161 research outputs found
Long-term changes in a zooplankton community revealed by the sediment archive
To reconstruct changes in zooplankton communities in response to past anthropogenic perturbations, one possibility is to use the sedimentary records. We analyzed the sediments at a coastal site in the Northern Baltic Sea to relate changes in the zooplankton community to anthropogenic eutrophication and the invasion of a predatory cladoceran, Cercopagis pengoi. We sampled 30-cm laminated sediment cores and dated the sediment layers back to the 1950s. From each 1-cm layer, we measured eutrophication indicators (delta C-13, delta N-15, TC, TN, TP) and identified and counted zooplankton resting eggs (cladoceran, calanoid copepod, rotifer). In addition, we estimated the abundance of the cladoceran Bosmina (Eubosmina) maritima by counting subfossils (carapaces, headshields, and ephippia) and estimated the experienced stress as the relationship between sexual and asexual reproduction. Using redundancy and variance partitioning analyses, we found similar to 16% of the variation in the zooplankton community to be explained by eutrophication, and 24% of the variation in B. (E.) maritima abundance and reproduction mode to be explained by eutrophication and the introduction of the alien predator. Our results show a long-term shift from calanoid copepods and predatory cladocerans toward small-sized zooplankton species, like rotifers. Furthermore, the results indicate that the invasion of C. pengoi induced a short-term increase in sexual reproduction in B. (E.) maritima. The results indicate that anthropogenic eutrophication since the 1950s has altered the zooplankton community toward smaller species, while the invasion of the predatory cladoceran had only a transitory influence on the community during its expansion phase.Peer reviewe
Primary, new and export production in the NW Pacific subarctic gyre during the vertigo K2 experiments
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1594-1604, doi:10.1016/j.dsr2.2008.04.013.This paper presents results on tracer experiments using 13C and 15N to
estimate uptake rates of dissolved inorganic carbon (DIC) and nitrogen (DIN).
Experiments were carried out at station K2 (47°N, 161°E) in the NW Pacific subarctic
gyre during July-August 2005. Our goal was to investigate relationships between new
and export production. New production was inferred from the tracer experiments using
the f ratio concept (0-50m); while export production was assessed with neutrally
buoyant sediment traps (NBSTs) and the e ratio concept (at 150m). During trap
deployments, K2 was characterized both by changes in primary production (523 to 404
mg C m-2 d-1), new production (119 to 67 mg C m-2 d-1), export production (68 to 24 mg
C m-2 d-1) and phytoplankton composition (high to low proportion of diatoms). The data
indicate that 17 to 23% of primary production is exportable to deeper layers (f ratio) but only 6 to 13% collected as a sinking particle flux at 150m (e ratio). Accordingly, > 80%
of the carbon fixed by phytoplankton would be mineralized in the upper 50m (1 â f),
while < 11% would be within 50-150m (f â e). DIN uptake flux amounted to 0.5 mM m-2
h-1, which was equivalent to about 95% particulate nitrogen (PN) remineralized and/or
grazed within the upper 150 m. Most of the shallow PN remineralization occurred just
above the depth of the deep chlorophyll maximum (DCM), where a net ammonium
production was measured. Below the DCM, while nitrate uptake rates became negligible
because of light limitation, ammonium uptake did continue to be significant. The uptake
of ammonium by heterotrophic bacteria was estimated to be 14-17% of the DIN
assimilation. Less clear are the consequences of this uptake on the phytoplankton
community and biogeochemical processes, e.g. new production. It was suggested that
competition for ammonium could select for small cells and may force large diatoms to
use nitrate. This implies that under Fe stress as observed here, ammonium uptake is
preferred and new production progressively suppressed despite the surplus of nitrate.This research was supported by the Research Foundation Flanders through grant
G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as well as the US National
Science Foundation programs in Chemical and Biological Oceanography
Feed of Siamese fighting fish, Betta splendens, (Regan, 1910) in open pond: live and formulated diets
Biogeochemical Control of the Coupled CO2âO2 System of the Baltic Sea: A Review of the Results of Baltic-C
Eutrophication potential of lakes: an integrated analysis of trophic state, morphometry, land occupation, and land use
Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)
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