Distribution, sex ratio and growth of Carassius gibelio (Bloch) in coastal and inland waters of Estonia (north-eastern Baltic Sea)

Gibel carp Carassius gibelio (Bloch) was first introduced into fish ponds and small lakes of Estonia in 1948–49, and first detected in Estonian brackish waters (Gulf of Riga) in 1985. Since the mid‐1990s, the species has spread along the entire Estonian Baltic coastline. Growth rate in the brackish water population does not differ much from freshwater populations, but the freshwater populations are gynogenetic (or show high dominance of females) in contrast to the Baltic Sea population, which presents a normal sex ratio. The recent explosion of this species in the Baltic Sea could be explained by unusually warm summers during the 1990s and by the low abundance of predatory fish.     

The marine splash midge Telmatogon japonicus (Diptera; Chironomidae)—extreme and alien?

We found all developmental stages of the midge Telmatogeton japonicus (Chironomidae) on offshore windmills near the major Swedish seaport Kalmar in the southern Baltic Sea. This might be the first record of an insect species really inhabiting the offshore areas of the Baltic Sea. A thorough analysis of previous findings of the species, its history in Europe and its ecology indicates that T. japonicus quite likely is an alien species in Europe introduced from the Pacific Ocean. Shipping is probably the vector, as all records in the Baltic Sea and several from the Eastern Atlantic Sea are near major seaports. Our analysis further suggests that T. japonicus might be both advantageous and disadvantageous to native species in the Baltic Sea. T. japonicus should be kept under observation within monitoring programmes as it might expand its distribution as a result of the construction of new windmills in the Baltic Sea and elsewhere in European marine and brackish water habitats.     

Multiple Invasions – A Polychaete Genus Enters the Baltic Sea

Since 1985, the nonindigenous polychaete species Marenzelleria neglecta has been found in the Baltic Sea. The species, which was introduced by ship ballast water, spreads rapidly and dominates in many habitats today. Using three gene segments of the mitochondrial DNA (16S rDNA, Cytochrom oxidase I, Cytochrom b), we investigated four populations of the western and northern Baltic Sea in a preliminary survey and compared them with four other populations from the North Sea, the Baltic Sea and from the Arctic. First, we could demonstrate the applicability of the markers to discriminate the species with certainty. Second, with M. viridis and M. arctia, we could detect two more species of the same genus, which have recently been introduced into the Baltic Sea. One of these, M. arctia, was hitherto known as an exclusive arctic member of the genus. The impact of these two recently invaded Marenzelleria species onto the autochthonous fauna needs to be evaluated in the future. The Baltic Sea as a ‘natural aquarium’ now offers the possibility to investigate sibling species simultaneously. However, correct identification and denomination of Marenzelleria species are indispensable prerequisites for all future studies. Molecular markers allow the exact identification of all Marenzelleria species and must be used whenever a classical taxonomic identification is uncertain.     

Effects of low salinity on settlement and strobilation of scyphozoa (Cnidaria): Is the lion’s mane <Emphasis Type="Italic">Cyanea capillata</Emphasis> (L.) able to reproduce in the brackish Baltic Sea?

Several species of scyphozoan medusae occur in river estuaries and other brackish waters but it is often unknown if the planulae settle and the scyphopolyps reproduce in those low-salinity waters. In the present study, scyphozoan species from the German Bight (North Sea) were tested in laboratory experiments to investigate their tolerance of low salinity. Planula larvae released from medusae in salinity 32 were still active after the salinity was reduced to 10 (Cyanea capillata, Cyanea lamarckii) and to 7 (Chrysaora hysoscella) in laboratory treatments. Planulae did not settle on the undersides of floating substrates when salinity was reduced to <20. By contrast, planulae released from C. capillata medusae in Kiel Bight (western Baltic Sea) in salinity 15 developed into polyps in laboratory cultures. Polyps reared from planulae in salinity 36 survived a reduction to 12 (C. capillata, C. lamarckii) and to 8 (Aurelia aurita). Polyps of all tested species strobilated and released young medusae (ephyrae) in salinity 12. These results show a high tolerance of planulae and polyps to low salinity, indicating their possible occurrence in estuaries and brackish waters. In addition to laboratory observations, young C. capillata ephyrae were collected in the western Baltic Sea (Kiel Bight) in salinity 15, which indicates that they were probably released by a local polyp population. We suggest that the polyps of the painfully stinging lion’s mane, C. capillata, may be more widespread in the Baltic Sea than previously assumed and that the occurrence of the medusae may not only depend on inflow of water masses from the North Sea.     

