1

CRUSTACEAN ECOLOGY IN OPI LAKE, NIGERIA

BY

AGAORU, CHINWEUBA GODSWILL

PG/M.Sc./09/50774

A PROJECT SUBMITTED IN PARTIAL FULFILMENT

FOR THE AWARD OF MASTERS DEGREE IN

HYDROBIOLOGY IN THE DEPARTMENT OF

ZOOLOGY AND ENVIRONMENTAL BIOLOGY

FACULTY OF BIOLOGICAL SCIENCES,

UNIVERSITY OF NIGERIA, NSUKKA

SUPERVISORS: PROF. J. E. EYO AND DR. G. E. ODO

JULY, 2012

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CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.1 Introduction

The importance of water cannot be over-emphasized; water is essential for life and

occupies a very important place in science, philosophy and religion (Avoaja, 2005). The qualities

of water control the productivity of the aquatic environment. It is a medium by which organic

and inorganic wastes and sediments are distributed throughout the ecosystem. Aquatic bodies

may be marine, fresh water or estuary, freshwater habitats are broadly classified into two main

groups, namely standing water or lentic, and flowing water or lotic. The lentic environment

sometimes known as the standing water series, includes all forms of inland water (lakes,

reservoirs, ponds, bogs, swamps, etc.) in which water motion is not that of continuous flow in a

definite direction. Essentially, the water is standing although a certain amount of water

movement occurs such as wave action, internal current of water flow near inlets and outlets.

Fresh waters are habitats for plants and animals. They are usually liable to variations due

to both physical and chemical concentrations, especially after heavy rainfall. Life of these plants

and animals are in constant struggle. Besides the physical and environmental factors, predators,

parasites and other competitors have to be contended with.

Physical factors have proved effective barriers to some organisms but many organisms

survive in freshwater habitats. Plants and animals do not live in isolation but breeding

populations. More often several populations, composed of different species will be found living

together as a community. It is obvious that the environment of the organisms living in a

freshwater ecosystem consists of a number of habitat factors such as temperature, transparency,

depth and its chemical compositions. All these influence the distribution of organisms living in a

particular habitat than others. Although some of these factors interact with one another on the

organisms, but for practical purpose, one may single out these factors which play important role

in the distribution and abundance of the organisms. Water qualities include all the physical,

chemical and biological factors that influence the usefulness of water. Temperature directly or/

indirectly exert many fundamental effects on lake stability, gas solubility and biotic metabolism

(Lind, 1979). The pH may reflect biological activity and changes in natural chemistry of waters

as well as pollution. Dissolved oxygen is necessary for the energy metabolism of all aerobic

aquatic organisms and calcium is important in the biological productivity of water

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(Boyd, 1981). Calcium is also a major constituent of the cell walls of higher aquatic plants and in

supporting structures of many aquatic animals such as the bony tissues of fish and shells of

mollusks etc. Magnesium has a role as an essential nutrient in plant growth and development.

Nitrate and phosphate are very important in phytoplankton growth and hence the productivity of

the waters (Kemdirim, 1993).

Water plants are of fundamental importance to animal life in a reservoir, for not only do

they serve as a source of organic food, but also because of their photosynthetic activities, they

give off oxygen required by animals for respiration (Brown, 1971). If their leaves and other

green parts are submerged, the oxygen dissolves in the surrounding water and becomes valuable

to aquatic animals, which by means of gills or their respiratory organs, are able to absorb the

dissolved oxygen. Aquatic plants also serve as shelter to small aquatic animals, and their

underwater stem, leaves and roots provide places on which animals can deposit their eggs

(Brown, 1971).

Aquatic invertebrates have been in existence since the creation and several species

inhabit fresh, marine and brackish waters. They can be classified according to their habitats such

as benthos and pelagic, as well as according to their sizes micro and macro invertebrates.

Crustaceans (Crustacea) form a very large group of aquatic arthropods, especially treated as a

subphylum, which includes such familiar animals as crabs, lobster, crayfish, shrimps, krill, and

barnacles etc. The 50,000 described species range in size of up to 4.3m and a mass of 441b

(20kg).

Opi Lake is a tropical freshwater habitat located in the valley of river Uhere, Northeast of

Nsukka, Enugu State, Nigeria (Echi et al., 2009). Studies of Evurunobi (1984) reported the

phytoplankton and physico-chemical of the Opi Lake, Hare and Cater (1984) studied the diet and

seasonal fluctuations in the lake. Inyang (1995) researched on the fish fauna of Opi Lake. Nweze

(2003) provided scientific information on the phytoplankton production in the Lake. Echi et al.,

(2009) discovered the co-parasitism and morphmetrics of Clinostomatis of the lake. This

research work aims at providing scientific information on the crustacean ecology of Opi Lake

since so many works have been done on Opi Lake as a natural tropical freshwater habitat for

aquatic life.

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1.2 The Specific Objectives

i To monitor physico-chemical parameters of Opi lake;

ii identify crustaceans of Opi Lake;

iii study the monthly and seasonal variations of physcio-chamical parameters

of Opi Lake and

iv examine the monthly and seasonal variations of cruataceans of Opi lake.

1.3 Literature Review

Nigeria is blessed with abundant water resources; there are about 149,919 Km2

of inland

waters made up of major lakes, ponds, flood plains, running and stagnant pools (Ita et al., 1985).

In the 1980’s there were about 347 reservoirs and lakes,839 flood plains and rivers and 5000 fish

ponds. Nigerian freshwaters are generally very productive at the primary (algal), secondary

(zooplankton) and tertiary (fish and other aquatic vertebrates) levels (Ogbondeminu, 1986).

However, in industrial areas and urban centers there is some pollution with high levels of faecal

califorms (Ogbondeminu, 1986), heavy metals and industrial wastes, which constitute public

health hazards (Oluwande et al., 1983). Although water quality is to some extent an index of

water pollution, the indices presently used in Nigeria are inadequate to indicate the damage that

is done by heavy metals, metalloids, organic and inorganic compounds and blue-green algae

(Oluwande et al., 1983).

1.4. Physico-chemical Properties

Water qualities include all the physical, chemical and biological factors that influence the

beneficial use of water. The integration of physical, chemical and biological studies of water is

necessary to provide a more complete and sound assessment of the aquatic environment (Cullen,

1990). Naturally, water is affected by a myriad of physical, chemical and biological variables,

which in turn affect the aquatic organisms. Freshwaters of ponds, lake and streams ultimately

come from ground waters. Actually rainwater contributes very little of the water reaching these

waters bodies Brown 1971. The poper balance of physical, chemical and biological properties of

water in pond, lakes and reservoirs is an essential ingredient for successful production of fish and

other aquatic resources. The presence or absence of chemical element in a water body might be a

limiting factor in the production of such water body. Also the abundance of a particular element

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in a water body might suggest the type of oganism that may be found as well as indication of

ecological unstable or unfavorable ecosystem which can have negative or positive effect on the

population. Studies have shown that water rich in silica will contain a high population of diatoms

(Pasche, 1980), while high species diversity of snail will contain a high concentration of calcium.

Also high concentratrion of nitrogen and phosphorous is indicative of euthrophication that may

lead to algal bloom and consequently deoxygenation and death of aquatic organisims. Physical

properties such as light penetration, temperature, water movement have been shown to play

important role in plankton distribution and lake’s stratification Evurunobi, 1984.

The physical and chemical limnology of a lake is characterised by hydologic impact,

autogenic nutrient dynamic and biological aspects. These factors combine with each other to

determine the quality and consequently community of the lake. Though some works have been

done on the physico-chemical characteristics of some man made lake and natural freshwater

bodies in Nigeria, these include the work of, Adeniyi (1978) on Kanji Lake, Adebisi (1981) on

upper Ogun River, Evurunobi, (1984) on Opi Lake, Hare and Cater (1984) on Opi Lake, Adeniji

(1990), Eyo and Ekwuonye (1995) on Anambara River Basin, Kolo (1996) on Shiroro Lake on

Jankara reservoir, Attama (2003), Nweze (2003) on Opi Lake, Odo (2004) on Anambra River

Basin, Avoaja (2005) on Umudike water Reservoir, Mustapha (2009) on Oyun Reservoir, etc.

The physico-chemical characteristics of a lake can be significantly altered by human activities

such as various agricultural practices and irrigation as well as natural dynamics which

consequently affect the water quality and quantity, species distribution and diversity, production

capacity and even distribution in the balance of ecological syetem operating in a lake.

Temperature is a very important factor for an excellent physiological state of organisms

in water especially since most of them are cold-blooded and will require a certain degree of

temperature to be physiologically active (Adeniji, 1986). According to Odum (1971) water has

unique thermal properties which combine to combine to minimize temperature changes, thus the

range of variaton is smaller in water than in air. Brown (1971) reported that fluctuations in the

temperature of water involes changes in the dissolved oxygen present.therefore temperature is a

major limiting factors in water as it affects the rate of chemical and biochemical reactions within

aqutic organisims. Hach (1993) observed that at higher temperatures processes such as dissolved

oxygen uptake by aquatic life will increase. Not only this, studies show that physiological

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responses of animals at higher temperature lead to sub-optimal conditions which often lead to

decrease in growth, reproduction and increase in mortality (Damson, 1992).

The depth of a water body is another important factor to be considered in any aquatic

environment, the amount of dissolved oxygen content varies with depth. Due to reduction in

wind actions and amount of light as depth increases, oxygen content is low. With increase in

depth goes incease in pressure, diminished light and fall in temperature. Living conditions are

therefore very difficult in deep lakes. Absence of light renders such waters relatively barren. The

dissolved oxygen content decreases with increase in depth. Deeep waters as a rule are less

productive of plankton (Cole, 1983).

Transperency of water is an important factor determining the length at which light

essential for photosynthesis can penetrate. All natural water contain suspended solids, which are

both organic and inorganic. The organic component are both plant and animal remains. The

chemical properties of water- turbidity, total residue and visibility are strongly influenced by the

nature of sediments.Davies Colley and Smith (2001) reported that the correlation between

turbidity, total residue and visibility may vary dramatically between watersheds. Esima (1993)

observed that the quality and quantity of suspended matters in water affect light penetration as

well as food production. Light therefore controls the basis of animal food chain.

