title: Copepod growth and diatoms: insensitivity of Acartia tonsa to the composition of semi-natural plankton mixtures manipulated by silicon:nitrogen ratios in mesocosms.
abstract: The feeding selectivity and the growth and reproductive success of the copepod Acartia tonsa have been studied in mesocosms fertilized at different Si:N ratios (0-1.75:1) and, therefore, at different compositions of the phytoplankton communities. Phytoplankton composition showed a strong response to nutrient ratios, with diatoms comprising >90% at Si:N ratios >1:1 of total biomass as opposed to <20% at the lowest ratio. A. tonsa strongly preferred feeding on motile prey (flagellates and ciliates) to feeding on diatoms. Nevertheless, diatoms comprised a substantial part of the diet at the highest Si:N ratios. A. tonsa egg production and the final (after 4 weeks) abundance of adults and copepodites showed no response to Si:N ratios while nauplii production slightly increased with Si:N ratios. It is concluded that the frequently reported deleterious effect of diatoms on copepod reproduction is rather unusual when copepods are confronted with a naturally diverse phytoplankton assemblage instead of clonal cultures in the laboratory.
authors.affiliation: Leibniz-Institute of Marine Sciences at Kiel University (IFM-GEOMAR), Düsternbrooker Weg 20, 24105, Kiel, Germany. usommer@ifm-geomar.de
authors.forename: Ulrich
authors.initials: U
authors.lastname: Sommer
mesh_terms: D000818:Animals; D033342:Copepoda / Q000254:growth & development*; D017377:Diatoms / Q000502:physiology*; D017753:Ecosystem; D005247:Feeding Behavior; D009584:Nitrogen / Q000737:chemistry* / Q000378:metabolism; D010933:Plankton / Q000502:physiology*; D011157:Population Dynamics; D012098:Reproduction / Q000502:physiology; D012825:Silicon / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009584:Nitrogen; D012825:Silicon