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

Chemical composition, respiration and feeding rates of the new alien ctenophore, Beroe ovata, in the Black Sea

Maximum daily rations of the ctenophore Beroe ovata Brugiere and predatory impacts on the Mnemiopsis leidyi A. Agassiz population were estimated via digestion time, prey biomass and predator and prey density in Sevastopol Bay and adjacent water regions. Digestion times ranged from 0.5 to 5.2 h and depended on the prey/predator weight ratio. Overall, the mean daily ration was 45% of B. ovata wet weight. Preliminary conclusions are given on the B. ovata population as an effective control of the M. leidyi population and on the dynamics and structure of the planktonic community as a whole

Chemical Composition respiration and feeding ratesof the new alien ctenophore berae ovata in the black sea

Maximum daily rations of the ctenophore Beroe ovata Brugiere and predatory impacts on the Mnemiopsis leidyi A. Agassiz population were estimated via digestion time, prey biomass and predator and prey density in Sevastopol Bay and adjacent water regions. Digestion times ranged from 0.5 to 5.2 h and depended on the prey/predator weight ratio. Overall, the mean daily ration was 45% of B. ovata wet weight. Preliminary conclusions are given on the B. ovata population as an effective control of the M. leidyi population and on the dynamics and structure of the planktonic community as a whole

Respiration rates of Beroe ovata in the Black Sea

Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20degreesC the respiration rates (Q, mug O-2 ind.(-1) h(-1)) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W(0.62) and Q=0.016W(0.99), respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021-100 mg diminished approximately 20-fold (from 0.35 to 0.017 mug O-2 mg(-1) h(-1), respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10-28degreesC, the mean Q(10) coefficient was equal to 2.17+/-0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5+/-0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity

Feeding, respiration and growth of ctenophore Beroe cf ovata in the low salinity conditions of the Caspian Sea

The ctenophore Beroe cf ovata, which spontaneously entered the Black Sea in the 1990s and suppressed the previous ctenophoran invader Mnemiopsis leidyi by its predatory impact, is currently considered for intentional introduction to the Caspian Sea as well. In order to assess its impact on Mnemiopsis in the Caspian, Beroe was transported during 2002 from the Black Sea and the Bosporus to the Khazerabad laboratory (Mazandaran), on the Caspian coast of Iran, where experiments on its survival in Caspian water, and on various physiological characteristics (feeding, respiration, reproduction and growth) of both ctenophore species were performed. Beroe cf ovata was found to adjust to Caspian salinity conditions without problems

Population dynamics, ingestion, growth and reproduction rates of the invader Beroe ovata and its impact on plankton community in Sevastopol Bay, the Black Sea

The impact of the introduced ctenophore Beroe ovata on its prey Mnemiopsis leidyi, another invader ctenophore voraciously feeding on mesozooplankton, and consequently on the mesozooplankton community, was evaluated by undertaking both laboratory and field studies in the northern Black Sea. Ingestion and growth rates as well as the gross growth efficiency of B. ovata were estimated from laboratory experiments. The daily ration of ctenophores was related to food abundance within a wide range of prey concentration and never reached saturation. Beroe ovata required high food rations (not less than 20% of body weight per day) for growth. The abundances, biomasses and population structures of these two introduced ctenophore species were also monitored, along with mesozooplankton, in inshore waters of the northern Black Sea (i.e. Sevastopol Bay and adjacent regions) over a period of 3 years (1999-2001) which is after B. ovata's arrival. The annual dynamics of the M. leidyi population were similar for the last 3 years: very low abundances and biomass values were observed during most of the year (unlike the previous years), with a sudden increase in summer-early autumn, but only for about a 2 month period. The B. ovata bloom during the peak M. leidyi biomass resulted in the M. leidyi biomass falling sharply to extremely low values. The predatory impact of M. leidyi on prey zooplanton was found to be reduced during the period of study compared with before

Physiological characteristics of the ctenophore Beroe ovata in Caspian Sea water

Riparian countries of the Caspian Sea have been evaluating the pros and cons of the predatory ctenophore Beroe ovata as a control agent against the invasive ctenophore Mnemiopsis leidyi, which has enormous adverse impacts on the fishery resources as well as on the biodiversity in this once fertile sea. To assess the viability of B. ovata establishment in the Caspian Sea, the survival and some physiological characteristics (feeding, respiration, reproduction and growth) of the predatory ctenophore were studied in Caspian Sea water (12.6 ppt salinity) conditions using animals transported from the Black and Marmara Seas to a laboratory on the Iranian Caspian coast. The findings of the study showed that when salinity was gradually decreased from 22 to 12.6 ppt, B. ovata were able to adapt well to Caspian Sea water. Most of the predatory ctenophores began to swim actively and to feed on M leidyi within 15 to 30 min following each step of acclimation. The feeding rate of B. ovata ranged from 14 to 765% of body wet weight and was highest for smaller individuals (i.e. 13 to 16 nun). Over the measured weight range of 0.23 to 3.87 g wet wt, the weight-specific respiration rate was independent of weight. The daily specific growth rate of adult ctenophores was 7 to 11% of body wet wt. B. ovata specimens were spawned and their eggs were hatched in Caspian Sea water, but the larvae survived for only a few hours. The energy budget of B. ovata calculated from food consumption, respwiration and growth rates revealed a mean assimilation efficiency of 0.72 +/- 0.1, a gross growth efficiency (K-1) of 0.48 +/- 0.12 and a net efficiency (K-2) of 0.66 +/- 0.06. Based on these physiological data, we suggest that in the Caspian Sea, B. ovata will be able to ingest M. leidyi intensively. However, concerning the reduction of the M leidyi population and consequently the reversal of its adverse impact on this ecosystem, the failure of larval growth observed under experimental conditions (most probably due to poor handling) remains the main obstacle to overcome in the successful establishment of B. ovata in the Caspian Sea