MACROINVERTEBRATE FAUNA OF A TROPICAL SOUTHERN RESERVOIR, EKITI STATE, NIGERIA.

Continental J. Biological Sciences 4 (1): 30 - 40, 201 1 ISSN: 2141-4122

© Wilolud Journals, 201 1 http://www.wiloludjournal.com

Printed in Nigeria

MACROINVERTEBRATE FAUNA OF A TROPICAL SOUTHERN RESERVOIR, EKITI STATE,

NIGERIA.

J.B. Edward 1 , and A.A.A. Ugwumba 2
1 Department of Zoology, University of Ado Ekiti, P.M.B. 5363, Ado Ekiti Ekiti State, Nigeria.

2

Department of Zoology, University of Ibadan, Oyo State, Nigeria.

ABSTRACT

A survey of the macroinvertebrate fauna of Egbe Reservoir, Ekiti State, Nigeria was carried out.
Sampling of surface waters and macroinvertebrates was carried out twice in a month from September
2004 to December 2006. Physico-chemical parameters determined include pH, conductivity, alkalinity,
dissolved oxygen and biochemical oxygen demand (BOD) using APHA methods. Macroinvertebrates
were collected by kick sampling and with Van veen grab. Data analysis was done using descriptive
statistics, Duncan multiple range, pearson correlation, paired t tests and diversity indices. Eighteen taxa
of macroinvertebrates in two Phyla of Mollusca and Arthropoda were identified. Gastropods had the
highest numerical abundance (41.8 %), diversity (d= 0.61, H=1.56) and evenness (J=0.87). Odonata
and Ephemeroptera (Insecta) had the lowest diversity (d=0.00, H= 0.00 and d= 0.14, H= 0.13) and
numerical abundance (0.4% and 6.3%, respectively). The gastropod, Melanoides tuberculata, which is
the most abundant macroinvertebrate is an indicator of polluted water. This suggests that the reservoir
may be tending towards organic pollution. This is further confirmed by the low abundance of
Ephemeroptera and Odonata which are indicators of clean water. Measures should be taken to prevent
the reservoir from further deterioration and eventual eutrophication.

KEYWORDS: Macroinvertebrates, Egbe Reservoir, Pollution.

INTRODUCTION

Macroinvertebrates are important at the food web of aquatic ecosystems. Benthic dipteran larvae e.g.
Chironomus species and mollusks are consumed in great quantities by many fishes and so play an important role
in the ecology of the aquatic ecosystems as shown by a lot of works on food and feeding habits of some
freshwater fishes (Imevbore and Bakare, 1970; Ogari and Dadzie, 1987; Fagade and Olaniyan, 1973 and
Ugwumba and Ikusemiju, 1994). They have being used to assess the biological productivity of lakes and rivers
(Mehmet et. al., 2002). Freshwaters are being polluted and facing various limnological problems due to
increasing anthropogenic activities. Benthic invertebrates are used in determining and observing eutrophication,
pollution and water quality, and many of them have been accepted as biomonitor species. Their diversity and
abundance is a reflection of the quality of water and its sediments.

There are many studies in various parts of the world on the benthic macroinvertebrates of freshwater bodies.
These include the works of Petr (1970) on the bottom fauna of the rapids of Black Volta River in Ghana,
Johnson and Brinkhurst (1976) on Quinte Lake, Ontario, Canada; Darlington (1977) on Lake George in Uganda.
In Nigeria, Victor and Dickson (1985) worked on macroinvertebrates of a perturbed stream in southern Nigeria;
Adebisi (1989) studied the planktonic and benthic organisms of Olupona fish farm, Ibadan, Oyo State; Oke
(1998) worked on the limnology and macrobenthos of Owena Reservoir in Ondo State; Ogbeibu and Oribharbor
(2002) on the upper reaches of Ikpoba River; Victor and Ogbeibu (1985a and b); Victor and Dickson (1985) and
Ogbeibu and Victor (1989) on some southern steams. Presently, no studies have been conducted on the general
benthic fauna of any stream or river in Ekiti State. Yet, this area lies within the tropical rainforest expected to
have a high diversity of aquatic organisms. This present study was therefore carried out to provide some
baseline information on the composition, seasonal abundance and distribution of the benthic fauna of Egbe
Reservoir, Ekiti State.

Study Area

Egbe Reservoir is the major source of domestic water supply to the people of Gbonyin Local Government Area

of Ekiti State and parts of Ondo State, mainly the Akoko areas (Fig. 1). The reservoir also serves as a source of

30

J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

irrigation of farmed lands as well as a means of livelihood for the local fishermen who depend mainly on the
fishery resources of the reservoir.

