The optical qualities of shallow wetland lined bays in Lake Victoria

In tropical lakes, the characteristics and dimension of the coastal wetlands can have a strong influence on the quality of the inshore waters. The interaction between littoral wetlands and the open water environment is complex and requires an understanding of the material and energy exchanges between these compartments. In the present analysis, we examine the impact of wetlands on the optical properties (underwater light environment) of two adjacent bays on the Ugandan side of Lake Victoria. We use both irradiance profiles within the water column as well as measurements of the dissolved and particulate fractions of the water column. By introducing a new term to identify that part of the solar spectrum most affected by wetland released dissolved organic matter, it is possible to determine the area of each bay that is influenced by the wetland. Depending on the period of analysis, wetland released chromophoric dissolved organic matter can play a dominating role in the attenuation of UV and visible radiation in the underwater environment.     

The use of stable carbon isotopes as tracers of ecosystem functioning in contrasting wetland ecosystems of Lake Victoria,Kenya

Aquatic macrophytes and sediments from two contrasting wetland ecosystems of Lake Victoria, Kenya (Lower Sondu Miriu and Kibos systems) were analyzed for their stable carbon isotopic composition in order to observe patterns in system functioning in these two ecosystems. The aquatic macrophytes had carbon isotope ratios ranging from –8.92 to –29.18 per mil (parts per thousand difference from the reference). For the dominant macrophytes, we observed most ¹³C enriched values for Cyperus papyrus and most ¹³C depleted values for Eichhornia crassipes. On transects from the river to the lake, Kibos sediments maintained lower carbon isotope signatures compared to the Lower Sondu Miriu sediments. The possible causes of the observed variation in the ¹³C signatures from sediments and aquatic macrophytes in the two-wetland ecosystems are outlined.     

Determinants of the parasite community of clariid fishes from Lake Victoria, Tanzania

The factors that determine parasite assemblages among the clariid fishes of Lake Victoria, Tanzania were studied between August 2003 and February 2005. Six hundred and fifty-six fish belonging to seven species were necropsied and examined for parasites, from which 31 species of metazoan parasites were recorded. The community was dominated by the nematodes both in species and numbers. Most species were generalists with only two trematodes, Diplostomum mashonense and Tylodelphys species, being specialists of Clarias gariepinus. Ten species were considered core and predictable. Parasite species richness, number of individuals per host and Shannon-Wiener diversity indices were generally high. At the compound community level, a mean number of 7.8 parasites were shared among different species of fish and the maximum number of parasites species per fish at the infracommunity level was seven. Levels of similarity in parasite species richness at the component community level ranged from 29.6 to 61.5%. The study concludes that parasite communities in clariid fishes of Lake Victoria are structured by ecological factors. At the infracommunity level, host size, diet and vagility promoted a richer parasite community. At the compound level, two factors were crucial, namely the intermixing of the waters in the lake and the predominant and mobile C. gariepinus.     

The origin and age of haplochromine fishes in Lake Victoria, east Africa

According to a widely held view, the more than 300 species of haplochromine cichlid fishes in Lake Victoria (LV), East Africa, originated from a single founder species in less than 12,000 years. This view, however, does not follow from the published geological and molecular evidence. The former does indeed suggest that the LV basin dried out less than 15,000 years ago, but it does not provide any information about the species that re-colonized the new lake or that remained in the rivers draining the area. The molecular evidence is inconclusive with respect to the origin of the LV haplochromines because cichlids from critical regions around LV were not adequately sampled; and as far as the age of the LV haplochromines is concerned, it in fact led to an estimate of 250,000-750,000 years old. In the present study, mitochondrial DNA (control region) variation was determined by heteroduplex and sequencing analyses of more than 670 specimens collected at widely distributed East African riverine and lacustrine localities. The analyses revealed the existence of seven haplogroups (I-VII) distinguishable by characteristic substitutions. All endemic LV samples tested fell into one of these haplogroups (V) which, however, was also found to be present at various other localities, both riverine and lacustrine, outside LV. Within this haplogroup, four subgroups (VA through VD) could be distinguished, two of which (VB and VC) were represented in LV and at other localities. The great majority of the LV haplochromine species could be classified as belonging to the VC subgroup, which was found only in LV and in the rivers draining into it. Hence, while the endemic haplochromine species of LV could not have originated from a single founding population, the lake does harbour a large species flock which probably arose in situ.     

