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Abstract

In order to understand the effect of changing nutrient conditions on benthic microalgae on hard substrates, insitu experiments with artificial substrates were conducted in Kiel Fjord, Western Baltic Sea. As an extension of previous investigations, we used artificial substrates without silicate and thus were able to supply nutrient media with different Si:N ratios to porous substrates, from where they trickled out continuously. The biofilm developing on these substrates showed a significant increase in biovolume due to N + P enrichment, while Si alone had only minor effects. The stoichiometric composition of the biomass indicated nitrogen limitation during most of the year. The C:N ratios were lowered by the N + P addition. The algae were dominated by diatoms in most cases, but rhodophytes and chlorophytes also became important. The nutrient treatment affected the taxonomic composition mostly at the species level. The significance of the results with regard to coastal eutrophication is discussed.

Evolution of Phytoplankton in Relation to Their Physiological Traits

“…Thus, even with small diffusion boundary layers (see Section 3.2 above), N, P and Fe limitation of primary productivity is widespread among marine phytoplankton. N limitation has also been shown for benthic marine diatoms in the oligotrophic western Baltic Sea [150]. For freshwater habitats, Maberly et al [151] examined nutrient limitation in an upland lake in the UK, and showed N limitation, P limitation and PN co-limitation to similar extents in phytoplankton and periphyton (microphytobenthos plus multicellular benthic algae and mosses).…”