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Growth and C:N:P ratios in copepods grazing on N- or Si-limited phytoplankton blooms
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Evolutionary Biology.
2004 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 514, no 1-3, 57-72 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate how nutrient limitation in phytoplankton blooms affects growth and C:N:Pratios in marine pelagic copepods.We performed two mesocosm experiments on the Atlantic coast near Trondhjem(Norway). Si-limitation in a phytoplankton bloom was triggered by N and P additions (NP treatment) and Nlimitationwas triggered by N, P and Si additions (NPSi treatment). Both nutrient treatments stimulated microalgalgrowth and increased the biomass of the phytoplankton manifold. The initial phytoplankton community consistedof flagellates and diatoms. Throughout both experiments, community composition stayed relatively stable anddiverse in the NP treatments, but in the NPSi treatments large and heavily silicified diatoms came to dominatecompletely. Phytoplankton C:N ratios in the Si-limited blooms were close to the Redfield ratio of 6.6 (on a molarbasis), but they were higher in the Control treatment without nutrient additions (ca. 8.6) and up to 14 in heavily Nlimitedblooms. When phytoplankton blooms (chlorophyll a > 25 nmol l−1) had established, wild copepods wereadded to the mesocosms. During Si-limitation the copepod density increased by ca. 40% in one of the experiments,while the C:N ratio was 5.5–6 in the copepods. During N-limitation, the copepod density stayed stable, while theC:N ratio increased to ca. 7 in the course of the experiment. In the other experiment the copepod density decreasedby ca. 25%, irrespective of nutrient treatment (C:N ratio ca. 9). The N:P ratios in the copepods varied between 16and 22 and were not different in the NP and NPSi treatments. Our study shows that N-limitation in phytoplanktoncells can increase the C:N ratio of their grazers, which has a reportedly negative effect on copepod growth andreproduction. Our study also shows that copepod populations can be regulated by seawater Si:N ratios via diatoms:at high ratios the growth from eggs/nauplii to copepodites was hampered. High Si:N ratios provide diatoms withpossibilities to escape from grazing (large species, heavy silicification, excretion of secondary metabolites), leadingto the accumulation of algal biomass without transfer to higher trophic levels.

Place, publisher, year, edition, pages
2004. Vol. 514, no 1-3, 57-72 p.
Keyword [en]
nutrient limitation, silicate, nitrogen, phosphorus, copepods, phytoplankton, mesocosm experiments
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-91660DOI: 10.1023/B:hydr.0000018206.02271.2bOAI: oai:DiVA.org:uu-91660DiVA: diva2:164465
Available from: 2004-04-26 Created: 2004-04-26 Last updated: 2011-03-04Bibliographically approved
In thesis
1. Experimental Studies on the Regulation of Pigment Dynamics in Phytoplankton and Copepods by Dissolved Inorganic Nutrients
Open this publication in new window or tab >>Experimental Studies on the Regulation of Pigment Dynamics in Phytoplankton and Copepods by Dissolved Inorganic Nutrients
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis examines the role of dissolved inorganic nutrients in generating changes in phytoplankton community and pigment composition and if such changes can affect the production of the antioxidant astaxanthin in the ecosystem via pelagic copepods. The background of my studies is the possible relationship between eutrophication and a reproductive disturbance in Baltic populations of Atlantic salmon (M74), which is associated with astaxanthin and thiamine deficiencies and oxidative stress. In the southern Baltic Sea, changes in nutrient loads correlate with observed trends of flagellates replacing diatoms in the phytoplankton. Copepods are the main producers of astaxanthin and a major link between phytoplankton and higher trophic levels. In laboratory and field experiments in the Baltic Sea proper and the Norwegian Sea, I show that astaxanthin synthesis in copepods is fast and depends on pigment composition of the phytoplankton diet. Among single-species diets, a diatom and a green algal cyst yielded the highest astaxanthin levels in copepods, and another diatom species, a green alga and a cyanobacterium the lowest. In nutrient-generated phytoplankton blooms in mesocosms, copepods grazing on diverse communities dominated by weakly silicified diatoms produced more astaxanthin compared with copepods grazing on communities dominated by strongly silicified diatoms. This suggests that diatoms invested in defence mechanisms and escaped grazing at surplus Si. A nutrient-starved diatom culture subjected to intraspecific competition exhibited decreased pigment levels, increased thiamine levels and increased oxidative stress.

My results suggest that diatoms are beneficial for astaxanthin and thiamine production compared to other phytoplankton groups, but not under all circumstances. Copepod growth and development also responded to inorganic nutrient availability and affected total astaxanthin production per volume seawater, with highest production when the copepods grazed on diatoms. From an ecosystem perspective, increased N and P loads seem to promote high astaxanthin production, but not when diatoms disappear completely.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 34 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 968
Keyword
Biology, Astaxanthin, Baltic Sea, carotenoids, diatoms, eutrophication, food web, mesocosms, microalgae, M74 syndrome, oxidative stress, phytoplankton blooms, zooplankton, Biologi
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-4230 (URN)91-554-5946-3 (ISBN)
Public defence
2004-05-26, The lecture hall, Dept. of Plant Ecology, Villavägen 14, Uppsala, 10:00
Opponent
Supervisors
Available from: 2004-04-26 Created: 2004-04-26 Last updated: 2011-03-04Bibliographically approved

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