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

Early anthropogenic transformation of the Danube-Black Sea system

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 2 (2012): 582, doi:10.1038/srep00582.Over the last century humans have altered the export of fluvial materials leading to significant changes in morphology, chemistry, and biology of the coastal ocean. Here we present sedimentary, paleoenvironmental and paleogenetic evidence to show that the Black Sea, a nearly enclosed marine basin, was affected by land use long before the changes of the Industrial Era. Although watershed hydroclimate was spatially and temporally variable over the last ~3000 years, surface salinity dropped systematically in the Black Sea. Sediment loads delivered by Danube River, the main tributary of the Black Sea, significantly increased as land use intensified in the last two millennia, which led to a rapid expansion of its delta. Lastly, proliferation of diatoms and dinoflagellates over the last five to six centuries, when intensive deforestation occurred in Eastern Europe, points to an anthropogenic pulse of river-borne nutrients that radically transformed the food web structure in the Black Sea.This study was supported by grants OISE 0637108, EAR 0952146, OCE 0602423 and OCE 0825020 from the National Science Foundation and grants from the Woods Hole Oceanographic Institution

The Mediterranean Sea Regime Shift at the End of the 1980s, and Intriguing Parallelisms with Other European Basins

Background: Regime shifts are abrupt changes encompassing a multitude of physical properties and ecosystem variables, which lead to new regime conditions. Recent investigations focus on the changes in ecosystem diversity and functioning associated to such shifts. Of particular interest, because of the implication on climate drivers, are shifts that occur synchronously in separated basins. Principal Findings: In this work we analyze and review long-term records of Mediterranean ecological and hydro-climate variables and find that all point to a synchronous change in the late 1980s. A quantitative synthesis of the literature (including observed oceanic data, models and satellite analyses) shows that these years mark a major change in Mediterranean hydrographic properties, surface circulation, and deep water convection (the Eastern Mediterranean Transient). We provide novel analyses that link local, regional and basin scale hydrological properties with two major indicators of large scale climate, the North Atlantic Oscillation index and the Northern Hemisphere Temperature index, suggesting that the Mediterranean shift is part of a large scale change in the Northern Hemisphere. We provide a simplified scheme of the different effects of climate vs. temperature on pelagic ecosystems. Conclusions: Our results show that the Mediterranean Sea underwent a major change at the end of the 1980s that encompassed atmospheric, hydrological, and ecological systems, for which it can be considered a regime shift. We further provide evidence that the local hydrography is linked to the larger scale, northern hemisphere climate. These results suggest that the shifts that affected the North, Baltic, Black and Mediterranean (this work) Seas at the end of the 1980s, that have been so far only partly associated, are likely linked as part a northern hemisphere change. These findings bear wide implications for the development of climate change scenarios, as synchronous shifts may provide the key for distinguishing local (i.e., basin) anthropogenic drivers, such as eutrophication or fishing, from larger scale (hemispheric) climate drivers

Decreased levels of the invasive ctenophore Mnemiopsis in the Marmara Sea in 2001

Mnemiopsis leidyi, an endemic ctenophore of the western Atlantic, was first reported in the Marmara Sea in summer 1992, at an average abundance of 27 ind. m(-3). We investigated its abundance and distribution together with that of the mesozooplankton (most species are prey organisms of M. leidyi) at eight stations during August 2001, in order to evaluate recent population developments with regard to the impact of its predator, Beroe cf ovata. The abundance of M. leidyi was found to be quite low (range 0.5-8.8 ind. m(-3), average 1.62 ind. m(-3)) compared to 1992. B. cf ovata was, although at very low abundance (0.1 - 1.1 ind. m(-3)), only present at stations where M. leidyi occurred. The zooplankton abundance was higher during our investigation than in previous years, which should at least partly be due to a decreased predation impact by M. leidyi

The first occurrence of the ctenophore Mnemiopsis leidyi in the North Sea

After the discovery of large densities of Mnemiopsis leidyi in the Baltic Sea near Kiel by Javidpour et al. (First record of Mnemiopsis leidyi A. Agassiz 1865 in the Baltic Sea, 2006) in October 2006, we investigated the gelatinous zooplankton in the North Sea near Helgoland and recorded Mnemiopsis leidyi for the first time in the North Sea, albeit in much lower densities than those recorded in the Baltic Sea

Development and lipid storage in Calanus euxinus from the Black and Marmara seas: Variabilities due to habitat conditions

Oil sac volume, gonad size and moulting patterns were investigated in the copepod Calanus euxinus inhabiting deep and shallow zones of the Black Sea and penetrating into the Marmara Sea. In summer the C. euxinus population in deep layers of the Black Sea was dominated by pre-diapause and diapausing postmoult copepodite stage V (CV) with small sexually undifferentiated gonads and mean lipid content of 14.1 +/- 6.0% of body volume. The lipid content of deep-living females was 7.2 +/- 4.2% of body volume. At the same time, intermoult and premoult CV with enlarged gonads and low lipid content (7.7 +/- 5.1% of body volume) and females with oil sac volume of 1.4 +/- 1.0% were found at shallow stations. Premoult CV with oil volume of 0.6 0.8% and mature females with little visual evidence of substantial lipid storage dominated in the Marmara Sea. The differences in moulting patterns and oil sac volumes of C. euxinus from deep zones and shallow regions suggest that vertical migrations to the oxygen minimum zone (OMZ) are necessary for formation of large lipid reserves providing high reproductive potential of this species. On the basis of an energy balance model it was shown that under low phytoplankton concentration of about 30 mu g C 1(-1) preadults and adults migrating to the OMZ could accumulate lipids (up to 5% of body energy content daily), in contrast to copepods constrained to shallow oxic water columns of the Black Sea and from the Marmara Sea. (c) 2005 Elsevier B.V. All rights reserved