Hydrogen ion concentration (pH) is a very important factor operating in aquatic bodies,

pH is related to the amount of carbonates present in water and varies with habitats. Carbonate

concentration increase as carbon dioxide is withdrawn. When enough carbonates are present pH

tends to be neutral with a value of approximately 7.0 pH and when no carbonates are avaliable as

buffering agent the medium tends to be acidic with values less than 7.0 pH (Lind, 1974). The

removal of carbon dioxide from water body by aquatic plants increases the pH of natural waters

(Boyd, 1982). Ogbeibu (2001) working on distribution, density and diversity of dipterans in a

temporary pond in Okomu Forest Reservoir observed that pH influenced temporal variation in

diversity of dipterans.

Dissolved Oxygen (DO) is important and is required for the existence of life. DO is

required for respiration and release of energy from food (Lagler et al., 1981). According to

Adeniji (1986), presence of DO in good quantity in water will improve the water quality by

rendering poisonous gases like hydrogen sulphide, ammonia and others into their nonpoisonous

forms. DO content of waters results from the photosynthetic and respiratory activities of the

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biota in the open water and the difffusion gradient at the air-water interphase and distribution by

wind.

Alkalinity is an important factor in natural waters; Boyd (1982) has reported that natural

waters normally contain more carbornate that results from ionization of carbonic acid in water

saturated with carbon dioxide. Changes in alkalinity are due to changes in carbon dioxide

concentration. During photosynthesis, phytoplankton uses more carbon dioxide for food

production thereby reducing the alkalinity of the environment. Alkalinity is a measure of the

buffering capacity carbonate-bicarbonate ions and the hydroxide ions in water. The main sources

of alkalinity in water is leaching of carbonate, bicarbonate and hydroxide compound from rocks,

borate, silicate and phosphate (Nwoke, 1991). The seasonal variation in alkalinity among

different water bodies have shown higher means in dry season (Olusanya, 1982) higher mean in

the rainy season (King and Ekeh, 1990) and on marked difference betweeen the seasons (King

and Nkanta, 1991). Alkalinity is important for fish and aquatic life because it buffers rapid pH

changes (Boyd, 1979).

Magnesium came mainly in natural waters from the leaching of igneous and carbonate

rocks (Lind, 1979). Boyd (1979) showed that in areas where these sources were common,

magnesium concentration in water often ranged from 5 to 50 mg/L. Magnesium is important to

limnologist because of its role as an essential nutrient in aquatic plant growth and development

especially as relates to its function in the chlorophyll molecules (Lind, 1979).

Nitrates and phosphates are known to be very important in plankton growth abundance

and productivity in waters (Kemdirim, 1993). Hecky and Kling (1981) noted that both nutrients

are limiting in aquatic plant productivity. Nwoko (1991) reported that nitrates-nitrogen could get

into the water through various source such as cattle dung, agricultural runoff and leaching.

Phosphate-phosphorus is also known to enter water bodies through the same way as nitrate-

nitrogen. Levels of nitrate-nitrogen recorded in Nigerian lakes are 59-60mg/l in a Jos Pond

(Nwankwo, 1990), and 55 - 57 mg/l in Shen Reservoir (Chidobem and Ejike, 1985). Nitrate-

nitrogen is found to be the primary limiting nutrient in the tropics, while phosphate-phosphorus

is the primary limiting nutrients in the temperate zone (Henry et al., 1984).

Calcium can be leached from rocks but is much prevalent in waters from regions with

deposits of limestone, dolomite and gypsum. Calcium is important to the aquatic productivity

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especially during formation of shell, scales and bones (Owen, 1974). Furthermore, high

concentration of calcium helps reduce salt loss through the gills of fish in freshwater ecosystem

(Warts, 2004).

Free CO2 showed marked seasonal variation in Ogun and Jong rivers (Adebisi, 1981).

The ambient free CO2 may be low in some lakes, due to the fact that diffusion of atmosphere

carbon dioxide into the water can support larger phytoplankton production in such lakes that lack

sufficient sources of internal carbon (Adeniji, 1986).

1.5 Biological Properties

Ezenwaji (1999) in his study of a tropical flood river basin (Lower Anambra River

Basin), observed that the vegetation in the basin was derived Guinea Savannah, where the lentic

water bodies were often fringed with macrophytes. Obot (1985) observed that efforts were often

directed toward the elimination of obnoxious macrophytes from the lake after impoundment. He

opined that aquatic plants, which eventually colonized manmade lake in Africa, were largely

determined by the hydraulic turnover of the lake. Vareschi and Vareschi (1984) studying the

ecology of lake Nakuru (Kenya) have this to say- ‘A biotope of spatial homogeneity but

temporal discontinuity with a few species dominating the flora and fauna, characterizes lake

Nakuru as a relatively simple ecosystem’’. Nigerian waters harbour aquatic plants of various

families and species. These included Pistia spp., Azolla spp., Ceratopyllum spp., Sagittaria spp.,

Salvania spp., Panicum spp., and Nelumbo spp., etc. (Imevbore, Evurunobi, 1984; Obot, 1987;

and Nweze, 2003).

Phytoplanktons in reservoirs are dominated by the Volvocales and Dinophyceae

(Egborge, 1974). Phytoplankton production is also strongly correlated with conductivity and

transparency (Egborge, 1974). Egborge (1977) also reported that 78% of the Phytoplankton in

the river Oshun did not survive impoundment of the river. Studies by Evurunobi (1984) and

Nweze (2003) reported on the phytoplankton production of a freshwater lake. High oxygen

concentration during the dry season was related to high phytoplankton activity in the Pankshin

freshwater (Kemdirim, 1990).

Zooplankton production characteristics are similar to those of phytoplankton (Awachie,

1981), and higher production had been noted in the floodplain during the low water. Among the

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Crustacea, essentially African species are few and include diptomid species and Daphnia

barbata (Awachie, 1981). Other components of tropical African zooplankton include a large

number of species of the Rotifera (Awachie, 1981). Adeniji (1973) observed that the dominant

zooplankton species in the Kainji Lake of the river Niger changed from Daphnideae before

impoundment to Bosminidae in the lake. Imevbore (1965) gave a checklist of the crustacean and

rotifer in the Eleiyele reservoir. Jeje (1982) focused his study on the taxonomy and distribution

of Nigeria zooplankton. Where 160 species were identified, comprising 62 species of Cladocera,

23 species of Copepoda and 75 species of Rotifer. The author found the distribution of Daphnia

species very common, occurring in almost all Nigerian freshwater habitats. The work of Jeje and

Fernando (1986) gave a good identification and illustration of Nigerian zooplankton community.

Large lakes and water courses which are fed from regions of high and frequent rainfall are

characterized by a varied and abundant zooplankton fauna (Jeje and Fernando, 1986). Although

comparable data on zooplankton biomass of tropical lakes are scarce, it is apparent that Lake

Nakuru (Kenya) has relatively high standing crop of Copepoda (Vareschi and Vareschi, 1984).

Most fluvial plankton studies have shown that zooplankton constitute a relatively small

proportion of the aquatic biomass. Greenberg (1964) noted that zooplankton were insignificant in

the Sacramento River, ranging from 0% to 10% of the total plankton composition. Reinhard

(1931) found that phytoplankton outnumber river zooplankton by 5 to 1 meanwhile the major

zooplankton taxa in Reinhard’s study; the non-pigmented protozoa comprised 3%, the Rotifera,

62% and the Crustacea, 7.9%. European studies have shown similar results.

Vareschi and Vareschi (1984), stated that the benthic fauna of Lake Nakuru (Kenya) is

remarkably poor in species. It consists of one and sometimes two chironomid species,

Leptochironomous deribae and Tanystarsus horni. Lake Chad in contrast has 47 chironomids

(Dejoux, 1968). Nematodes were found very occasionally and the undersides of stones along the

western shore of the lake were populated by the coleopteran, Helochares spec (Hydrophiliidae).

Characteristics benthic species of other lakes, e.g Oligochaetes, chaoborides, ostracods or

mollusks, are completely absent in Lake Nakuru ( Vareschi and Vareschi, 1984). In a tropical

flood river basin, the common invertebrate taxa are crustaceans, insects and gastropod mollusks

(Ezenwaji, 1982 and Eyo and Ekwonye, 1995).

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1.6 Freshwater Crustaceans of Nigeria

Nigeria has a good number of natural and manmade water bodies which inhabit so many

aquatic organisms, ranging from micro, nano and macro flora and fauna, such as phytoplankton,

zooplankton, micro invertebrate and macro invertebrates. Crustaceans have been studied in some

manmade and natural aquatic habitat in Nigeria. Mustapha (2009) reported on the influence of

physico-chemical properties of Oyun reservoir, Offa, Nigeria on cladocera and copepoda where

they are more abundant during the rainy season. He also reported that factors such as

temperature, nutrient, food availability, shape and hydrodynamic of the reservoir strongly

influenced the generic composition and population density of zooplankton. Olomokoro and

Oronsaye (2009) carried out work on cladocera and copepod and suggested that Gulf of Guinea,

Nigeria is a good natural nursery ground for most of the fauna. Achionye- Nzeh and Isimaikaiye

(2009) also reported that crustaceans and other aquatic flora and fauna are abundant in a man-

made reservoir, showing that the water quality of the reservoir was rich in nutrients indicating

their sustainability. Olomukoro and Oronsaye (2009) studied the phytoplankton and zooplankton

of Nigeria fresh and brackish water bodies and they found out those crustaceans (copepod) are

more abundant, constituting 40.45% of the total fauna and are distributed in all the station

sampled, and this agreed with Odum (1971), that natural tropical coastal ecosystem are good

nursery grounds for most of the aquatic crustaceans (fauna). Studies on the feeding ecology of

Chrysichthys by Nwadiaro and Okorie (1987) a commercially important freshwater bagrid in

Nigeria shows that crustacean subclass such as copepod, cladocera and ostracocde constitutes

major food of this commercially important freshwater bagrid, not only this, Ikusemiju and

Olaniyan (1977) reported that young Chrysichthys nigrodigitatus in Lekki Lagoon Nigeria

consumed more of crustaceans than the adult.

1.7 Economic Importance of Crustaceans

Crustaceans form the major important primary and secondary consumers in many aquatic

systems, critically so in fresh waters, some species support direct fishery and aquaculture for

human food or fish bait while some may help to control aquatic vegetation. Studies on the

feeding ecology of Chrysichthys Chukwuemekanim (1985) a commercially important

freshwater bagrid in Nigeria shows that crustacean subclass such as copepod, cladocera and

ostracode constitutes major food of this commercially important freshwater bagrid. Also Nair

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(1980) reported that the diets of Otolithes ruber and some other fishers mainly consisted of

zooplankton, primarily crustaceans. Not only this, Ikusemiju and Olaniyan (1977) reported that

young Chrysichthys nigrodigitatus in Lekki Lagoon Nigeria consumed more of the crustacean

than the adult, some of the suborder of Decapods like shrimp and prawn are commercially

cultivated in aquaculture business and human consumption which could be sold frozen and

marked based on their categorization.

