Non-lethal effects of the predator Meganyctiphanes norvegica and influence of seasonal photoperiod and food availability on the diel feeding behaviour of the copepod Centropages typicus.

Predators can induce changes in the diel activity patterns of marine copepods. Besides vertical migration, diel feeding rhythms have been suggested as an antipredator phenotypic response. We conducted experiments to assess the non-lethal direct effects of the predator Meganyctiphanes norvegica (northern krill) on the diel feeding patterns of the calanoid copepod Centropages typicus. We also analysed the influence of seasonal photoperiod and prey availability on the intensity of copepod feeding rhythms. We did not detect any large effect of krill presence on the diel feeding behaviour of copepods, either in day-night differences or total daily ingestions. Seasonal photoperiod and prey availability, however, significantly affected the magnitude of copepod feeding cycles, with larger diel differences in shorter days and at lower prey concentrations. Therefore, the role of non-lethal direct effects of predators on the diel feeding activity of marine copepods remain debatable and might not be as relevant as in freshwater zooplankton.

Toxicity of treated bilge water: The need for revised regulatory control.

Water accumulating in the bottom of ships (bilge water), contains a mixture of oil, detergents and other compounds from on board activities. To evaluate ecological effects of released bilge water the chemical composition and toxicity of treated bilge water from seven passenger ships was analysed. The oil content was below 15mgL-1, the threshold for legal discharge, in all but one ship. Still, significant reductions in feeding and reproduction of Acartia tonsa were found after 48h exposure in dilutions with 2.5-5% of bilge water. Mortality was significant at dilutions of 5-10% in 4 of the 5 bilge water samples. Surfactants were the most significant contributor to the toxicity on copepod vital rates and survival. Toxicity was also tested with Microtox where an EC50 was found at dilutions between 4.3% and 52%. The results show that ecological effects might occur also in diluted suspensions of bilge water.

Solid phase extraction and metabolic profiling of exudates from living copepods.

Copepods are ubiquitous in aquatic habitats. They exude bioactive compounds that mediate mate finding or induce defensive traits in prey organisms. However, little is known about the chemical nature of the copepod exometabolome that contributes to the chemical landscape in pelagic habitats. Here we describe the development of a closed loop solid phase extraction setup that allows for extraction of exuded metabolites from live copepods. We captured exudates from male and female Temora longicornis and analyzed the content with high resolution LC-MS. Chemometric methods revealed 87 compounds that constitute a specific chemical pattern either qualitatively or quantitatively indicating copepod presence. The majority of the compounds were present in both female and male exudates, but nine compounds were mainly or exclusively present in female exudates and hence potential pheromone candidates. Copepodamide G, known to induce defensive responses in phytoplankton, was among the ten compounds of highest relative abundance in both male and female extracts. The presence of copepodamide G shows that the method can be used to capture and analyze chemical signals from living source organisms. We conclude that solid phase extraction in combination with metabolic profiling of exudates is a useful tool to develop our understanding of the chemical interplay between pelagic organisms.

Evidence of diel vertical migration in Mnemiopsis leidyi.

The vertical distribution and migration of plankton organisms may have a large impact on their horizontal dispersal and distribution, and consequently on trophic interactions. In this study we used video-net profiling to describe the fine scale vertical distribution of Mnemiopsis leidyi in the Kattegat and Baltic Proper. Potential diel vertical migration was also investigated by frequent filming during a 24-hour cycle at two contrasting locations with respect to salinity stratification. The video profiles revealed a pronounced diel vertical migration at one of the locations. However, only the small and medium size classes migrated, on average 0.85 m h(-1), corresponding to a total migration distance of 10 m during 12 h. Larger individuals (with well developed lobes, approx. >27 mm) stay on average in the same depth interval at all times. Biophysical data suggest that migrating individuals likely responded to light, and avoided irradiance levels higher than approx. 10 µmol quanta m(-2) s(-1). We suggest that strong stratification caused by low surface salinity seemed to prohibit vertical migration.

The importance of uptake from food for the bioaccumulation of PCB and PBDE in the marine planktonic copepod Acartia clausi.

The accumulation of (14)C-labelled PCB 31, PCB 101, PCB 153 and PBDE 99 was investigated at the two lowest trophic levels of the pelagic food web. Accumulation was measured in the small phytoplankter Thalassiosira weissflogii (Coscinodiscophyceae: Thalassiosirales) and in the neritic zooplankter Acartia clausi (Copepoda: Calanoida) exposed to the substance either only via water or through ingestion of contaminated T. weissflogii. Bioaccumulation factors (BAFs) for all four compounds were significantly higher in A. clausi feeding on contaminated phytoplankton than in animals exposed only via water. The logBAF for the PCBs increased linearly with the octanol-water partitioning coefficients (logK(OW)) in both the algae and the copepods, but with steeper slopes for feeding than non-feeding animals. Reported values for K(OW) for PBDEs vary by almost an order of magnitude and it was therefore not meaningful to calculate a logBAF-logK(OW) ratio for PBDE 99. It is clear that the nutritional status of the zooplankton affects the uptake of the compounds and that the bioaccumulation cannot be modelled as a passive partitioning between the organisms and the surrounding water. Small copepods are typical of coastal waters and point sources (both temporal and spatial) may be the rule for HOC releases into the sea. Thus, the pathways shown in this study are important and realistic.

Passive partitioning of polychlorinated biphenyls between seawater and zooplankton, a study comparing observed field distributions to equilibrium sorption experiments.

From previous studies, it remains unclear whether polychlorinated biphenyls (PCBs) are biomagnified in zooplankton or if concentrations are simply governed by passive partitioning. In this study, in the Gullmar Fjord on the Swedish west coast, field-determined lipid-normalized partition coefficients (log Klip) were compared to equilibrium partition coefficients from laboratory sorption experiments with dead and preserved zooplankton. There was no significant difference between the linear regressions of log Klip-log Kow (analysis of covariance [ANCOVA], p < 0.05) for field and laboratory-determined partition coefficients, supporting passive partitioning being the dominant uptake pathway for PCBs in the Gullmar Fjord zooplankton. The field-observed partition coefficients were also suggestive of passive partitioning, as all field-log Klip-log Kow regressions were significant (p < 0.05, r2 = 0.74-0.95) and apparently linear. Further, there was generally no positive correlation between apparent biomagnification factors (BMF; concentration in zooplankton [pg/kgoc]/concentration in phytoplankton [pg/kgoc]) and trophic level (on the basis of delta15N). The in-situ organic carbon (-oc)-normalized concentrations in zooplankton (>200 microm) were not statistically different from oc-normalized concentrations in phytoplankton (0.7-50 microm), which supports the absence of significant biomagnification.