Particle capture in the musselMytilus edulis: The role of latero-frontal cirri

Microscope video graphs of particle paths near one-filament-thick mussel gill preparations, stimulated with a nerve transmitter (10^–6 M serotonin which restores normal ciliary activity), were used to disclose the capture of 6 m algal cells. Suspended algal cells carried with the water were stopped for a while at the entrance to the interfilament gap by the action of the latero-frontal cirri (Ifc), and transferred to the frontal side of the filament to be transported towards the marginal food groove. The event of transfer took place during approximately a time interval of 1150 to 1/25 s. To gain a better understanding of the capture mechanism and retention efficiency versus particle size, the flow through and around the Ifc was theoretically estimated. Normally beating Ifc create periodic, unsteady, three-dimensional flows at the entrance to the interfilament canal. During the active beat most of the water is deflected to flow around the branching cilia of the Ifc while some of the water is strained by these. Large particles (> 4 m) are stopped and transferred to the frontal current, whereas smaller particles either follow the flow around the Ifc and escape or they are stopped by the branching cilia.     

Seasonal differences in citrate synthase and digestive enzyme activity in larval and postlarval antarctic krill, Euphausia superba

Antarctic krill maintain large population sizes despite dramatic seasonal fluctuations in food availability, but the mechanisms for this are still debated. The aim of this study was to compare seasonal differences in enzyme activity and respiration rates of larval and postlarval krill to provide insights into their overwintering strategies. Respiration rates, activity of the metabolic enzyme citrate synthase (CS), and those of the digestive enzymes laminarinase and total proteinase were measured in austral summer west of the Antarctic Peninsula, and in autumn in the southwestern Lazarev Sea. The 100-fold difference in chlorophyll a concentrations between the two studies is representative of the classic transition from a summer bloom to sparse winter conditions. Correspondingly, adult krill showed reduced respiration rates and CS activity in autumn. However, their digestive enzyme activity was significantly higher, suggesting more efficient assimilation of food at low food levels. Similar-sized larvae showed no summer-autumn differences in respiration rates and enzyme activity, supporting suggestions that they need to feed and grow year-round. However, trends in enzymatic activity varied between the larval stages measured, implying ontogenetic changes in body structure and function. Published online: 1 August 2002     

The inactive temporary component: an unexplored fraction of meiobenthos

Numerous morphotypes and great abundances of resting stages falling within the meiobenthic size-range were found in meiobenthos samples collected in a coastal lagoon of the North Adriatic Sea. Biodiversity, abundances and energetic values of both active and inactive meiobenthic organisms were analysed by the traditional techniques of meiobenthology. Inactive stages were represented by more than 100 morphotypes and formed 52% of the meiobenthos in terms of numbers of individuals. Inactive meiobenthos came mostly from plankton: the second and third most abundant groups of all meiobenthic organisms were the eggs of a rotifer and the cysts of a dinophyte, respectively. Resting stages of plankters fit the definition of temporary meiobenthos, making up the “inactive temporary meiobenthos”, but they are usually not considered in meiobenthology. The diversity and abundance of the meiobenthos is, thus, currently underestimated; this leads to neglect of the role of meiobenthos in several processes linking different ecosystems. It is hypothesised, for instance, that the meiobenthic resting stages of planktonic organisms (besides being the “seeds” for the perpetuation of planktonic communities) might also be the prey of meiofaunal organisms with piercing mouth parts. If this proves correct, a regulatory role might be proposed for the meiofauna in respect to plankters with benthic stages. Received: 10 September 1998 / Accepted: 12 April 1999     

Adsorption von Blei und Cadmium an Tonen

Clay minerals as major components of soils can adsorb heavy metals. The release of toxic heavy metals such as lead and cadmium into soil presents a serious problem. To evaluate the behaviour of these elements in the environment, it is necessary to develop methods which allow precise analysis of heavy metals. This article compares and optimizes AAS methods for lead and cadmium.     

Post-bloom grazing byCalanus glacialis,C. finmarchicus andC. hyperboreus in the region of the Polar Front,Barents Sea

The plankton community in the Polar Front area of the Barents Sea was investigated during a cruise from 14 to 28 July 1987. The colonial algaePhaeocystis pouchetii andDinobryon pellucidum dominated the phytoplankton. Depth integrated carbon assimilation rates varied from 190 to 810 mg C m^–2 d^–1. A high carbon:chlorophyll ratio (which varied from 123 to 352) prevailed at the three stations investigated, which may relate to facultative heterotrophic behaviour byD. pellucidum. The herbivorous zooplankton community was dominated byCalanus glacialis, C. finmarchicus, andC. hyperboreus. Maximum zooplankton biomass was found in the same depth strata as phytoplankton chlorophyll maximum. The herbivorous copepod populations did not display consistent day-night vertical migration patterns. Phytoplankton consumption rates of the various life stages were estimated from the turnover rate of plant pigments in the gut. The gut defecation rate constant (R) varied from 0.014 to 0.027 min^–1 at 0°C in copepodites (Stage II to adult female) ofC. glacialis, independent of developmental stage.Calanus spp. community carbon ingestion rates calculated from particulate carbon:chlorophyll ratios, were 10, 65 and 400% of daily phytoplankton carbon fixation rates at Stations 1, 2 and 3, respectively.