Development and lipid storage in Calanus euxinus from the Black and Marmara seas: Variabilities due to habitat conditions

Oil sac volume, gonad size and moulting patterns were investigated in the copepod Calanus euxinus inhabiting deep and shallow zones of the Black Sea and penetrating into the Marmara Sea. In summer the C. euxinus population in deep layers of the Black Sea was dominated by pre-diapause and diapausing postmoult copepodite stage V (CV) with small sexually undifferentiated gonads and mean lipid content of 14.1 +/- 6.0% of body volume. The lipid content of deep-living females was 7.2 +/- 4.2% of body volume. At the same time, intermoult and premoult CV with enlarged gonads and low lipid content (7.7 +/- 5.1% of body volume) and females with oil sac volume of 1.4 +/- 1.0% were found at shallow stations. Premoult CV with oil volume of 0.6 0.8% and mature females with little visual evidence of substantial lipid storage dominated in the Marmara Sea. The differences in moulting patterns and oil sac volumes of C. euxinus from deep zones and shallow regions suggest that vertical migrations to the oxygen minimum zone (OMZ) are necessary for formation of large lipid reserves providing high reproductive potential of this species. On the basis of an energy balance model it was shown that under low phytoplankton concentration of about 30 mu g C 1(-1) preadults and adults migrating to the OMZ could accumulate lipids (up to 5% of body energy content daily), in contrast to copepods constrained to shallow oxic water columns of the Black Sea and from the Marmara Sea. (c) 2005 Elsevier B.V. All rights reserved

The ecological and physiological state of the ctenophore Mnemiopsis leidyi (Agassiz) in the Black Sea in autumn 1996

The survey was made in off-shore waters of the Black Sea near the Anatolian coast of Turkey during a research cruise of the R/V Bilim (24 Sept - 4 Oct 1996). The biomass of gelatinous macroplankton and the glycogen content in the body of the ctenophore Mnemiopsis leidyi were studied at 14 stations. Though the ctenophore still dominated the plankton in terms of biomass (average biomass +/- standard deviation 276 +/- 115 g/m(2)), this estimate was significantly lower than corresponding estimates obtained for the same months in recent years. A simultaneous reduction in the stock of small-sized fodder zooplankton and the large copepod Calanus euxinus indicates this case may be due to a general aggravation of trophic conditions for ctenophores. Data on the ctenophore's body glycogen content varied from 21 to 44 mu g/g fresh weight and accounted for 52.5 +/- 14.2% of total polysaccharide content on average, the condition of M. leidyi observed during the conducted survey corresponded to that expected after a two-day fasting period. Tentative experiments have shown that metabolic rates of the examined ctenophores were notably reduced. The rate of oxygen consumption (R, mu l O-2 . ind(-1) . h(-1)) was 1.7-1.8 less than that which would indicate a sufficient food supply; depending on the estimate of fresh body weight (UT, g) at 12-14 degrees C, it may be described by the following equation: R = 2.50 W-0.83

Physiological and ecological studies of Calanus euxinus (Hulsemann) from the Black Sea with comments on its life cycle

Ecological and physiological study of Calanus euxinus population from the Black Sea was carried out during the cruise of RN Bilim in Autumn 1996. The population was divided into two: active individuals, represented by all developmental stages, and diapausing CVs. The active CIV-CVIs underwent daily vertical migrations, while the diapausing CVs stayed at depth all day long. The population seemed to reproduce actively indicated by the large number of eggs and nauplii in the samples as well as the large proportion of spawning females (up to 80% of the total number of adult females). Egg production rate ranged from 5 to 25 eggs/female/day. The percentage of copepods with food changed with location and time; at night it varied from 10 to 97 in the upper layer, being less than 1 at the depth. Food remains was never observed in the guts of diapausing CVs. Up to 60% of gut in the upper layer, being less than 1 at the depth. Food remains was never observed in the guts of diapausing CVs. Up to 60% of gut contents consisted debris. The recognizable remains were parts of crustacean exoskeleton and dynoflagellates 10-60 mkm in size.Shipboard feeding experiments showed extremely low consumptions of chlorophyll (2.39-7.41 ng/ind/d in CVs and 5.67-14.33 ng/ind/d in females). The analysis of size classes distribution allowed the distinction of two groups among both diapausing and active CVs pointing on the heterogenity of the population. No difference between the length of males and females CVs was found. The state of gonad development differed between active and diapausing CVs. In the former gonad size ranged from 0.075 to 0.65 mm, in the latter small (0.1-0.15 mm) gonads before sex differentiation prevailed. An increase in gonad size was accompanied by a decrease in oil content. The active and diapausing CVs differed in their motor activity, respiration and excretion rates. Relationships between these indices and oxygen concentration were obtained. Under all oxygen concentrations studied, the indices for active CVs were higher than for diapausing CVs by a factor of 2 or 3