Distribution of rotifers in African fresh and inland saline waters

The distribution of rotifers in African fresh and inland saline waters is discussed in the light of historical expeditions and modern limnological research. Number of papers published and number of rotifer species described for each country are given. Some peculiarities of African rotifer fauna are described.     

Bacteriophage in polar inland waters

Bacteriophages are found wherever microbial life is present and play a significant role in aquatic ecosystems. They mediate microbial abundance, production, respiration, diversity, genetic transfer, nutrient cycling and particle size distribution. Most studies of bacteriophage ecology have been undertaken at temperate latitudes. Data on bacteriophages in polar inland waters are scant but the indications are that they play an active and dynamic role in these microbially dominated polar ecosystems. This review summarises what is presently known about polar inland bacteriophages, ranging from subglacial Antarctic lakes to glacial ecosystems in the Arctic. The review examines interactions between bacteriophages and their hosts and the abiotic and biotic variables that influence these interactions in polar inland waters. In addition, we consider the proportion of the bacteria in Arctic and Antarctic lake and glacial waters that are lysogenic and visibly infected with viruses. We assess the relevance of bacteriophages in the microbial loop in the extreme environments of Antarctic and Arctic inland waters with an emphasis on carbon cycling.     

Fish diversity and its relationships with environmental variables in a West African basin

Fish distribution in relation with environmental variables was investigated in the Boubo River, a coastal river in Ivory Coast. Fourty freshwater fish species belonging to 17 families and 26 genera were captured. Five brackish water species, two introduced species and one hybrid complete the list. Seven species are reported for the first time in this river. A significant correlation between species distribution and environmental variables was found. Rocky and leaves-dead wood substrates, oxygen, canopy closure, width, depth and velocity were the main environmental variables influencing fish distribution. Our findings are opposed to the tendency for species composition to increase from the source to the mouth of the river, which is probably due to two major human activities (dam construction and discharge of waste of palm oils and motor oils in the main channel). These activities could constitute in the future a real threat for the fish population and other aquatic organisms.     

The proportion of different eco-ethological sections of reproductive guilds of fishes in some African inland waters

Synopsis The continent of Africa has a wide variety of inland waters ranging from rift valley lakes to endorheic and coastal lakes, floodplains and rivers. This paper makes a preliminary comparison of the number of species in different eco-ethological sections of the reproductive guild categories of non-guarders, guarders and bearers in ancient African Great Lakes (Malawi, Victoria and Tanganyika), fluctuating endorheic lakes (Ngami, Chad and Chilwa), typical rivers (Orange-Vaal, Limpopo, Phongolo, Sabi-Lundi, Middle and Lower Zambezi, Kafue, Cunene, Okavango, Niger, Luongo, Lower Zaire) and wetlands (Okavango Delta and Kafue floodplain). The results indicate that the highest percentage of bearers and guarders is found in the ancient African Great Lakes, which are characterised by relatively predictable physico-chemical regimes, whereas a higher percentage of non-guarders is found in the rivers and wetlands, which have less predictable physico-chemical regimes. The management implications of this observation are discussed, and the usefulness of the species as a unit in ecology is assessed.     

Distinguishing technology from biology: a critical review of the use of GPS telemetry data in ecology

In the past decade, ecologists have witnessed vast improvements in our ability to collect animal movement data through animal-borne technology, such as through GPS or ARGOS systems. However, more data does not necessarily yield greater knowledge in understanding animal ecology and conservation. In this paper, we provide a review of the major benefits, problems and potential misuses of GPS/Argos technology to animal ecology and conservation. Benefits are obvious, and include the ability to collect fine-scale spatio-temporal location data on many previously impossible to study animals, such as ocean-going fish, migratory songbirds and long-distance migratory mammals. These benefits come with significant problems, however, imposed by frequent collar failures and high cost, which often results in weaker study design, reduced sample sizes and poorer statistical inference. In addition, we see the divorcing of biologists from a field-based understanding of animal ecology to be a growing problem. Despite these difficulties, GPS devices have provided significant benefits, particularly in the conservation and ecology of wide-ranging species. We conclude by offering suggestions for ecologists on which kinds of ecological questions would currently benefit the most from GPS/Argos technology, and where the technology has been potentially misused. Significant conceptual challenges remain, however, including the links between movement and behaviour, and movement and population dynamics.     