Crustaceans are found to cause or harbour infectious diseases. They can form habitat

association with other living organism in aquatic habitat to cause disease. Crustacean and

nematode infection can cause 60% of the susceptible fish host that are infected with disease.

Cyclops is intermediate hosts of the tape worm (Diphillobothrium latum) and Dracunclus

medinensis, subclass malacostraca (crab and other decapods crustaceans). Crab is the second

intermediate host of the lung fluke (Paragonimus westermani). As with other seafood,

crustaceans are high in calcium, iodine and protein but low in food energy. Cholesterol content

(2007) reported that most meal is also a significant source of Cholesterol, meals made of

crustaceans however is considered healthy for the circulatory system because the lack of

significant levels of saturated fat in shrimp means that the high cholesterol content in shrimp

actually improves the ration of LDL to HDL cholesterol and lowers triglycerides (Elizabeth, et

al., 1996). Humans consume many crustaceans and nearly 10,700,000 tons were produced in

2007; the vast majority of this output is of decapods crustaceans: crabs, lobsters, shrimp, and

prawn. Over 60% by weight of all crustaceans caught for consumption are shrimp and prawns

and nearly 80% is produced in Asia, with China alone producing nearly half the world’s total.

Non-decapods crustacean are not widely consumed, with only 118,000 tons of krill being caught,

despite krill having one of the greatest biomasses on the planet (Nicol and Endo, 1997).

Crustacean apart from being food for aquatic organisms are purposely cultivated for human

consumption. Crustacean like shrimp, crayfish, prawn, crab etc. are eaten all over the world. In

Nigeria, crustacean like crayfish, crab and shrimp etc. are usually smoked and occasionally sun-

dried and they form an indispensable food item in the diet of the people of the entire southern

states in particular and Nigerian as a whole. It is the core Nigerian cooking. Small crustaceans

can be adequately fixed directly in 70-80% ethanol. Larger specimens are best fixed in neutral

5% formalin and transferred to 70% ethanol with few days. Kahle’s fluid quickly decalcifies

crustacean’s exoskeleton, but preserves the rest very well. Isopropyl alcohol is of no use in

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preservation of crustaceans as they become explosively brittle. Gently boiling the specimen in

water or 70% ethanol is often a suitable substitute for formalin. Most color patterns are lost

during storage so notes should be taken while the specimens are fresh.

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CHAPTER TWO

MATERIALS AND METHOD

2.1 The Study Area

Opi lake is a typical freshwater lake located between 6o

45’ 0’’-45’ 28’’N and 7o 29’ 35’’

E (GPS N 06.75275 , E 007.49104) in the valley of river Uhere, Northeast of Nsukka, Enugu

State, Nigeria. The lake is about 300 metres from Uhere River. The soil is porus and subject to

severe erosion. The vegetation and climate of the lake has been described by (Hare and Carter,

1984). The lake has no permanent inlet but during the flood period the lake overflows through a

small channel at the southern end. The lake has a gentle sloppy shoreline with thick marginal

vegetation (Echi et al., 2009). The western side of the lake has a wide beach overgrown with

saprophytes dominated by Crytosperma senegalenses (Scholt); Jussiaea repens Var diffusa

(Fordk) and Rynchospora species. Its surface area and maximum depth fluctuates seasonally and

ranges between 1.3 and 2.0 and 2.0ha and 3.9m respectively (Inyang, 1995). The mid lake

deposit is mud mixed with coarse organic matter from the marginal vegetation on the other part

of the shoreline.

After preliminary appraisal trip to the lake, three sampling stations were selected based

on the nature of the lake (Figure 1), Station 1 was situated in the southern or overflow end which

have more vegetation, shade and receive in runoff during heavy rainfall and outlet. Station 2 was

situated in the middle of the lake and has lesser vegetation and lesser shade. Station 3 was

situated at the northern end with least vegetation and no shade. Sampling was done within 8am

and 12 noon once in a month.

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Figure 1: A SKETCH MAP OF OPI LAKE WITH ITS GEOGRAPHICAL FEATURES AND SAMPLING

LOCATIONS 1, 2 AND 3.

Source: Modified after Evurunobi (1984).

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2.2 Meteorological Data

Data on rainfall, relative humidity, temperature, wind speed and hours of sunshine for the

period of investigation were collected from the University of Nigeria, Nsukka Meteorological

Station situated within 20km, northwest of the lake.

2.3 Sampling Methods

Twelve months of field work (once in a month) was carried out on Opi Lake which

covered both dry and rainy season and started from October 2010 – September 2011.

2.3.1 Physico-Chemical Monitoring

At each station some physico-chemical determinations were examined and recorded.

Water temperature was determined with the use of thermometer. The thermometer was

tied to a calibrated rope and immersed in the water at a depth of 0.5m for about 3-5 minutes in

three different locations and the average reading was taken, this was done in all the three stations

for every month.

Transparency: This was determined using a standard seechi disc which has 20cm

diameter with black and white quarters (Biswas, 1973). The seechi disc was suspended on a

calibrated string and was gradually lowered into the water at three different locations and the

depth at which it disappeared was recorded, the disc was gradually drawn up and the depth at

which it reappears was recorded too. The average of the two depths was taken as the

transparency reading. The procedure was carried out in all the station for every month.

Depth: This was measured at the center of the three different stations. A calibrated rope

tied on a metallic object was lowered into the water; the depth at which the object touched the

ground was recorded.

Hydrogen ion concentration (pH): The monthly pH was determined with the use of a

digital pH meter, (model EIL 3055). Water sample from each of the stations was collected from a

depth of 0.5m with bottle samplers and these were taken to laboratory for analysis after which

the average reading of each station was recorded per month.

Dissolved Oxygen (DO): This was determined using the Winkler’s method (Boyd,

1979). With the use of 250ml reagent bottles that were washed and oven dried, in each of the

stations, the bottle was rinsed with the lake water and poured at the bank of the lake. After

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corking the bottle, it was lowered at a depth of 0.5m and uncorked for water to fill it till it

overflew, the bottle was corked in a way that air bubbles were avoided and at the bank of the

lake, the oxygen content of the water was fixed by adding 2mls of manganese regent corked and

inverted for ten times, followed by 2mls of alkaline iodide solution and equally inverted for

about ten times. After this the bottles were taken to the laboratory for further analysis. To

determine the DO of the water sample, 1ml of concentrated sulphuric acid was added and the

bottles were corked and inverted to mix well in order to acidify the water. 100ml from each of

the bottles was transferred into three different 250ml conical flask and 3drops of freshly prepared

starch solution was added to each of the 250ml conical flask as indicator. The water sample

solution was titrated with N/40 Sodium Thiosulphate until the blue/black disappears. The

titration was done three times to get the average titer value and was calculated as follows;

DO in mg/l = (ml of titrant) (N) 1000

ml of sample

Where N = normality of titrant.

Alkalinity: The alkalinity was determined by adding 4 drops of phenolphahalein

indicator to the water sample until the pink colour appeared, indicating presence of OH-

or

normal carbonate. Again the water sample plus 2 drops of methyl orange indicator was titrated

with standard sulphuric acid of 0.1N solution until the colour disappeared. The phenolphthalein

alkalinity is calculated as

mgCaCO3 per liter = A x N x 5000 = A x 10

ML sample

Where N = normality

A = ml of titrant

ML = ml of the sample

Calcium, Magnesium, Nitrate, Phosphate, and Iron: These were determined using

Spectrophotometer Model DREL 5, a modern multichemical analysis apparatus.

Free CO2: This was determined titrimetrically using 0.0027N NaOH and phenolphtalein

and methyl orange indicators

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2.3.2 Macroinvertebrate sampling

Aquatic macro invertebrate was sampled with the use of equipment such as scoop net

which have a fine mesh aperture of about 200-300 micrometer, mesh size of about 60

micrometer and other materials that were of important such as bucket, white try, etc. In each of

the stations, samplings were done within the entire range of habitats available (open waters,

shallow water over hard and soft bare benthos or over submerged aquatic macrophytes, along

shores of habitat and also masses of aquatic debris and vegetation which were collected drained

slightly and spread out in order to see and collect some organisms that crawled out from these

material). A collection in five-eight minutes from a variety of location within each station was

done. After collecting the aquatic organisms, they were transported to Hydrobiology unit

Department of Zoology, University of Nigeria Nsukka for proper preservation and identification.

Identification keys (Identification Guide for Freshwater Macroinvertebrate, Stroud Water

Research Center; key to Aquatic Macroinvertebrate Departement of Environmental Conservation

New York; Aquatic Macroinvertebrate Identification key; Ladybird Survey Nothern Ireland

2005; Taxonomy key to Benthic Macroinvertebrate and How to know the Insects were used for

the identification of sampled organisms.

2.3.3 Plankton sampling

In each of the sampling station, minimum of two liters of water was emptied into a

bucket and each content of the was concentrated into 20ml by draining water out through

another 55 µ mesh net size to prevent loss of plankton. The inside of the net was later turned into

the bucket to return probably plankton attached to the net. Then the plankton samples collected

were filtered through another net of about 64 µ mesh net size (Avoaja, 2005).To separate the

zooplankton from the phytoplankton, the zooplankton samples were collected in the specimen

bottles, labeled and preserved in 4% formalin. The phytoplankton was equally preserved in the

bottles with 4 % formalin. These samples were allowed to stand for at least 24 hours before

analysis. During the analysis of the zooplankton, the supernatant was carefully pipette off and

the zooplankton sample was concentrated to 10ml volume. 1ml was carefully viewed under an

Olympus binocular microscope; model CH 0337331 on a slide with the use of dropper.

Identification of the phytoplankton and zooplankton was done by keys (Jeje and Fernando 1986,

Nweze (2005), Robert (2003) and Smile (2008).

18

2.4 Identification of crustaceans

Identification of specimens were sorted and identified with suitable keys (Jeje and

Fernando 1986; Robert, 2003; Smile, 2008).

2.5: Statistical Analysis

This was done with SPSS version 17, one way ANOVA was used to determine the

monthly variation of physico-chemical, T- test for seasonal variation of crustaceans and physico-

chemical, relationship within crustaceans and other aquatic fauna, flora and physico-chemical

were determined using correlation analysis, evenness and diversity index were calculated using

Simpson and Shannon-Weaner indices.

