Showing papers in "Journal of Plankton Research in 1985"

Elemental and isotopic fractionation of carbon and nitrogen by marine, planktonic copepods and implications to the marine nitrogen cycle

Abstract: Les copepodes etudies proviennent d'une station cotiere au nord-ouest du Golfe du Mexique (principalement Temora longicornis et T. stylifera); ils utilisent l'azote d'une facon plus efficace que le carbone pour la production des tissus; ils produisent des tissus enrichis et des feces appauvris en C 13 et N 15 en relation avec la matiere particulaire en suspension. Implications des resultats dans le cycle marin de l'azote

Differential grazing by Acartia tonsa on a dinoflagellate and a tintinnid

Abstract: The calanoid copepod, Acartia tonsa Dana, ingests both the dinoflagellate, Heterocapsa triquetra (Ehrenberg) Stein, and the tintinnid ciliate, Favella sp. In laboratory experiments its inges- tion rate increases with increasing dinoflagellate density to a maximum at ~650 cells ml"1, then declines. With Favella as the sole food item, ingestion rate increases up to and possibly above prey densities of 3.4 Favella ml"'. In mixtures of the two prey, the clearance rate of Acartia for Favella decreases with increasing concentration of Heterocapsa. At a Favella concentration of — 1 ml"' and a Heterocapsa concentration of 280 cells ml"», Acartia ingests the same biomass of each prey type. The copepods preferentially feed on Favella even when the dinoflagellate is more abundant in terms of carbon and nitrogen than the tintinnid. If the effect of food density on the growth of Favella is con- sidered as well as copepod predation, it is evident that both of these factors, and their interaction, can be important in regulating populations of this ciliate.

Variability of filter structures in eight Daphnia species: mesh sizes and filtering areas

Abstract: The morphology of the filtering apparatus of eight Daphnia species (62 individuals of all size classes) was investigated by scanning electron microscopy. In the majority of animals the intersetular distances (= mesh sizes) showed a normal distribution and the mean values were between 0.2 and 1.0 /un. The total filtering area increased approximately proportionally to the second power of the body length. Absolute values were between 0.063 and 2.6 mm3, with open portions of between 64% and 77% of the total area. In the relationship between mesh size and filtering area three types of allometric growth can be distinguished: (i) with increasing body length the mesh size remains small, but filtering area (FA) increases considerably (D. magna); (ii) both mesh size and FA increase with body length (D. pulicaria); and (iii) FA remains small but the mean mesh size becomes larger (D. cucullata).

Seasonal variability in the relationship between body length and individual dry weight as related to food abundance and clutch size in two coexisting Daphnia species

Abstract: Dry weights of individual Daphnia galeata and D. hyalina, which coexist in Lake Con- stance, were determined weekly during a two year investigation. From each sample and each species a length — weight relationship (LWR) was calculated resulting in 54 (65) regression equations based on N = 2466 (3032) in D. galeata (D. hyalina). The constants (Ln(A)) and (B) of the LWRs showed a marked seasonal variability, ranging from Ln(A) = 1.0784 - 2.4740(1.0152 - 2.3860) and B = 2.14 — 4.20(2.11 - 4.15). The seasonal variability of the LWR was estimated with four different models. Condensing the 54 (65) equations into one seasonal cycle resulted in a model with an explained variance of r 1 = 0.873 (0.869). Three more models were established by calculating multiple regres- sions with lake stratification, average fecundity (E), and food concentration as determining variates. Differences in LWRs of the two Daphnia species were significant (p <0.001). As the most useful approximation during the period of stratification, LWRs are recommended for D. galeata: Ln(W) «= (1.5674 + 0.0287*(E)) + Ln(L)*(3.3611 + 0.0111*(E)) as a generalized LWR for an epilimnetic daphnid, and for D. hyalina: Ln(W) = (1.5593 + 0.0613'(E)) + Ln(L)*(3.2709 + 0.0017*(E)) as LWR for a daphnid which migrates diurnally between epi and hypolimnion. The explained variance of this model is r2 = 0.843 (0.826). The influence of food concentration in the epilimnion on LWRs was found to be significant on Ln(A) but not on (B).

Predaceous feeding habits of Limnocalanus macrurus

Abstract: Etude, en laboratoire, des proies preferentielles et de la consommation saisonniere de L.m. provenant du lac Michigan

Differences in in vivo fluorescence yield between three phytoplankton size classes

Abstract: The size-dependent relationship between in vivo fluorescence (IVF) and chlorophyll a was deter- mined for monthly phytoplankton samples from the San Francisco Bay estuary. Chlorophyll a and IVF were both measured on netplankton (>22 pm), nanoplankton (5-22 pm), and ultraplankton (<5 prn) samples that were separated with screens. IVF and chlorophyll a were linearly related for each size class, but the IVF per unit chlorophyll a (R) was significantly different between these three size classes. The ultraplankton R was twice that of the nanoplankton which was in turn twice the netplankton R. Hence, accurate size frac- tionation of phytoplankton biomass from measures of IVF requires correction for size-dependent variations in R.

The effects of Po River induced eutrophication on the distribution and conimunity structure of ciliated protozoan and micrometazoan populations in the northern Adriatic Sea

Abstract: La biomasse moyenne du microzooplancton de la colonne d'eau augmente de 2 a 3 fois dans la partie ouest de l'Adriatique Nord au voisinage du delta du Po, en relation etroite avec l'eutrophisation. Augmentation considerable de la biomasse des cilies avec l'eutrophisation