The reservoir was formed as a result of damming the River Osse, a major river that takes its source from Kwara
State and runs through Ekiti to Ondo States. The river was dammed at Egbe Ekiti, and was constructed in 1975
and commissioned in 1989. The transverse survey is 272.5 hectares and the depth of the reservoir is 56.4m at its
deepest point . The reservoir is located on an undulating plane and lies between latitudes 7°36 N and 7 39 North
and longitude 5°32'E and 5 36' East of the Equator as shown in Figure 1. It is surrounded by highlands from
which runoffs also feed the reservoir during raining season. The bottom substratum of the reservoir is rocky.

Four sampling stations were chosen in the reservoir. Station 1 (Dam station) is about 200m from the water
treatment house of the reservoir. Vegetation around this station is mainly grasses and various species of birds
including cattle egrets frequent this site, perching on the rocks. Activity around here includes only cattle
grazing. Station 2 (Rocky station) is 399m from station 1. The area has thick vegetation comprising mainly of
palm trees.

The major activities around here are farming and fishing. Station 3 (Bridge station) is located along the road,
close to a bridge and is 450m to station 2. This area also has thick vegetation cover and the major activities
around here include farming, fishing and car washing and laundering. Station 4 (River Osse inlet station) is
about 300m from the previous site and is bounded by vegetation. Water birds also frequent this site and
activities around this place include farming, fishing, cattle grazing, bathing and laundering. Virtually all the
available landmass around the reservoir and its environs is essentially used for agricultural activities. Some of
the local fishermen also build their huts close to the reservoir. These areas also have high density of animal
confinement, rocks, and coastal plain sands.

The Reservoir is surrounded on each side by a stretch of thick forest made up of trees like Chlorophora excelsa
(African teak, "Iroko"), Terminalia Superba (Limba "Afara") and Senna occidentalis - coffee. Floating plants
include Ceratophyllum

5 '^OQ 5^323CT 5'53'uj

1 Kilometers

Fig 1 : Map of Egbe Reservoir showing Sampling stations(1,2,3,and 4).

Figure 1: Egbe Ekiti showing the location of the reservoir and the sampling stations

submersum, Mormodica balsamina (Balsaam pear), Commelina diffusa waterside Commelina), Cyperus
articulatus (Sedge) and Pistia stratioles. Weeds at the bank of the Reservoir include Chromolaena odorata
(Siam weed), Aspilia africana (Bush marigold), and Cynodon_plectostachynm.

The Reservoir also supports a commercial fishery of about twenty-five fishermen fishing daily with traps, sets
and cast nets, hook and line. However, only nine of these fishermen were available during this period of study.
Fish species in the Reservoir include Tilapia zillii, Oreochromis niloticus, Channa obscurus, Clarias
gariepinus, C. anguillaris, Hepsetus odoe, Sarotherodon melanopteron, and Mormyrus sp.

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J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

MATERIALS AND METHODS

Macroinvertebrate Sampling and Identification

Kick sampling method was used to collect the macroinvertebrates of the river bank sediments. This method was

carried out by using a stick to agitate lm 2 area of the substratum. The dislodged macroinvertebrates that moved

downstream were then collected with a 150um mesh size net held against the water current with the mouth

facing upstream. Three replicate samples were collected at each sampled station.

In the laboratory, the sediments collected were washed through graduated sieves of 0.5mm, 1mm, 2mm, and
3mm. The washed sediments with macroinvertebrates were poured into a white tray and sorted out. Sorting of
the macroinvertebrates in the sediment sample was enhanced by staining the washed sediment samples with
Rose Bengal solution. The macroinvertebrates collected from each station were then sorted into different
taxonomic groups using a x 10 scanning lens. Each taxonomic group was placed in a specimen bottle containing
4% formalin and properly labeled. The macroinvertebrates were later identified to genus or species level where
possible with a compound microscope using identification guides of Pennak (1978), APHA / AWWA / WPCF
(1992) and Yoloye (1994). Each identified taxon was counted and the number of individuals recorded per unit

RESULTS

The macroinvertebrates identified in Egbe Reservoir are listed in Table 1 showed the checklist and data on the
numerical abundance and percentage composition by number of macrobenthic invertebrates from the various
sampling stations for the overall as well as the dry and rainy season of the study period.