19

CHAPTER THREE

RESULTS

3.1. Meteorological Parameters

Meteorological data for the month of October 2010 are missing.

Rainfall (RF) – during the period of the investigation the range of rainfall was between

0.00 – 0.02mm, the first peak was in February (2011) after which there was a decrease in March.

A subsequent sharp increase continued across the months until July 2011 which had the highest

value. There was a continuous decrease till Sep.2011when this investigation ended as shown in

Table 1.

Relative Humidity (R.H) - this was highest in August and lowest in Jan. there was a

progressive increase from January to August and a decrease in September when this

investigation ended (Table 1).

Atmospheric Temperature (A.T) – there was a declined temperature from the onset of the

investigation November to January, there was an increase from February to March which had the

peak after which a continuous decrease was recorded from April to August, there was an increase

at the end in September (Table 1).

Wind Speed (W.S) – there was maximum record of wind speed in March and minimum

record at the end of the investigation in September as expressed in Table 1.

Hour of Sunshine (H.S) – during this period of investigation November had the minimum record

and there was a progressive increase from December to March which was the peak (Table 1).

3.2: Physico-chemical Parameters of Opi Lake

Table 2 showed the mean values of physico – chemical parameters. The minimum mean

temperature (25.090C) was in the month of December while the maximum was in April

(29.780C). Transparency had a minimum mean value (0.42m) in May and maximum (0.63m) in

December. Depth was highest in October. (2.93m) and lowest in May (0.90m). pH recorded the

maximum value in November. (6.98) and lowest in July (5.27). DO was maximum in October.

20

(7.27 mg/L) and minimum in April (1.44 mg/L). Alkalinity was at the peak in Nov. (32.68 mg/L)

and lowest in April (11.56 mg/L). Magnesium was recorded highest Sep. (29.14 mg/L) and

minimum in October (6.81 mg/L). Calcium was maximum in June (13.53 mg/L) and minimum

April (6.50 mg/L). Total Hardness was maximum in June (42.02 mg/L) and minimum in October

(18.52 mg/L). Phosphate was maximum in Feb. (0.72 mg/L) and minimum in June (0.12 mg/L).

Nitrate was recorded the highest value in August (0.31 mg/L) and least was in April (0.08 mg/L).

Iron had peak value in January (0.78 mg/L) and lowest in November (0.07 mg/L). Total

Dissolved Solute (TDS) had the same value all through the research period. Free CO2 had

maximum value in October (0.86 mg/L) and minimum in May (0.04 mg/L).

3.2.1 Monthly variation of physico-chemical parameter of Opi Lake

a. Temperature

The pooled mean values of temperature in the months of May and June were significantly

different (p < 0.05) while that of June and July were statistically not different (p > 0.05). The

subsequent months from July to September differed significantly (p < 0.05) as shown in Table 2.

b. Transparency

Moderate transparency values were recorded during this investigation with minimum

mean value of 0.42 ± 0.04 m in May and maximum mean value of 0.64 ± 0.10 m in September.

Significant differences (p < 0.05) in the mean transparency values were recorded only between

the months of November to January, April to June and August to September (Table 2).

c. Depth

Depth in Opi Lake ranges from 0.90 ± 0.20 m to 2.93 ± 0.30 m. the maximum depth of

the lake was in October (2.93 ± 0.30 m), this did not differ significantly (p > 0.05) from that of

November (2.25 ± 0.38 m) expressed in Table 2.

d. pH

The mean monthly pH values of Opi Lake are as shown in Table 2. The maximum pH

values in November (6.98 ± 0.15) differed significantly (p < 0.05) from those of January to

September but not from that of October (6.89 ± 0.23).

21

Table 1: Meteorological Data for Nsukka Metropolis from October 2010 to September 2011.

Months Parameters

RF (mm) A.T(0C) R.H (%) W.S (m/s) H.S(W/ms)

Oct. 2010 * * * * *

Nov 2010 0.0000 26.7400 74.4148 0.9846 0.0016

Dec 2010 0.0000 26.4507 49.6843 0.8761 136.7500

Jan 2011 0.0000 26.2425 35.2042 0.9985 134.8737

Feb 2011 0.0082 27.5410 67.0635 1.2057 133.9071

Mar 2011 0.0039 28.6680 65.4893 1.3288 172.4526

Apr 2011 0.0110 27.2071 72.0696 1.2310 160.9111

May 2011 0.0159 26.5186 76.1152 1.1906 156.7732

Jun 2011 0.0134 25.3982 79.4404 1.0284 136.0137

Jul 2011 0.0203 24.6269 81.0707 1.0324 133.1553

Aug 2011 0.0187 23.8423 83.8343 0.9245 90.6605

Sep 2011 0.0349 24.6205 81.8003 0.9084 119.2596

* missing data

22

e. Dissolved Oxygen (DO)

The mean DO values decreased progressively from 7.27 ± 0.25 in October to 1.44 ± 0.17

in April. The peak DO value was recorded in June (Table 2).

f. Alkalinity

The mean value of alkaline concentration was between 11.56 ± 6.96 mg/L and 32.6 8 ±

2.2. The mean values differed significantly across preceding month of October to January (p <

0.05). July to September were not significantly different (p > 0.05) shown in Table 2.

g. Magnesium

The mean value recorded in August shown in Table 2 was not significantly different from

the maximum mean value (29.12 ± 0.79mg/L) recorded in September (p > 0.05).

h. Calcium

The mean values of calcium concentration in October and November did not differ

significantly at (p > 0.05) as shown in Table 2. November to January at (p < 0.05) significantly

differed. The mean values of August and September were not significantly different at (p > 0.05).

i. Total Hardness

The recorded mean values for the months of October to December were significantly not

different same at (P > 0.05) level of significance, while August and September significantly

differed at ( p < 0.05) expressed in Table 2

j. Phosphate

The minimum recorded mean value of phosphate was in the month of June with 0.12±

0.02 mg/L and the maximum value was in April with 1.03 ± 0.42 mg/L. November to January

mean values differed (P < 0.05) but August and September (P > 0.05) were not significantly

different (Table 2).

23

k. Nitrate

The recorded mean value of nitrate shown in Table 2 were generally moderate, April had

the least recorded mean value of 0.08 ± 0.05 mg/L and this was significantly different from May

0.30 ± 0.09 mg/L (p < 0.05) while the peak mean value was in August with 0.31 ± 0.01 mg/L

and was not significantly different in September (p < 0.05 )

l. Iron

Mean values of October to December were not significantly different (p > 0.05). Across

each preceding month from January to September, there was no significant difference at (p >

0.05) shown in Table 2.

m. Total dissolved solute (TDS)

In Table 2 the recorded mean values of TDS concentration throughout the research period

were the same (10.00 ± 0.00 mg/L)

n. Free CO2

The concentration of mean value of free CO2 recorded was between 0.04 ± 0.01mg/L

(May) and1.13± 1.07 mg/L (June). The mean values of October to January were not significantly

different (p > 0.05), January and February were significantly different (p < 0.05) while February

to September were not significantly different from each preceding month (p <0.05) as expressed

in Table 2.

3.2.2: Seasonal variation if physico-chemical parameters of Opi Lake

Mean values of different parameters determined in dry and rainy seasons are shown in

Table 3: Statistical significance was found between the dry and rainy season values of

transparency, DO, pH, alkalinity, magnesium, total hardness nitrate and free CO2.

24

Table 2: Monthly Mean Values of Physico-Chemical Parameters of Opi Lake

Months Pooled Monthly Mean

Temp.(0C) Tran.(m) Depth(m) pH DO(mg/L) Alk.(mg/L) Mag.(mg/L)

Oct. 2010 28.46 ± 0.81cde

0.56 ± 0.06bc

2.93 ± 0.30g 6.89 ± 0.23

e 7.27 ± 0.25

f 29.42 ± 4.28

e 6.81 ± 0.46

a

Nov 2010 28.07 ± 0.73c 0.62 ± 0.13

cd 2.25 ± 0.38

fg 6.98 ± 0.15

e 7.24 ± 0.33

f 32.68 ± 2.72

g 7.22 ± 0.37

a

Dec 2010 25.09 ± 1.06a 0.67 ± 0.08

e 2.05 ± 0.16

df 6.33 ± 0.19

c 7.07 ± 0.11

f 20.81 ± 1.43

c 10.31 ± 1.25

b

Jan 2011 25.67 ± 0.71a 0.62 ± 0.03

cd 1.84 ± 0.32

cd 6.58 ± 0.15

d 6.22 ± 0.89

d 26.41 ± 1.87

d 25.28 ± 2.56

d

Feb 2011 28.94 ± 0.30 def

0.62 ± 0.02cd

1.22 ± 0.24b 6.16 ± 0.10

b 2.34 ± 0.22

b 27.44 ± 1.98

d 25.93 ± 1.42

d

Mar 2011 29.12 ± 0.45efg

0.62 ± 0.04cd

1.03 ± 0.24ab

6.04 ± 0.17b 2.29 ± 0.25

b 27.26 ± 1.80

d 25.27 ± 2.23

d

Apr 2011 29.78 ± 0.62g 0.63 ± 0.02

c 1.04 ± 0.25

ab 6.57 ± 0.13

d 1.44 ± 0.17

a 11.56 ± 0.96

a 22.69 ± 1.68

c

May 2011 29.20 ± 0.75g 0.42 ± 0.04

a 0.90 ± 0.26

a 6.56 ± 0.18

d 3.22 ± 0.53

c 18.32 ± 1.49

b 21.76 ± 2.18

c

Jun 2011 28.33 ± 0.29cd

0.52 ± 0.15b 1.63 ± 0.26

c 5.28 ± 0.16

a 7.31 ± 0.14

f 25.98 ± 0.86

d 28.51 ± 1.61

e

Jul 2011 28.28 ± 0.96cd

0.58 ± 0.05bc

1.72 ± 0.21c 5.27 ± 0.19

a 6.13 ± 0.24

d 18.82 ± 1.25

b 28.79 ± 1.53

e

Aug 2011 27.11 ± 0.26b 0.60 ± 0.10

bcd 1.76 ± 0.28

c 5.37 ± 0.28

a 6.59 ± 0.31

e 18.38 ± 1.25

b 28.21 ± 0.76

e

Sep 2011 27.86 ± 0.47c 0.64 ± 0.10

de 1.89 ± 0.29

cd 5.43 ± 0.13

a 7.02 ± 0.09

e 17.42 ± 0.88

b 29.14 ± 0.79

e

The mean values with the same superscript on the same column are not significantly different (p > 0.05)

