41 research outputs found
Environmental cues and constraints affecting the seasonality of dominant calanoid copepods in brackish, coastal waters: a case study of Acartia, Temora and Eurytemora species in the south-west Baltic
Information on physiological rates and tolerances helps one gain a cause-and-effect understanding of the role that some environmental (bottomâup) factors play in regulating the seasonality and productivity of key species. We combined the results of laboratory experiments on reproductive success and field time series data on adult abundance to explore factors controlling the seasonality of Acartia spp., Eurytemora affinis and Temora longicornis, key copepods of brackish, coastal and temperate environments. Patterns in laboratory and field data were discussed using a metabolic framework that included the effects of âcontrollingâ, âmaskingâ and âdirectiveâ environmental factors. Over a 5-year period, changes in adult abundance within two south-west Baltic field sites (Kiel Fjord Pier, 54°19âČ89N, 10°09âČ06E, 12â21 psu, and North/Baltic Sea Canal NOK, 54°20âČ45N, 9°57âČ02E, 4â10 psu) were evaluated with respect to changes in temperature, salinity, day length and chlorophyll a concentration. Acartia spp. dominated the copepod assemblage at both sites (up to 16,764 and 21,771 females mâ3 at NOK and Pier) and was 4 to 10 times more abundant than E. affinis (to 2,939 mâ3 at NOK) and T. longicornis (to 1,959 mâ3 at Pier), respectively. Species-specific salinity tolerance explains differences in adult abundance between sampling sites whereas phenological differences among species are best explained by the influence of species-specific thermal windows and prey requirements supporting survival and egg production. Multiple intrinsic and extrinsic (environmental) factors influence the production of different egg types (normal and resting), regulate life-history strategies and influence matchâmismatch dynamics
Advertising, earnings prediction and market value: An analysis of persistent UK advertisers
YesThis paper examines whether major media advertising expenditures help in predicting future earnings. We consider the role of media advertising in firmsâ marketing efforts and posit that persistent advertisers are more likely to benefit from advertising activities in creating longâlived intangible assets. Employing a sample of persistent UK advertisers over the period 1997â2013, we find that advertising expenditures are significantly positively associated with firmsâ future earnings and market value. We also report size and sectorâbased differences in the association between advertising and firmsâ future earnings. Our additional analysis provides support for the arguments that despite the recent rise in digital advertising budgets, traditional advertising media are still effective in positively influencing firmsâ performance. Overall, the results of this study are consistent with the view that advertising expenditures produce intangible assets, at least for firms in certain sectors. These findings have implications for marketers in providing evidence of the value generated by firmsâ advertising budgets, for investors in validating the relevance of advertising information in influencing future earnings, and for accounting regulators in relation to the provision of useful insights for any future deliberations on financial reporting policies for advertising expenditures
Zooplankton feeding in the Westerschelde and the Gironde
Feeding of E. affinis and A. tonsa on natural Westerschelde particulate matter was measured using a combination of methods: addition of C14 tracer food, gut fluorescence and counting by microscope. The results show that both E. affinis and A. tonsa select peaks of live phytoplankton cells when these occur. C14 measurements in the Gironde show that in this estuary, E. affinis, A. tonsa and T. longicornis also feed mainly on the dominant phytoplankton peak
Genetic diversity among the Eurytemora affinis species complex in the Scheldt estuary and its tributaries using ISSR-PCR marker assay.
ACLInternational audienceno abstrac
Copepod Feeding in the Westerschelde and the Gironde
As in most European estuaries, the mesoplankton of the Westerschelde and the Gironde is dominated by calanoid copepods. In the Westerschelde, Eurytemora affinis dominates the brackish water area between station 7 and 10 in winter and spring while Acartia tonsa is dominant in summer. Maximum abundance of A. tonsa is located slightly more seawards than that of E. affinis. Acartia bifilosa occurs in winter and spring in lower abundances than A. tonsa and its maximum abundance is located between the brackish and the marine area. In the Gironde, E. affinis dominates in winter and spring between station J and K, with its maximum around station K. The second important species in the Gironde is Acartia bifilosa with a maximum abundance in summer, located around station E and J. In the Gironde, A. tonsa occurs in the same area as A. bifilosa only in late summer and early autumn
Seasonal abundance and feeding patterns of copepods Temora longicornis, Centropages hamatus and Acartia spp. in the White Sea (66°N)
Trophic efficiency of the planktonic food web in a coastal ecosystem dominated by Phaeocystis colonies
The trophic efficiency of the planktonic food Web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of thea available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column. (C) 2000 Elsevier Science B.V.info:eu-repo/semantics/publishe
Zooplankton distribution and dynamics in a temperate shallow estuary
Abstract The spatial, temporal and tidal dynamics of the zooplanktonic community of the Mondego estuary was studied from January 2003 to 2004. The monthly sampling procedure included the measurement of hydrological parameters (salinity, temperature, Secchi transparency, chlorophyll a and nutrients) and the collection of zooplankton with a Bongo net of 335 ”m mesh size. Zooplankton composition, distribution, density, biomass and diversity were determined. The principal component analysis (PCA) revealed the existence of a spatial gradient with the upstream sampling stations, associated to high values of nutrients, in opposition to the downstream stations characterized by higher salinity and transparency values. The Copepoda was the main dominant group and Acartia tonsa revealed to be the more abundant taxon. The spatial and temporal dynamics of zooplanktonic communities analysed by non-metric MDS showed the existence of four assemblages of species-sites, reflecting differences in zooplankton composition between both branches of the estuary. The results suggest that abundance, biomass and diversity of the zooplanktonic community are strongly influenced by the hydrological circulation pattern and by direct or indirect human impacts that occur in each branch. The northern branch is dominated by the river flow suffering from regular dredging activities and the southern branch is dominated by tidal circulation suffering from an ongoing eutrophication process