AQUATIC MACROINVERTEBRATE STRUCTURE AND DIVERSITY IN ANGUEDEDOU STREAM (ANGUEDEDOUBASIN : COTE D’IVOIRE)

by the Gasteropoda, Malacostraca, Acheta and one species in Oligocheta. The highest values of diversity indices were collectedin the upstream station A1; while highest values of Sorensen similarity index were found between the midstream stations (i.e. A3, A4, A5). A strong positive correlation between conductivity, turbidity, salinity, and a negative correlation with dissolved oxygenwas found with the Chironominae subfamily, and the species Diplonychus sp., Hydrobius sp., Hydracharina sp., Hydrochara sp. and Physa marmorata , while the Tanypodiinae subfamily was highly associated with increased of dissolved oxygen. composition was found significantly affected by anthropogenic disturbances.

On this watershed, more than 37 % is occupied by several anthropogenic activities and about 60 % is covered by the Anguédédou Classified Forest (ACF). This watershed is characterized by the presence of many industries of Yopougon citie. Moreover, Anguededou Stream basin is populated with a high number of anarchical building without adequate sanitation system. Anguededou Stream is also subject to domestic sewage, municipal waste waters, surface run-off, agricultural farms etc. coming from neighbouring cities of Anguededou.
The climate in this watershed is typical of equatorial rain forest, comprising four seasons: a great dry season (December-March), a great rainy season (April-July), a small dry season (August-September) and a small rainy season (October-November). The air temperatures of watershed average 26°C -27°C (Environment and Development Group, 2000), with an annual precipitation average of 2004.29 mm (SODEXAM, 2014).
In order to assess the variability of environmental and biotic parameters of the stream, six sampling stations (A1-A6) were chosen. The sample stations were positioned according to the longitudinal gradient of the stream, the accessibility of water channel and the presence or absence of anthropogenic disturbances. Macroinvertebrates were sampling monthly from March 2018 to February 2019 at the six sampling stations.Station A1 is located in the upstream area, station A2 on the tributary.Three stations (A3, A4 and A5) are in the midstream area (on Anguededou Classified Forest) and the last one station A6 is positioned in the downstream area near the bay of Ebrié lagune (Fig. 1). At each station, the length of sampled area covered ten times the channel width (AFNOR, 1992; Lazorchak et al., 1998). Table 1 summarizes the main characteristics of these sampling stations.

Macroinvertebrate sampling
Aquatic macroinvertebrates were sampling monthly at the six sampling stations during twelve sampling campaigns with a kick-net (500 µm mesh size and 1 m length). For each sample, the net was dragged over the stream bed for a distance of 10 m, maintaining contact with the substrate. At each sampling campaigns, two replicate samples were collected by station, considering all possible microhabitats over representative sections of the stream. The materials that were collected in the sampling net were rinsed through a 1 mm sieve bucket, and large debris were examined for macroinvertebrates, rinsed into the sieve, and discarded. All macroinvertebrate individuals were sorted and preserved in plastic sampling bottles with 90 % ethanol. In the laboratory, all the macroinvertebrates recorded were identified to lowest possible taxonomic level under a stereomicroscope (Olympus SZ 40), with use of appropriate taxonomic keys. The keys used in this study are (Monod, 1980) and (Powell, 1980) for the Decapoda; (Brown, 1994) 200 for Mollusca; (Dejoux et al., 1981) and (Tachet et al., 2010) for Insecta and Oligochaeta. After the identification, the organisms were preserved in 70 % ethanol.

Environmental variable
Five environmental variables were used to describe physico-chemical water condition at each sampling station. Conductivity, pH, water temperature and dissolved oxygen were determined directly at the same sampling station using a portable multi-parameter (HANNA), turbidity was measured using a turbidimeter(HANNA).All these variables were measured monthly between 7 and 12 a.m in the field before aquatic macroinvertebratres sampling. The habitat variables included are current velocity, water depth, wetted channel width, canopy cover and the main substrate type. Current velocity (m/s) was measured in mid-channel on five occasions by timing a floating object (polystyrene cube) over five meters stretch of the river. It was determined as the average of the five trials. Water depth (m) and wetted channel width (m) were measured (five transects) to the nearest centimetre inside each station, using a decametre. Canopy cover (%) and the main substrate type (mud, sand, gravel and woody debris as % of station bottom area covered by each substrate type) were estimated visually at each sampling stations (Arab et al., 2004 ;Rios and Bailey, 2006).