25

Table 2 Continues: Monthly Mean Values of Physico-Chemical Parameters of Opi Lake

Months Pooled Monthly Mean

Cal.(mg/L) T.H (mg/L) Phosphate (mg/L) Nitrate Iron (mg/L) TDS Free CO2

Oct. 2010 11.70 ±1.95ef

18.52 ± 2.18a 0.28 ± 0.11

ab 0.14 ± 0.03

b 0.08 ± 0.01

a 10.00 ± 0.00 0.86 ± 0.35

f

Nov 2010 11.96 ± 1.38f 19.18 ± 1.32

a 0.24 ± 0.04

ab 0.24 ± 0.00

cd 0.07 ± 0.09

a 10.00 ± 0.00 0.81 ± 0.35

ef

Dec 2010 10.11± 1.18cd

20.40 ± 1.45a 0.72 ± 0.16

d 0.27 ± 0.04

cde 0.29 ± 0.11

a 10.00 ± 0.00 0.77 ± 0.31

def

Jan 2011 7.27 ± 1.84a 32.53± 4.28

c 0.28 ± 0.09

ab 0.22 ± 0.09

c 0.78 ± 0.15

c 10.00 ± 0.00 1.13 ± 1.07

f

Feb 2011 6.09 ± 0.76a 32.02± 2.06

c 0.72 ± 0.16

d 0.22 ± 0.03

cd 0.36 ± 0.11

abc 10.00 ± 0.00 0.22 ± 0.25

abc

Mar 2011 6.66 ± 0.89a 31.93 ± 2.65

c 0.65 ± 0.13

cd 0.23 ± 0.02

cd 0.72 ± 0.20

bc 10.00 ± 0.00 0.21 ± 0.25

abcd

Apr 2011 6.50 ± 0.33a 29.13 ± 1.81

b 1.03 ± 0.42

e 0.08 ± 0.05

a 0.38 ± 0.08

ab 10.00 ± 0.00 0.06 ± 0.04

ab

May 2011 6.60 ± 0.29a 28.36 ± 2.37

b 0.45 ± 0.19

bc 0.30 ± 0.09

e 0.33 ± 0.06

a 10.00 ± 0.00 0.04 ± 0.01

a

Jun 2011 13.53 ± 1.02g 42.04 ± 1.83

g 0.12 ± 0.02

a 0.28 ± 0.05

de 0.44 ± 0.10

ab 10.00 ± 0.00 0.45 ± 0.10

abc

Jul 2011 10.58 ± 1.67de

39.34 ± 1.98e 0.24 ± 0.10

ab 0.23 ± 0.08

cd 0.33 ± 0.02

a 10.00 ± 0.00 0.39 ± 0.07

abcde

Aug 2011 8.55 ± 1.04b 36.75 ± 1.68

d 0.57± 0.32

cd 0.31 ± 0.01

e 0.32 ± 0.04

a 10.00 ± 0.00 0.43 ± 0.03

abc

Sep 2011 9.01 ± 0.63bc

38.16 ± 1.14de

0.62 ± 0.39cd

0.28 ± 0.03cde

0.38 ± 0.02ab

10.00 ± 0.00 0.49 ± 0.09cde

The mean values with the same superscript on the same column are not significantly different (p > 0.05)

26

Table 3: The mean (±SE) seasonal value of physico-chemical parameters for dry and rainy seasons of Opi Lake

Seasons Parameters

Tem.

(0C)

Tra.

(m)

Depth(m

)

pH DO

(mg/l)

Alk.

(mg/l)

Mag.

(mg/l)

Cal.

(mg/l)

TH

(mg/l)

Posh.

(mg/l)

Nit.

(mg/l)

Iron

(mg/l)

Fr.CO2

(mg/l)

Dry season 27.87 ±

1.80

0.65 ±

0.97

1.68 ±

0.61

6.51 ±

0.36

4.84 ±

2.53

25.08

±

6.87

17.65 ±

8.58

8.61

±

2.70

26.25

±

6.53

0.56

±

0.33

0.20

±

0.08

0.38 ±

0.51

0.58 ±

0.60

Rainy season 28.16 ±

0.97

0.55 ±

0.12

1.58 ±

0.43

5.58 ±

0.53

6.06 ±

1.52

19.79 ±

3.36

27.28 ±

3.14

9.65 ±

2.54

36.93

±

5.00

0.40

±

0.31

0.28

±

0.65

0.36 ±

0.07

0.36 ±

0.17

P 0.344 <

0.0001

0.308 0.040 <

0.0001

<

0.0001

< 0.0001 0.202 <

0.0001

0.733 <0.000

1

0.744 0.0190

27

3.4: Crustacean Fauna of Opi Lake from October 2010 to November 2011.

Sampled fauna of Opi Lake include zooplankton (Crustacea, Rotifera fish egg and fish

larvae), macroinvertebrate (Insecta, Arachnida and Hirudina) Crustacean were made up of seven

genera – Daphnia (30.44%), Naplius (18.34%), Captocerus (14.30%), Eurycerus (8.56%),

Bosmina (9.29%), Canthocamptus (8.56%) and Cyclops (10.51%)

The number and percentage of total crustaceans collected in the three different Stations

are shown below (Table 5). Station 1 had the maximum number 379 (46.33%) This was followed

by Station 2 (N = 249, 30.44%) and Station 3 had (N = 190, 23.23%). The monthly recorded

number of crustaceans sampled are presented in Table 6, April recorded the peak value (100 with

12.20%) while November recoded the least value (53 with 6.46) of the sampled crustaceans

during the investigation period.

The mean density of Daphina and Naplius were significantly higher (p < 0.05) in Station

1 when compered to that of Station 2 and 3.no significant difference (p < 0.05) was seen in the

mean density of Canthocampus, Bosmina and Camptocerus across the \station while the mean

density of Eurycerus and Cyclop Station 1 and 2 were the sameas shown in Table7.

3.5. Seasonal variation of crustaceans of Opi Lake

There was significant difference between the seasonal mean vales of crustaceans sampled

in Opi Lake (Table 8).

3.6: Crustacean Diversity and Richness of Opi Lake

Table 9 expresses the richness and abundance of the sampled crustaceans in the stations.

Daphnia was more abundant in all the Stations while Canthocamptus was the least in abundance.

3.7: Flora of Opi Lake

The sampled flora were phytoplankton and macrophyte,phytoplankton sampled

composed six families: Bacillariophycea, Chlorophyceae, Cryptophyceae, Cyanophyceae,

Dinophyceae and Xanthophyceae while 12 species of macrophytes were sampled (Kyllingn

squamalata, Nymphaea lotus, Acroceras zizanioid, Cyperacea difformislinn, Alchonea

28

Table 4: Crustacean Fauna of Opi Lake.

Zooplankton Class

Crustacea Name (Genus) Composition

(ml), n = 820

(%)

Daphnia 30.44

Naplius 18.34

Captocerus 14.30

Eurycerus 8.56

Bosmina 9.29

Canthocamptus 8.56

Cyclops 10.51

29

Table 5: Station Composition of Crustacean of Opi Lake form October 2010t o September 2011.

Number of stations 1 2 3

Number of monthly visits 12 12 12

Number of crustacean species

indentified

7 7 7

Total number of Crustaceans

collected

379 249 190

Crustacean percentage (%) 46.33 30.44 23.23

30

Table 6: Monthly Distribution of Crustaceans in Opi Lake

Months Total number/ml Percentage (%)

Oct. 2010 60 7.31

Nov 2010 53 6.46

Dec 2010 54 6.59

Jan 2011 64 7.80

Feb 2011 60 7.31

Mar 2011 80 9.76

Apr 2011 100 12.20

May 2011 63 7.68

Jun 2011 71 8.66

Jul 2011 69 8.41

Aug 2011 75 9.15

Sep 2011 71 8.66

Total 820 100

31

Table 7: Mean (±SE) station densities of crustaceans collected from October 2010 to September

2011.

Crustaceans Station 1 Station 2 Station 3 Total

Daphnia 9.83 + 1.01b 6.42 + 0.94

a 4.50 + 0.74

a 6.92 + 0.63

Nauplius 5.67 + 0.58b 4.00 + 0.58

a 2.83 + 0.46

a 4.17 + 0.35

Camptocerus 4.00 + 0.51a 3.00 + 0.49

a 2.75 + 0.60

a 3.25 + 0.31

Eurycerus 2.92 + 0.34b 2.00 + 0.49

ab 1.33 + 0.40

a 2.08 + 0.25

Bosmina 2.75 + 0.64a 1.83 + 0.21

a 1.75 + 0.43

a 2.11 + 0.27

Canthocamptus 3.00 + 0.91a 1.58 + 0.48

a 1.42 + 0.51

a 2.01 + 0.39

Cyclops 3.40 + 0.61b 2.08 + 0.54

ab 1.67 + 0.51

a 2.39 + 0.34

The mean density values with the same superscript are not significantly different (p > 0.05)

32

Figure 2: Monthly variation in Daphnia from Oct. 2010 to Sep. 2011

Figure 3: Monthly variation in Nauplius from Oct. 2010 to Sep. 2011

33

Fi

gure 4: Monthly variation in Camptocerus from Oct. 2010 to Sep.

2011

Figure 5: Monthly variation in Eurycerus diversity from Oct. 2010 to Sep. 2011.

34

Figure 6: Monthly variation in Bosmina from Oct. 2010 to Sep. 2011.

Figure 7: Monthly variation in Canthocamptus from Oct. 2010 to Sep. 2011.

35

Figure 8: Monthly variation in Cyclops from Oct. 2010 to Sep. 2011.

36

cordifolra, Echinochloa stagnica, Panicum laxum, Hydrolytica, Sagrttaria species and Braseria

shreberia). Among the phytoplankton families, Chlorophyceae had the highest percentage

composition in all the 3 staions while Xanthophyceae had the least recorded percent. Cyperacea

difformislinn, Alchonea cordifolra and Echinochloa stagnica were not present in station 3 while

Panicum laxum was not present in station 2 among the macrophyte (Table 10).

3.8: Phytoplankton Density There was no significant difference in the mean density of

phytoplankton across the station at (p > 0.05) shown in Table 11.

3.9: Zooplankton Density

There was no significant difference at (p > 0.05) among the 3 stations (Table 12).

