a bottleneck for both marine and freshwater species distribution and diversity.This foreseen salinity change is likely to have large impacts on marine ecology, it́s monitoring, modelling as well as fisheries.

Salinity changes in the Baltic Sea have been attributed to a lack of balance between irregular pulses of North Sea water penetrating the Danish Straits and the freshwater runoff to the Baltic Sea. Both pulses and runoff are controlled by climatic factors in the Atlantic. The occurrence of major pulses of oceanic water has proved unpredictable, being non‐existent during the 1980s. We used dynamic regression models to relate the response of the Baltic Sea salinity to hypothetical controlling factors: westerly winds, freshwater runoff, and, ultimately, the Northern Atlantic oscillation (NAO). Our results provided evidence for general chain‐of‐events relationship between the NAO and a subsequent weather effect over the North Sea, which was finally extended to the Baltic Sea salinity. Westerly winds followed changes in the NAO with a lag of <1 month. Total freshwater runoff to the Baltic Sea followed changes in the NAO with a lag of <2 months. Furthermore, the salinity responded to freshwater runoff with a time lag of <1 yr, and a significant decreasing trend was found in the salinity series. On the basis of the existing lags, we foresee a possibility to predict not only oceanographic, but also biological interactions in the Baltic Sea.

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BackgroundAlmost 3500 tick samples, originally collected via a nationwide citizen science campaign in 2015, were screened to reveal the prevalence and distribution of a wide spectrum of established and putative tick-borne pathogens vectored by Ixodes ricinus and I. persulcatus in Finland. The unique geographical distribution of these two tick species in Finland allowed us to compare pathogen occurrence between an I. ricinus-dominated area (southern Finland), an I. persulcatus-dominated area (northern Finland), and a sympatric area (central Finland).ResultsOf the analysed ticks, almost 30% carried at least one pathogen and 2% carried more than one pathogen. A higher overall prevalence of tick-borne pathogens was observed in I. ricinus than in I. persulcatus: 30.0% (604/2014) versus 24.0% (348/1451), respectively. In addition, I. ricinus were more frequently co-infected than I. persulcatus: 2.4% (49/2014) versus 0.8% (12/1451), respectively. Causative agents of Lyme borreliosis, i.e. bacterial genospecies in Borrelia burgdorferi (sensu lato) group, were the most prevalent pathogens (overall 17%). “Candidatus Rickettsia tarasevichiae” was found for the first time in I. ricinus ticks and in Finnish ticks in general. Moreover, Babesia divergens, B. venatorum and “Candidatus Neoehrlichia mikurensis” were reported for the first time from the Finnish mainland.ConclusionsThe present study provides valuable information on the prevalence and geographical distribution of various tick-borne pathogens in I. ricinus and I. persulcatus ticks in Finland. Moreover, this comprehensive subset of ticks revealed the presence of rare and potentially dangerous pathogens. The highest prevalence of infected ticks was in the I. ricinus-dominated area in southern Finland, while the prevalence was essentially equal in sympatric and I. persulcatus-dominated areas. However, the highest infection rates for both species were in areas of their dominance, either in south or north Finland.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3131-y) contains supplementary material, which is available to authorized users.