Eighteen (18) macroinvertebrate genera were identified and they were of two phyla of Mollusca and
Arthropoda. The Mollusca were all of one class of gastropoda (pond snails). Arthropoda were represented by
two classes, Arachnida represented by one genera of Hydracarina and Insecta, represented by four orders of
Odonata, Diptera, Hemiptera and Ephemeroptera.

The macroinvertebrates of the reservoir was dominated by the gastropoda with five species and one genus. They
constituted 41.8% of the total number of macroinvertebrates (Fig 2). Amongst them, Melanoides tuberculata
had the highest percentage composition (14.2%) followed by Bulinus globossus (8.9%). The least abundant
gastropod was Gabiella sp. which made up 1.2% of the total number of macroinvertebrate.

Amongst the Arthropods, the Order Diptera is the most dominant Insect, comprising of four genera which made
up 31.8% of the total macroinvertebrate abundance by number (Fig. 2). In this order, Anopheles larvae made up
the highest percentage composition 25.3% of the total number of macroinvertebrate (Table 1). The least
abundant insect in this order was Tipula sp. with 0.8% of the total macroinvertebrate population.

The order Hemiptera was next in abundance which was also made up of one species and three genera. It
constituted 19.3% of the total number of macroinvertebrate (Fig. 2). Notonecta sp. was the most abundant
making up 18.1% of the total macroinvertebrate by number. The least abundant was Sigara sp. constituting
only 0.2% of the total macroinvertebrates (Table 1).

Ephemeroptera were represented by one species Ephmerella excrucians and one genus Caenis sp. They
constituted 6.3% of the total number of macroinvertebrate (see Fig. 2). Odonata was represented by only one
species of Macromia magnified which had
the least percentage composition, 0.3% of the total macroinvertebrate by number.

The Class Arachnida was represented by only one genus Hydracarina of the order Acarina. It comprised the
least percentage composition, 0.3% of the total number of macroinvertebrate of the reservoir.

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J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

Table 1: Checklist, Numerical and percentage abundance of macroinvertebrates in Egbe Reservoir

Macroinvertebrate

Dry Season

Rainy Season

Overall

Gastropoda (Pond snails)

Abund.

%

Abund.

%

Abund.

%

Melanoides tuberculata

1485

11.8

3659

15.4

5144

14.2

Bulinus globossus

1155

9.2

2094

8.8

3249

8.9

Lymnaea natalensis

1008

8.0

2119

8.9

3127

8.6

Biomphalaria pfeifferi

496

3.9

1895

8.0

2391

6.5

Physa waterlotti

148

1.2

711

3.0

859

2.4

Gabiella sp.

234

1.9

201

0.8

435

1.2

Total

4526

36.0

10679

44.9

15205

41.8

Diptera

Anopheles larvae

3191

25.4

5997

25.2

9188

25.3

Palpomyia sp.

306

2.4

1441

6.1

1747

4.8

Symbiocladius sp.

323

1.4

323

0.9

Tipula sp.

103

0.8

180

0.8

283

0.8

Total

3600

28.6

7941

33.5

11541

31.8

Hemiptera

Notonecta sp.

2893

23.0

3960

0.3

6583

18.1

Lethocerus americanus

83

0.7

148

0.7

231

0.6

Gerris sp.

46

0.5

89

15.4

135

0.4

Sigara sp.

30

0.2

33

0.1

63

0.2

Total

3052

24.4

3960

16.6

7012

19.3

Ephemeroptera

Ephemerella excrucians

1211

9.6

1008

4.2

2219

6.1

Caenis sp.

47

0.4

53

0.2

100

0.2

Total

1258

10.0

1061

4.4

2319

6.3

Odonata

Macromia magnifica

75

0.6

64

0.3

139

0.4

Total

75

0.6

64

0.3

139

0.4

Arachnida

Hydracarina sp.

56

0.4

71

0.3

127

0.4

Total

56

0.4

71

0.3

127

0.4

Grand Total Abundance

12567

100

23776

100

36343

100

19.3

41.8

□ Gastropoda
m Ephemeroptera

□ Diptera
m Odonata

ra Hemiptera
□ Arachnida

Figure 2: Relative abundance by number of macroinvertebrates in Egbe Reservoir during
(Sept. 2005Dec. 2006).

the period of study

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J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

Seasonal distribution of Macroinvertebrates

In the dry season gastropods still had the highest percentage composition by number 36.0% of the total number
of macroinvertebrates (Fig. 3). Melanoides tuberculata was also the most abundant gastropod (11.8%), followed
by Bulinus globossus (9.2%), and the least abundant was Physa waterlottii (1.9%) (Table 1). During the wet
season, gastropods were higher in abundance constituting (44.9%) of the total number of macroinvertebrates
(see Fig. 4.), with Melanoides tuberculata having the highest percentage composition, 15.4% by number of the
total macroinvertebrate abundance. Next in abundance was Lymnaea natalensis which made up 8.9% of the total
number of macroinvertebrates. The least abundant gastropod was Gabiella sp. comprising only 0.8% of the total
number of macroinvertebrates (Table 1).