37

Table 8.The seasonal mean (±SE) values of crustaceans of Opi Lake from October 2010 to

September 2011.

Dry season 9.63± 5.51

Rainy season 9.97± 8.25

P 0.013

38

Table 9: Crustacean diversity and richness of Opi Lake from Oct. 2010 to Sep. 2011

Crustacean

species

Station 1 Station 2 Station 3

H D H D H D

Daphnia 1.8250 0.3025 1.7336 0.4176 1.7204 0.0443

Nauplius 1.5650 0.5921 1.5519 0.3689 1.5123 0.4850

Camptocerus 1.3115 0.7559 1.4367 0.6144 1.4770 0.4573

Eurycerus 1.1350 0.8129 0.9463 0.8929 1.0196 0.8621

Bosmina

1.0379 0.8760 1.1032 0.8886 1.1383 0.8739

Canthocamptus 0.9758 0.8027 0.6090 0.9087 0.6689 0.8644

Cyclops 1.1609 0.7571 0.8927 0.5511 0.9195 0.7758

H - Shannon Weiner Index D - Simpson Index

Increase in H = Increase in species richness

Decrease in D = Increase in species richness

39

Table 10: Flora of Opi Lake form October 2010 to September 2011.

Phytoplankton Name (family) Station 1(%) Station 2(%) Station 3(%)

Bacillariophyceae 12.15 13.10 13.13

Chlorophyceae 31.38 31.26 30.20

Cryptophyceae 12.75 11.26 17.97

Cyanophyceae 27.73 28.28 26.70

Dinophyceae 13.36 13.10 10.07

Xanthophyceae 2.63 2.99 1.98

Macrophyte Name Station 1 Station 2 Station 3

Kyllingn squamalata * * *

Nymphaea lotus * * *

Acroceras zizanioid * * *

Cyperacea

difformislinn

* * -

Alchonea cordifolra * * -

Echinochloa stagnica * * -

Panicum laxum * - *

Hydrolyticao spp. * * *

Sagrttaria spp. * * *

Nelumbo letea * * *

Braseria shreberia * * *

* = PRESENT

- = ABSENT

40

Table 11: Mean density of phytoplankton of Opi Lake from Oct. 2010 to Sep. 2011.

Species Station 1 Station 2 Station 3 Total

Bacillariophyceae 5.00 ± 1.00a 4.75 ± 1.12

a 5.00 ± 1.02

a 4.92 ± 0.59

Chlorophyceae 12.92 ± 1.35a 11.33 ± 1.42

a 11.50 ± 1.24

a 11.92 ± 0.76

Cryptophyceae 5.25 ± 1.33a 4.08 ± 0.98

a 6.83 ± 1.25

a 5.34 ± 0.70

Cyanophyceae 11.42 ± 0.96a 10.25 ± 1.07

a 10.17 ± 0.76

a 10.61 ± 0.53

Dinophyceae 5.50 ± 1.08a 3.92 ± 0.70

a 3.83 ± 1.28

a 4.42 ± 0.60

Xanthophyceae 1.25 ± 0.37a

1.66 ± 0.49a 0.75± 0.41

a 1.06 ± 0.24

The mean density values with the same superscript on the same row are not significantly

different (p > 0.05)

41

Table12: Zooplankton (order than crustaceans) mean density of Opi Lake from Oct. 2010 to Sep.

2011

Species Station 1 Station 2 Station 3 Total

Rotifera 5.75 ± 1.37 a

5.08 ±1.23 a 4.58 ± 1.31

a 5.14 ± 0.72

Larvae 1.50 ± 0.38 a 1.50 ± 0.31

a 0.92 ± 0.23

a 1.31 ± 0.18

Fishegg 4.42 ± 1.18 a 2.25 ± 0.68

a 3.58 ± 1.41

a 3.48 ± 0.65

The mean density values with the same superscript on the same row are not significantly

different (p > 0.05).

42

3.10. Mean Density of Sampled Macroinvertebrate

Among the 23 species of macroinvertebrate sampled, 19 species were identified to

species level while 4(insects) were unidentified. The mean densities of 14 species were not

significantly different (p > 0.05) within the 3 sampling stations. The mean density of Ranatra

fusca in station 3 was significantly different from Station 1 and 2 while Nepa spp mean density

in 1 and 2 were significantly different (p < 0.05), shown in Table 18.

3.11. Correlations of physico-chemical, fauna and flora of Opi Lake

Correlation matrix between physico-chemical parameters in Opi Lake is shown in

Table 13. There was positive correlation between transparency and depth, transparency and

phosphorus, alkalinity and calcium (p<0.01) while negative correlation was observed between

DO and pH, temperature and Nitrate (p< 0.05).

Correlations between crustaceans and physico-chemicals are shown in Table 14.

Daphnia and Magnesium showed negative relationship (p < 0.01), Daphnia and nitrate and

Daphnia and iron observed a negative correlation (p < 0.05). Positive correlation was observed

between Eurycerus, bas and Cyclops and calcium (p <0.05).

In Table 15, correlation matrix between crustaceans and other zooplankton is

expressed, Rotifer and Daphnia, showed positive correlation (p < 0.01) while Fish egg and

Daphnia equally had a positive correlation (< 0.05).

Among crustaceans and phytoplankton, Daphnia and Dinophyceae, showed positive

correlation also and Cyclops and Cryptophyceae. while Eurycerus and Xanthophyceae and had a

negative correlation (< 0.05), as represented in Table 16.

Among the crustaceans, there were observed positive correlations between Eurycerus

and Cyclops, Canthoamptus and Cyclops (p< 0.01) while Napilus and Canthocamptus showed

positive interaction (p< 0.05). no negative interaction was observed, shown in Table 17.

Arctocria interrupta, Ranatra fusca were observed to have a negative correlation with

Daphnia (p< 0.01) while Leech and Bosmina had a positive correlation (p < 0.01).positive

correlation was observed between F, Z1 and Naplius and Naplius (shown in Table 19).

43

Table 13: Correlation matrix of physic-chemicals of Opi lake from Oct. 2010 to Sep. 2011.

Temp. Trans. Depth pH DO Alka Mag. Cal. TH Phos. Nit. Iorn TDS FreeCO2

Temp 1 -.165 -.387** .280 -.562** -.088 .145 .164 .099 .086 -.232* -.058 a -.386**

Trans 1 .375** .029 .054 .076 -.118 -.066 -.147 .296** -.152 .035 a .200*

Depth 1 .117 .759** .364** -.484** .517** -.333** .323** .022 -.158 a .625

pH 1 -.189* .341** -.733** -.167 -.826** .018 -.366** -.090 a .240*

DO 1 .279** -.267** .737** .032 -.514** .308** -.174 a .513**

Alk. 1 -.409* .274** -.337** -.441** .082 -.079 a .359**

Mag. 1 -.309** .946** .078 .235 .327 a -.345**

Ca 1 .015 -.505** .088 -.221* a .191

TH 1 -.086 .277** .269** a -.300**

Phos. 1 -.180 .058 a -.275**

Nit. 1 .035 a .070

Iron 1 a

.098

TDS a a

FreeCO2 1

SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05 and a- variance is constant

44

Table 14: Correlation matrix of relationship between crustaceans and physico-chemical of Opi Lake form Oct. 2010 to Sep. 2011.

Temp Trans. Depth pH DO Alka. Mag. Cal TD Phos. Nit. Iorn TD FreeCO2

D. .586** -.419 .133 .478** .489** .383* -.412** .423* -.328 -.308 -.385* -.396* A .102

N. .178 -.235 .135 .178 .330* .126 -.286 .263 .241 -.125 -.274 -.346* A .050

C. .017 -.174 -.045 -.091 .024 .299 -.240 .284 -.170 .187 -.251 -.146 A -.109

E. .323 -.037 .242 .389* .293 .191 -.443** .369* -.401* -.215 -.327 .487** A -.141

B. .241 -.111 .105 .006 .192 .009 -.265 .390* -.158 .062 -.224 -.240 A -.126

Can. .250 -.212 .072 .230 .243 .280 -.061 .129 -.019 -.175 -.224 -.177 A -.136

Cy. .224 -.048 .100 .297 .305 .309 -.199 .422* -.066 -.229 -.077 -.328 A -.293

**- SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05 and a- variance is constant.

D = Daphnia, N = Naplius, C = Camptocerus, E = Eurycerus, B = Bosmina, Can =

Canthocamptus and Cy =Cyclops

45

Table 15: Correlations between crustaceans and zooplankton of Opi Lake form Oct. 2010 to Sep. 2011.

D N C E B Can Cy

Rotifera .454** .196 .027 -.006 -.230 -.179 .087

Larvae .069 .225 .142 -.305 -.020 -.289 -.159

Fishegg .397* .191 -.095 -.191 -.039 -.130 .115

**- SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05

D = Daphnia, N = Naplius, C = Camptocerus, E = Eurycerus, B = Bosmina, Can =

Canthocamptus and Cy =Cyclops

46

Table 16: Correlations between crustaceans and phytoplankton of Opi Lake form Oct. 2010 to Sep. 2011.

Bac Chl Cry Cya Din Xan.

D -.200 -.210 -.063 -.144 .394* -.160

N -.115 -.087 -.226 -.053 .121 -.087

C -.205 .-.024 -.258 .134 .051 .099

E .246 .212 -.323 .117 .307 .407*

B .220 .218 .301 .075 .310 -.063

Can 340* .380* .333 .250 .386* -.175

C .211 .298 .093* .148 .048 .275

**- SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05

D = Daphnia, N = Naplius, C = Camptocerus, E = Eurycerus, B = Bosmina, Can =

Canthocamptus and Cy =Cyclops

Bac = Bacillariophyceae, Chl = Chlorophyceae, Cry = Crptophyceae, Cya = Cyanophyceae, Din

= Dinophyceae and Xan = Xanthophyceae.

47

Table 17: Relationship among crustaceans in Opi Lake from Oct. 2010 to Dec. 2011.