Fish hatching strategies: a review

The paper presents differences in the distribution of hatching gland cells, and the location of egg envelope digestion, the significance of hatching movements, and the ways larvae escape from egg envelopes. A review of the literature on the hatching orientation of 34 fish species is compared. No correlation was seen between hatching orientation and egg diameter or newly hatched larva length, nor newly hatched larvae length ratio to egg diameter. Photographs of twelve freshwater species present the moment of hatching either head first or tail first. Some differences were shown in swelling between eggs incubated in commercial hatchery and developed in natural conditions, as well as possible effect of these differences on hatching.     

African histoplasmosis: a review

African histoplasmosis caused by Histoplasma capsulatum var. duboisii is an important deep mycosis endemic in Central and West Africa and in the island of Madagascar. The disease is characterized by presence of granulomatous lesions in the skin, subcutaneous tissues and bones. Lungs and other internal organs are rarely involved. The natural reservoir of the etiological agent has only been recently discovered in a bat cave in Nigeria. The status of asymptomatic infection is not certain. Investigations on skin and serum reactivity have suggested frequent prevalence of asymptomatic infections due to H. capsulatum var. duboisii among the residents in the vicinity of the cave microfocus of the fungus. The exact portal of entry into the body is not known, but inhalation into the lungs and direct inoculation in the skin have been incriminated. Laboratory diagnosis is confirmed by in vitro conversion into large yeast forms (8-15 mum in diameter) and by the demonstration of these forms within giant cells of tissues of experimentally infected animals There are no major clean-cut physiological differences between the two varieties, viz. capsulatum and duboisii. The cell wall of H. capsulatum var duboisii contains a glucan with beta 1-4 linkages in addition to a galactomannan shared with H. capsulatum var. capsulatum. Like the var. capsulatum var. duboisii has marked proteinase and collagenase activities in both mycelial and yeast forms, suggesting a possible pathogenic role for these enzymes. Both varieties have a common exoantigen. The yeast form of H. capsulatum var. duboisii contains the antigen found in the serotype 1,4 of var. capsulatum. A monoclonal antibody test has been developed that can recognize some epitopes in H. capsulatum var. capsulatum but not in the var. duboisii. There is need to develop specific serological diagnosis for the disease. Also there should be greater international awareness about African histoplasmosis. Amphotericin B and several antimycotic azoles like ketoconazole, itraconazole and fluconazole have been successfully employed for treatment.     

Stock assessment in inland fisheries: a foundation for sustainable use and conservation

Fisheries stock assessments are essential for science-based fisheries management. Inland fisheries pose challenges, but also provide opportunities for biological assessments that differ from those encountered in large marine fisheries for which many of our assessment methods have been developed. These include the number and diversity of fisheries, high levels of ecological and environmental variation, and relative lack of institutional capacity for assessment. In addition, anthropogenic impacts on habitats, widespread presence of non-native species and the frequent use of enhancement and restoration measures such as stocking affect stock dynamics. This paper outlines various stock assessment and data collection approaches that can be adapted to a wide range of different inland fisheries and management challenges. Although this paper identifies challenges in assessment, it focuses on solutions that are practical, scalable and transferrable. A path forward is suggested in which biological assessment generates some of the critical information needed by fisheries managers to make effective decisions that benefit the resource and stakeholders.     

