Ecology and Fish Biodiversity of Man-Made Lakes of Southern Benin (West Africa): Implications for Species Conservation and Fisheries Management

Man-made lakes are alternative and potential habitats for biodiversity conservation, fisheries and extensive aquaculture. We investigated the ecology and the fish community structure of two (2) sand-dragged man-made lakes, Lake Ahozon and Lake Bewacodji of Southern Benin, with implications for species conservation, fisheries management and aquaculture valorization. From August 2014 to July 2015, habitats conditions were evaluated and fishes were sampled monthly with seine, cast net, experimental gill net and hooks in the open water and aquatic vegetation habitats of both lakes. Overall, the water quality of Lake Ahozon was globally favorable for the growth and the survival of the fish resources whereas Lake Bewacodji exhibited a poor water quality indicated mainly by an acid pH (mean: 6.32 ± 0.58) and low dissolved oxygen concentrations (mean: 3.52 ± 1.25 mg/l) caused by dense floating plants, Nymphea sp mainly and huge daily dumping of domestic wastes. The study revealed low species richness, d = 5.89 and d = 3.87, and low species diversity, H’ = 0.76 and H’ = 0.48 for Lakes Ahozon and Bewacodji, respectively, with Lake Ahozon more diverse than Lake Bewacodji. The fish community of Lake Ahozon comprised six (6) species, 3 cichlids Sarotherodon galilaeus, Oreochromis niloticus and Tilapia guineensis, the silver catfish, Chrysichthys nigrodigitatus (Claroteidae), the African bonytongue, Heterotis niloticus (Osteoglossidae), and the African catfish, Clarias gariepinus (Clariidae). Numerically, S. galilaeus dominated Lake Ahozon and made 85.21% of the sample. In Lake Bewacodji, the fish composition comprised four (4) species, Sarotherodon galilaeus multifasciatus, the dominant species making numerically 91.58% of the total sample, T. guineensis, C. gariepinus and C. nigrodigitatus. With regard to trophic structure, the fish assemblages of both lakes were numerically dominated by planktinovores/ detritivores, mainly S. galilaeus, O. niloticus, T. guineensis and C. nigrodigitatus making together 99.46% of Lake Ahozon fish community, and S. galilaeus multifasciatus, T. guineensis and C. nigrodigitatus accounting together for about 98.59% of Lake Bewacodji. In Lake Ahozon, standard length (SL) frequencies histograms showed an unimodal size distribution for H. niloticus, the nile tilapia O. niloticus and C. gariepinus whereas the two cichlids, S. galilaeus and T. guineensis exhibited a bimodal size distribution. In Lake Bewacodji, S. galilaeus multifasciatus, C. nigrodigitatus and C. gariepinus exhibited an unimodal size distribution. A sustainable exploitation of both man-made lakes requires the implementation of an integrated management scheme which should include habitat restoration and protection plan, fisheries/aquacultural valorization, ecological sound agriculture/ecotourism and environmental monitoring.

Oral disease is linked to low nestling condition and brood size in a raptor species living in a highly modified environment

Anthropogenic stressors can favor the occurrence of noninfectious disease that can be worsened by the impact of opportunistic pathogens,making the epizootiology of environmental diseases difficult to unravel.The incidence and impact of oral lesions in nestlings of a facultative scavenger species,the black kite Milvus migrans,were examined over seven breeding seasons in the highly degraded environment close to Madrid,Spain.We found an overall prevalence of 31%of nestlings with oral lesions,with no clear spatial pattern in nests with affected and unaffected individuals.The occurrence and number of oral lesions were negatively associated with nestling body condition and brood size.Broods,where all siblings had oral lesions,were smaller than those where some or all siblings were apparently healthy,suggesting that oral disease could be causing nestling mortality and,consequently,brood size reduction.In turn,nestling body condition was negatively affected by lesion occurrence,brood size,and laying date.Although these relationships were bidirectional,piecewise structural equation modeling analyses showed a greater negative effect of body condition on lesion occurrence than vice versa,indicating that nestlings in poorer body condition were more likely to develop oral lesions(which could contribute to aggravate their state of deterioration)than those in better condition.Nestlings from small broods were also more likely to have oral disease(directly or indirectly through their lower body condition)than nestlings from large broods.Nestlings that hatched last in the broods showed greater development stress than those that hatched first.Anthropogenic stressors could trigger poor body condition,and contribute to microbiota dysbiosis-related diseases.Although further research is needed to determine the consequences for the long-term fitness of individuals,actions should be taken to mitigate adverse conditions that may favor the appearance of environmental diseases associatedwithperi-urbanareas,giventheirrapidexpansion overnatural areas.

