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Cambridge
Scientific Abstracts Database: Record 21 of 64 TI: Title Transparency measurements (at 400 to 700 nm) were made on living specimens of 29 common species of gelatinous zooplankton from the Northwestern Atlantic Ocean and Gulf of Mexico. Percent transparency ranged from 91% for the hydromedusa Sibogota typa to 0.51% for the pteropod Clione limacina. Percent transparency was linearly and positively correlated with wave-length, with slopes of the regression lines (normalized to the percent transparency at 480 nm) ranging from 0.027%/nm for Sibogota typa to 0.51%/nm for the ctenophore Mnemiopsis macrydi (average 0.17 plus or minus 0.019%/nm). There was no significant correlation between the percent transparency of an animal and its daytime depth distribution. The relationship between percent transparency and sighting distance when viewed from below was modeled and showed that, due to the increase of the minimum contrast threshold for object detection at lower light levels, the usefulness of transparency as camouflage increases dramatically with depth. A preliminary account of these results was presented by the authors at the fourteenth meeting of the Ocean Optics Society in November 1998. Record 22 of 64 TI: Title Historical stock assessments of the Black Sea sprat (1957-1992) and whiting (1976-1992) have been performed using Virtual Population Analysis. Relationships between fish stock parameters (recruitment, spawning biomass, mortality rates) and environmental variables (wind speed and duration, sea temperature, light, phyto- and zooplankton biomasses) have been analyzed using multiple regression models. Strong correlation has been found between sprat recruitment and western winds during November-December and January-March. The western winds force the upwelling of deep waters and their progress shorewards. As the upwelled waters are rich in nutrients and organic matter, they contribute to the intense productivity in ihe Black Sea. The role of the other variables appears to be less significant. The need for including more reliable data on plankton and ctenophore Mnemiopsis niaccradii in the analysis is pointed out. Record 23 of 64 TI: Title The object of investigations is a model research of Mnemiopsis (Ctenophora) distribution in the Black Sea (Russia) ecosystem as well as its temporary variability. The Ctenophora distribution is supposed to be formed under the influence of its growth, reproduction and death and also due to its transference with water masses. Seasonal and interannual variability of the number and biomass as well as the total biomass for the different periods of the year are considered. Record 24 of 64 TI: Title Peritrich ciliates of the genus Trichodina are internal or external symbionts of invertebrate and vertebrate hosts. We describe here Trichodina ctenophorii n. sp., a symbiont of Mnemiopsis mccraydii and Beroee ovata (Phylum Ctenophora). The morphology of fixed and living specimens is revealed by silver impregnation, scanning electron microscopy, and differential interference microscopy. Distinguishing features of Trichodina ctenophorii include a denticular morphology composed of falcate, blunt-tipped blades, and long, straight thorns, with five pins per denticle. Trichodina ctenophorii is found only on the comb plates of these ctenophores. To the best of our knowledge, this is the first report of a trichodinid from the Gulf of Mexico and the first associated with ctenophores. Record 25 of 64 TI: Title Ctenophores (Mnemiopsis leidyi) are a phylum of diploblastic marine animals displaying biradial symmetry organized along an oral-aboral axis. One of the apomorphic sets of adult structures in ctenophores are the eight external comb rows, which run along the oral-aboral axis. Comb rows consist of serial arrays of individual comb plates of cilia, which beat in a coordinated fashion for locomotory behavior. Classical cell lineage experiments using chalk particles indicated that comb rows are derived exclusively from the four e sub(1) micromeres at the 16-cell stage. This conclusion was also supported by the fact that no ctene rows (or their underlying endodermal canals) form when all four e sub(1) micromeres were deleted. We have used intracellular diI cell lineage tracing to determine that, in addition to e sub(1) micromeres, the four m sub(1) micromeres also make significant contributions to the ctene rows. Thus, e sub(1) micromere derivatives not only generate comb plates but are required for ctene row formation by m sub(1) derivatives. These results demonstrate that inductive interactions are an important component of early development in ctenophores and indicate that e sub(1) micromeres influence the development of adjacent cell lineages (both m sub(1) and endodermal lineages) during ctenophore embryogenesis. In addition, intracellular labeling has revealed that there are subtle variations in the composition of clones derived from identified embryonic blastomeres. Together these findings reveal a picture of ctenophore embryogenesis, which is in marked contrast to the former rigid 'mosaic' reputation of ctenophore development, and