Growth and C:N:P ratios in copepods grazing on N- or Si-limited phytoplankton blooms
2004 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 514, no 1-3, 57-72 p.Article in journal (Refereed) Published
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.
nutrient limitation, silicate, nitrogen, phosphorus, copepods, phytoplankton, mesocosm experiments
IdentifiersURN: urn:nbn:se:uu:diva-91660DOI: 10.1023/B:hydr.0000018206.02271.2bOAI: oai:DiVA.org:uu-91660DiVA: diva2:164465