Description: 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.

Description: Although blooms of opportunistic fast-growing macroalgae now occur frequently in coastal ecosystems affected by eutrophication, their initiation and control is little understood. Most previous studies have focused on the ecophysiology of adult algae only. We show that spores and/or germlings may represent critical stages in the life cycles and mass-developments of co-occurring opportunistic macroalgae in the Baltic (Pilayella littoralis and Enteromorpha spp.). We investigated the overwintering of spores, timing of germination, subsequent growth, and grazing on spores and germlings, in order to explain the initiation of mass blooms and species dominance patterns. In the field, Enteromorpha spp. showed 10- to 50-fold higher abundances of overwintering microscopic forms (up to 330 individuals cm-2) than P. littoralis. Moreover, we found continuous production of spores (up to 1.2 million settling spores m-2 h-1) from April to October in Enteromorpha spp., while there was evidence of only a short reproductive period in Pilayella. However, in spring, germlings and adults of P. littoralis appeared earlier in the field and reached a 10-fold higher biomass than Enteromorpha spp. In factorial laboratory experiments including temperature and light, there were clear differences in timing of germination. P. littoralis germinated at 5°C whereas Enteromorpha spp. required temperatures of 10-15°C for germination. In contrast, we detected only minor differences in growth response among adults of P. littoralis and Enteromorpha spp. Germination, not growth of adults, appeared to be the ecophysiological bottleneck for initiating mass spring development. Following the spring Pilayella bloom, Enteromorpha germlings occurred massively in the field (April-September), but rarely developed into adults. In laboratory feeding experiments we tested whether crustacean mesograzers common in summer may control development of Enteromorpha germlings. Both germination of settled spores and growth of germlings were reduced by 93-99% in the presence of grazers (Idotea chelipes and Gammarus locusta). Thus in addition to ecophysiological constraints, grazers, if present, may play a decisive role in the early life stages of macroalgal mass developments. These results mirror patterns of overwintering of seeds, germination control, seed and seedling predation in terrestrial plant communities.

Description: Seaweed responses to eutrophication and their role in coastal eutrophication processes were compared at 8 different sites along the European coasts from the Baltic to the Mediterranean as part of the EU-ENVIRONMENT Project Marine Eutrophication and benthic Macrophytes (EUMAC). Structural and functional changes of marine benthic vegetation typical of eutrophic waters, in particular mass development (blooms) of certain seaweeds, are not merely the result of increased nutrient loading, but must be attributed to complex interactions of primary and secondary effects during the eutrophication process. Due to species-specific physiological properties of the algae (nutrient kinetics, growth potential, light, temperature requirements), the combined effects of abiotic and biotic factors on juvenile or adult developmental stages control the development of algal blooms in different ways. In particular the role of light, temperature, water motion and oxygen depletion, as well as of grazers, on early and adult developmental stages of the algae are considered. The result are discussed in the context of coastal eutrophication control and management

Description: 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.

Description: Ein in situ-Meßsystem für Untersuchungen zum Stoff- und Energiefluß in isolierten benthischen Flachwassergemeinschaften wird beschrieben. Die Messung des Gaswechsels sowie anorganischer und organischer gelöster Substanzen erfolgt in geschlossenen (Säcke) oder offenen (Durchflußsystem) Meßeinrichtungen, die unter Verwendung von flexiblen Plastikfolien konstruiert wurden, um möglichst ungestörte Turbulenzverhältnisse zu gewährleisten. Die Anwendung der Meßeinrichtungen wird anhand von Meßbeispielen erläutert. A measuring system is described for in situ investigations on the flow of energy and matter in isolated benthos communities in shallow waters. Measurements of gas exchange and inorganic as well as organic dissolved matter are carried out either in closed (bags) or open (flow through) devices. Flexible plastic film is used for the construction of the devices in order to obtain favourable turbulence conditions in the systems. Practical application is illustrated by examples of measurements.

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.