The conservation of the fishes of Lake Victoria,Africa: an ecological perspective

Synopsis The African Great Lakes are considered to be dynamically fragile ecosystems that are relatively resistant to minor changes with which they have co-evolved but vulnerable to major perturbations such as overfishing, the introduction of alien species and pollution. These lakes are inhabited by large species flocks of cichlid fishes which are characterised by a complex structure of interaction both between and within species, as is typical of mature ecosystems. Major perturbations, such as the disruption of trophic interactions through the introduction of alien fishes, may reverse the domination of relatively precocial, specialised forms and result in the creation of conditions that are conducive to the survival of more altricial, generalised forms with strong colonising abilities. The introduction of Nile perch and Nile tilapia, as well as other alien fishes, into Lake Victoria, combined with overfishing for the indigenous cichlid species, has resulted in marked changes to the fish communities and the fisheries that depend on them. The most important impacts of the Nile perch appear to be predation and aggressive effects whereas those of the tilapias include hybridization, overcrowding, competition for food and possibly the introduction of parasites and diseases. While the three proposed methods of conserving the indigenous flocks of cichlid fishes (captive propagation, reducing Nile perch stocks and closure of the haplochromine trawl fishery) all have merit, the changes that are occurring in Lake Victoria are basically irreversible. The highest priority should be to assist the governments of the riparian countries (Tanzania, Uganda and Kenya) with monitoring and research programmes and to support their policies of non-introduction of further alien fishes into any of the African Great Lakes so as prevent the same cycle of events from occurring, for example, in Lakes Tanganyika and Malawi. The diverse animal and plant communities of the African Great Lakes are a heritage of all mankind and it is the duty of every country to play a role in their conservation. It is therefore proposed that an internationally funded research programme should be mounted on the African Great Lakes on the scale of the tropical forest biome project of the IUCN. Editorial     

Managing the natural capital of papyrus within riparian zones of Lake Victoria,Kenya

The harvesting of natural products such as papyrus (Cyperus papyrus L.), whether for subsistence value or for the production of commodities intended for sale at local markets, contributes to the well-being of riparian peoples around Lake Victoria, Kenya. Serious losses of papyrus wetlands across East Africa have been reported, most of which are attributed to increasing anthropogenic stressors. Recent studies have called for restoration of these wetlands, emphasizing the need for sustainable harvesting strategies to be put in place, although few have provided suggestions as to how this might happen in practical terms and, crucially, with the consent and active participation of local communities as key stakeholders. Here we explore the socioeconomic characteristics of livelihoods based on papyrus, presenting data generated from surveys, interviews and group discussions collected at multiple sites within the Nyando river basin, Kenya. Conceptualizing papyrus stands as living stocks of natural capital, we then outline our proposal for maintaining the provisioning services of this species, without compromising the critical ecohydrological functions of these swamps as land–water buffer zones. Finally we suggest how this approach might be adapted for wider dissemination around Lake Victoria and beyond, motivated by what we believe to be the first reported case of successful papyrus restoration by a local community.     