Seasonality of aquatic invertebrates in low-latitude and Southern Hemisphere inland waters

The seasonality of freshwater aquatic invertebrates in Southern Hemisphere and low-latitude inland waters in Africa, Australasia and South America is reviewed. Fauna from the tropics to temperate latitudes manifests some seasonality, the amplitude of which tends to increase, albeit inconsistently, with latitude. The wide diversity of habitats considered, and deficiencies in the data preclude generalizations about patterns and magnitude of seasonal response, which principally reflect system-specific events and interactions. For example, zooplankton declined after mixing events in some stratified systems, but increased in others, food availability being implicated. Zooplankton was most abundant in summer in some stratifying systems, and in winter in others, while in most non-stratifying systems, it was most abundant around the winter solstice, and in several, declined during the rainy season.Seasonality of the zoobenthos was frequently linked to hydrological events such as fluctuations in water level which potentially influence food and habitat availability. Seasonal anaerobiosis in shallow sheltered waters and deeper hypolimnia imposes spatio-temporal restrictions on the benthic fauna. Low oxygen solubility, rapid oxygen depletion and decomposition of organic food matter at the elevated temperatures are probably significant influences. Life histories of Southern Hemisphere stream fauna appear seasonally flexible and opportunistic by contrast with the apparently synchronous cycles exhibited by north temperate representatives. Such flexibility may be selective both in respect of climatic unpredictability and equability.The influences of predation and resource availability upon seasonal dynamics remain to be explored more fully, particularly in aquatic ecosystems in warm, arid regions which lack the climatic predictability of the cooler, humid, temperate zones.     

The attenuation of ultraviolet and visible radiation in Dutch inland waters

The vertical attenuation coefficients (K _d) of downward ultraviolet (UV) and visible irradiance (PAR) were measured in 19 different inland waters in the Netherlands using a scanning spectroradiometer. Water chemistry variables such as dissolved organic carbon (DOC), absorbance of dissolved matter (a _d), chlorophyll-a, and particulate matter were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in K _d. In addition to the field measurements, laboratory measurements were performed to test the relationships between water properties and light attenuation. The attenuation properties of Dutch inland waters vary. In most systems the penetration of UV-B radiation (280–320 nm) is limited to the upper decimetres. Lake Maarsseveen was the clearest waterbody in this study, with K _dUVB of 9.1 (m^–1). The DOC concentration had limited power in predicting UV attenuation in this study (r ²=0.33), because of the large differences in carbon-specific absorption. A _d300 was a much better predictor of UV attenuation (r ²=0.75). The relationships obtained in the laboratory experiments can be used to give a good prediction of in situ K _d values, based on 3 variables (chlorophyll-a, ash weight, and absorption of dissolved matter).     

Preliminary study of microbiological parameters in eight inland recreational waters

A pilot survey of the counts of total coliform bacteria, thermotolerant coliform bacteria, Escherichia coli and faecal streptococci was carried out at eight inland recreational waters at weekly intervals during July 1991. The aims were to assess the feasibility of determining candidate indicators of recreational water quality and to assess the possible scale of variability of these parameters. The numbers of total coliforms were difficult to determine reliably because of interference from the background bacterial flora. There was a strong correlation between thermotolerant coliforms and E. coli and faecal streptococci. The average counts of the indicator organisms varied between and within the eight recreational waters by up to 10000-fold. The greatest variation was between the eight recreational waters. At any one water, the greatest source of variation was time but there was substantial variation between sample points at one time. Counts in samples collected 1 m apart exhibited greater than random variation. Counts from surface samples tended to be higher than those at 30 cm or 100 cm depth. The proportion of thermotolerant coliforms confirmed to be E. coli varied from water to water between 60% and 96%.     

Specific diversity and community structure of Rotifera in a salinity series of Ethiopian inland waters

The communities of planktonic Rotifera in thirty localities in Ethiopia were examined. All the localities lay at altitudes of over 1100 m and some were over 2000 m. The salinities ranged from 0.12 to 56.3% and in those lakes with salinities over 2% there was a marked reduction in the number of rotifer species, with Brachionus dimidiatus the most frequently dominant. The mean momentary species number in these Ethiopian samples is significantly higher than the means given by Pennak (1947) for Colorado and the rest of the world. Long-term planktonic species numbers in lakes Ziway and Awasa were about three times the mean momentary species number. The dominance ratios in the samples ranged from 19 to 91, but in general were lower than those given by Pennak. The most frequently dominant species were members of the family Brachionidae. Comparison with the data of Tonolli (1962) on the Lago Maggiore indicates that more data are needed on species diversity and dominance before valid geographical comparisons can be made.     