Data analysis
Aquatic macroinvertebrates structure was described through taxonomic richness, frequency of occurrence, Sorensen similarity index and diversity index (Shannon-Weaver diversity index, Pielou evenness and Rarefied richness). Taxonomic richness was rarefied in each station per sampling period.Rarefied richness was used to avoid any biais related to differences in abundance between samples (Grall and Coïc, 2005).The Sorensen similary index was used to evaluate similarity of aquatic macroinvertebraterichness between sampling station. The frequency of occurrence (FO) was calculated using the following formula: FO = (Ni/Nts) ×100; with Ni = number of samples containing a given species i, and Nts = total number of samples collected. The FO was used to classify taxa following (Dajoz, 2000): FO>50 = very frequent taxa; 25<FO ≤50 = frequent taxa; FO≤25 = rare taxa.
Before performing comparison analyses, data normality was checked using Shapiro test. As the biotic and environment data distribution follow non-normal distribution (P˂0.05), the non-parametric test of Kruskal-Wallis was performed to compare data variability between sampling stations. The Kruskal-Wallis test followed by the multiple comparaison rank test of Tukey were performed to verify significant differences in environmental variables and entomofauna metrics among sampling stations. Analyses were conducted using STATISTICA 7.1 computer package. A level of p<0.05 was considered significant.
Focused Principal Component Analysis (FPCA) (Falissard, 1999) was used to assess relationships between the very frequent taxa (FO>50%)and environmentale variables. FPCA is a variation of the traditional principal component analysis. It uses the same types of matrix as the PCA but differs from it because it is centred or focused on a variable xi. Indeed, it allows a graphical representation of the correlations that exist between this variable xi and the other variables. The graph provides access not only to the nature (positive or negative) but also to the significance (p < 0.05) of the correlations between variable xi and the other variables. It is also possible to observe on the graph the correlations between the other variables. In this study, the FPCA was used to determine the variables that influence the presence of the very frequente macroinvertebrate taxa along the stream bed. Twelve environmental parameters and eight taxawere returned for the analysis.This analysis was performed using the psy package on the R software.

Environmental variables
The pH in Anguededou Stream basin varied between 5.24 (A1) to 9.89 (A2 ; tributary)(Tab.2). In the main channel stations, the pH valuesare significantly higher at midstream station A3, than those in the other sampling stations (Kruskal-Wallis, p< 0.05).Regarding water temperature, except the tributary station A2, the main channel stations values are not significantly different (Kruskal-Wallis, p< 0.05) and varied between 25.9°C (A3) and 30.8°C (A2). Concerning the water conductivity, it ranged from 38.1 µS/cm (A1) to 1017 µS/cm (A2). Relatively to water turbidity, the highest value (1000 UTN) was observed on the tributary (A2) whereas the lowest value (2.4 UTN) was registered at upstream station A1. Water salinity (Nacl) varied from 0.1 % (A1) to 2 % (A2). In the whole, pH, conductivity, turbidity and salinity values were significantly higher in the tributary station (A2) than in the main channel stations (Kruskal-Wallis, p< 0.05).Regarding the the main channel stations conductivity, turbidity and salinity values were significantly lower at upstream station A1 than those reported in the other stations(Kruskal-Wallis, p< 0.05).Inversely, the dissolved oxygen values are significantly higher at upstream station A1 (4.38 -7.18 201 mg/L) than that registered in the other main channel stations (A5 = 1.15 mg/L; A3 = 5.39 mg/L). Tributarystation A2 recorded the most lower values of dissolved oxygen. Current velocity, water depth and wetted channel width varied from upstream to downstream (Kruskal-Wallis, p< 0.05).Current velocity varied from 0.12 m/s (A5) to 0.87 m/s (A6). Water depth ranged from 0.11 m (A2) to 1.45 m (A3) and Wetted channel width varied between 2.1 m (A4) and 13.6 m (A5).

