Species Composition of Benthic Diatoms and Distribution of Chlorophyll a on an Intertidal Flat in the Dutch Wadden Sea

A linear transect with 12 sampling points was sampled in a tidal estuarine environment during 1973 for chlorophyll a and pheophytin, and for species composition of epipelic diatoms. A gradual pattern in sediment from coarse to fine was found from the most seaward station towards the most landward station of the transect. Differences in station level gave emersion times of 37 to 67 % of the tidal cycle. In the course of the year, fluctuations in chlorophyll a content (mg chlorophyll a m-* in the top 2 cm of the sediment) appeared to be distinctly parallel at all stations. However, mean yearly values differed widely from station to station, ranging between 20 and 100mg chlorophyll a m-2. Chlorophyll a concentration was positively related to the amount of particles < 16 pm in the sediment; this proportion was considered to relate negatively to the degree of exposure to currents and wave action. It is likely that low daily winter irradiances limited diatom growth. Heavy rain and strong wave action during storms suddenly reduced the chlorophyll a content considerably. Species composition of epipelic benthic diatoms could partly be related to the sediment gradient and time of year. It seems that high biomass values are formed almost exclusively by single species which are indifferent in their spatial distribution

Method of plant tissue culture and regeneration

Plants may be regenerated from stomatal cells or protoplasts of such cells. Prior to regeneration the cells or protoplasts may be genetically transformed by the introduction of hereditary material most preferably by a DNA construct which is free of genes which specify resistance to antibiotics. The regeneration step may include callus formation on a hormone-free medium. The method is particularly suitable for sugar beet

The cost-effectiveness of alternative vaccination strategies for polyvalent meningococcal vaccines in Burkina Faso: A transmission dynamic modeling study.

BACKGROUND: The introduction of a conjugate vaccine for serogroup A Neisseria meningitidis has dramatically reduced disease in the African meningitis belt. In this context, important questions remain about the performance of different vaccine policies that target remaining serogroups. Here, we estimate the health impact and cost associated with several alternative vaccination policies in Burkina Faso. METHODS AND FINDINGS: We developed and calibrated a mathematical model of meningococcal transmission to project the disability-adjusted life years (DALYs) averted and costs associated with the current Base policy (serogroup A conjugate vaccination at 9 months, as part of the Expanded Program on Immunization [EPI], plus district-specific reactive vaccination campaigns using polyvalent meningococcal polysaccharide [PMP] vaccine in response to outbreaks) and three alternative policies: (1) Base Prime: novel polyvalent meningococcal conjugate (PMC) vaccine replaces the serogroup A conjugate in EPI and is also used in reactive campaigns; (2) Prevention 1: PMC used in EPI and in a nationwide catch-up campaign for 1-18-year-olds; and (3) Prevention 2: Prevention 1, except the nationwide campaign includes individuals up to 29 years old. Over a 30-year simulation period, Prevention 2 would avert 78% of the meningococcal cases (95% prediction interval: 63%-90%) expected under the Base policy if serogroup A is not replaced by remaining serogroups after elimination, and would avert 87% (77%-93%) of meningococcal cases if complete strain replacement occurs. Compared to the Base policy and at the PMC vaccine price of US$4 per dose, strategies that use PMC vaccine (i.e., Base Prime and Preventions 1 and 2) are expected to be cost saving if strain replacement occurs, and would cost US$51 (-US$236, US$490), US$188 (-US$97, US$626), and US$246 (-US$53, US$703) per DALY averted, respectively, if strain replacement does not occur. An important potential limitation of our study is the simplifying assumption that all circulating meningococcal serogroups can be aggregated into a single group; while this assumption is critical for model tractability, it would compromise the insights derived from our model if the effectiveness of the vaccine differs markedly between serogroups or if there are complex between-serogroup interactions that influence the frequency and magnitude of future meningitis epidemics. CONCLUSIONS: Our results suggest that a vaccination strategy that includes a catch-up nationwide immunization campaign in young adults with a PMC vaccine and the addition of this new vaccine into EPI is cost-effective and would avert a substantial portion of meningococcal cases expected under the current World Health Organization-recommended strategy of reactive vaccination. This analysis is limited to Burkina Faso and assumes that polyvalent vaccines offer equal protection against all meningococcal serogroups; further studies are needed to evaluate the robustness of this assumption and applicability for other countries in the meningitis belt

Annual variability in the seasonal cycles of chlorophyll, nutrients and zooplankton on the North-West European continental shelf

Seasonal cycles of salinity, nutrients, chlorophyll and zooplankton at 8 locations on the West-European shelf were analysed with respect to their timing and magnitude in the period 1980-1984. A late spring bloom with low chlorophyll values (2-4 mg.m-³) is observed in the Irish Sea, off the Scottish east coast and the Channel entrance. An early spring bloom and relatively high chlorophyll values (7-12 mg.m-³) are found in the southern Bight and the Skagerrak, whereas a late spring bloom with high chlorophyll concentrations (24 mg.m-³) is found along the Dutch and Belgian coast. In contrast to the other regions, the peak of the phytoplankton cycle in the German Bight (Helgoland) occurs in the summer period instead of the spring period. The peak in the yearly abundance of copepods shifts from May-June in the south to July-August in the north of the shelf. In the Irish Sea and the Channel entrance two seasonal copepods peaks are observed. The January nitrate values in Irish Sea, the southern Bight and the Skagerrak are about 20 % higher than those in the Atlantic input signal in the Channel entrance and east off Scotland. The January DIP values in these regions are comparable to those of the input signal, but the Irish Sea forms an exception here the level is increased by 10-20%. If compared with the Atlantic input signal the January values for nitrate and DIP at the Dutch and Belgium coast are about 10 and 4, and in the German Bight (Helgoland) 4 and 3 times higher, respectively. At most sites changes in the seasonal cycles of chorophyll coincide with changes in nutrient concentrations, wheras the maximum level of the seasonal signal is related to the nutrient levels

Future observational and modelling needs identified on the basis of the existing shelf data

NOWESP has compiled a vast quantity of existing data from the North-West European Shelf. Such a focused task is without precedence. It is now highly recommended that one, or a few national and international data centres or agencies should be chosen and properly supported by the EU, where all available observational data, including the NOWESP data, are collected, stored, regularly updated by the providers of the data, and made available to the researchers. International agreement must be reached on the quality control procedures and quality standards for data to be stored in these data bases. Proper arrangements should be made to preserve the economic value of the data for their "owners" without compromising use of the data by researchers or duplicating data collecting efforts. The continental shelf data needed are concentration fields of temperature, salinity, nutrients, suspended matter and chlorophyll, which can be called "climatological" fields. For this purpose at least one monthly survey on the whole European shelf is needed at least during five years, with a proper spatial resolution e.g. 1 degree by 1 degree, and at least in those areas where climatological data are now totally lacking. From the modelling point of view an alternative would be the availability of data from sufficiently representative fixed stations on the shelf, with weekly sampling for several years