Four arguments why so many alien species settle into estuaries, with special reference to the German river Elbe

In one of the largest European rivers, the Elbe, from its source in the Czech Republic to the German North Sea, 31 alien macrozoobenthic species have been recorded in total. Most of these species have been introduced by shipping activities. With a total number of 21 species, many of the established aliens occur—partly exclusively—in the brackish area of the Elbe estuary. In order to explain this observed settlement characteristic, four main arguments come into consideration: (1) estuaries with intensive international shipping have a higher potential infection rate than other aquatic zones; (2) brackish water species have, due to specific physiological characteristics, a better chance of being transported alive than euhaline or freshwater species and they also probably have a higher perennation and establishment potential after release; (3) brackish waters have the greatest natural ‘indigenous species minimum’, so that more alien species can potentially establish; and (4) salt-tolerant limnetic alien species introduced into inland water reached the coast at first in the estuaries. It seems that the combination of brackish water with its unsaturated ecological niches and intensive international ship traffic has the highest potential infection rate for aquatic systems with alien macrozoobenthic species. And, estuaries are subjected to a two-sided invasion pressure by alien species, via the ocean (mainly shipping) and via inland waters (mainly shipping canal construction). The identification of such patterns is an important prerequisite for the development of a forward-looking alien monitoring and management strategy.     

Distribution Patterns of Isomorphic Cold-Water Dinoflagellates (Scrippsiella/Woloszynskia Complex) Causing ‘red tides’ in the Baltic Sea

During the latest years medium-sized (15–30 μm), single-celled dinoflagellates have been reported to form blooms in the northern Baltic Proper and the Gulf of Finland in winter and spring. Recent studies (Kremp et al., 2003. Proceedings of the 7th International conference of Modern and Fossil Dinoflagellates, September 21–25, Nagasaki, Japan, 66 pp.) indicate that those blooms are caused by two isomorphic species – Scrippsiella hangoei (Schiller) Larsen, and a new species, tentatively belonging to the genus Woloszynskia. Until now there has been no report on how widely distributed these phytoplankton species are in the Baltic Sea. In this study, the occurrence of Scrippsiella/Woloszynskia complex in the entire Baltic Sea was investigated, by using monitoring data from 1997 to 2003. The species occurred in a salinity range from 2 to 8 PSU. Highest concentrations were observed at salinity 4.5–6.5 PSU. Maximum cell densities of Scrippsiella/Woloszynskia complex in the water column were mainly obtained in April or in the beginning of May by the water temperature <3 °C prior to stratification was formed. In the central Gulf of Finland, the second maximum was found in 1999 and 2002 by the temperature >6 °C. Bloom formations in the Baltic Proper and in the Gulf of Finland may not only be explained by optimum temperature and salinity, but also with other factors e.g. high nutrient concentrations and good seeding conditions from the sediments.     

Alien or endangered? Historical development of Chara connivens in the Baltic coastal waters and its implication for the species management

The occurrence of Chara connivens (Charophyta, Characeae) and its status in the Baltic Sea may raise controversies regarding its origin and historical dispersal pathways in the area. This study critically revises the protection status of C. connivens in the countries around the Baltic Sea, as well as its status on the red lists of endangered plant species (including the HELCOM Red List). The first reports on the presence of C. connivens in the Baltic Sea area were published in the aftermath of Carl Baenitz’s talks given in the early 1870s. Already then, the scientific community was well aware of the fact that C. connivens had been introduced as a ballast plant to the known Baltic areas of occurrence – the first known record of the species is from 1829. Since Poland is the only country where C. connivens is protected, the historical and contemporary distribution of this charophyte in the Polish coastal waters is presented against the background of the available historical and recent records of the species in the Baltic Sea. Recent reports from the second half of the 20th century and the beginning of the 21st century have confirmed a fairly common occurrence of C. connivens in Estonia, Sweden and Poland. This species still occurs on the German coast and has also been reported from Finland (the Åland archipelago). In recent decades, however, the species was considered rare in the Baltic Sea area. In Poland, C. connivens was even classified as extinct, despite earlier data on its occurrence in the Vistula Lagoon in the 1970s, where it was rediscovered in 2011. It was also found in the Szczecin Lagoon a year later. Both localities well suit Luther’s pattern of C. connivens occurrence in areas with intensive shipping and ballast discharge operations in historical times. Based on this in-depth revision of historical and current distribution, it is postulated that C. connivens, as non-indigenous, should not be red-listed in the Baltic Sea area, following the example of Finland. Moreover, its legal status in Poland of a strictly protected species should be reconsidered.     

