Potential pathways of invasion and dispersal of Mnemiopsis leidyi A. Agassiz 1865 in the Baltic Sea

The rapid spread of Mnemiopsis leidyi across the entire Baltic Sea after its first observation in 2006 gave rise to the question of its invasion pathway and the possible vector of its transport. To investigate pathways of M. leidyi invasion, the years 2005–2008 have been simulated by a three-dimensional coupled sea ice-ocean model of the Baltic Sea. In addition, a Lagrangian particle-tracking model has been utilized to test possible transport routes of this invader for 2006/2007. Based on the model, we exclude advection from the Kattegat as the main area of origin of M. leidyi and further spreading through the entire Baltic Sea. To explain the dispersion of M. leidyi in 2007 an earlier invasion already in 2005 is most probable. Alternatively, an invasion originating from main harbors with high ship traffic could also be a potential pathway. Drift simulations with drifter release in the main harbors are in good agreement with the observed distribution pattern of M. leidyi

Seasonal changes and population dynamics of the ctenophore Mnemiopsis leidyi after its first year of invasion in the Kiel Fjord, Western Baltic Sea

We analyzed the seasonal variations of the ctenophore Mnemiopsis leidyi weekly collected since its first record in the western Baltic Sea in October 2006. The distribution pattern together with the seasonal dynamics and population outbreaks in late summer 2007 indicate recent successfully establishment of M. leidyi in this area. Seasonal changes showed two periods of high reproductive activity characterized by a population structure dominated by small size classes, followed by an increase of larger ones. These results further revealed that the bulk of the population remains in deep layers during the periods of low population density, whereas it appeared situated in upper layers during the proliferation of the species. We further emphasized the strength of the population outbreaks, which can reach abundances >10-fold higher in time periods shorter than a week. The predatory impact this species may have in pelagic ecosystems warns on the importance of its recent range of expansion

Salinity Gradient of the Baltic Sea Limits the Reproduction and Population Expansion of the Newly Invaded Comb Jelly Mnemiopsis leidyi

The recent invasion of the comb jelly Mnemiopsis leidyi into northern European waters is of major public and scientific concern. One of the key features making M. leidyi a successful invader is its high fecundity combined with fast growth rates. However, little is known about physiological limitations to its reproduction and consequent possible abiotic restrictions to its dispersal. To evaluate the invasion potential of M. leidyi into the brackish Baltic Sea we studied in situ egg production rates in different regions and at different salinities in the laboratory, representing the salinity gradient of the Baltic Sea. During October 2009 M. leidyi actively reproduced over large areas of the Baltic Sea. Egg production rates scaled with animal size but decreased significantly with decreasing salinity, both in the field (7–29) and in laboratory experiments (6–33). Temperature and zooplankton, i.e. food abundance, could not explain the observed differences. Reproduction rates at conditions representing the Kattegat, south western and central Baltic Sea, respectively, were 2.8 fold higher at the highest salinities (33 and 25) than at intermediate salinities (10 and 15) and 21 times higher compared from intermediate to the lowest salinity tested (6). Higher salinity areas such as the Kattegat, and to a lower extent the south western Baltic, seem to act as source regions for the M. leidyi population in the central Baltic Sea where a self-sustaining population, due to the low salinity, cannot be maintained

Xenophyophores (Protista, Foraminifera) from the Clarion-Clipperton Fracture Zone with description of three new species

