Annual cycle of the production and fate of DMS and DMSP in a marine coastal system

The production of DMSP by phytoplankton and the fate through the marine system of both DMSP and DMS were followed for a period of 21 mo in the natural environment by studying a Wadden Sea tidal inlet. The major production and emission of DMS appeared to be Limited to a period of only 2 mo, which was closely linked to the presence of phytoplankton blooms. The production of DMS in the water column was not well correlated with chlorophyll a concentrations or plankton species composition. It was however, found to be closely related to the start of a Phaeocystis bloom early in spring. Contrary to our expectations, the senescence phase of this Phaeocystis bloom did not result in high DMS accumulation. It is postulated that this phenomenon could be the result of a bacterial consumption which increased with time in combination with a decreasing DMSP-lyase activity of Phaeocystis. A simple model, into which the overall DMSP consumption could be introduced, could very well imitate the measured concentrations of DMS in the water column of the natural system studied

Demographic responses of Daphnia magna fed transgenic Bt-maize

The food/feed quality of a variety of genetically modified (GM) maize expressing Cry1Ab Bt-toxin was tested over the life-cycle of Daphnia magna, an arthropod commonly used as model organism in ecotoxicological studies. Demographic responses were compared between animals fed GM or unmodified (UM) near isogenic maize, with and without the addition of predator smell. Age-specific data on survival and birth rates were integrated and analysed using life tables and Leslie matrices. Survival, fecundity and population growth rate (PGR) data generally disfavoured transgenic Bt-maize as feed for D. magna compared to animals fed the unmodified (UM) near isogenic line of maize. Decomposition of age-specific effects revealed that the most important contributions to a reduced PGR in the GM-fed group came from both fecundity and survival differences early in life. We conclude that juvenile and young adult stages are the most sensitive experimental units and should be prioritized in future research. These stages are often omitted in toxicological/ecotoxicological studies and in feeding trials

Flash Flood simulation and valve behavior of Mytilus galloprovincialis measured with Hall sensors

Mussels close their shell as a protective strategy and the quantification of this behavioral marker may represent an alarm signal when they are exposed to environmental stressors. In the present study, we investigated the ability of the Mediterranean mussel Mytilus galloprovincialis to recover and then the resilience or inertia of valve activity after a pulsing exposition to diverse levels of salinity (5, 10, 20 and 35 PSU as reference value). The trial simulated an event of drastic and sudden reduction of seawater salinity thus mimicking an event of Flash Flood from intense rain. Valve gaping and movements were measured in continuous cycle for ten days using a customized magneto-electric device which uses Hall sensors. Results showed that under normal conditions of salinity (35 PSU) the general pattern of valve movements was a continuously open state with sporadic spikes indicating a closing motion. At salinity of 5 PSU mussels reacted by closing their valves, leading to a 77% mortality on the fourth day. At salinity of 10 PSU animals were observed with closed valves for the entire duration of the exposure and no mortality occurred, they showed a significant reduction in the valve activity once the reference value of salinity was re-established. In contrast, salinity of 20 PSU did not trigger a significant behavioral response. Interestingly, there no define rhythms of valve movements were recorded during salinity challenges

Dimethylsulphide production by plankton communities

The trends of dimethylsulphide (DMS) production by plankton communities in mesocosm systems were studied under various conditions. The results show that the DMS concentration in the water column can be highly variable over time, even within days, and under apparently identical conditions. DMS release in the water column appears to be highly correlated with phytoplankton senescence rather than growth. The development of the DMS peak could not be attributed to the zooplankton activity. It is argued that bacterial consumption may be an important sink for DMS