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Growth and nutrient uptake studied in sand-agar microphytobenthic communities
Nilsson, C.; Sundbäck, K. (1991). Growth and nutrient uptake studied in sand-agar microphytobenthic communities. J. Exp. Mar. Biol. Ecol. 153(2): 207-226. hdl.handle.net/10.1016/0022-0981(91)90226-M
In: Journal of Experimental Marine Biology and Ecology. Elsevier: New York. ISSN 0022-0981, more
Peer reviewed article  

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Keyword
    Marine
Author keywords
    Chl a; Crangon crangon; Microphytobenthos; Nutrient uptake; Primary productivity; Sand-agar substratum

Authors  Top 
  • Nilsson, C.
  • Sundbäck, K.

Abstract
    A sand-agar microalgal community was used in an outdoor flow-through experiment to study the response of marine microphytobenthos to changed nutrient levels mediated by the activity of a predator (brown shrimp Crangon crangon L.) and by addition of inorganic nitrogen (N) and phosphorus (P) to the overlying water. A microalgal assemblage was separated from ambient sandy sediment and allowed to settle onto thin sand-agar plates in order to minimize the interactive effects of other biogeochemical processes than algal uptake on nutrient flux. The response of the algal community was assessed by measuring changes in composition, biomass, primary productivity, and nutrient uptake rates. A natural dense population of juvenile Crangon did neither affect the inorganic nutrient concentration in the overlying water nor the sand-agar microalgal community. The NP addition stimulated algal growth and productivity. The proportion of flagellates increased with NP addition, although a clear shift in the dominance of the major algal groups was not found in the course of the 3-wk experiment. The initial microalgal community on the sand-agar substratum did initially imitate that of shallow-water sediments in the respect that the major taxonomical and morphological groups were the same. During the experiment the composition of diatoms was shifted to a dominance of larger motile cells at the expense of small epipsammic forms, probably both as a result of the nature of the substratum and the lack of abrasion by moving sand grains. The response of the algal community to changed nutrient status had an acceptably high degree of similarity to that of the sediment. The fact that the quantitative response of the algal community was faster and more pronounced in the absence of sediment is an advantage when the aim is to simplify a system for laboratory experiments. The nutrient uptake measured was shown to reflect algal uptake with low interactive effects of biogeochemical processes present in natural sediment. Thus, a thin sand-agar substratum appears to be a useful tool in short-term experiments where it is desirable to simplify the complicated sediment community to specifically study nutrient uptake as well as response of the microphytobenthos to environmental changes.

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