Genetic variation in the marbled lungfish Protopterus aethiopicus in Lake Victoria and introduction to Lake Baringo, Kenya

Marbled lungfish Protopterus aethiopicus in Lake Victoria and two nearby smaller lakes were found to have high levels of DNA sequence variation in their mitochondrial control regions (35 haplotypes in 61 fish) but no population genetic structure (Φ_ST= 0·00). In contrast, marbled lungfish in Lake Baringo, Kenya, appeared to be fixed for a single control region haplotype, which occurred at low frequency in the other lakes. Using FLUCTUATE software, the female effective population size in Lake Victoria during the late Pleistocene was estimated to be c. 500 000, similar to the value estimated for the present-day population. These observations suggest that, during the late Pleistocene dry period, a large marbled lungfish population survived either in wet refugial areas within the lake basin or in surrounding areas. Marbled lungfish were reported to have been introduced into Lake Baringo 30 years ago with a founding population of only three individuals. The lack of control region variation in the Lake Baringo population is consistent with that situation.     

Functioning and dynamics of wetland vegetation of Lake Victoria: an overview

The aquatic macrophytic vegetation constituting the wetlands situated along the coast of Lake Victoria provides valuable services to both local and regional communities as well as an important ecological function through the transition between terrestrial and aquatic ecosystems. The wetland vegetation is typically rooted in the substrate on the landward side of the lake, but forms a floating mat towards the middle of the wetland and at the wetland/lake interface. Cyperus papyrus and Miscanthidium violaceum vegetation typically dominate the permanently inundated wetland areas along most of the shores of Lake Victoria. Due to the prevailing climatic and hydrological catchment conditions, these macrophytic plants (papyrus in particular) tend to exhibit high net productivity and nutrient uptake which strongly influences both wetland status and lake water quality. In addition, these wetlands provide important economic livelihoods for the local populations. The integrity and physical structure of these wetlands strongly influences their associated mass transport mechanisms (water, nutrients and carbon) and ecosystem processes. Wetland degradation in Africa is an increasing problem, as these ecosystems are relied upon to attenuate industrial, urban and agricultural pollution and supply numerous services and resources. In an integrated project focused on the wetlands of Lake Victoria, the ecological and economic aspects of littoral wetlands were examined and new instruments developed for their sustainable management.     

The aquatic plant communities of the Lake Naivasha wetland,Kenya: pattern,dynamics and conservation

The spatial and temporal patterns of the wetland plant communities at Lake Naivasha over the past decade, and the past five years in particular, are discussed in relation to the major controlling factors. The four communities are:- the emergent swamp, dominated by Cyperus species; the floating raft, dominated by the aliens Salvinia molesta and Eichhornia crassipes; the floating-leaved plants, represented only by Nymphaea caerulea; and the submerged angiosperms, consisting of three species of Potamogetons — P. pectinatus, P. schweinfurthii, P. octandrus — together with Najas pectinata. The major factors affecting their dynamics are:- water level changes which influence agricultural clearance, introduced crayfish Procambarus clarkii, and interactions between communities such as the physical effects of mobile floating rafts. The value of the different communities to the ecological and economic value of the lake is highlighted, and the possible damage from future activities discussed.     

Socio-economic values and traditional strategies of managing wetland resources in Lower Tana River, Kenya

Understanding local people's socio-economic values of wetlands and traditional mechanisms of managing natural resources forms the basis of conserving them. In order to sustainably manage wetland resources in Tana River National Primate Reserve (TRNPR) and its environs, a study was carried out to document values, threats and traditional strategies of managing natural resources. The target communities were the Pokomo and Wardei who inhabit the TRNPR. The study was carried out in different periods in the year 2000 and 2001 and entailed administration of questionnaires, interviews and focused group discussions. Thirty residents were interviewed from six villages in the west bank of Tana River. The study found that oxbow lakes and Tana River formed the main types of wetlands and provided multiple values such as farming, transportation, security and social-cultural values to the local people. These values formed an important premise for conservation. Farming and fishing were the main economic activities of the Pokomo people while Wardei combined livestock rearing with occasional shifting cultivation. The two communities used different traditional systems in managing resources that they needed for their livelihood. The study concludes that the local people can and indeed must play a central role in the conservation of threatened wildlife and habitats in the Lower Tana River.     