Survival of transplanted nests of the red wood ant Formica aquilonia （Hymenoptera： Formicidae）： The effects of intraspecific competition and forest clear-cutting

The fitness and survival of ant colonies depend on the resources near their nests. These resources may be limited due to poor habitat quality or by intra- and interspecific competitions, which in extreme cases may cause the ant colony to perish. We tested the effect of intraspecific competition and habitat degradation （forest clear-cutting） on colony survival by transplanting 26 nests of the red wood ant （Formica aquilonia Yarrow, 1955） in 26 different forest areas that contained 0-11 conspecific alien nests per hectare. F. aquilonia is highly dependent on canopy-dwelling aphids, thus the removal of trees should cause food limitation. During the course of the 4-year experiment, 9 of the forests were partially clear- cut. We found that while forest clear-cutting significantly decreased the colonies＇ survival, intraspecific competition did not. As a highly polygynous and polydomous species, E aquilonia seems to tolerate the presence of alien conspecific colonies to a certain extent.

Comparison of gastrointestinal parasite communities in vervet monkeys

Globally,habitat degradation is accelerating,especially in the tropics.Changes to interface habitats can increase environmental overlap among nonhuman primates,people,and domestic animals and change stress levels in wildlife,leading to changes in their risk of parasite infections.However,the direction and consequences of these changes are unclear,since animals may benefit by exploiting human resources(e.g.,improving nutrition­al health by eating nutritious crops)and decreasing susceptibility to infection,or interactions with humans may lead to chronic stress and increased susceptibility to infection.Vervet monkeys are an excellent model to under­stand parasitic disease transmission because of their tolerance to anthropogenic disturbance.Here we quantify the gastrointestinal parasites of a group of vervet monkeys(Chlorocebus aethiops)near Lake Nabugabo,Ugan­da,that frequently overlaps with people in their use of a highly modified environment.We compare the parasites found in this population to seven other sites where vervet monkey gastrointestinal parasites have been identi­fied.The vervets of Lake Nabugabo have the greatest richness of parasites documented to date.We discuss how this may reflect differences in sampling intensity or differences in the types of habitat where vervet parasites have been sampled.

Effect of complex hydraulic variables and physicochemical factors on freshwater mussel density in the largest floodplain lake,China

Background Habitat degradation and flow regime alterations are two of the most prominent and common impact factors to freshwater mussel populations.Knowledge of the correlation between freshwater mussel distribution,density and habitat characteristics is important for maintaining and restoring their biodiversity and ecological functions.Information on predicting habitat suitability of freshwater mussels is lacking in China.Here,we aimed to analyze the correlation between freshwater mussel density and complex hydraulic and physicochemical variables to predict habitat suitability.Results The results showed that four complex hydraulic variables(boundary Reynolds number,critical shear stress,bed roughness and mean sediment particle size)and four physicochemical variables(water temperature,chlorophylla,transparency and pH)were key factors for predicting habitat suitability of freshwater mussels.Freshwater mussel density was significantly correlated with Froude number,water temperature and chlorophyll-a.Conclusions Our results confirmed that higher freshwater mussel density would be associated with areas that are stable in complex hydraulic and physicochemical variables.These results provide an important insight into the conservation of freshwater mussel diversity and their habitat restoration in China and globally.

Estimation of estuarine habitat degradation and its influence on the reproduction process of the crab Eriocheir sinensis in the Yangtze River Estuary

Background The provision of habitat for fishery species in estuaries is highly valued and represents one of the most challenging ecosystem service values to quantify.However,quantifying this value is challenging due to complex relationships between habitat change,ecological processes,and environmental variations.This study aims to estimate estuarine habitat degradation and its impact on the reproduction process of the crab Eriocheir sinensis by characterizing the changes in breeding habitat and investigating relationships between the species and its habitat in the Yang-tze River Estuary.Methods A species distribution model recently developed was applied to estimate the extent and quality of breeding habitat changes from 2014-2021.The intrinsic(physiological)and external(structural)reproductive attributes of the breeding process were measured to assess the effects of habitat change.The relationships among habitat change,reproductive attributes and environmental factors were analyzed to understand the underlying driving forces of habitat degradation for breeding process by multivariate statistical analysis.Results About 34.24%of essential habitat was lost,mainly in highly suitable areas due to reclamation and waterway construction.Habitat degradation significantly affects female distribution and their reproductive processes,particularly gonad development during the pre-reproductive period and fecundity during the reproductive period,without altering population structure.These results indicated that the main ecological function served by the highly suitable breeding ground was the provision for development of gonad and improvement of fecundity.Increases of salinity and turbidity,caused by hydrodynamic changes from large-scale waterway construction,were identified as the environmental determinants contributing to cumulative habitat degradation.These influences ultimately led to a decrease in the fecundity of E.sinensis.Conclusions Our research sheds light on the quantification of habitat degradation in the Yangtze River Estuary and its implications for the reproduction process of E.sinensis,which can serve as a foundation for assessing and quantifying the ecosystem service values provided by these breeding grounds.This information is valuable for policymakers and resource managers in making informed decisions regarding habitat conservation and the sustainable utilization of fishery resources.