The Diptera made up 28.6% and 33.5% of the total number of macroinvertebrates during the dry and rainy
seasons respectively (Figures 3 and 4). Anopheles larvae had the highest percentage composition (25.4% and
25.2%) during both dry and wet seasons respectively, while Tipula sp. also recorded the least abundance of
0.8% during both seasons (Table 1).

Hemiptera was higher in abundance during dry season constituting 24.4% of the total number of
macroinvertebrates and 16.6% during rainy seasons (Figures 3 and 4). In this Order, Notonecta sp. was the most
abundant making up 23.0% of the total number of macroinvertebrates during dry season and 15.5% during the
rainy season (see Table 1). The least abundant Hemiptera was Sigara sp. constituting only 0.2% and 0.1% of
the total number of macroinvertebrates during dry and rainy seasons respectively (Table 1).

Ephemerella excrucians an Ephemeroptera had higher percentage composition by number during both dry and
wet seasons (9.6% and 4.4%) than Caenis sp. (0.4% and 0.2%, respectively,Table 1). The Odonata Macromia
magnifica constituted the least percentage composition by number (0.6% and 0.3%) of Insecta during both dry
and rainy seasons respectively. The Class Arachnida recorded the least percentage composition by number of
macroinvertebrates (0.4% and 0.3%) during both dry and wet seasons respectively (see Table 1).

24.4

28.6

□ Gastropoda
E3 Ephemeroptera

□ Diptera
■ Odonata

OH Hemiptera
□ Arachnida

Figure 3: Relative abundance by number of macroinvertebrates in Egbe Reservoir during dry season

34

J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

□ Gastropoda
■ Ephemeroptera

Diptera
■ Odonata

Hemiptera
□ Arachnida

Figure 4: : Relative abundance by number of macroinvertebrates in Egbe Reservoir during rainy season

Spatially, gastropods were most abundant (43.7% by number) at the Rocky station and least (39.4% by
number) at the Dam station. The Diptera had their highest (33.9%) composition by number also at the Rocky
station and its least (28.1%) at the Inlet station. Hemiptera was highest in abundance numerically (23.4%) at the
Inlet station and lowest (17.1%) at the Rocky station. Ephemeroptera had its highest numerical abundance
(8.0%) at the Dam station and the least (4.9%) at the Rocky station, while Odonata recorded 0.7% by number at
the Bridge station and 0.2% at the Rocky station. Arachnida was the least abundant macroinvertebrate in all the
sampled stations with 0.5% by number at the Dam station and 0.2% by number at the Inlet station (Fig. 5).

During the seasons, gastropods were also the most abundant macroinvertebrate numerically. They constituted
the highest numerical percentage (40.0%) at the Bridge station and the least (32.9%) at the Inlet station during
the dry season, while they had 46.5% by number at the Rocky station and the least 42.4% at the Dam station
during the rainy season (Fig. 5). Diptera were next in abundance numerically. They recorded the highest
composition by number (30.5%) at the Inlet station and the least 27.8% at the Dam station during the dry
season. In the rainy season, their abundance was higher (36.6%) at the Dam station and least (26.7%) at the inlet
station. Hemiptera was most abundant numerically (26.4%) at the Inlet station and least (21.5%) at the Bridge
station during the dry season, while in the rainy season, it recorded 21.9% at the Inlet station and 13.5% at the
Rocky station (Fig. 5).

Ephemeroptera were higher in abundance during the dry season in all the sampled stations. Its highest numerical
abundance (12.8%) was recorded at the Dam station and the least (8.3%) at the Rocky station. During the rainy
season, Ephemeroptera had 5.6% by number at the Bridge station and 3.5% both at the Rocky and Inlet stations.
Odonata were also more in abundance in the dry season than in the rainy season, having its highest composition
by number 0.9% at the Bridge station and the least 0.1% at the Rocky station, while in the rainy season, it
recorded 0.6% by number also at the Bridge station and 0.1% at the Dam station. Arachnida was the least
abundant macroinvertebrate during both seasons. It recorded 0.8% abundance by number at the Bridge station
and 0.2% by number both at the Rocky and Inlet stations during the dry season. In the rainy season, it had 0.5%
by number at the Dam station and 0.2% both at the Bridge and Inlet stations (Fig. 5).

