9 research outputs found
Planktological data from the central Red Sea and the Gulf of Aden : (R. V. "Meteor", cruise No. 5-2, January - March 1987)
Primary production of phytoplankton estimated by means of the dilution method in coastal waters
Dilution effects on microzooplankton in dilution grazing experiments
International audienceIn dilution experiments, filtered seawater is used to create a gradient of grazing pressure on phytoplankton. Microzooplankton grazing is estimated by examining phytoplankton growth within the gradient. However, the dilution series also represents a resource gradient for microzooplankton. Here we report the effects of dilution on grazers. In 2 standard dilution experiments, using communities from the eutrophic (chlorophyll a = 12 to 15 mu g l(-1)) Rhode River Estuary, we examined the effects of dilution on different groups of microzooplankters: rotifers, tintinnid ciliates, oligotrich ciliates, predacious ciliates, and Mesodinium rubrum. Apparent growth rates of tintinnids and oligotrichs varied with prey concentration, decreasing with the dilution factor from about +0.5 d(-1) in undiluted whole water to about -1 d(-1) in the 5% whole water, closely resembling numerical response curves. Among tintinnids, there was an increase in the relative abundance of larger tintinnids in the time 24 h samples of dilute treatments compared to the less dilute treatments. No consistent dilution effect was shown by rotifers or predacious ciliates. The growth rates of the photosynthetic ciliate M. rubrum increased with dilution, resembling the typical pattern of chlorophyll a and autotrophic nanoplankton. Grazer growth in undiluted waters and grazer mortality in dilute water may be common and result in uncertainty in measured grazing rates. We urge that grazers be examined in grazing experiments not only to assess possible artifacts in grazing rate estimates, but also to provide information, beyond a simple grazing rate, on the grazer populations
The role of ciliates, heterotrophic dinoflagellates and copepods in structuring spring plankton communities at Helgoland Roads, North Sea
Relation of RNA/DNA ratios to growth for the scallop Euvola (Pecten) ziczac in suspended culture
Phytoplankton community structure and primary production in small intertidal estuarine-bay ecosystem (eastern English channel, France).
FR2116International audienceFrom May 2002 to October 2003, a fortnightly sampling programme was conducted in a restricted macrotidal ecosystem in the English Channel, the Baie des Veys (France). Three sets of data were obtained: (1) physico-chemical parameters, (2) phytoplankton community structure illustrated by species composition, biovolume and diversity, and (3) primary production and photosynthetic parameters via P versus E curves. The aim of this study was to investigate the temporal variations of primary production and photosynthetic parameters in this bay and to highlight the potential links with phytoplankton community structure. The highest level of daily depth-integrated primary production Pz (0.02â1.43 g C mâ2 dâ1) and the highest maximum photosynthetic rate PB max (0.39â 8.48 mg C mg chl aâ1 hâ1) and maximum light utilization coefficient aB [0.002â0.119 mg C mg chl aâ1 hâ1(lmol photons mâ2 sâ1)] were measured from July to September. Species succession was determined based on biomass data obtained from cell density and biovolume measurements. The bay was dominated by 11 diatoms throughout the year. However, a Phaeocystis globosa bloom (up to 25 mg chl a mâ3, 2.5 · 106 cells lâ1) was observed each year during the spring diatom bloom, but timing and intensity varied interannually. Annual variation of primary production was due to nutrient limitation, light climate and water temperature. The seasonal pattern of microalgal succession, with regular changes in composition, biovolume and diversity, influenced the physico-chemical and biological characteristics of the environment (especially nutrient stocks in the bay) and thus primary production. Consequently, investigation of phytoplankton community structure is important for developing the understanding of ecosystem functioning, as it plays a major role in the dynamics of primary production