Phytoplankton Spring Bloom Intensity Index for the Baltic Sea Estimated for the years 1992 to 2004

We introduce an index for estimating the annual phytoplankton spring bloom intensity in the Baltic Sea. It is based on chlorophyll a estimates calculated from automatically sampled fluorescence and chlorophyll a measurements on board cargo ships from 1992 to 2004. The intensity is described by an index including information on the chlorophyll a concentration and duration of the spring bloom period. In all of the years studied, the spring bloom was most intense in the Gulf of Finland. In the Gulf of Finland and the Northern Baltic Proper there was a slight tendency for the bloom to start earlier in the spring.     

Yangtze Dams Increasingly Threaten the Survival of the Chinese Sturgeon

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Streblonema (Ectocarpales,Phaeophyceae) infection in the kelp Laminaria saccharina (Laminariales,Phaeophyceae) in the western Baltic

The brown alga Laminaria saccharina is the dominant subtidal macroalga in Kiel Bay, western Baltic. It is infected by the microscopic brown alga, Streblonema aecidioides. Infected thalli may show symptoms of Streblonema disease, i.e. alterations of blade and stipe, ranging from dark spots to heavy deformations and completely crippled thalli. Samples taken from a single locality all year round show that (i) the host population is infected at a high rate of 87±13% (SD), but that (ii) a considerable proportion of thalli containing Streblonema does not show disease symptoms, and that (iii) juvenile hosts, which mainly appear in autumn, are infected at almost the same rate. Thus the infection seems to occur early in the host's life. Juveniles in nature show fewer symptoms of the disease than adults. Two months after infection, oxygen production and growth in laboratory-raised experimentally infected juvenile hosts was not different from uninfected controls. Experimental thalli showed more severe morphological alterations than uninfected controls only four months after infection. Both field and laboratory observations indicate that a lag phase exists between infection and outbreak of the disease.     

Egg-to-fry survival of the sea trout in some streams of Gotland

The quality of the surface water of Gotland (Sweden) streams was good, and did not limit sea trout egg-to-fry (ETF) survival. The oxygen concentration of the interstitial water was positively correlated to the permeability of the stream bed, and to the geometric mean diameter of the substratum. When the oxygen at 15 cm inside the stream bed was undiminished from surface values, the permeability of the stream bed was at least 6000 cm h^–1 and the geometric mean diameter of the substratum at least 15.0 mm. When the interstitial oxygen concentration increased, the interstitial ammonium concentration decreased, the NO₂ concentration remained stable and the NO₃ concentration increased. The ETF survival up to hatching was highly dependent upon the oxygen concentration of the interstitial water. For survival from hatching to emergence, the geometric mean diameter of the substratum was the most important factor. ETF survival >50% was observed where the interstitial oxygen concentration averaged at least 10mg I-¹, the substratum permeability at least 2000cm h-¹ and the substratum geometric mean diameter at least 15 mm. Other factors, such as overdigging and drying out of the spawning grounds could increase the ETF mortality.     

Estimation of export production in the coastal Baltic Sea: effect of resuspension and microbial decomposition on sedimentation measurements

Hydrography, nutrient concentrations, primary production and sedimentation of particulate matter were studied during spring, late summer and autumn in the coastal area of the northern Baltic Sea, SW Finland. Vernal phytoplankton productivity peak and biomass maximum in early May were followed by high sedimentation rates of organic matter at the end of May. In summer, sedimentation rates of organic material were generally low. The decay rates of organic carbon in the sediment traps, estimated by measuring oxygen uptake of settled organic matter, varied between 0.005 to 0.08 d^–1 and were on average 0.02 d^–1. Decomposition of organic matter inside the sediment traps was mainly controlled by temperature, while also organic contents of settled material were significant. Microbial decomposition decreased sedimentation rates of organic carbon and nitrogen on average by 11% and 15%, respectively, during the whole study period of ca. 6 months. Resuspension of organic matter from sediment surface was estimated to contribute ca. 17 and 24% of the total sedimentation of organic carbon during spring and summer, respectively. Export production (i.e. primary sedimentation of organic carbon corrected by decomposition) was estimated to be 32% of the net primary production during the whole productive season and 42% in spring when the flux of primary settling material was greatest. Sedimentation of the spring bloom was the major annual supply of organic matter to the benthos (>80% of the total primary sedimentation).     

Vertical migration of autotrophic micro-organisms during a vernal bloom at the coastal Baltic Sea – coexistence through niche separation

Vertical migration of two dinoflagellate species (Peridiniellacatenata and Scrippsiella hangoei) and a phototrophic ciliate(Mesodinium rubrum) were studied during the peak and decline of avernal bloom at the SW coast of Finland. During the diel cycle, part of thepopulations of P. catenata and M. rubrum wereobserved in the deeper layers with elevated nutrient concentrations, whileS. hangoei remained in the upper nutrient depleted mixed layer.Using a correspondence analysis the vertical distribution patterns of thespecies and chlorophyll a were examined over a temporal scale of hoursand weeks. The vertical migration was reflected in much higher variabilityin the depth distribution of P. catenata and M. rubrum over a diel scale, compared to S. hangoei. The analysisrevealed also significant differences in species specific depth distributionpatterns over both time scales. It is discussed that the co-existence of thetwo dominant dinoflagellate species during the vernal bloom is due to nicheseparation through behavioural adaptations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of ammonium load on the growth of attached microalgae in the northern Baltic Sea

The effect of ammonium discharge from a food factory on the growth of attached microalgae was monitored north of the Hanko peninsula, on the southwestern coast of Finland. The impact of the discharge was studied at twelve localities, at four stages of seasonal succession. The microalgae were sampled from glass slides exposed at 0.4 m depth for two weeks. The variables measured for the microalgal growth were chlorophylla, primary production and total organic carbon (TOC). These were compared with planktonic chlorophylla and nutrient concentrations. The growth of attached microalgae displayed a consistent pattern of spatial distribution. Depending on season, TOC and primary production values were 7 to 70 times higher and chlorophylla values up to 1000 times higher close to the effluent outlet than in undisturbed areas of the archipelago. The microalgal samples near the discharge were characterized by low TOC/chlorophylla and TOC/primary production ratios. The temporal consistency of microalgal distribution illustrates the advantages of using attached algal assemblages in monitoring programmes.