Harvest index: a review of its use in plant breeding and crop physiology

This review charts the use of the concept of harvest index in crop improvement and physiology, concentrating on the literature from the last 20 years. Evidence from abstract journals indicates that the term has been applied most to small grain cereal crops and pulses, in India, Western Europe and the USA, and that it has been less useful for maize and tuber crops. Standard methods of measuring harvest index, the associated problems of measurement and interpretation, and representative values for a range of world species are reviewed. The values for modern varieties of most intensively-cultivated grain crops fall within the range 0.4 to 0.6. Variation between varieties of the same species is illustrated by trends in the harvest indices of old, outclassed and recent varieties of temperate and mediterranean wheat and barley (compared under uniform conditions); this shows a progressive increase throughout the present century, although improvement has been much slower in Australia and Canada than in the UK. In most cases, the improvement in harvest index has been a consequence of increased grain population density coupled with stable individual grain weight. The high heritability of harvest index is explored by examining its (rather weak) response to variation in environmental factors (fertilisation, population density, application of growth regulators) in the absence of severe stress. A fuller perspective is gained by reviewing aspects of the harvest index of rice, maize and tropical pulses. With rice, attention must be paid to the fact that the adhering lemma and palea (not primarily part of economic yield) can make up 20% of grain weight; and there are important interactions among biomass, grain yield and season length. Maize differs from most small grain crops in that harvest index (in N. American varieties) was already high at the start of this century, and increases in yield potential have been largely the consequence of increased biomass production. The harvest index of many pulse species and varieties tends to be low because selection has been for some yield in all seasons. Extension of the harvest index concept to express the partitioning of mineral nutrients as well as dry matter (e.g. the nitrogen harvest index) has provided a range of responses whose implications for production and breeding remain to be explored. It is concluded that even though the principal cereal crops appear to be approaching the upper limit of harvest index, and future yield gains will have to be sought by increased biomass production, there will still be a need for the concept of harvest index as a tool in interpreting crop response to different environments and climatic change.     

Patterns of resource limitation of bacteria along a trophic gradient in Mediterranean inland waters

The nature of the resource that limits heterotrophic bacteria, i.e. mineral nutrients or carbon (C), has consequences for biogeochemical cycles in aquatic ecosystems. Our aim was to identify the resource [C or phosphorus (P)] that mainly limits bacteria in a set of 31 Mediterranean inland water ecosystems spanning a wide trophic range. We followed an intersystem observational approach with three complementary perspectives, comparing the bacterial demand with the resource supply in terms of both the quantity (demand : supply ratio for C and P) and quality (C : P ratio of demand and supply), and assessing the relative strength of each resource in controlling bacterial production. The trophic gradient revealed a shift in the main limiting resource for bacteria, from C at the oligotrophic end (typically high-mountain, low-productivity lakes) to mainly P at the eutrophic end (typically nonmountain, high-productivity lakes). The patterns of resource limitation of bacteria found here may be related to the autotrophic nature of most of the studied ecosystems linked to a Mediterranean climate regime as representative of lakes with low inputs of allocthonous C. These patterns are consistent with the theoretical approaches and may potentially shape the contribution of this type of ecosystems to biogeochemical cycles.     

