Beschreibung: Macroalgal blooms are a growing environmental problem in eutrophic coastal ecosystems world wide. These blooms are dominated typically by only one out of several co‐occurring opportunistic species, which are all favored by increased nutrient loads. We asked whether pronounced dominance of filamentous Pilayella littoralis Kjellm. (Phaeophyceae) over foliose Enteromorpha intestinalis L. (Chlorophyceae) in the Baltic Sea can be explained by interspecific physiological differences. In laboratory experiments, we analyzed uptake kinetics of nitrate, ammonium, and phosphate and the time dependency of uptake rates for both species. We further examined growth rates and nutrient assimilation in relation to single and combined enrichment with nitrate and phosphate, and three different nitrogen sources. Overall, we did not detect distinct differences in uptake, growth, and assimilation rates between P. littoralis and E. intestinalis. Minor differences and the related advantages for single species are discussed. Highest maximal uptake rates were found for ammonium, followed by nitrate and phosphate. Strong time dependency of uptake occurred, with the highest rates during the first 15 to 30 min. Nitrate enrichment had far more of an effect on growth than phosphate. Enrichment with urea, ammonium, and nitrate significantly increased growth rates without interspecific differences. A larger surface area to volume (SA/V) ratio in Pilayella compared with Enteromorpha did not translate into greater physiological capacity. We conclude that species dominance patterns in macroalgal blooms are not always a direct result of different ecophysiological traits among species. Ecological traits such as susceptibility to herbivory are important factors in determining species distribution in the field.

Beschreibung: A large scale quantitative survey of the benthic vegetation of the Kiel Bight (Western Baltic Sea) has been performed by analysis of underwater television observations and samples obtained by SCUBA diving during 1985-86. This investigation was compared to a semiquantitative survey carried out in 1962-64 by SCHWENKE (1964, 1969). For the total study area (2571 km2), distinct changes in biomass and species composition have been observed. There is an increase of biomass above the 12 m level (probably with exception of the 6 m level) and a decrease below 12 m. Extensive Furcellaria lumbricalis populations have disappeared. Furcellaria lumbricalis has been replaced by Phyllophora truncata and Phycodrys rubens which are the predominant species at present. Among other possible causes for these changes, the role of commercial stone fishing and effects of increasing eutrophication in the Kiel Bight are discussed.

Beschreibung: Considerable amounts of nutrients enter as a result of human activity the Western Baltic Sea in the form of discharge or seepage from land or as atmospheric input. Benthic macrophytes which preferably inhabit the nutrient recipient shallow near-shore areas, and where they often constitute the major primary producers may thus play an important role in eutrophication processes by uptake and accumulation of nutrient elements, enhanced primary production and following degradation of the produced organic material. Nutrient uptake, binding capacity and limitation as well as nutrient dependent growth of the two community forming seaweeds Phycodrys rubens and Fucus vesiculosus have been investigated and related to the seasonal patterns of the nutrient conditions in their respective habitats. Nutrient concentrations, both phosphorus and nitrogen, in the algal beds are markedly higher than in the surface water of the open Kiel Bight. In general, the seaweeds seem not to be nutrient limited under natural conditions except for nitrogen in Phycodrys during summer. Nutrient tissue contents are saturated only for nitrogen during winter. The significance of these findings is discussed in view of the observed increasing nutrient levels and changes of the vegetation in the Kiel Bight.