invite speculation as to the role of the cleavage program in embryonic patterning in the lower Metazoa. Record 26 of 64 TI: Title After a short introduction describing the environmental status of the Black Sea, information is presented on the marine algae, and the phytoplankton and zooplankton, including the events following the introduction of the predatory ctenophore, Mnemiopsis leydei. The existing historical information available on the resources of more than 14 commercial fish in the Black Sea is summarized, and placed in context with information on the marine environment together with an evaluation of the impact of environment changes. Record 27 of 64 TI: Title After a short introduction describing the environmental status of the Black Sea, information is presented on the marine algae, and the phytoplankton and zooplankton, including the events following the introduction of the predatory ctenophore, Mnemiopsis leydei. The existing historical information available on the resources of more than 14 commercial fish in the Black Sea is summarized, and placed in context with information on the marine environment together with an evaluation of the impact of environment changes. Record 28 of 64 TI: Title The ctenophore Mnemiopsis leidyi is known to be eaten by the scyphomedusan Chrysaora quinquecirrha, which can control populations of ctenophores in the tributaries of Chesapeake Bay. In the summer of 1995, we videotaped interactions in large aquaria in order to determine whether M. leidyi was always captured after contact with medusae. Surprisingly, M. leidyi escaped in 97.2% of 143 contacts. The ctenophores increased swimming speed by an average of 300% immediately after contact with tentacles and 600% by mid-escape. When caught in the tentacles of C. quinquecirrha, the ctenophores frequently lost a portion of their body, which allowed them to escape. Lost parts regenerated within a few days. The striking ability of M. leidyi to escape from C. quinquecirrha may be critically important in maintaining ctenophore populations in situ. Record 29 of 64 TI: Title The use of intracellular lineage tracers in conjunction with simple operative techniques has been instrumental in establishing the fates of identified blastomeres during development and regeneration. By injecting the fluorescent lineage tracer DiI into identified blastomeres of the lobate ctenophore Mnemiopsis leidyi, we recently showed that the eight rows of locomotory comb plates characteristic of the Ctenophora are derived, not from one, but from two distinct embryonic cell lineages, the m sub(1) as well as the e sub(1) micromeres. Killing e sub(1) micromeres at the 16-cell stage leads to the complete absence of comb plate formation during the embryonic period; therefore, the e sub(1) micromere lineage is required to induce comb plates from m sub(1) lineage descendants. This "organizing activity" of distinct cell lineages (e sub(1) descendants) is surprising given the widely touted "mosaic" nature of ctenophore development. Record 30 of 64 TI: Title A complex method of race determination based on the genetic, parasitological and morphological traits of the population was proposed to obtain a reliable scheme of distribution and migrations of the Azov and Black Sea anchovy (Engraulis encrasicolus) stocks. The abundance of anchovy was determined using the data from surveys performed with standard trawl and hydroacoustic equipment. Experiments revealed considerable changes in the Azov anchovy's gene pool. The main reason was the increasing of water salinity as a result of river in-flow regulation. The excessive industrial catching also promoted the process. As a result, the proportion of hybrids increased. According to the data of the acoustic surveys in the waters of the former USSR in the period from 1980 to 1988, the average biomass of the Black Sea anchovy aggregations was 309,000 tons, and the biomass of the Azov anchovy, 169,000 tons. Since 1988 the situation of these stocks have dramatically changed. A great decrease of the populations has occurred. That has in all evidence been caused by excessive captures of anchovy by the USSR and Turkey. An additional important negative factor were the intrusions of a jellyfish, Mnemiopsis leidyi. The biomass of the anchovy near the Georgian coast increased up to 165,000 tons after the Mnemiopsis outbreak had passed its peak in winter 1991-92. Record 31 of 64 TI: Title One characteristic set of structures displayed by most adult ctenophores are the eight longitudinal rows of comb plates (comb or ctene rows) that are used for locomotion. Comb plates arise from polster cells of the outer epidermis and are composed of hundreds of thousands of individual cilia bound together by compartmenting lamellae. Ctenophores have a highly stereotyped cleavage pattern, so individual blastomeres can be identified and their fates followed throughout embryogenesis. Previous cell lineage experiments, using chalk particles, revealed that each pair of comb rows is derived from one of the four e sub(1) micromeres. Deletion of e sub(1) micromeres prevents the formation of ctene rows and their associated endodermal canals during the