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J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

50 n

45

40
o 35 H
"§ 30

P

S 25

S3

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CD
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£ 15 -I

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D Dam station
Rocky station
B Brigde station
□ Inlet station

Gastropoda Diptera Hemiptera Ephemeroptera

Macroinvertebrates

Odonata

Arachnida

Figure 5: Percentage abundance by number of macroinvertebrates in the four stations of Egbe
the period of study (Sept. 2005- Dec. 2006).

Reservoir during

Macroinvertebrate Diversity

Tables 2-4 showed the macroinvertebrate diversity indices. Gastropoda generally had the highest diversity (d =
0.61; H = 1.56) and its equitability value was also high (J = 0.87) for the overall sample (Table 24). The next
most diverse taxa were the Diptera (d = 0.38; H = 0.60) and Hemiptera (d= 0.41; H= 0.28). However, the
Diptera was more evenly distributed (J= 0.43) than Hemiptera (J= 0.21).

During the seasons, a similar trend as above was also noticed. Gastropoda also exhibited the highest diversity
during both rainy (d = 0.64; H = 156) and dry seasons (d = 0.72; H = 1.52). Its equitability values were also
highest in both seasons, J = 0.87 and J = 0.85 for rainy and dry seasons respectively (Tables 3 and 4). Diptera
were also the next most diverse and evenly distributed (d = 0.40; H = 0.66 and J = 0.48 for rainy and d = 0.72; H
= 1.52 and J = 0.85 for the dry seasons).

The pattern of diversity and distribution observed above was also evident among the five locations of the
reservoir. That is, gastropods still had the highest diversity and distribution, in the two seasons too, and were
followed by the dipterans (see Table 3 and 4).

DISCUSSION

The macroinvertebrate fauna composition of Egbe Reservoir is characterized by low taxa number. This is not
unusual in tropical waters; for instance, in Lake George, Uganda, the bottom fauna was poor in species
(Darlington, 1977). Victor and Dickson (1985) and Umeozor (1996) also observed a similarly low taxa number
and diversity in Ikpoba River and Calabar River, Nigeria respectively. Edokpayi et al. (2000), Ogbeibu (2001),
Adakole and Annune (2003) also reported low taxa number in some tropical streams and rivers. They ascribed
this low species diversity to some physico-chemical conditions of water like fast flow, high pH, low dissolved
oxygen and low conductivity. These factors probably caused disruption of life cycle, reproductive cycle, food
chain and migrations or imposed physiological stress on even the tolerant macroinvertebrate (Adakole and
Annune, 2003).

However, in the case of Egbe Reservior, the low taxa number observed could in addition be due to factors other
than physico-chemical conditions of the water such as habitat preference, resource partitioning, and food
availability. For instance, Odum (1971) had reported that diversity tends to be low in physically controlled
systems such as ponds and dams. This could be the case here in Egbe Reservoir because the artisanal fishermen
regularly clear the waterways of macrophytes for smooth sailing of their boats.

36

J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

Table 2: Diversity index values of macroinvertebrate during the period of study

Taxa D H J

1.56 0.87

0.60 0.43

0.28 0.21

016 023

D= Margalefs diversity index, H= Shanon-Wiener's index, J= Equitability measure

Table 3: Diversity index values of macroinvertebrate during the dry and rainy seasons

