Life cycle and population dynamics of Pycnogonum litorale (Pycnogonida) in a natural habitat

A natural population of Pycnogonum litorale Ström was examined every 4 weeks over a period of 15 months and thereafter at yearly intervals for 15 years. Adult pycnogonids – mating couples and males carrying egg batches – and freshly hatched protonymphon larvae within these egg batches were found throughout the year. The second, third, and fourth instar larvae were only found from April to July, during the vegetation period of their hydroid host Clava multicornis. After metamorphosis to the fifth instar (first juvenile instar) the pycnogonids have a significantly larger proboscis than during the larval period, and they feed on the sea anemone Metridium senile. First juvenile instars were found on M. senile from May to August. Older and larger juvenile stages were found over longer time spans throughout the year, and the maximum number of successive instars shifted slowly from June to December. Freshly moulted adults occurred throughout the year. Males, which on the average are smaller, usually reach the adult stage during late autumn of the first year and females, at the end of the following spring. We conclude that in nature the development from egg to adult stage is completed within one year. Continuous reproduction and asynchronous embryonic development provide offspring throughout most of the year. The annual cycle is synchronized by the vegetation period of C. multicornis, the only host of these pycnogonid larvae in the investigated habitat, and by the arrest of growth during low winter temperatures. The low level of locomotory activity of P. litorale probably requires an environment in which both host species coexist. The abundance of C. multicornis, M. senile, and juvenile pycnogonids decreased from 1990 to 1996, maybe due to hydrographic conditions.     

Methyl tert-butyl ether (MTBE) in urban and rural precipitation in Germany

The use of the oxygenate methyl tert-butyl ether (MTBE) in gasoline has led to detectable concentrations in urban and rural air up to 160 ppbV. Results from MTBE measurement in precipitation have not been reported so far. In the present study, 120 samples of precipitation collected at 17 sampling locations all over Germany have been analyzed for their MTBE content. Analysis is performed by a combination of headspace-solid-phase microextraction (HS-SPME) and gas chromatography/mass spectrometry (GC-MS). A 75 μm poly(dimethylsiloxane)/Carboxene fiber and a cryostat is used for SPME. The detection limit is 10 ng/l. In precipitation samples, MTBE was detected in wintertimes only with a maximum concentration of 85 ng/l. Measurement at Frankfurt/M City from 6 September 2000 to 12 March 2001 provided for 49% of the data concentrations in the range of 30–85 ng/l (n=17). Sampling in winter 2000/2001 at several German cities and rural locations showed that MTBE is more often detectable in urban (86%, n=78) than in rural (18%, n=42) precipitation. By comparing the results with corresponding temperatures and amounts of precipitation it can be concluded that the detection of MTBE in urban precipitation is observed at ambient temperatures lower than about 10–15°C. Moreover, the first precipitation after a dry period accumulates more MTBE than precipitation during or at the end of a wet period (wash-out effect). Highest concentrations occurred in snow samples. Corresponding mean air equilibrium concentrations of 0.04 ppbV (urban samples) and 0.01 ppbV (rural samples) are calculated. This is about one magnitude lower than year round and summertime measurements in the US and in Switzerland. Urban runoff (n=12) and corresponding precipitation sampling indicate that urban runoff might be composed of about 20% MTBE that is already transported by air and precipitation, whereas about 80% may be attributed to direct uptake of vehicle emissions and leakage near the road during precipitation.     

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