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The study on the physic-chemical parameters and benthic fauna diversity of Otamiri River,
Nigeria was carried out from June to December 2015. Water and benthic organisms samples
were collected monthly from three sampling stations along the stream. Dissolved oxygen bottles
of 1000 ml were used to collect water samples which were fixed with wrinkle’s reagent at the
sampling stations. Eckman grab, scoop net, hook and line, cast net, traps and dugout canoe with
paddle were used to collect the benthic macro fauna for six months (June-August and October to
December). The results of the study yielded 229 benthic organisms belonging to 15 species and
14 families. In relation to stations, Station 3 had more species and higher abundance of benthic
organisms than other sampled stations. In Station 1, only six species of benthic organisms were
recorded while Station 2 had 11 species and Station 3, 13 species of benthic organisms. Majority
of the sampled benthic organisms were localized and restricted to one sampled station which was
Station 3. The abundance of benthic organisms in Otamiri River was dependent on season. More
benthic organisms were recorded in dry season than in rainy season. The diversity indices
yielded high diversity in Station 3 than the other two studied stations. More species dominated
with high diversity index in dry season than in wet season in all the sampled stations. Mean
values of surface water temperature 26.67±0.63 0C, depth 1.96±0.48 m, COD 25.11±0.24 mg/L,
BOD 5.47±0.04 mg/L, DO 5.91±0.19 mg/L, Alkalinity 10.66±0.21 mg/L, pH 6.73±0.16, TDS
315.2±48.5 mg/L, Hardness 0.64±0.08 mg/L, Turbidity 4.52±0.16 NTU and TSS 8.68±0.75
mg/L were recorded. There were fluctuations between the physico-chemical parameters caused
by anthropogenic activities, stress to the aquatic life and pollution. Shannon wieners diversity
index H = 2.24 was higher in Station 2, while Simpson’s dominance index D= 8.5 was also high
at Station 2. Temperature, Depth, BOD and TSS correlated positively and favoured the
abundance and of Synodontis spp. Temperature, BOD, Turbidity and TSS were also positively
correlated and favoured the abundance of C. nigrodigitatus and C. armatum. Negative
correlation was recorded in P. serratus in all parameters and in all seasons and stations C.
nigrodigitatus was the most abundant species recorded in the present study (32.65%) while the
least abundance species was P. serratus (1.25%) and both were found only in Station 3. The pH,
BOD, TDS, hardness, turbidity, DO, BOD, COD and temperature ranges fall within WHO
recommendations. Government should make laws restricting dredging and sand mine activities
in the sampled area.





Title Page – – – – – – – – – – – – i
Approval Page – – – – – – – – – – – ii
Dedication – – – – – – – – – – – – iii
Acknowledgements – – – – – – – – – – – iv
Table of Content – – – – – – – – – – – v
List of Tables – – – – – – – – – – – viii
List of Figures – – – – – – – – – – – ix
Abstract – – – – – – – – – – – – xi
1.1 Introduction – – – – – – – – – – – 1
1.2 Justification of the Study – – – – – – – – – 4
1.3 Objective of the Study – – – – – – – – – 5
1.4 Literature Review – – – – – – – – – – 5
1.4.1 Water quality parameters – – – – – – – – – 5 – – – – – – – – – – – 6 Turbidity – – – – – – – – – – – 6 pH – – – – – – – – – – – – 7 Dissolved oxygen – – – – – – – – – – 7 Total hardness – – – – – – – – – – 8 Alkalinity – – – – – – – – – – – 8 Total dissolved solids – – – – – – – – – 9 Total suspended solids – – – – – – – – – 9 Conductivity – – – – – – – – – – – 9
vi Chloride – – – – – – – – – – – 10 Sulphate – – – – – – – – – – – 10 Total phosphorus – – – – – – – – – – 11 Orthophosphate – – – – – – – – – – 11 Total nitrogen – – – – – – – – – – 11
1.4.2 Benthic fauna – – – – – – – – – – 12 Subdivisions of fauna – – – – – – – – – 14
1.4.3 Relationship between water quality and benthic fauna – – – – – 15
2.1 Study Area – – – – – – – – – – – 17
2.2 Sampling Method- – – – – – – – – – 19
2.3 Collection of Samples – – – – – – – – – – 19
2.4 Collection of Water Sample for Physico-chemical Analysis – – – – – 19
2.5 Collection of Vertebrate Samples – – – – – – – – 23
2.6 Collection of Macro-invertebrate Samples – – – – – – – 23
2.7 Statistical Analysis – – – – – – – – – – 24
3.1 Species Diversity of the Vertebrates and Macro-Invertebrates of Otamiri River- – 25
3.2 Physico-chemical Parameters of Otamiri River – – – – – – – 28
3.2.1 Temperature – – – – – – – – – – – 28
3.2.2 Depth – – – – – – – – – – – – 30
3.2.3 Chemical oxygen demand – – – – – – – – – 32
3.2.4 Biological oxygen demand – – – – – – – – – 34
3.2.5 Dissolved oxygen – – – – – – – – – – 36
3.2.6 Total alkalinity – – – – – – – – – – 38
3.2.7 pH – – – – – – – – – – – – 40
3.2.8 Total dissolved solids – – – – – – – – – – 42
3.2.9 Total hardness – – – – – – – – – – – 44
3.2.10 Turbidity – – – – – – – – – – – 46
3.2.11 Total suspended solids – – – – – – – – – 48
3.3 Correlation of Species Abundance of Benthic Organisms with Physico-chemical Parameters
– – – – – – – – – – – – – 50
3.4 Effect of Season on Physico-chemical Parameters and Composition of Benthic Fauna– 66
4.1 Species Diversity and Composition- – – – – – – – 68
4.2 Water Quality Parameters of Otamiri River – – – – – – – 69
4.3 The Relationship between Water quality Parameters and Composition of Benthic Fauna
– – – – – – – – – – – – – 73
4.4 The Effect of Season on Physico-chemical Parameters of Water and Composition of Benthic
Organisms – – – – – – – – – – – – 74
4.5 Conclusion – – – – – – – – – – – 74
4.6 Recommendation – – – – – – – – – – 74
REFERENCES – – – – – – – – – – – 75




1.1 Introduction
The benthic macro fauna are those organisms that live at the bottom of a water body and are used to
detect changes in the natural environment (Idowu and Ugwumba, 2005; Akaahan et al., 2015).
