ALBERT

Description: We present Mg/Ca analyses performed via a Flow Through sequential dissolution device connected to an ICP-OES on the planktonic foraminifer Globorotalia inflata. The aim of the study is to explore the possibility to reconstruct the thermal gradient in the water column by separating non-crusted and crusted calcite phases in the tests of G. inflata using the difference between their Mg/Ca ratios as a measure of the thermal gradient. An important assumption is that the non-crusted part of the tests is calcified in shallow, warmer water than the crusted part. For analyses a range of different preparation steps were used to determine the ideal way of separating the phases. Foraminifer tests were (not) cleaned, (not) crushed, and (not) pulverized before online analysis with the FT device. To analyze samples with a FT device the foraminifer tests are placed on a filter with a mesh of 0.45 μm preventing clay minerals to wash through. A sequential dissolution protocol first rinses the samples with buffered Seralpur water before QD HNO3 is added in small steps to create a ramp of increasing acid strength. As acid is kept constant at each concentration for several minutes, dissolution of a specific calcite phase can take place. Initial results show that it is most effective to slightly crush the tests without applying standard cleaning procedures, but rather analyze them without cleaning. Samples were selected from the South Atlantic (core tops and specific downcore samples) and the Mediteterranean (plankton tows). All samples were chosen based on previous work on them to provide comparison with routinely analysed Mg/Ca ratios. The South Atlantic samples have been analyzed extensively as bulk samples separated in difference size fractions and crusted vs. non-crusted (Groeneveld and Chiessi). The Mediterranean samples were not only analyzed as bulk samples but also by Laser Ablation ICP-MS (von Raden et al.). Results show that bulk analyses are reliably reproduced by the FT method, especially for samples which are dominated by crusted calcite. Samples which were uncrusted often gave much higher Mg/Ca ratios than the bulk analyses. These higher Mg/Ca ratios mainly occur in the plankton tow samples and were also identified with Laser Ablation ICP-MS. A possible reason for this could be the presence of a high Mg amorphous calcite layer on the outside of foraminifer tests which have not completed their calcification yet as was recently also pointed out in several other studies. Identification of the crusted and uncrusted phases, and therewith a thermal gradient, seems to give the expected differences but a more rigorous statistical treatment is needed to pinpoint singular dissolution phases.

Description: Die 72. Reise der FS Poseidon fand zwischen dem 9. und 13. März 1981 im Skagerrak statt.

Description: Three large plastic enclosures (3-4 m3) were anchored in the outer harbour of Helgoland (German Bight) and filled with natural seawater which was filtered free of algae. The enclosed water bodies were enriched with inorganic nutrients and inoculated with the diatom Thalassiosira rotula. During the growth of the algae diurnal changes in concentration of dissolved free amino acids (DFAA) occurred. The periodic concentration changes of individual amino acids with a low carbon to nitrogen ratio showed significant interrelationships with the partly synchronous devisions of the diatoms. From the exponential to the stationary phase the carbon to nitrogen ratio of DFAA shifted to higher values pointing at an adaptation of the organisms to the decreasing inorganic nitrogen source. During the bloom amino acids relatively rich in nitrogen were mainly excreted but by the end of the growth amino acids with a higher carbon content predominated. At phases of high photosynthetic activity the organisms probably reduced the high osmotic pressure by exudation of DFAA.

Description: Copepods are an important link in the marine food web, and, in particular, serve as food for fish larvae. Schizopera elatensis, a marine harpacticoid copepod, was reared in the laboratory, and the effect of various environmental factors, i.e., diet, temperature, salinity and height of water column on its growth was determined. Schizopera elatensis multiplies at a wide range of salinities, 10‰ to 70‰, and temperatures, from at least 18° C to an upper limit of 36° C, with an optimum of 25° C, and grows in high densities (300-400 individuals per ml): the lower the water column, the higher the density. The prospective use of S. elatensis as a live food organism in mariculture is discussed.

Description: The importance of bacteria in the feeding of marine bivalves has been demonstrated by several authors. Some examples of good growth of molluscs were noted on a bacterial diet only. But, while the intense filtration of bacteria by molluscs has been observed, the exact role of bacteria in the nutrition of bivalves was not completely known. The filtered particles were sometimes eliminated as pseudofaeces, without any intestinal transit. On the other hand, live cells could also pass through the gut without being degested. To study in detail the fate of bacterial cells distributed as food to young bivalves, we used a new method which combines histology and scanning electron microscopy. This made it possible to observe, on serial histological sections of whole animals, the gut content and the condition of the ingested cells at the different levels of the intestinal tract. The ingestion and digestion by young mussels (Mytilus edulis) of some marine bacterial strains belonging to different taxonomic groups were studied by this method. Thus, partially digested bacterial cells were observed in the stomach, when the hind gut contained undamaged cells, three hours after food distribution. The results obtained for all the strains we tested are presented and discussed in this paper.

Description: Eutrophication by sewage effluent has led to the development of extensive mats of green algae over much of the former open mudlands of Langstone Harbour on the south coast of Britain. The presence of the mal reduces the biomass and diversity of the mud-dwelling infauna but a great increase in the number and biomass of epibenthic animals (primarily Hydrobia ulvae Pennant) produces a total biomass almost twice that of open mudlands. Although the common invertebrates are favoured prey for many estuarine birds these algal areas are avoided by the dense aggregation of waders and wildfowl.

Description: From April to September 1978 benthos and plankton samples were taken at three different sites in the Schlei fjord (German Baltic coast) with different salinity (ca. 15, 10 and below 5‰). Abundances of benthos and plankton taxa were compared with abundances of the taxa occurring in the guts of Pomatoschistus microps and P. minutus, caught at the same places at the same time. Main food were calanoids, oligochaetes and harpacticoids. Calculations showed that young gobies most probably regulate the population of harpacticoids to a large extent by grazing.

Description: Feeding, digestion and assimilation are usually treated as separate aspects in studying the physioecology of copepods. A general model predicting the assimilation rate from ingestion rate, phytoplankton species compositon and digestive or physiological state of the animal is presented. The assumption is made that digestion is accompanied by a subsequent decrease in cell volume, which is equal to the assimilated part of the cell. In addition, a time delay between ingestion and the onset of digestion is assumed to describe the digestion properties of the algal cells. The model predicts a decrease in assimilation efficiency with increasing ration. The minimum gut passage time and the digestion rate seem to be the most important parameters for the production of copepods. These and other characteristics of the model are discussed in relation to available information.