The ecological relationships of aquatic plants at Lake Naivasha,Kenya

The distribution and abundance of the aquatic flora of Lake Naivasha has been constrained by two ecosystem-level processes. One is the natural and unpredictable fluctuation of water levels which the lake experiences, resulting in a drawdown zone of several vertical meters. The other is the consequence of herbivory by several alien species, linked with competition between rooted aquatic plants and phytoplankton. The effects of alien introductions in the 1960s and 1970s was to eliminate submerged vegetation from the lake completely by 1982, principally by crayfish herbivory. Vegetation has been progressively returning since 1984 and this return is coincident with a decline in crayfish population density. Concentrations of phytoplankton have progressively increased since 1982 as a result of nutrient increase caused by a decline in water level and papyrus swamp clearance for agriculture. The relationship between high levels of phytoplankton and extensive littoral weed beds is discussed.     

Enhancing the fish production potential of Lake Victoria papyrus wetlands,Kenya, using seasonal flood-dependent ponds

We present the findings of a participatory experiment on integrated aquaculture-agriculture systems (Fingerponds) at the Lake Victoria wetlands, Kenya. Fingerponds are flood-based lacustrine or floodplain wetland fishponds. The aim of the study was to explore, within a wetland/floodplain interface environment, the potential of semi-intensive fish production to enhance the wetland fishery and protect the natural ecosystem from wide-scale, destructive encroachment. The ponds were stocked naturally by flood water. After flood recession, livestock manure was added to the ponds and the effects of manuring on water and sediment quality and fish yields were studied. Manuring had positive effects on the nitrogen, phosphorous and chlorophyll a concentrations of the pond water. Regression analysis results indicated that site, manuring and environmental and climatic variables explained 58–70% of the variation in dissolved nitrogen and phosphorous, and 71% of the variation in chorophyll a. Manuring enhanced the total phosphorus concentration in the sediment but it only had marginal effects on total nitrogen. Although the net fish yields were highly variable between sites and seasons, ranging from 402 to 1069 kg ha⁻¹, the data showed that manuring was advantageous. The duration of the culture period, site variability and manuring explained 82% of the variation in fish yields. We conclude that Fingerponds fertilized with livestock manure from abutting riparian subsistence agriculture can improve fish production, enhance food diversity and security and contribute to more efficient use of papyrus wetlands for food production. This in turn may reduce large-scale conversion of wetlands to agriculture.     

Nutrient concentrations in Nyanza Gulf, Lake Victoria, Kenya: light limits algal demand and abundance

Nyanza Gulf is a large shallow embayment connected to Lake Victoria by the deep narrow Rusinga Channel. Between December 2000 and May 2002 the gradient of nutrients along the axis of Nyanza gulf into the main lake was determined. Nutrient concentrations in the gulf were found to be different from those in the main lake with phosphorus fractions, SRP and TP being significantly higher in the main lake than in the gulf. Well oxygenated conditions in the gulf keep the PO₄–P strongly bound to mineral particles whereas in the main lake, where deeper depths allows for development of anoxia, it is released into solution. The low TN:TP molar ratio in the gulf and in the main lake indicates many algae may be N-limited and heterocystous N-fixing cyanobacteria may be favored. However, the high mineral turbidity in the gulf reduces light availability and hence limits algal abundance resulting in easily measure concentrations of mineral nutrients and in particular high levels of dissolved reactive silica. The gulf is a net source of dissolved silica and total nitrogen to the main lake while the main lake is potentially a source of P to the gulf depending on interchange through Rusinga Channel.     