Estimating salinity stress via hsp70 expression in the invasive round goby (Neogobius melanostomus): implications for further range expansion

Species invasions often occur on coasts and estuaries where abiotic conditions vary, e.g. salinity, temperature, runoff etc. Successful establishment and dispersal of non-indigenous species in many such systems are poorly understood, partially since the species tend to show genetic and ecological plasticity at population level towards many abiotic conditions, including salinity tolerance. Plasticity may be driven by shifting expression of heat shock proteins such as Hsp70, which is widely recognized as indicator of physical stress. In this study, we developed a qPCR assay for expression of the hsp70 gene in the invasive round goby (Neogobius melanostomus) and tested the expression response of fish collected from a brackish environment in the western Baltic Sea to three different salinities, 0, 10 and 30. hsp70 expression was highest in fresh water, indicating higher stress, and lower at brackish (ambient condition for the sampled population) and oceanic salinities, suggestive of low stress response to salinities above the population’s current distribution. The highest stress in fresh water was surprising since populations in fresh water exist, e.g. large European rivers and Laurentian Great Lakes. The results have implications to predictions for the species’ plasticity potential and possible range expansion of the species into other salinity regimes.

     

HETEROCAPSA ARCTICA SUBSP. FRIGIDA SUBSP. NOV. (PERIDINIALES,DINOPHYCEAE)—DESCRIPTION OF A NEW DINOFLAGELLATE AND ITS OCCURRENCE IN THE BALTIC SEA1

Characteristics important in identification of Heterocapsa species (i.e., thecal plate pattern, body scale structure, and shape and position of the nucleus and pyrenoid) are practically identical in the dinoflagellate investigated here and in Heterocapsa arctica T. Horig. described from the Canadian Arctic. Analysis of internal transcribed spacer (ITS) sequences confirms that the two dinoflagellates are very closely related; however, there is a clear difference in their size and shape. Our experiments show that the low‐salinity Baltic Sea brackish water does not reduce the size of the marine H. arctica to match that of the Baltic Sea morphotype. On the basis of these dissimilarities in general morphology and its geographic isolation in the Baltic Sea, we consider our material sufficiently differentiated from the typical H. arctica to warrant the status of a new subspecies, H. arctica subsp. frigida subsp. nov. Being of a distinct cell shape, the occurrence of subsp. frigida has been recorded in Algaline phytoplankton monitoring data collected since 1993. Although it has never been responsible for high biomass blooms, it commonly occurs in spring in the Northern Baltic Proper and in the western Gulf of Finland, when the water temperatures are <5°C.     

Distribution and dispersal capacity of the Ponto-Caspian tubificid oligochaete Potamothrix moldaviensis Vejdovský et Mrázek, 1903 in the Baltic Sea Region

Over the last few centuries, several Ponto-Caspian tubificid oligochaetes have gradually dispersed from the Black Sea – Caspian Sea region to the north-west and west over Europe. The present world distribution comprising also the Great Lakes of North America clearly demonstrates that anthropochorous vectors of dispersal are involved. Passive transportation in the ballast water of ships has radically changed the possibilities of dispersal for many invertebrate species and has even made dispersal between continents possible. The construction of navigable canals has furthermore facilitated the crossing of watersheds and continents. Other likely vectors of longway dispersal for oligochaetes, as well as for other small-size aquatic invertebrates, are birds and mammals. The dispersal of the Potamothrixspecies is likely to have taken place in successive waves (three) with front-lines still on the move from the east to the west over the Baltic States and Scandinavia. The rheophilous species Potamothrix moldaviensishas presently reached – apart from the large rivers of Russia and many Central-European water bodies – also the Baltic States and south-eastern Sweden. Trajectories of dispersal demonstrate routes across the Baltic Sea – via the ballast water of ships. In the largest rivers of the Eastern Baltic Region (Neva, Daugava, Nemunas), downstream dispersal is the most likely way of transportation. P. moldaviensis together with P. heuscheri(second wave) and P. vejdovskyi(third wave) are presently forming front-lines running obliquely from the north-east to the south-west over south Sweden. In mesotrophic-eutrophic basins of eastern Lake Mälaren, the abundance as well as the species diversity of oligochaetes is particularly high wherever Ponto-Caspian Potamothrixspecies – often several species together – are involved.