ALBERT

Description: The method proposed for the measurement of the picoplankton density, uses epifluorescence microscopy, which allows the detection of all the cells with their own or/and induced fluorescence. Direct counts may lead to an overestimation of the viable counts since we cannot discriminate between living and dead cells. We appropriately modified the method of KOGURE et al. (1979) for the fraction of cells capable of division. This method is applied both to autofluorescent organisms and to all the cells stained by fluorochrome (DAPI). Direct counts are compared with those obtained from Marine Agar, a selective medium for marine heterotrophic bacteria. The results obtained in different Mediterranean areas allow us to realize how effective this method is in comparatively evaluating different planktonic dimensional fractions occurring in the marine ecosystem.

Description: The intention was to study recruitment of benthic macrofauna to an exposed shore. Two mesh-sizes (1.0 and 0.5 mm) were used. The additional abundance and biomass in the finer sieve show both temporal and spatial variations. Maximum values were found in the autumn and at the shallowest station (5 m). The reasons for this are discussed.

Description: Nitrogen fixation measurements carried out in 1974 and 1975 in the Baltic Sea showed that heterocyst fixed nitrogen c. 3.5 pg (2)-1. According to our preliminary calculations the amount of nitrogen fixed in 1974 in the northern and central Baltic proper was c. 100000 tons.

Description: A coralline alga from the Baltic (Belt Sea, Samsö) belonging to the genus Phymatolithon has been investigated. The mineral skeleton consists of magnesium calcite and shows the following composition (expressed in percent of the dry weight): 94-96% skeletal carbonates, 4-6% organic matter, 32.1-33.4% Ca, 3.3-3.5% Mg and 0.15-0.17% Sr. MgC03 determined by the peak shift method (X-ray diffraction) is in the region of 10-11 mol % . The kinetics of 45Ca uptake consist of a fast step and a low step. The fast step is due to equilibration of isotope with the soft tissues and spaces between cells. The slow step is attributed to net deposition of calcium in the skeleton. From the rate constant of the slow step calcium net deposition was found to be 5.6 1 μg Ca/g dry weight/h or 14 μg CaC03/g dry weight/h. Pulse chase experiments show that the calcification is the resultant of calcium exchange between the alga and the seawater. Light-dark calcification ratios are in the range of 1.1-1.3. The O2 production amounts to 0.04 mg 02/g dry weight/h at an irradiance of 0.085 KW/m2. When expressed per unit weight of total organic matter, this assimilation rate would fall into the range commonly found for other noncalcifying Rhodophyta. The results form the basis for further work on calcification mechanism and CaC03 production in coralline algae.

Description: A respirometer for small benthic marine invertebrates is presented. The advantages of this construction are: compactness and easy transport of the equipment, small respiration chamber, entrance and exit electrodes close to respiration chamber, exact temperature control and equilibration of the experimental medium, exact regulation of the flow-through speed, digital display of consumed O2 values. The equipment is suitable for long-term measurement of O2 consumption by benthos organisms in low oxygen conditions and for a rapid picture of the reaction of experimental animals to abrupt changes in their environment (e.g. temperature, salinity, composition of the medium). Procedure for experiments involving a lowering of the O2 content of the medium is explained.

Description: Phytoplankton production was measured 19-25 times at three stations in the Sound during 1972 and 1973. The annual production in 1972 was about the same at all stations, 70- 77 g C m-2 yr-1. In 1973 a considerable difference was obtained, 73, 148 and 183 g C m-2 yr-1 for the three stations. The most obvious difference between the two years was observed during spring and summer in the north and central part of the Sound. The production in 1972 was about twice as high, and in 1973 4-5 times as high as previously reported for the Sound. The increased production in the Sound is to a large degree a result of eutrophication, but the natural changes in the unstable area must be considered important. A comparison with production values from adjacent waters and a discussion of factors controlling primary production in the Sound is presented.

Description: An attempt is made to describe the large-scale changes in the benthic soft bottom macrofauna in the deep parts of the Bornholm Basin, the Gulf of Gdansk, the Central Basin and the Gulf of Finland, from the beginning of Baltic zoobenthos research to the present day. The authors also try to correlate these changes with fluctuations in the oxygen content and salinity in near-bottom water layers. The paper surveys the literature and presents recent, earlier unpublished results. During the later part of last century and the first decades of the twentieth century no area of the Baltic Sea seems to have been total ly devoid of macrofauna. Unfortunately there are considerable gaps in our knowledge of the time before the middle of this century. The most striking decline has taken place, generally speaking, after the exceptionally great inflow in 1951-1952, and the subsequent prolonged stagnation. The first records of "dead" bottoms in the Bornholm Basin are from 1948, when no macrofauna was recorded below 80 m. Records from 1954 show that the deepest parts of the Eastern Gotland Basin and the deep area between Öland and Gotland were devoid of macrofauna at that time, but that the deep areas of the northernmost Baltic proper and the Gulf of Finland were still populated. The change continued, and during the 1960s the communities dominated by lamellibranchs in the Bornholm and Gdansk Deeps disappeared, and were subsequently replaced by polychaete cummunities. These have been wiped out during periods of bad oxygen conditions, but quickly re-established when conditions had improved. The lamellibranch community has not been restored. In the Northern Central Basin and the Gulf of Finland the depopulation of the deep bottoms probably began later, in the late 50s. In the 70s practically no macrofauna has been recorded below the permanent halocline in the Central Basin (except the southernmost parts of it) and the Gulf of Finland. During the 60s and 70s the area with periodically unfavourable oxygen conditions has covered about 100000 km2, which is c. 25 % of the total area of the Baltic Sea.