Crustacean invasions in the Estonian coastal sea

INTRODUCTION Together with habitat loss and climate change, invasions of nonindigenous species are one of the most serious threats to global biodiversity. This human-aided process has initiated significant, unpredictable, and irreversible changes to both the abiotic and the biotic environment and has caused severe economic damage in a variety of waterbodies worldwide (e.g. Canton, 1996; Vitousek et al., 1997; Sala et al., 2000). Concurrently with this global trend several new crustacean species have also been found in the Estonian coastal sea in recent years. The gammarid amphipod Gammarus tigrinus Sexton originates from the North American coast of the Atlantic Ocean. The species was introduced to Europe probably in ballast water and was first discovered in England in 1931 (Chambers, 1977). Although G. tigrinus was found in the Baltic Sea already in 1975, its significant range expansion started in the 1990s (Jazdzewski et al., 2002, 2005; Szaniawska et al., 2003). In the northern Baltic Sea G. tigrinus was first found in the northern Gulf of Riga (Herkul et al., 2006) and the northern Gulf of Finland in 2003 (Pienimaki et al., 2004). In 2005, G. tigrinus was found in the Neva Estuary, the easternmost part of the Gulf of Finland (Berezina, 2007). This species has caused a significant decrease in the diversity and density of native amphipods in the southern Baltic Sea (Grabowski et al., 2006) and Estonian coastal sea (Kotta et al., 2006; Orav-Kotta et al., 2009). The amphipod Chelicorophium curvispinum (Sars) originates from large rivers connected to the Black Sea and the Caspian Sea. It was found in the Baltic Sea already in the 1920s (Bij de Vaate et al., 2002). The species invaded to the Baltic and North seas through rivers and canals attached to the hulls of ships and in ballast water. Regardless of its long invasion history in the Baltic Sea, C. curvispinum was not found in the northern Baltic until 2005 when it was detected in the eastern part of the Estonian coast of the Gulf of Finland (Herkul & Kotta, 2007). In the next year, 2006, C. curvispinum was found in Luga Bay, Russia (Malyavin et al., 2008). Similarly to C. curvispinum, the gammarid amphipod Pontogammarus robustoides (Sars) originates from the lower reaches of Ponto-Caspian rivers and from brackish and freshwater lakes around the Black Sea (Bij de Vaate et al., 2002). In 1960-1961, the species was intentionally introduced into the Kaunas Water Reservoir on the Nemunas River, Lithuania (Bij de Vaate et al., 2002; Gumuliauskaite & Arbaciauskas, 2008). It successfully spread in the Nemunas drainage system including the Curonian Lagoon of the Baltic Sea. In 1999 P. robustoides was first found in Neva Bay, the easternmost part of the Gulf of Finland (Panov et al., 2003) and in 2006, in Lake Ladoga (Kurashov & Barbashova, 2008). In 2006 the species was recorded for the first time in the Estonian coastal sea. Similarly to G. tigrinus, P. robustoides has a potential to reduce the diversity and density of native gammarids (Panov et al., 2003; Gumuliauskaite & Arbaciauskas, 2008). The mysids Paramysis intermedia (Czerniavsky) and P. lacustris (Czerniavsky) are native to rivers connected to the Caspian Sea and Black Sea (Birshteina et al., 1968). In the 1970s P. lacustris and P. intermedia were introduced to Lake Peipsi but neither of the species has been sighted later (Timm et al., 2001). Both species were also introduced to Lake Vortsjarv, southern Estonia, in the 1970s, but only P. lacustris formed a permanent population there (Kangur et al., 2004). However, there is only a single record of P. lacustris in the Estonian coastal sea dating back to 1963 (Yarvekyulg, 1979). We are not aware of any successful introductions of P. intermedia in the Baltic Sea drainage area while P. lacustris inhabits the Curonian Lagoon, the southern Baltic Sea, already since the 1960s. In 2008 P. intermedia was found for the first time in the Baltic Sea. …