Dynamics in carbohydrate composition of Phaeocystis pouchetiicolonies during spring blooms in mesocosms

Dynamics in carbohydrate composition of Phaeocystis pouchetiicolonies during spring blooms in mesocosms
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Journal Article
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Alderkamp AC, Nejstgaard JC, Verity PG, Zirbel MJ, Sazhin AF, vanRijssel M

Journal of Sea Research
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algae, Polysaccharides, Mucus, Glucan, Laminarin, Diel, Phaeocystis pouchetii, mesocosm, Raunefjorden, Espegrend, Bergen, Norway, 11 m3


The colony-forming microalgae Phaeocystis produces two major pools of carbohydrates: mucopolysaccharides in the colonymatrix and intracellular storage glucan. Both have different functions and separate degradation pathways in the ecosystem, so apartial precipitation method was developed to distinguish the dynamics of the two pools. Changes in concentration in response tovariation in nutrients and irradiance were followed during a spring bloom of Phaeocystis pouchetii colonies in mesocosms nearBergen, Norway. Upon nutrient limitation, the carbohydrate to carbon ratio of the colonies increased from 15% during the growthphase, to more than 50% during the decline phase. During the growth phase of the bloom, the carbohydrate concentration andcomposition were influenced by irradiance: glucan concentrations showed strong diel dynamics and increased with higher lightlevels, whereas mucopolysaccharide concentrations were unaffected. During the exponential growth phase, glucan contributed 6–11% to P. pouchetii carbon, depending on the time of the day. During the decline of the bloom, the glucan contribution increased upto 60%. We provide further evidence for the concept that the Phaeocystis colony matrix is built with a relatively small but constantamount of carbohydrates, compared to the large quantities of glucan produced during Phaeocystis spring blooms. Since a majorpart of Phaeocystis primary production is recycled in the water column by bacteria, this vast glucan injection is a potentialdeterminant of the magnitude and composition of the microbial community following a bloom

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