Composition, distribution and frequency of occurrence of macroinvertebrates
A total of 171 macroinvertebrates taxa were recorded in this study. They were distributed among 77 Families and 14 Orders and six Classes : Insecta (150 taxa ; 87.20% of total richness), Gasteropoda (twelve taxa), Malacostraca (five taxa), Acheta (three taxa)and Oligocheta (one taxa) (Tab.3).
Relatively to Acheta, three taxa (Helobdella sp., Glossiphonia sp., Haementeria sp.) belonging to Glossiphoniidae family were found along the stream. Concerning the Oligocheta, only one specie (Tubifex sp.) from at Tubificidae family was recorded in Anguededou stream.
The high numbers of taxa were obtained at upstream station A1 (91 taxa) and downstream station A6 (102 taxa) in the main channel. The number of taxa recorded in the tributary station (A2) was low (61 taxa), than that in the main channel stations.

Diversity index
Overall, the Shannon-Weaver index is higher at station A1, where the median value is greater than 2.5 ( Fig. 2A). It gradually decreases at stations A2, A3, A4 and A5 where the median remains below 2, before growing up slightly at downstream station A6 with a median higher to of 2.3.The Shannon -Weaver indexobtained at upstream station A1 is significantly higher than those observed at others sampling stations (Kruskal-Wallis, p< 0.05). Pielou's Evenness Index evolution is similar to Shannon -Weaver index. This index is higher at upstream station A1, with a median 202 greater than 0.60 (Fig. 2B).This index decreases at stations A2, A3, A4 and A5 where the median remains below 0.4, then rises again at downstream station A6 with a median of 0.46. The Pielou's Evenness Index obtained at upstream station A1 is significantly higher than those observed at others sampling stations (Kruskal-Wallis, p< 0.05).Concerning the Rarefied richness, it is higher at station A1 (median > 9) (Fig. 2C). It decreases through stations A2, A3, A4 and A5 (median less than 7.5), before going up slightly at downstream station A6 with a median higher to 7.8. The Rarefied richnessis significantly higher than those observed at others sampling stations (Kruskal-Wallis, p< 0.05). Table 5 shown the values of the Sorensen similarity index between the studied stations. The high values of this Sorensen similarityindex were found between the midstream stations A4-A5 (66.97 %), between the stations A3-A5 (66.67 %), and between the tributary station A2 and downstream station A6 (64.67 %). The low values were recorded between the upstream station A1 and the tributary station A2 (31.37 %).It is also low between the upstream station A1 and downstream station A6 (38.34 %).

