The influence of mixing on rotifer assemblages of Michigan lakes

Seasonal changes in the rotifer assemblages of 42 lakes in northern lower Michigan was closely related to lake mixing characteristics, basin morphometry, and the presence of an oxygenated coldwater refuge. Three major classes of lakes (dimictic, discontinuous polymitic, and continuous polymictic) were evident by their capacity to maintain coldwater species as seasons progressed from winter through fall. The disappearance of coldwater assemblages from dimictic lakes coincided with oxygen depletion in the hypolimnion or with erosion of the hypolimnion through mixing. Coldwater species disappeared from large discontinuous polymictic lakes when deep epilimnetic mixing occured in late summer and fall. Species assemblages of nearly all stratified lakes converged with those of continuous polymictic lakes when the hypolimnetic refuge deteriorated in summer and fall. Local weather conditions, however, between years had a pronounced effect on the persistence of cold water species through the seasons by affecting the temperature and oxygen conditions of the hypolimnion. Large lakes of the region contain many of the coldwater species of the Laurentian Great Lakes but some taxa are conspicuosly absent. Cold stenothermal rotifers persist in the lakes of the region despite adverse environmental conditions. Their life histories and ability to form resting stages permit them to escape periods of oxygen depletion and thermal stress. In contrast, the crustacean glacial marine fauna (i.e. Mysis relicta, Limnocalanus macrurus, and Scenecella calanoides) was absent from all of the study lakes even though many of the present-day basins were once connected to the Laurentian Great Lakes. These species long life cycles, lack of diapausing stages, and limited dispersal may make them vulnerable to local extinction with the deterioration and loss of the coldwater refuge.     

How ecological indicators construction reveals social changes—The case of lakes and rivers in France

Social and scientific factors are deeply enmeshed in each other within the development and the use of ecological indicators (EI). Yet low research has assessed which factors contribute to selecting ecological indicators on the long-term. This article proposes to study the historical construction of EI by examining ecological, political, and social background of specific places where EI were developed, in France on lakes and rivers. Our major findings in France were that ecological indicators were never optimised for the present market or political arena. Instead EI development was typically recycling previous tools that were elaborated for other purposes by environmentally committed outsiders, without regular funding. We found that regular funding for monitoring an EI was only provided when it matched an institution's goal. Beyond the geographically limited relevance of the case studies, these results therefore improve the theoretical framework we deploy when constructing or relying on indicators.     

Feeding Rate of Brachionus plicatilis O. F. Müller on Two Types of Food Depending on Ambient Temperature and Salinity

Feeding rates of Brachionus plicatilis were studied for two types of food — algae Monochrysis lutheri and baker's yeast Saccharomyces cerevisae. The main regularities of changes in filtration rate and ration were studied in small culture volumes (1 ml) for adult amictic females depending on food concentration (1, 2, 4, 8 and 16 · 10⁶ cells · ml⁻¹), ambient temperature (16 and 26 °C), and salinity (5, 10, 15, 20, 25 and 30 ppt). B. plicatilis ration did not depend on the salinity, but was largely determined by temperature and food concentration. It was found that at 16 and 26 °C the dependence of the ingestion rate (ration) on food concentration differed greatly. A hypothesis was suggested to explain this phenomenon. A critical concentration of both types of food at which the increase in the rotifer ration ceased is 4 · 10⁶ cells · ml^−1. This is the minimum “background” food concentration for B. plicatilis mass cultivation. The average rations measured at the concentration of M. lutheri and S. cerevisae of 4 · 10⁶ cells · ml⁻¹ where 1.3 ± 0.1 and 4.8 ± 1.3 μg dry weight. · ind⁻¹ · day⁻¹ at 26 °C and 0.54 ± 0.1 and 1.9 μg d. w. · ind⁻¹ · day⁻¹ at 16 °C, respectively. The rations obtained in the laboratory were corrected for the conditions of rotifer commercial production in the open field in summer time. The correct values were 0.86 and 0.72 μg d. w. · ind⁻¹ · day⁻¹ for algae and yeast, respectively.     

Feral populations of the Australian Red-Claw crayfish (<Emphasis Type="Italic">Cherax quadricarinatus</Emphasis> von Martens) in water supply catchments of Singapore

The Red-Claw crayfish, Cherax quadricarinatus von Martens, is native to freshwater habitats of northern Australia and Papua New Guinea. Owing to its large size and suitability for aquaculture, C. quadricarinatus has been widely translocated around the world. Unfortunately, C. quadricarinatus is also recognised as invasive, having already established feral populations in South Africa, Mexico, Jamaica and Puerto Rico. The hardiness and conspicuous colouration of C. quadricarinatus has also made it popular in the aquarium trade worldwide, including Singapore. Here, we report the establishment of feral populations of C. quadricarinatus in the water supply catchments of Singapore.     