Daphnia Nauplius Camptocerus Eurycerus Bosmina Canthocamptus Cyclops

Daphnia 1 0.323 0.147 0.296 0.258 0.199 0.240

Nauplius 1 0.275 0.022 0.161 0.344* 0.098

Camptocerus 1 0.170 0.140 -0.161 0.041

Eurycerus 1 0.054 0.221 0.468**

Bosmina 1 0.158 0.048

Canthocamptus 1 0.553**

Cyclops 1

**- SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05.

48

Table 18: Macroinvertebrate mean (±SE) density of Opi Lake from Oct. 2010 to Sep. 2011

Species Station 1 Station 2 Station 3 Total

Arctocoriax

interrupta

9.08 ± 2.73a 10.58 ± 3.25

a 5.42 ± 1.90

a 8.36 ± 1.55

Damselfiy 19. 33 ± 5.39 b

9.83 ± 2.52 ab

3.25 ± 1.12 a

10.81 ± 2.26

Ranatr fusca 4.92 ± 1.6 a

6.17 ± 2.11 a

4.67 ± 2.30 b

5.25 ± 1.14

Aeshna brevistyla 18.68 ± 5.8a 14.42 ± 5.72

a 10.67 ± 3.17

a 14.58 ±2.88

Nepa species 1.50 ± 0.57a b 0.33 ± 0.19

a 0.66 ± 0.26

ab 0.83 ± 0.23

F 10.25 ± 4.20 b

3.17 ± 1.88 ab

1.00 ± 0.62 a

4.81 ± 1.64

Helobata larvalis 0.92 ± 0.45b 0.00 ± 0.00

ab 0.08 ± 0.08

a 0.33 ± 0.16

Coccinell species 0.17 ± 0.17 a

0.00 ± 0.00 a

0.08 ± 0.08 a

0.08 ± 0.06

Water penny 100.00 ± 0.00 a

100.00 ± 0.00 a

100.00 ± 0.00 a

100.00 ± 0.00

Argyronta

aquatic

7.50 ± 2.92 a

5.08 ± 2.52 a

4.25 ± 2.10 a

5.61± 1.44

Water strider 2.00 ± 0.67 1.85 ± 0.53 a

0.79 ± 0.23 a

1.84 ± 031

Lethocerus

americannus

2.17 ± 0.64 a

0.92 ± 0.50 a

1.33 ± 0.62 a

1.47 ± 0.34

M 0.08 ± 0.83 a

0.67 ± 0.31 a

0.00 ± 0.00 a

0.25 ± 0.69

Leech 3.00 ± 2.47 a

0.17 ± 0.11 a

0.58 ± 3.36 a

1.25 ± 0.84

Water mite 100.00 ± 0.00 a

100.00 ± 0.00 a

100.00 ± 0.00 a

100.00 ± 0.00

Antipodochlora

braueri

2.92 ± 0.98 a

1.17 ± 0.56 a

1.17 ± 0.46 a

1.75 ± 0.42

Oniscigaster

wakefieldi

0.58 ± 0.36 a

0.08 ± 0.08 a

0.25 ± 0.18 a

0.31 ± 0.14

Orectochilus

orbisonorum

3.50 ± 2.30 a

1.58 ± 0.92 a

3.25 ± 1.28 a

2.78 ± 0.91

W 0.92 ± 0.50 a

0.17 ± 0.11 a

0.17 ± 0.11 a

0.42 ± 0.18

Z1 0.42 ± 0.28 a

1.92 ± 1.14 a

0.50 ± 0.42 a

0.94 ± 0.42

Acroneuria

cycorias

0.42 ± 0.28 a

1.92 ± 1.14 a

0.50 ± 0.42 a

0.94 ± 0.42

F,M,W,and Z1-unidentified species. Mean with same superscript on the same row are not

significantlydiff. (p < 0.05).

49

Table 19: Correlations between crustaceans and macroinvertebrate of Opi Lake form Oct. 2010 to Sep. 2011.

Dap. Nau. Cam. Eury. Bos. Canth. Cyclops

Arctocoriax

interrupta

-.398* .111 .218 .028 -.117 -.095 -.101

Damselfly .490** .355* .148 -.050 -.097 -.079 .016

Ranatr fusca -.471** -.137 -.098 .009 .075 -.230 -.065

Aeshna brevistyla -.145 -.019 .095 .351* .128 .243 .094

Nepa species -.025 -.059 .183 .402* .281 .018 .024

F .112 .340* -.017 .263 .209 .347* -.028

Helobata larvalis .130 .014 .307 .434* .155 .222 .192

Coccinell species .077 .128 .134 .391* .032 .198 .301

Water penny a a a a a A A

Argyronta aquatic .246 .005 .095 .079 -.225 -.048 .056

Water strider .235 .188 .248 .175 -.151 .085 .117

Lethocerus

americannus

.035 .232 -.031 .005 .018 .077 .037

M -.156 .205 .027 -.181 .077 .070 -.072

Leech .171 -.154 .315 .090 .590** -.099 .044

Water mite a a a a a A A

Antipodochlora

braueri

.247 .261 -.270 .183 .141 .237 -.003

Oniscigaster

wakefieldi

-.065 .036 .115 .092 -.091 -.089 .081

Orectochilus

orbisonorum

-.056 -.046 .127 -.069 .248 .064 .002

W .275 .094 .214 .237 .595** .247 .015

Z1 -.165 .370* .045 -.227 -.082 -.101 -.236

Acroneuria

cycorias

-.165 .370* .045 -.227 -.082 -.101 -.236

**- SIGNIFICANT AT P < 0.05,*- SIGNIFICANT At P < 0.05 and a- variance is constant.

50

CHAPTER FOUR

DISCUSSION

The ranges and fluctuations of values for physico-chemical parameters recorded in Opi

Lake during the investigation were within the range of physico-chemical parameters values, of

natural and manmade freshwaters for optimal growth and survival for aquatic life in tropical

Africa (Adeniji, 1973; Adebisi, 1981; Boyd, 1981; Eyo and Ekwuonye, 1995; Nweze, 2003;

Odo, 2004 and Avoaja, 2005).

Water temperature has fundamental effects on gas solubility and biotic metabolism and it

has been found necessary for aquatic life (Lind, 1979). The low recorded values of water

temperature in the months of December and January might be attributed to the cooling effects of

harmattan wind during the period when the environment including waters were cold as suggested

by Biswas (1973), Evurunobi (1984) and Avoaja (2005). The rise in water temperature observed

in February, March and April in the lake agrees with Biswas (1973) that in early dry season,

there is usually an increase in water temperature. The insignificant difference between the dry

and rainy seasons water temperature was in consonance with the assumptions by Beadle (1974)

and Evurunobi (1984) that water temperatures are not expected to vary much with seasons due to

almost uniform intensity of sunshine throughout the year in the tropics.

Transparency is affected by so many biotic chemical and physical factors (Beadle, 1974).

This explains the positive correlation observed between transparency and depth in Opi Lake

which was equally reported by Nweze (2003). The insignificant negative relationship between

iron and transparency observed in the lake could be as a result of the inability of high bottom

iron content that affected the transparency of the surface layer except when brought into

circulation during overturn and this record was in common with the observations of Evurunobi

(1984) and (Odo) 2004. The observed high transparency in the dry season could be attributed to

reduced rainfall and low wind speed leading to calm weather conditions (Livingston and Melack,

1979; Howard-Williams and Ganf, 1981; Evurunobi, 1984 and Odo, 2004). The recorded low

transparency during the rain in the lake was due to inflow and runoff (which are major sources of

water into the lake as noted by Hare and Cater, 1984 and Evurunobi, 1984) which brought in

humus materials, suspended matter and probably colloidal iron that lowered light penetration and

51

this was not different from the findings of Adeniji (1982) in Asa Lake, Evurunobi (1984) in

Ogelube Lake and Oluasanya (1988) in Opa Reservoir.

As it was discovered that the depth of the lake started increasing progressively from June

to September, it was observed that the lake had the highest recorded vale for depth in the month

of October at the onset of the investigation and this could be as a result of much accumulation of

water from the past rainy season before the study started. It was noted that there was no

significant difference between the dry and rainy seasons depth of the lake which was in

consonance with Davies et al. (2009). On the contrary, this result was not in agreement with

Biswas (1970), Beadle (1974), Livingston and Malack (1979), Allanson et al. (1981) and

Evurunobi (1984) (in the same lake) that rainfall and depth has been recorded to have positive

correlation in the tropical lakes.

The pH of most natural waters falls in the range of 4.0 to 9.0 and much more often in the

range of 6.0 to 8.0 (Lind, 1979). The range of pH (5.27 to 6.98) obtained in this research work

was adequate for aquatic life. pH range of 5.50 to 9.50 (Avoaja, 2005) is suitable for aquatic

production, similar range of pH was recorded by Eyo and Ekwonye (1995), Attama (2003) and

Odo (2004). There was marked seasonality in the pH with 6.51 (dry season) and 5.58 (rainy

season) which was in common with a general trend noted by Biswas (1973), Lind (1979), Boyd

(1982), Evurunobi (1984), Hare and Cater (1984) and Avoaja (2004) that there is usually a dry

season rise and flood season fall in pH of African freshwaters.

The dissolved oxygen (DO) content of water results from the photosynthetic and

respiratory activities of the biota in the open waters, the significant decrease in DO content

during the dry season in Opi Lake is probably as a result high organic load of the water mainly

in the form of leaf liter whose decomposition increases the oxygen depletion while the increase

in DO content in rainy season would be due to the increased aeration during rainfall and

increased wind speed experienced in that period. The seasonal pattern of the DO content is

similar with the previous findings of Nweze (2003), Ayoade et al. (2006) and Echi et al. (2009).

There was a negative correlation of DO and temperature which agreed with Biswas (1972),

Adeniji (1973), Egborge, (1977), Lind (1979), Adebisi (1981) and Eyo and Ekwonye (1995) that

increase in water temperature reduces the DO content as a result of increase DO demand of

aquatic fauna which is caused by high metabolic activities. The insignificant relationship of DO

52

content and transparency was in line with Evurunobi (1984) but in contrast with the observation

of Biswas (1976) that DO followed secchi depth curve in VoltaLake probably due to the

association on DO content with photosynthetic activity of the phytoplankton. The significant

positive correlation between depth and DO was not in agreement with findings of Evurunobi

(1984) and this could have resulted from high recorded mean values of DO content at the early

dry season (October, November and December) that had the highest recorded depth.

Lakes are expected to have the capacity to duffer environmental effects Beadle (1974)

and this was discovered during the study in Opi Lake, the positive relationship between

alkalinity and pH noted was in support with the results previously recorded by Biswas (1972),

Adebisi (1981), Boyd (1981), Eyo and Ekwonye (1995), Attama (2003) and Mustahpa (2009).