Animal xenodiversity in Italian inland waters: distribution, modes of arrival, and pathways

The paper provides a list of the non-indigenous animal species occurring today in Italian inland waters. Xenodiversity was found to amount to 112 species (64 invertebrates and 48 vertebrates), which contribute for about 2% to the inland-water fauna in Italy. Northern and central regions are most affected, and Asia, North America, and the rest of Europe are the main donor continents. The large majority of non-indigenous species entered Italy as a direct or indirect effect of human intervention. A difference between invertebrates and vertebrates was found for their mode of arrival (unintentional for invertebrates and intentional for vertebrates). Accidental transport, in association with both fish (for aquaculture or stock enhancement) and crops, has been the main vector of invertebrate introductions, whereas vertebrates were mostly released for stocking purposes. Overall stock enhancement (47.92%) and culture (37.5%) prevailed over the other pathways. Seventeen and 7 species of our list are included among the 100 worst invasive species of Europe (DAISIE) and of the world (IUCN), respectively. For some (but not all) non-indigenous species recorded in Italy the multilevel impact exerted on the recipient communities and ecosystems is known, even if rarely quantified, but knowledge on their chronic impact is still missing. Additional research is needed to provide criteria for prioritizing intervention against well established invaders and identify which new potential invader should be targeted as “unwanted”.     

Subsurface irradiance reflectance spectra of inland waters differing in morphometry and hydrology

A database has been established for relating subsurface irradiance reflectance, i.e. water ‘colour’, to the optical properties and water quality parameters of more than 120 Dutch inland water bodies. The concentrations of total chlorophyll-a (TChl-a = chlorophyll-a plus phaeopigment), total suspended matter and the Secchi-disc depth varied between 0.6 and 468 mg m^-3, 0.8 and 98 g m^-3, and 0.15 and 5.50 m, respectively. The water bodies represented very different water types based on morphometry and hydrology. The depth ranged from 0.4 to 40 m, and the surface area from 0.25 ha (fens in the moorland Peel) to 1200 km² (Lake IJsselmeer). The mean specific phytoplankton absorption coefficient at 676 nm was 0.013 ± 0.003 m² (mg TChl-a)^-1. The absorption by tripton and dissolved humic substances at 440 nm varied between 0.1 and 16.4 m^-1, and 0.1 and 65.5 m^-1, respectively. By using the spectral position and magnitude of the subsurface irradiance reflectance peak alone, it was possible to distinguish groups of water bodies according to a classical typology based on morphometry and hydrology. This revised version was published online in July 2006 with corrections to the Cover Date.     

The spectral distribution and attenuation of underwater irradiance in Tasmanian inland waters

SUMMARY. 1. Measurements were made of the attenuation and spectral distribution of downwelling and upwelling photosynthetically-available radiation (PAR) in all the principal types of natural waters found in Tasmania. 2. Most lakes in the State are clear and non-turbid, with water itself and the low concentrations of gilvin being the principal determinants of the green underwater light climate. Many others are deeply coloured by dissolved and colloidal organic material (gilvin, gelbstoff) which rapidly attenuates short wavelengths, specifying a shallow, predominantly red euphotic zone. 3. A spectrophotometric measure of colour, the absorption coefficient at 440 nm, is statistically related to measurements on the platinum scale with good precision. 4. Few Tasmanian lakes are turbid but in those that are the underwater light climate is almost identical to that of non-turbid, humic lakes. 5. Reflectance, R, varied with depth but not in the asymptotic way previously encountered. A linear relationship existed between the scattering coefficient, b, and nephelometric turbidity, but not at the approximate 1:1 ratio reported elsewhere. 6. Most Tasmanian lakes are oligotrophic or dystrophic and phytoplankton rarely influenced the underwater light field. 7. Seasonal variation in optical character is not great in natural lakes and their optical properties and light fields can be used typologically. 8. Simple and multiple regression analysis showed that Secchi depth was a poor predictor of euphotic depth but the optical properties and the underwater light field of inaccessible lakes could be reasonably predicted from laboratory measurements made on small water samples, using regressions developed for a wide range of lake types and by reference to the quantaradiometric scans of lakes with comparable optical properties. 9. An optical classification of Tasmanian lakes made by cluster analysis agreed reasonably well with one based on edaphic, vegetational and chemical criteria.