We describe three new and one poorly-known species of psamminid xenophyophores (giant foraminifera), all of which were found attached to polymetallic nodules in the Russian claim area of the Clarion-Clipperton Fracture Zone (CCFZ; abyssal eastern equatorial Pacific, 4,716–4,936 m water depth). Semipsammina licheniformis sp. nov. is the second species of the genus to be formally described. The test encrusts the surface of the host nodule forming a flat structure with a rounded outline and rather irregular concentric zonation. The wall comprises a single layer, composed mainly of radiolarian skeletons, covering granellare branches and stercomata strings that lie directly adjacent to the nodule surface. Psammina multiloculata sp. nov. has an approximately semi-circular, upright test with a weak concentric zonation that is attached to the nodule by a short stalk. The outer test layer comprises radiolarian fragments, sponge spicules, and mineral grains; the interior is divided into small compartments containing the stercomare and granellare. Psammina limbata sp. nov. has a plate-like, sometimes curved, semi-circular test attached to the nodule surface by basal root-like structures. The composition of the test is similar to that of P. multiloculata, but the interior is not compartmentalised. The most distinctive feature is the lighter colour of the curved outer margin compared to other parts of test. With the addition of these and other species described during recent decades, Psammina has become a rather unwieldy taxon that requires revision. Spiculammina delicata Kamenskaya 2005, previously known from a single specimen, is the most abundant species in our collection. The test exhibits considerable morphological variation, particularly in terms of the degree of branching. The new specimens confirm the placement of this species in the family Psamminidae rather than the Syringamminidae, which it superficially resembles, as well as its sessile mode of life. Two additional species in our material, Stannophyllum radiolarium Haeckel, 1889 and Stannophyllum sp., belong to the order Stannomida. Like the psamminid species, both were found attached to nodules. Xenophyophores are a dominant megafaunal taxon within the CCFZ. Although limited, our new material suggests that this region hosts many novel taxa

Basal monothalamous and pseudochambered benthic foraminifera associated with planktonic foraminiferal shells and mineral grains from the Porcupine Abyssal Plain, NE Atlantic

We present a survey of ‘live’ (stained) and dead monothalamous (single-chambered, mainly spherical) and pseudochambered (chain-like) foraminifera associated with planktonic foraminiferal shells and mineral grains, based on two samples from one abyssal plain site (F2, 4,880 m water depth) and one abyssal hill site (H4, 4,330 m water depth) on the Porcupine Abyssal Plain (PAP), northeast Atlantic. Our study is the first to focus on this poorly known component of abyssal foraminiferal faunas and highlight their abundances and diversity at the PAP. In both samples these monothalamids and pseudochambered forms represented 27–35 % and 18–23 %, respectively, of the entire ‘live’ and dead foraminiferal assemblage (>150 ?m, 0–1 cm sediment layer). Among 1,078 stained and dead specimens we recognise a total of 18 distinct morphotypes on the basis of test characteristics. Another 144 specimens could not be assigned to any morphotype and are regarded as indeterminate. Most of the monothalamids are small (<150 ?m), although some incorporate planktonic foraminiferal shells to create larger structures. In absolute terms, stained and dead individuals of these morphotypes were more abundant at the abyssal hill site, although data from additional samples are needed to confirm if this is representative of differences between abyssal hills and the surrounding abyssal plain at the PAP. Agglutinated spheres and domes similar to some of our abyssal forms have been reported from shelf and slope settings, but they are generally much larger. Small agglutinated spheres are very common in the abyssal Pacific, at depths close to or below the carbonate compensation depth (CCD). However, they are composed largely of siliceous particles, including mineral grains, radiolarians and diatom fragments. In contrast, carbonate oozes at the PAP, situated above the CCD, are rich in coccoliths and planktonic foraminiferal shells, which are used in the construction of agglutinated spheres and domes. Our results underline the important contribution made by largely underestimated foraminiferal taxa to abyssal communities

Large, enigmatic foraminiferan-like protists in the eastern part of the Clarion-Clipperton Fracture Zone (abyssal north-eastern subequatorial Pacific): biodiversity and vertical distribution in the sediment

Komokiaceans and similar large (millimetre-sized to centimetre-sized) testate protists resembling Foraminifera are a ubiquitous and often dominant component of abyssal macrofaunal assemblages. Yet they are often overlooked and many forms are undescribed, often at the genus or higher taxon level. As a result, they represent a major source of unknown biodiversity in the deep sea. We studied the diversity and vertical distribution of these delicate, often fragmentary organisms in sediment samples (0- to 6-cm layer) collected from three sites in the eastern part of the Clarion-Clipperton polymetallic nodule field (subequatorial NE Pacific) during the 1997 cruise of the RV Professor Logachev organised by the Interoceanmetal Joint Organization (IOM). A total of 102 morphospecies and morphotypes was recorded (28-69 per station), indicating an extremely diverse assemblage. Although most were found in the uppermost 2 cm, deeper sediment layers also yielded some species. This is one of only a few studies of komokiaceans and related organisms in this part of the Pacific. It contributes to baseline knowledge of abyssal communities in an area targeted for future commercial nodule mining operations