Gastropoda

0.61

Diptera

0.38

Hemiptera

0.41

Ephemeroptera

0.16

Dry Season

Rainy Season

Taxa

D

H

J

D

H J

Gastropoda
Diptera
Hemiptera
Ephemeroptera

0.72
0.29
0.46
0.14

1.52
0.40
0.25
0.13

0.85
0.37
0.18
0.18

0.64
0.40
0.41
0.18

1.56 0.87
0.66 0.48
0.30 0.23
0.20 0.26

D= Margalefs diversity index, H= Shanon-Wiener's index, J= Equitability measure

The aquatic macrophytes serves as habitats for most macroinvertebrates especially gastropods and their eggs.
Influx of agrochemicals, bathing and laundry activities could also impact negatively on these aquatic fauna.
These activities cause pollution of the water body and may affect species diversity of macroinvertebrates of the
reservoir. Umeozor (1996) in his study on the new Calabar River reported that the important factors governing
the occurrence and distribution of macroinvertebrates are the physico-chemical qualities of the water and the
nature of immediate substrates. Any severe alterations of these factors will substantially affect the
macroinvertebrate community. Bishop (1973) also reported that pollution in its total effect tends to disrupt the
natural complexity and stability of an ecosystem and lead to a less stable state in which diversity is reduced and
the self-regulating buffering capacity against change is diminished. It may therefore be implied in this study that
as the waters of the reservoir is observed to be slightly polluted, this may have influenced the overall
distribution of the benthic fauna.

The higher abundance of macroinvertebrates in the rainy season is contrary to the reports of Umeozor (1996) on
the macroinvertebrate abundance in the New Calabar River; Zabbey (2002) on the benthic macroinvertebrates of
Woji Creek off Bonny River, and Zikoki and Zabbey (2006) on the benthic community of the middle reaches of
Imo River. These authors recorded a higher abundance of macroinvertebrates in the dry season than rainy
season. They explained that during the rains, sedimentary particles become unstable causing dislodgement of
the benthic animals. However, the gastropods and insecta that dominated the invertebrate population of Egbe
Reservoir have been documented to be relatively tolerant of physical and chemical variations in the
environment, and are present in a broad range of environment irrespective of the seasons (Ormerod, 1988).

The most important factors which influence the abundance and distribution of macroinvertebrates apart from
physical and chemical qualities of water include habitat area, immediate substrate, trophic structure, resource
partitioning and predation (Bishop, 1973; Ogbeibu and Victor, 1989, Ogbeibu and Egborge, 1995). Another
important feature of freshwater systems that may account for the higher abundance recorded during the rainy
season is that predators other than fish and aquatic invertebrates exploit invertebrate prey better in the dry
season than they do in the rainy season. This is because in the dry season, the water level becomes reduced and
clearer, the substrate also stabilizes and the population builds up, thereby making available for the fish and avian
predators more prey items. Predatory losses to such carnivorous endotherms as birds can also be particularly
high (Cooper et al, 1991 Ormerod and Tyler, 1988). Different species of these water-loving birds were present
around Egbe Reservoir. This factor may have contributed to the observed reduced abundance during the dry
season.

Habitat preference among the invertebrates may be one of the chief factors responsible for the decrease in
abundance with sampling stations. The substrate around the Dam station is rocky. It is located close to the base
of a rock; and the bottom substrate is composed of coarsed sand and gravels; vegetation around here is mainly
aquatic macrophytes like Ceratophyllum and Nymphea. Aquatic birds and cattle also frequent this site.
Vegetation around the other stations are also aquatic macrophytes and often thick, though with varying bottom

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J.B. Edward, and A.A.A. Ugwumba: Continental J. Biological Sciences 4 (1): 30 - 40, 2011

substrates.

Other factors which may influence the abundance and distribution of invertebrates include the possible role of
competition and resource partitioning, physical tolerances, and the trophic structure. These factors, coupled
with habitat differences observed in this study probably acted singly or in combination to influence the
variations in abundance of macroinvertebrates.

The low values of diversity indices may indicate decimating impact of impoundment on the benthic
communities. Impoundment of water bodies have been known to have profound effect on the distribution and
abundance of the resident organisms in Tropical waters (Egborge, 1977; 1979b; 1979c; 1981 and Ogbeibu et al.,
2002). The low values may also indicate pollutional stress which is further confirmed by the low eveness (J)
values of all the sampled stations for Odonata and Ephemeroptera which are clean water insects. Abundance of
macroinvertebrates in Egbe Reservoir revealed a distinct pattern of dominance: a lotic system which is
characterized by single species dominance. This depicts a simple homogenous environment favouring the
dominance of a single group, thus making the system less robust and fragile (Ogbeibu and Egborge, 1995).

REFERENCES

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urban sream, Zaria, Northern Nigeria. Journal of Aquatic Science. 18: 85-92.

Adebisi (1989). Planktonic and Benthic Organisms in some ponds in the Olupona Fish Farm, Olupona, Oyo
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Received for Publication: 04/04/201 1
Accepted for Publication: 28/05/201 1

Corresponding author

J.B. Edward

Department of Zoology, University of Ado Ekiti, P.M.B. 5363, Ado Ekiti Ekiti State, Nigeria

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