embryonic period, supporting this cell fate assignment. We killed two adjacent adesophaeal e sub(1) micromeres of the ctenophore Mnemiopsis leidyi with glass needles at the 16-cell stage and then injected two other identified blastomeres in the surviving embryo with the fluorescent lineage tracer DiI dissolved in soybean till according to previously published techniques. The blastomeres injected included the two 1E macromeres, two 1M macromeres, and two m sub(1) micromeres which were all located on the same side as the two deleted e sub(1) micromeres. In addition, we wanted to see whether the same lineage that makes ctene plates during embryogenesis also makes them during 'post-generation', and so we also injected the two surviving e sub(1) micromeres on the side of the embryo opposite the two deleted e sub(1) micromeres. This operation generated post-embryonic juveniles (cydippid larvae) that were completely deficient in four of their eight ctene rows. Experimental embryos were examined 24-72 h after the operation for the presence of DiI in their newly formed (post-generated) comb plates. Record 32 of 64 TI: Title Clearance rates of Chrysaora quinquecirrha ephyrae were quantified in the laboratory using monocultures of different plankton organisms as prey, as well as mixed natural zooplankton assemblages. Further, growth of ephyrae was measured at different densities of rotifers or ctenophores as prey. The ciliate Strobilidium (strain CRE) and the rotifer Brachionus plicatilis were cleared in monocultures at medium rates: 4 ml/h /ind. and 1 ml/h/ind. respectively. Clearance of copepod nauplii was low (0.5 ml/h/ind.) and the dinoflagellates Gymnodinium sanguineum were not eaten by the ephyrae. In a mixed zooplankton assemblage, rotifers and copepod nauplii were cleared at rates similar to those obtained in monocultures, and tintinnids also were eaten. In contrast, larvae of the ctenophore Mnemiopsis leidyi were cleared at a much higher rate (30 ml/h/ind.) than microzooplankton. When the rotifer B. plicatilis were offered in excess to ephyrae, a maximum specific growth rate of 0.3/d was measured. Growth rate more than doubled (0.7/d) when ctenophore larvae were offered. The growth rate obtained on ctenophore larvae is the highest rate reported so far for any scyphomedusan species. We suggest that M. leidyi may be of critical importance for the high growth of C. quinquecirrha ephyrae in natural populations during springtime in Chesapeake Bay, USA. Record 33 of 64 TI: Title Clearance rates of Chrysaora quinquecirrha ephyrae were quantified in the laboratory using monocultures of different plankton organisms as prey, as well as mixed natural zooplankton assemblages. Further, growth of ephyrae was measured at different densities of rotifers or ctenophores as prey. The ciliate Strobilidium (strain CRE) and the rotifer Brachionus plicatilis were cleared in monocultures at medium rates: 4 ml/h /ind. and 1 ml/h/ind. respectively. Clearance of copepod nauplii was low (0.5 ml/h/ind.) and the dinoflagellates Gymnodinium sanguineum were not eaten by the ephyrae. In a mixed zooplankton assemblage, rotifers and copepod nauplii were cleared at rates similar to those obtained in monocultures, and tintinnids also were eaten. In contrast, larvae of the ctenophore Mnemiopsis leidyi were cleared at a much higher rate (30 ml/h/ind.) than microzooplankton. When the rotifer B. plicatilis were offered in excess to ephyrae, a maximum specific growth rate of 0.3/d was measured. Growth rate more than doubled (0.7/d) when ctenophore larvae were offered. The growth rate obtained on ctenophore larvae is the highest rate reported so far for any scyphomedusan species. We suggest that M. leidyi may be of critical importance for the high growth of C. quinquecirrha ephyrae in natural populations during springtime in Chesapeake Bay, USA. Record 34 of 64 TI: Title Eggs and yolk-sac larvae of bay anchovy, Anchoa mitchilli, were surveyed at seven sites in Chesapeake Bay on 12 days in July 1991 to estimate abundances and mortality rates of daily cohorts and the relative biomasses of adults that spawned them. An objective was to determine variability in abundance and mortality rates among sites and survey dates. Estimated abundances of eggs spawned each day and their hourly mortality rates were considered in relation to 1) in situ predator abundances, 2) environmental factors, and 3) initial egg and yolk-sac larval abundances. The mean initial abundance of bay anchovy eggs on each day during the 12 experiments was 6,630 eggs/m super(2) (427.0/m super(3)). Mean initial abundance of yolk-sac larvae was 385 larvae/m super(2) (24.6/m super(3)). Mean adult biomass at the survey sites, estimated from the egg productions, was 18.0 g/m super(2) (1.16 g/m super(3)). A correlation analysis indicated that spawning by bay anchovy may be most intense in areas with high zooplankton biomass and where the ctenophore Mnemiopsis leidyi, a potential predator on eggs and larvae, was least abundant. Mean cohort instantaneous egg mortality was 0.066 eggs/h; on average, 73% of spawned eggs died before hatching. Yolk-sac larvae incurred a mean cohort instantaneous mortality of 