Alkalinity as been noted to be enhanced by some factors like free CO2, phosphate etc, which tend

to lower the buffering capacity of freshwaters when they are in low concentrations (which could

result from photosynthetic or respiratory activities), was positively correlated with free CO2 and

phosphate. The positive correlation was in agreement with the findings of Attama (2003) on

studies of physico-chemical characteristics of effluent from RIMCO Vegetable oil Company

Nigerian Breweries and their receiving freshwater ecosystem. The seasonal variation determined

in dry season (25.08 mg/L) and rainy season (19.79 mg/L) was not in consonance with Davies et

al. (2009) but in line with Trivedi el al. (2003).

The range of magnesium 6.81 mg/L – 29.14mg/L (as a common constituent nutrient of

natural freshwaters is essentially important for plant growth and development the) recorded was

within the tolerable range for natural freshwater in the tropics Avoaja (2005).

Calcium supports many structures of animal such as tissues of fish and shells of mollusk.

The insignificant difference in the seasonal content of calcium discovered ion Opi Lake during

the research work could be associated to minor amount of calcium content of flood water which

is usually a major source of calcium to the water body as suggested by Evurunobi (1984).

Magnesium and calcium ions in a lake form the total hardness of the water. The lake

could be classified as soft lake since its calcium and magnesium content did not exceed 120

mg/L as stated by Lind (1979) and Mustapha and Omotosho (2005).

53

Phosphorus in water is present in several soluble and particulate forms; including

organically bound phosphorus, inorganic polyphosphate and inorganic orthophosphate. At pH

(less than pH 9.0) the dihydrogen and monohydrogen phosphate (PO4) ions are prevalent

(Avoaja, 2005). It has been observed that phosphorus is a biologically active element, it recycles

through many states in the aquatic ecosystem and this could be the reason why there was no

significant difference in PO4 concentration with seasons. The high PO4 level in the dry and rainy

seasons indicated pollution since it was above the United State Environment Protection Agency

(USEPA) standard limit of 0.025 mg/L in natural aquatic bodies (Davies et al., 2009) and this

could be as a result of flood water from farmland surrounding the lake which brought in soil

component associated with in fertilizer and animal (mainly cattle) faeces which are washed into

the lake after grazing at the nearby farmland.

The maximum nitrate concentration of 0.28 mg/L was lower than most other freshwaters in

Nigeria, 4.0 mg/L in Jebba Lake (Adeniji et al., 1984), 0.54 mg/L in Shiroro Lake (Kolo, 1996),

5.1 mg/L in Oyun Lake (Muatapha, 2003) 4.41 mg/L in Anambara River (Odo, 2004), 0.43 mg/L

in Umudike Water Reservoir (Avoaja, 2005), 0.64 mg/L in Minichnda Stream, Niger Delta

(Davies et al., 2009), and 2.10 mg/L in River Benue (Okayi et al., 2011) and at the same time

was in conformity with the stipulated concentration for natural freshwaters (Kemdirim, 1993).

The rainy season increase could be as a result of enrichment of the water by nitrate ions during

floodwater which was equally noted by Davies et al. (2009) but on the other hand was not in line

with the findings of Odo (2004) where there was a dry season increase due to nitrate enrichment

from previous rainy season.

The sharp decrease of free CO2 content in the months of April would possibly be as a

result of lower content of alkalinity observed during that month, as it was suggested by Attama

(2003) that free CO2 goes a long way to enhance water alkalinity.

The total number of 820 crustaceans comprising of 7 species (Daphnia, Nauplius,

Camptocerus, Eurycerus, Bosmina, Canthocamptus and Cyclops) encountered in the study area

appeared to be normal inhabitants of natural lakes, ponds, streams, and artificial impoundment in

Nigeria and tropical countries (Jeje, 1986; 1988; Mustahpa, 2009; Arimoro, 2010 and Kolo et al.,

2010). Daphnia with the highest percentage composition among the crustacean species could be

as a result of its ability to survive and graze effectively on most phytoplankton and fellow

54

zooplankton, and this is in consonance with Jeje (1986), Akin-Oriola (2003) and Mustapha

(2009). Percentage composition of Bosmina was not in agreement with the finding of Imoobe

and Adeyinka (2010) where Bosmina species was recorded to be more abundant than every other

zooplankton crustacean and Daphnia being absent. It was observed that no species of crustacean

was restricted to any of the three stations throughout the sampling period and this could be

attributed to uniform distribution of plankton resulting from activities like flood water, wind

speed and the little human activities in Opi Lake. All the stations were ecologically suitable for

the crustaceans as there was no station restriction of any plankton in Opi Lake as suggested by

Hare and Cater (1982), Evurunobi (1984) and Nweze (2003). Station 1 with the highest number

of composition (n = 379) could be associated with movement of water through an outlet in that

station during the flood period (October and November) which could drift most of the planktons

to that station (Hare and Cater, 1982) and its vegetated nature suggest that station 1 is

ecologically likely to be the most accepted habitat for crustaceans survival, growth and

development (Edema et al., 2002).

Apart from the composition of crustacean fauna in Opi Lake, rotifer, macroinvertebrate

(Insecta, Arachnida and Hirudina), fish egg and fish larvae sampled were not unexpected as they

are faunal composition in tropical freshwaters (Eyo and Ekwuonye, 1995; Odo, 2004 and

Achionye-Nzeh and Isimaikaiye, 2009).

April that was the end of dry season recorded the peak number of crustacean with N =

100 and November (early dry season) with the least number N = 53 could be due to food

availability (phytoplankton) on which they graze on at these periods (Nweze, 2003) and the

degree at which light was able to penetrate the water body Mustapha (2009) and Lawal-Are et al.

(2011). The difference in station 1 (high) densities experienced among Daphnia, Naulius,

Eurycerus and Cyclops could have resulted from movement towards an outlet during flood

period and more macrophyte which might have concentrated these species within the its

environment.

The seasonal variation of crustaceans in Opi Lake did not coincide with the usual

decrease in the total density of most zooplankton during white flood (wet season) as explained

by Achionyde-Nzeh and Isimaikaiya (2009); Imoobe et al. (2010); Arimoro and Oganah, (2010)

and Offem et al. (2011). High population density observed during the wet season could be traced

55

to high population of phytoplankton food source which were assumed to be highly in abundance

within the lake Muatapha (2009) and this study confirms the existence of seasonality in the

ecology of crustacean in Opi Lake.

An important consideration is attributed to zooplankton crustaceans where usually

predominance of small species like Nauplius has high evenness and diversity as a result of

smaller body size, constant influence by wind action or due to predation pressure by

planktivorous organisms (Carpenter et al., 1985; Stemberger and Lazorchak, 1994 and Imoobe

and Adeyinka, 2010). Daphnia with the highest evenness and distribution despite its large size,

and its ability to graze effectively on other zooplankton (Muatapha, 2009) in all the stations

suggests that the nature of the three stations (in terms of difference in emergent grasses, plant

shade and location) had no negative effect on its distribution and at the same time is equally

ecologically suitable for increase in Daphnia population.

Floral composition in the lake corresponds with Nigerian freshwater plants (Evurunobi,

1984; Hare and Cater, 1984; Nweze, 2003; Davies et al., 2009; Echi, et al., 2009; Hassan, et al.,

2010; Achionyde-Nzeh and Isimaikaiya, 2010 and Okayi et al., 2011).

The insignificant difference in mean density of all the phytoplankton and other sampled

zooplankton (other than crustaceans) within the three stations could suggest uniform distribution

and no station influence on the organisms.

The correlations of crustaceans with phosphate and nitrate may not necessarily be a direct

relationship of the species utilizing the nutrients, but could be attributed to the dependency of the

phytoplankton (which serves as food for the crustaceans) on these nutrients. The insignificant

negative correlation of all the crustaceans with transparency could result from low transparency

of the water which hinders zooplankton growth and abundance Mustapha (2009). Alkalinity and

pH were also found to favor crustacean growth and abundance in the lake as seen from the

positive correlation of alkalinity and pH in all the species except Camptocerus. Negative

(insignificant) correlation of most of the crustaceans with CO2 could be the reason why dry

season CO2 content of the lake was higher and this did not agree with Mustapha (2009). Similar

trend in the relationship between crustaceans and physico-chemical, phytoplankton and other

56

zooplankton has been reported by many scientists such as Carpenter et al (1985), Jeje (1986)

Akin-oriola (2003) and Mustapha (2009).

Feeding effects of Daphnia, Eurycerus and Canthocamptus were found to have

significant positive effect on the some phytoplankton. As a result of no significant negative

feeding effect observed between crustaceans and phytoplankton, all the crustacean species were

unable to reduce phytoplankton population density in their community, which could suggests the

abundance of phytoplankton (food) throughout the period Hare and Cater (1984), Carpenter et al.

(1985), Mustapha (2009), Achionyde-Nzeh and Isimaikaiya (2010). The correlation among

crustaceans group did not show any form of negative competition for food.

57

CONCLUSION

The study of crustacean ecology in Opi Lake, Nigeria has revealed that there are

abundant crustaceans (zooplankton) in the system; the organisms are highly diverse and seasonal

in abundance and distribution.

The crustacean fauna has been found similar to the species of crustaceans found in other

Nigerian lakes and other freshwater bodies. The physico-chemical parameters, plankton

abundance, macro flora and fauna in Opi Lake fell within the productive values for aquatic

ecosystem and indicated that the lake is eutrophic. The study also revealed the interaction

between crustaceans and biotic/abiotc factors in an example of a natural tropical freshwater

habitat.

The correlation coefficient between Daphnia and physico-chemicals were more

significantly pronounced than the rest of the other crustaceans of the lake. All the crustacean

species were unable to reduce phytoplankton population density in their community as there was

no significant negative feeding effect observed between crustaceans and phytoplankton, which

suggested the abundance of phytoplankton (food) throughout the period.

The majority of the macroinvertebrates present in this report belonged to the different

orders of the class insecta, and it is important to note that no macroinvertebrate crustacean was

discovered in the lake throughout the investigation despite the adequate calcium concentration to

support its life in the lake.

58

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Adebisi, A. A. (1981). The physio-chemical hydrology of tropical rivers, Ogun. Hydrobiologia,

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Adebisi, A. A. (1989). Planktonic and benthic organisms in some ponds on the Oluponna fish

farm, Oluponna, Oyo State, Nigeria. Hydrobiologia, 78: 1-16.

Adeniji, H. A. (1973). Preliminary investigation into the composition and seasonal variations of

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Adeniji, H. A. (1982). Studies on the pelagic primary production on Asa Lake. Kaniji Lake

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