On the presence of the Australian redclaw crayfish, <Emphasis Type="Italic">Cherax quadricarinatus</Emphasis>, in Mexico

The first reports of wild caught Australian redclaw crayfish from Mexico, in the states of Morelos and Tamaulipas, are presented. Redclaw crayfish were first brought to Mexico in 1995 to initiate experimental cultures at several research centers. In the following years a number of private ventures started commercial cultures, several of which in the states of Morelos and Tamaulipas are thought to have been the sources for the wild populations recorded in this study. The farms that acted as the original sources have not been operating for at least 2 years. In Morelos, high densities and all size classes of redclaws, including ovigerous females, were captured in natural waterways; whereas in Tamaulipas they were found at four sites occurring in irrigation canals in an agricultural district. The size attained by the wild redclaws, the abiotic conditions in which they were found and the potential for spread within the drainage systems of the Balsas and Tamesi Rivers are discussed.     

Biogeochemical fluxes of iron from rainwater,rivers and sewage to a Galician Ria (NW Iberian Peninsula). Natural versus anthropogenic contributions

The total iron (TFe) concentrations in five rivers to a Galician Ria (averages 1.0–4.5 μM) was within the pristine range, but in rainwater it was higher (17 μM). TFe values of small sewage treatment plants (STP) ranged between 3 and 4 μM, whereas in the largest was 11 μM. Particulate iron in rivers was five times more abundant than dissolved iron, except in the Lagares where it was 20 times higher, but in the STDs the dissolved/particulate coefficients varied from 0.1 to 1.1 and in the rainwater it was lower than 0.4. Equations of water flow versus iron flux were obtained to quantify the iron contribution from the freshwater sources to the Vigo Ria. It receives annually 490 tons of iron (6% in dissolved form) and 90% of this comes from industries focused on metal processes. The contaminated Lagares River accounts for the main input of TFe (327 t a⁻¹), followed by rainwater (78 t a⁻¹), the Oitavén River (28 t a⁻¹) and Vigo STP (33 t a⁻¹). Anthropogenic activities have increased the amount of iron flowing into the Ria by roughly ten times and this could upset the biogeochemical cycle in similar coastal systems.     

Preliminary comments on a redescription of Pseudolithophyllum fuegianum and Titanoderma conspectum (Rhodophyta,Corallinales) in Tierra del Fuego,Argentina

The effect of twelve drugs and chemical compounds on the narcosis of Brachionus plicatilis was studied using standardized laboratory conditions. Drug efficacy was compared by calculating EC₅₀ (effective concentration causing narcosis in 50% of animals), time necessary to reach narcosis in 50% of animals, concentration range of activity, and degree of extension after preservation. The local anesthetic Bupivacaine was found to be most effective by all criteria. Our previous data and preliminary field experiments indicated that drug sensitivity varies widely, even between congeneric taxa. The anesthetic effect of carbonated water was also investigated.     

The potamoplankton of the Middle Loire and the role of the ’moving littoral‘ in downstream transfer of algae and rotifers

The seasonal succession of the potamoplankton of the Middel Loire was studied fortnightly from June to October 1995, a period of low water flow. The increase in dissolved oxygen, suspended matter, BOD₅ and chlorophyll a, associated with the decrease in nutrients downstream, are typical of eutrophic rivers. Algae were the principal components of the suspended matter flux in the river. Their density increased from the upper site of Dampierre-en-Burly to the lower site of Saint-Laurent des Eaux, with respective maxima of 68 ×10⁶ cells l^-1 and 106 × 10⁶cells l^-1. A large rotifer community developed in association with the algal growth, with densities up to 3700 ind l^-1 at Dampierre-en-Burly and up to 5800 ind l^-1 at Saint-Laurent des Eaux. They had a high Shannon-Weaver diversity, while grazing appeared to control the algae. As the year progressed to the warmer season, the biomass of the β and β α mesosaprobic rotifer species increased parallel with algae. The water theoretically transported potamoplankton at 0.2 ms^-1 during mid-summer, which meant that the biomass of the algae doubled in minimum 17 km and that of the rotifers in 34 km. From these values and the distances between sampling stations, we deduce that inoculation points were located in areas which could be as short as a hundred meters. Not only algae, but also rotifers are capable of restoring an inoculum of organisms from place to place. Summer hydrodynamics, close to localised lentic areas, were responsible for an increase in plankton abundance in the stream. These movements had an ecotone effect at the boundary between standing and running water, creating pulses. The lower regions were progressively enriched by successive inoculates, dilution and seeding inputs, which did not prevent the growth of algae and of parthenogenetic species in the river. Such processes, which occur in years of low flow, are responsible for the large variations in plankton density observed between years. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reproductive ecology of the striped bitterling Acheilognathus cyanostigma (Cyprinidae: Acheilognathinae)

The reproductive ecology of the striped bitterling Acheilognathus cyanostigma was investigated in a small pond in Mie Prefecture, central Honshu, Japan. A. cyanostigma was the only species of bitterling in the study pond, where only a single species of mussel Anodonta woodiana was present. Spawning of A. cyanostigma was recorded between early April and early July, peaking between late April and mid-June in 2003. Ovipositor length during the spawning period ranged from 19.2 to 42.8 mm, and was positively correlated with female body length, but did not show significant seasonal variation. The eggs are elliptical with a volume of approximately 1.5 mm³. Egg size correlates positively with female body size, and both egg shape and volume changed significantly with season. The embryos were located on host mussel gills approximately 30 mm from the exhalant siphon and were found more frequently on the inner rather than the outer mussel gills. The possible ecological significance of these observations is discussed in the context of the adaptations of A. cyanostigma for utilizing mussels for oviposition.