Influence of the surface microlayer on nutrients,chlorophyll and algal diversity of a small eutrophic bog pond

Nutrients, chlorophyll, phaeophytin and algal abundances were investigated in the surface microlayer and at subsurface depths in a small eutrophic bog pond. Nutrient levels were consistently higher in the microlayer while algal abundance was sometimes higher but sometimes lower in the microlayer than at near subsurface depths. Algal diversity values were strongly influenced by the depth of flagellate blooms, and in contrast to previous studies, diversity in the microlayer was higher than at near subsurface depths. These results are discussed in terms of weather parameters, affinity of algal species for the surface and differences between microlayer ecology in shallow and deep water systems.     

Embryonic development times of entomostracan zooplankton from Lake le Roux (Orange River,South Africa), and their possible relationships to seasonal succession

Embryonic development times of the principal entomostracan zooplankton of Lake le Roux, Orange River, South Africa, are described. Durations decreased monotonically with temperature over the thermal tolerance range and are described using Blehrádek's equation. The present data are compared with other observations on rate-temperature responses of warm-water and temperate zooplankton. Small, but ecologically significant, differences are discerned. The possible significance of species-specific rate-temperature responses to the phenomenon of seasonal succession is explored.     

The endomembrane system of differentiating carposporangia in the red algaChondria tenuissima: Occurrence and participation in secretion of polysaccharidic and proteinaceous substances

Summary The endomembrane system during carposporogenesis inChondria tenuissima was studied using electron microscopy and histochemistry. Profiles of the nucleus are convoluted, resulting in a highly increased surface area. Stacked cisternae are found within the peripheral part of the nucleus. Vesicles, tubules and membrane bound fibrillar bodies occur within the nucleoplasm. The endoplasmic reticulum surrounds the nuclear envelope.The endoplasmic reticulum and the Golgi apparatus, together with small transition vesicles, represent a functional unit. They form two different secretory substances during carposporogenesis. In young stages, carbohydrates are produced by normal dictyosomes within large, normal exocytotic Golgi vesicles. They do not react positively with PAS or Thiéry method and are believed to represent cell wall material. In later stages, the central area of the Golgi cisternae becomes filled with electron dense material. The individual cisternae are transformed into cored vesicles at the trans-face of the dictyosomes. The dense core of the vesicles is proteinaceous and stains with coomassie brilliant blue R. The peripheral fibrillar material is polysaccharidic and reacts positively using the Thiéry method. The contents of the cored vesicles are believed to participate in carpospore attachment. The ER gives rise to cytolysosomes in which starch grains are sequestrated and digested. Mucilaginous sacs seem to be similarly formed.     

Consequences of iron deficiency on photosynthetic and respiratory electron transport in blue-green algae

Growth of Aphanocapsa in low iron media resulted in a decrease of the endogenous iron pool. Below a critical concentration photosynthetic electron transfer was specifically depressed. This was caused by a strong inhibition of the synthesis of cytochromes b-559 of PSII, cytochromes b-563, f-557, and the Rieske Fe-S center of the cytochrome complex and especially the Fe-S centers of PSI. The influence of iron limitation on respiration and chlorphyll formation was negligible.Paper presented at the FESPP meeting (Strasbourg, 1984)     

Observations on the seasonal and yearly occurrence and the distribution ofAtyaephyra desmaresti (Millet, 1831) (Crustacea,Decapoda, Natantia) in The Netherlands

Summary The seasonal occurrence ofAtyaephyra desmaresti in The Netherlands has been studied by sampling the cooling-water filtering screens of power stations situated along the rivers Rhine and Meuse. The shrimps were only found in large numbers at the two power stations with vegetation in the cooling-water intake areas. Fluctuations in the seasonal occurrence showed great similarity for these two localities. Highest numbers of shrimps were impinged in November. High numbers also occurred in September, while a lower peak in numbers was found in May.Changes in the numbers of records during the last 30 years in The Netherlands were compared with climatological fluctuations (severe or mild winters), indicating that this mainly southern-European species is living here at the limits of its ecological and geographical range.The distribution in The Netherlands reveals thatAtyaephyra desmaresti mainly occurs in freshwater habitats, although it tolerates higher chlorinities.     

The behaviour of Dutch fresh water ecologists in response to environmental concern

Due to the rise of environmental concern ecologists have been asked for advice more frequently since the late 1960s. This article discusses how the changing relationship between ecologists and society has affected the behaviour of one particular group of ecologists, namely Dutch fresh water ecologists, by focussing on their behaviour towards job market control and public interest activities. The analysis has been based on interviews with 65 Dutch fresh water ecologists together with an analysis of their publications.In contrast with American ecologists, Dutch fresh water ecologists have made little effort to control their job market by formal arrangements such as formulating a code of ethics and certification procedures. Secondly, Dutch fresh water ecologists generally conceive of their own role in contributing to the solution of environmental problems in relation to that of the environmentalists by doing good research and reliable advisory work. Although a significant number of researchers also address lay publics by writing popular articles and/or holding lectures, only a minority actively participates in environmental politics.     

Effects of particle concentration and season on the filtration rates of the freshwater clam,Sphaerium striatinum Lamarck (Bivalvia: Pisidiidae)

The effects of particle concentration and season on the filtration rates of the freshwater clamSphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 μm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2–64 mg 1⁻¹, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam⁻¹ h⁻¹. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams. It is estimated that clams occupying 1 m² of stream substrate removed about 3.67 gCa⁻¹. This is equivalent to 0.0004% of the carbon that flows past them annually. Filter-feeding provided only 24% of the calculated energy needs of the population, suggesting that another mode of feeding (e.g. deposit-feeding) may provide an important energy source for these forms. Funded in part by a grant-in-aid to D. J. Hornbach from Sigma-Xi, The Research Society. Funded in part by a grant-in-aid to D. J. Hornbach from Sigma-Xi, The Research Society.     

Primary production and respiration of the phytoplankton in the Blue and White Niles at Khartoum

Phytoplankton production and respiration in the Blue Nile and White Nile at Khartoum were measured during the period November 1969–January 1971 using the light and dark bottle technique. Maximum rates of production coincided with periods of maximum phytoplankton densities. In the Blue Nile gross production varied between 0.00 gCm^–3d^–1 during the flood season and 2.19 gCm^–3d^–1 (0.49 mgO₂l^–1h^–1) during November 1969. In the White Nile the range was from 0.41 gCm^–3d^–1 (0.09 MgO₂l^–1h^–1) in May to 3.74 gCm^–3d^–1 (0.83 MgO₂l^–1h^–1) in November. The maximum rates of respiration in the Blue Nile and White Nile were 0.10 and 0.63 MgO₂l^–1h^–1 respectively. The ratios net:gross production were generally higher in the White Nile than in the Blue Nile.