0.053/h, i.e. 64% mortality during the first 24-h posthatch. Together, the mean egg and yolk-sac larval mortality rates indicated that >93% of bay anchovy daily cohorts die within 2 days after egg fertilization and before larvae reach the first-feeding stage. The range of cohort-specific mortality rates at a single station sampled on five consecutive days was equal to that observed at the seven sites. The high abundances, combined with high and variable cohort mortality rates, emphasize the probable importance of the egg and yolk-sac larval stages in the recruitment process of bay anchovy. Record 35 of 64 TI: Title The ctenophore (Mnemiopsis leidyi) first recorded in the Azov Sea in 1988 is regarded as a biological pollutant. Changes in the aquatic communities since 1988 are considered in relation to the ctenophore population dynamics. Record 36 of 64 TI: Title Record of encysted metacercariae in hydrozoan jellyfishes
and ctenophores of the southern Atlantic Three species of pelagic coelenterates and ctenophores captured in Mar del Plata port, Buenos Aires, Argentina, were examined for digenean parasites. Encysted metacercariae were observed and collected. Cysts were found in the mesoglea of the hydromedusae Phialidium sp. and Liriope tetraphylla, and in the ctenophore Mnemiopsis macradyi. The morphology of the worms resembles that of the lepocreadiid digeneans. This is the first Record for a metacercaria encysted in hydromedusae or ctenophores. Record 37 of 64 TI: Title Material collected in October 1992 is analyzed for the composition, biomass and production of phytoplankton, the abundance, biomass and production of bacteria, the composition and distribution of planktonic protazoans as well as the store of assimilable organic matter in the water column, the store of labile sulphides in bottom sediments and their turnover rate. The data are used to evaluate the ecological state of the Marmara Sea at the time of the ctenophore Mnemiopsis leidyi outbreak. Record 38 of 64 TI: Title After a short introduction describing the environmental status of the Black Sea, information is presented on the marine algae, and the phytoplankton and zooplankton, including the events following the introduction of the predatory ctenophore, Mnemiopsis leydei. The existing historical information available on the resources of more than 14 commercial fish in the Black Sea is summarized, and placed in context with information on the marine environment together with an evaluation of the impact of environmental changes. Record 39 of 64 TI: Title The lobate ctenophore Mnemiopsis leidyi is a periodically abundant and voracious plankton predator in coastal waters along the east coast of the United States. In the 1980s it was accidentally introduced to the Black Sea where it caused a dramatic reduction in fisheries. We investigated how M. leidyi is affected by infestation with parasitic larvae of the sea anemone Edwardsia lineata. Infested M. leidyi contained 1-30 (median 7) E. lineata larvae. Within M. leidyi most larvae had their mouth in the gastrovascular system near the aboral end of the pharynx. Parasitic E. lineata ingested all food previously ingested and pre-digested by M. leidyi. Non-infested M. leidyi had higher growth rates than infested individuals, which had zero or negative growth rates. Egg production was similar for infested and non-infested M. leidyi of similar size. Simulation based on the empirical data suggests that growing, non-infested, M. leidyi are expected to have a larger life-time egg production than infested shrinking individuals. E. lineata could be at least partially responsible for the sharp decline of M. leidyi populations in fall in US coastal waters. Advantages and disadvantages of E. lineata as a potential candidate for the control of the artificially introduced M. leidyi population in the Black Sea are discussed. Record 40 of 64 TI: Title The Turkish straits system, the Dardanelles, Bosphorus and Marmara Sea, represents a transitional zone between the Mediterranean and Black Sea basins. As such it constitutes either a barrier, a corridor or an accl imatization zone for living organisms. The peculiar hydrological characters of the Turkish straits limit the distribution of some species. Once major biological corridors for pelagic fish migrating between the Mediterranean and the Black Sea, they have ceased to be so due to the destabilization of the pelagic and benthic ecosystems. On the other hand the straits allow the acclimatisation of certain species of Mediterranean origin, such as decapod crustaceans, anthozoans and sponges, penetrating to the Marmara Sea and Black Sea. Alien species, such as Rapana thomasiana, Mnemiopsis leidyi and Cunearca cornea, have also become resident. Major sources of pollution, overfishing, ship accidents and heavy marine traffic, constitute major threats for the biological diversity of the Turkish straits system and hence for the ecological balance of adjacent seas, as exemplified by the disappearance of resident populations of Phocoena phocoena, Tursiops truncatus, Delphinus delphis and Monachus monachus from the straits. |
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