Discussion:-
Environmental variables analyses revealed that in the whole, pH, temperature, conductivity, turbidity and salinity values were highest in the tributary station A2 than in the main channel stations. High values of these parameters were surely due to the rough effluent of many industries of Yopougon city, to stormwater and municipal wastes from Abobo N'dotré city discharged upstream of this station. Indeed, the anarchic land used, overpopulation, domestic and industrial activities are factors that interfered hypoxic condition of water, very high values of pH, temperature, conductivity, turbidity and salinity.All these conditionstestified the highly polluted state of the water sampling at station A2(tributary) of stream. These results corroborate those of (Camara et al. Dissolved oxygen values are significantly higher at upstream station A1 than that registered in the other main channel stations.This highest oxygenation of the Anguédédou Stream at station A1 is surely due to his location in the upstream area located in forest. Indeed, in upstream of forest zone high photosynthetic activities of stream basin, natural ventilation and the presence of rapid flow rate and curved flow of water which lead to disturbance and recirculation of water, favor its reoxygenation at the water/air interface (Onana et al., 2016).Furthermore, the low conductivity, turbidityand salinity recorded throughout the study period at upstream station A1, could indicate on one hand, low mineralization of water, and on the other hand, a low organic matter loads, thus indicating good water quality of this station. These results are in accordance with those obtained by   Thisstudy represents the first published data on aquatic macroinvertebrates in Angédédou Stream basin.A total of 171 taxa belonging to 77 families, 14 orders and six class were recorded. The taxonomic richness registered in this study is highwhen compared with earlier studies from West Africa, particularly in Côte d'Ivoire. For example, (Simmouet al., 2015) used an Van Veen sampler to collect 137 taxa from four small coastal streams in South east. This difference in taxonomic richness can probably be explained by the sampling methods used and the types of habitats sampled. On the other hand, the number of taxa found in the Anguededou Stream is also higher compared with studies using the same sampling methods in other ivoirian streams, such as Banco Stream (132 taxa) in Banco National Park . This difference in taxonomic richness was probably due to the stream sizes. In fact, Anguededou Stream is long (12 km length) compared with Banco Stream (09 km length).Of the taxa collected in this study, aquatic insects were the most diversified, corresponding to 87.20 % of 171 taxa sampled. Insecta represent one of the most important groups of freshwater invertebrates especially due to its diversity (Tachet et al., 2010).Among insects, Odonata are best represented with 37 taxa. The high diversity of Odonata is primarily related to the great diversity of aquatic macroinvertebrates on the stream which they feed. Indeed, Odonata are predators and consume other organisms using different strategies to capture them (Ramírez and Gutiérrez-Fonseca, 2014).In this study, many taxa of Ephemeroptera, Trichoptera and Plecoptera (ETP) were frequently found in the upstream station A1. This confirm thegood waters qualityof this station. Indeed, this station present the high values of dissolved oxygen and low values of conductivity, turbidityand salinity. According to (Qu et al., 2010), this taxa are often used as indicators of good waters quality.Diptera taxa such as Acanthocnema sp.,Clogmia sp.,Culicinae, Eristalis sp.,Odontomyia sp. andSciomyzidae were recorded only at station A2 (tributary) and downstream station A6. The presence of these Diptera confirms their great degradation level of water at these stations. According to (Rueda et al., 2002), this Diptera taxa were commonly found in sewage-polluted stream. Furthermore, Eristalis sp. (Syrphydae) ability to survive is the result of using their retractile anal respiratory siphons (Tachet et al., 2010;Camara et al., 2012). Concerning Gasteropoda, most of taxa identified were mainly recorded at downstream station A6. On the tributary station A2, the most recorded Gasteropoda were Bulinus troncatus,Melanoides tuberculata and Physa marmorata. The high frequency of these taxa in this two stations can be explained by the fact that these waters are subjected to mainy anthropogenic disturbances and heavy organic matter load coming from neighbouring cities. Gasteropoda are known as tolerant organisms, they live in such disturbed environments and these organisms have developed special adaptations.Similar observation were documented by (Camara et al., 2012), who found that in the Banco National Park (Côte d'Ivoire) snails were present only at one site which received domestic sewage, and by (Tchakonté et al., 2014) in the urban streams of Douala (Cameroon). Moreover, experimental works carried out by (Marsden and Swinscoe, 2014) showed the prominence of a pulmonate snail at the most contaminated site close to a waste treatment discharge point in New Zealand. Tchakonté et al. (2014) confirmed that the pulmonate snails (Bulinus,Melanoides,Physa)were mainly encountered in main discharge point for storm waters, urban sewages, household refuse and industrial effluents.Four shrimps species were identify in this study and their frequency of occurrence revealed that they are very frequent at upstream station A1. The only crab specie (Liberonautes chaperi) was recorded at this station. The presence of those species in this station is undoubtedly related to substrate nature, canopy and good water quality. At this station, the bed is