On the age and origin of the species flock of haplochromine cichlid fishes of Lake Victoria

Recent suggestions concerning the age and origin of the flock of haplochromine cichlid fishes in Lake Victoria (East Africa) are considered. These accept as proven the suggestion that Lake Victoria dried out completely in the Late Pleistocene, was dry for several thousand years, and refilled ca. 12400 years ago. Apart from the fact that other geophysical evidence contradicts this claim, its biological implications, which do likewise, have never been considered by those who have accepted it. Like those of all previous authors who have seized on the presence of the haplochromine flock of perhaps more than 600 species as evidence of extremely rapid evolution since the lake allegedly refilled, the account completely overlooks the fact that any such desiccation must have eliminated not only the haplochromine cichlids but the entire biota of the lake. Nevertheless, its present fauna not only includes the haplochromines but many other endemic organisms that would not be expected, and whose presence and history demand an explanation if the lake did indeed dry out. No such explanation has been offered, nor does such seem possible. The recent interpretation of events is questioned and rejected.     

Gastropod diversity,distribution and abundance in habitats with and without anthropogenic disturbances in Lake Victoria,Kenya

We investigated freshwater gastropod diversity, abundance and distribution in habitats with and without anthropogenic disturbance in two localities, Ndere in the Winam Gulf and Mbita Point, Lake Victoria, Kenya, from May 2002 to January 2004. A total of 133 984 gastropod specimens belonging to 15 species were recorded, 14 from Mbita and 12 from Ndere. Two species, Ferrissia kavirondica and Cleopatra cridlandi, which were recorded only from undisturbed habitats, could be indicators of least disturbed habitats. Water chemistry did differ between fish landing sites and undisturbed habitats at some sampling times, indicating that differences due to human impact do exist, but these are dependent on periods of calm weather. The study shows that anthropogenic disturbances cause ecological changes that can be exploited by some snail species, especially Biomphalaria choanomphala and Melanoides tuberculata, while other species may not tolerate these changes. In order to protect gastropod diversity and avoid dominance of intermediate hosts, such as B. choanomphala, a management plan for the use of these fish landing sites should be developed. This could include rules on how to dispose of fish remnants and other wastes so as to reduce local eutrophication, thereby reducing risks associated with transmission of potential snail-borne diseases.     

Effects of vegetation and weather on trap catches of Glossina fuscipes fuscipes near Lake Victoria, Kenya

Glossina fuscipes fuscipes Newstead was sampled in isolated thickets and forest patches near Lake Victoria, Kenya using unbaited biconical traps, between March 1992 and June 1993. Traps set at 1 m from the forest edge caught 3.3 times as many males and 5 times as many females as those set inside or 10 m away. The corresponding figures at 1 m from the edge of thicket were about 1.43 and 1.64 times, respectively. Hourly catches of males and females were positively correlated with temperature, light intensity and host (monitor lizard) prevalence, and negatively correlated with relative humidity. Light intensity and temperature were the most important variables affecting the catches of each sex. The results are discussed in relation to control and monitoring of G. f. fuscipes using traps.     

Species composition and length‐weight relationship of fishes in the Candaba wetland on Luzon Island,Philippines

The length‐weight relationships or LWR (W = aL^b) of 18 of the 21 fish species caught in 2007–2008 from the Candaba wetland in central Luzon, Philippines are reported. These species belong to 14 families and the LWR of six species are first documented in this paper. Cyprinids comprised the greatest number of species. The high significance of the LWR parameters indicate that fish weight may be predicted from length, at least within the range of the fish lengths recorded. This first reference to the LWR of fishes from the Candaba wetland provides baseline data for the conservation management of fish biota in this threatened ecological resource.     

新疆艾比湖湿地主要植物的种间关联分析

根据新疆艾比湖湿地植物群落样方调查的存在-缺失数据,应用主成分分析和聚类分析方法研究了湿地内多物种关联性以及生态种组分类.与传统的成对物种关联分析方法相比较,基于多元分析框架的多物种关联分析和种组分类结果更为可靠、有效;艾比湖湿地的主要植物种划分为3个生态种组,各生态种组内的植物种之间具有相似的生境和生态位.结合统计分析结果与实地调查发现,艾比湖湿地植物种间的正、负关联性以及生态种组的划分主要由植物对水分和盐分生境因素的适应性决定.从多物种关联性和生态种组角度考虑艾比湖湿地生态恢复和保护植物多样性更具有实践价值.