rich in large amounts of litter which constituted essential food ressources of shredder Decapoda. Tenkiano Doumbou (2017) showed that macroinvertebrates associated with litter in Guinea's rivers were largely dominated by shredder Decapoda.The low number of taxa recorded in the tributary station A2 compared with those observed in the main channel stream stations can be explained by the highly polluted state as indicated by the results of physico-chimical analysis.In the whole, the highest values of Shannon-Weaver index, Pielou's Evenness index and rarefied richness are respectively observed in the upstream station A1 and downstream station A6 along the main channel stations of Anguededou stream. This would reflect a good biological quality of the stream (Camargo et al., 2004 ;Peterson, 2006). However, in downstream station A6, this organization of the aquatic macroinvertebrate population results essentially from the diversification and proliferation of polluo-tolerant taxa. This could be related to anthropogenic activities influencing the watercourse. Indeed, the anthropogenic practiced in the area, as well as domestic discharges in this station could contribute considerably to the installation of particular conditions favorable to the presence of a diversified population of polluted taxa. The high value of those index observed in the upstream station A1 show that the waters had good ecological health, the distribution of aquatic macroinvertebrates taxa is more or less balanced, rich in taxa and therefore the least impacted. Furthermore, the three diversity metrics are lower at midstream stations (A3, A4, A5), thus confirming the influence of antropogenic pressure, namely the intensification of pig farming, the organic fertilizer plant in areas and as well as the domestic discharges, urban and industrial wastes, municipal untreated 204 waste waters and surface run-off from station A2 (on tributary).The high values of Sorensen similarity index were recorded between the midstream stations (A3, A4, A5). However, the lowest values were registered between the upstream station A1 and the stationA2(tributary) and the station A6 (downstream). This high similarity between the midstream stations is undoubtedly due to their proximity and the fact that they are subjected to same anthropogenic pressures. Furthermore, lower similarity can be explained by the fact that in the stations A2 and A6, non-treated domestic sewage are regularly discharged into the stream, causing water quality deterioration whereas the station A1 is not subject at same anthropogenic pressures.The results of Focused Principal Component Analysis (FPCA) on the seven very frequent taxa (Chaoborus sp., Chironominae,Diplonychus sp.,Hydrobius sp.,Hydracharina sp.,Hydrochara sp., Physa marmorata, Tanypodiinae) recorded along Anguededou stream revealed that in the whole Chironominae, Diplonychus sp.,Hydrobius sp.,Hydracharina sp.,Hydrochara sp. andPhysa marmoratawere significantly and positively correlated with conductivity,turbidity and salinityand negatively correlated with dissolved oxygen. That correlation can be explained by the fact that those taxa are more widespread in waters polluted and is known to live in degraded environments. Indeed, according to (Adriansens et al.(2004) and Simião-Ferreira et al.(2009), Chironominae sub-familie is one of the most resistant benthic organisms to organic pollution, and (Alba-Tercedor, 1996) revealed that Hydrophilidae (Hydrobius sp.,Hydrochara sp.) is one of the families of Coleoptera more tolerant to pollution. Camara et al. (2012) and Tchakonté et al. (2014) comfirmed that the genus Physa was most frequently encountered in water bodies polluted by high amounts of human and animal excrements, as well as domestic sewage.Furthermore, Tanypodiinae was highly associated with increased of dissolved oxygen, gravel, canopy and woody debris, this could be explained by the fact that it dwell in water no polluted, thus it is suggested that this species can be used as indicator species for aquatic ecosystem status. Chaoborus sp. présented a positive and significantcorrelation with sand, woody debris and significantly and negatively influenced by current velocity, turbidity, pH and temperature. Considering that taxa belong to the trophic guild of the predator, it can be suggested the prey availlability, as well as the presence of the predactor, regulate the distribution of these organisms that have migratory ability and a varied diet. Chaoborus sp. eat mainly planktonic organisms and usually migrates daily in the water column (Castilho-Noll and Arcifa, 2007).

Conclusion:-
This study identifies for the first time a wide range of aquatic macroinvertebrates in the Anguededou Stream and identifies differences in taxonomic between areas affected to some degree by more human activities. Our study revelead that upstream station A1 with naturally vegetated had higher biological integrity, while others stations were adversely affected by household disposals, and municipal and industrial wastes; and showed great shifts and profound modifications in their aquatic macroinvertebrates communities.   Fig. 3 Graphs showing the results of the Focused Principal Component Analysis (FPCA) based on the very frequent taxa (FO>50%) as a dependent variable and environmental variables as independent variables. Yellow dots correspond to items negatively correlated to taxa occurrence; green dots indicate items positively correlated to taxa occurrence. The dots inside the red circle represent items significantly correlated (p<0.05) with taxa abundance. T = temperature; CND = conductivity; pH = hydrogen potential; Turb = turbidity; DO = dissolved oxygen; Grav = gravel;Wdeb = woody debris; ; CurV = current velocity; Cano = canopy.