Studies of aquatic bodies have established the existence of relationships between water quality and
macro and micro-invertebrate diversity (Teferi et al., 2013). They serve as monitor for the presence
of pollutants, their effects on the ecosystem and the progress of environmental clean-up process
(Nkwoji et al., 2010). The assessment of the biotic condition compliments the physico-chemical
parameters in aquatic environment condition determination (Madhushankha et al., 2014).
Macro-invertebrate organisms form an integral part of an aquatic environment and are of ecological
and economic importance as they maintain various levels of interaction between the community and
the environment (Sharma et al., 2013). According to Marques et al., 2003), knowledge of the
structure of the benthic macro-invertebrate community provides precise and local information on
recent events, which can be seen in their structuring. The use of invertebrates and fish as bioindicators
of water quality has been advocated by several researchers (Adakole and Annune, 2003).
The use of macro-invertebrate diversity for bio-assessment provides a simpler approach compared
to other environmental quality assessment procedures. This is because, macro-invertebrates can be
sampled quantitatively and the relative sensitivity or tolerance of some of them to contamination is
known (Adakole and Annune, 2003). Species vary in their degree of tolerance with the result that
under polluted conditions, a reduction in species diversity is the most obvious effect (Emere, 2000;
Olomukoro and Egborge, 2003; Sharma et al., 2013).
Macro-benthic invertebrates are used as bio-indicators because of their extended residency period in
specific habitats. More so, the presence or absence of particular benthic species in a particular
environment act as a pointer to the water quality status. The abundance of benthic fauna mainly
depends on physical and chemical properties of their habitat as they respond more quickly if any
changes in water quality occur. They are most frequently used in biomonitoring for these reasons
(Mohan et al., 2013). Modification to macrobenthic invertebrate distribution affects important role
they play such as mineralization, mixing of sediments and flux of oxygen into sediment and cycling
of organic matter (George et al., 2009), which further contribute to indication of water status. The
technique of using macro-benthic invertebrates as bio-indicators is a cost effective method widely
used in the Northern American and European ecoregions (Azrina et al., 2005) but not a popular
method in the African region in river classification due to the lack of expertise and information on
benthic macro-invertebrate populations.
There have been several studies on the relation of the aquatic macrobenthos diversity and water
sediment with physic-chemical status of the aquatic ecosystem (Garg et al., 2009; Quasin et al.,
2009; Edokpayi et al., 2010 and Madhushankha et al., 2014). In lentic freshwaters, the benthic
invertebrates play essential roles in key ecosystem processes, such as food chain dynamics,
productivity, nutrient cycling and decomposition. The lotic and lentic inland waters, as well as
brackish and marine waters in the tropics are habitats for a variety of macro-invertebrate fauna.
Work on the macro-invertebrate fauna in the tropics has shown that the quantitative collection of
key species from natural aquatic habitat or that modified by man can provide a means of estimating
various ecological parameters, such as richness or evenness in diversity (Odo et al., 2007). Their
distribution and abundance are directly related to different environmental factors such as food
availability and quantity, sediment type, substrate, and water quality (Arslan et al., 2007, and
Odabasi et al., 2009). They also show considerable spatial variation with lake and across lakes
(Baudo et al., 2001; Pamplin and Rocha, 2007; Smiljkov et al., 2008). In reservoirs, the benthic
macro-invertebrate community may be particularly susceptible to water-level changes that alter
sediment exposure, temperature regime, wave-induced sediment redistribution and basal
productivity (McEwen and Butler, 2010).
The occurrence and distribution of macro-invertebrate are governed mostly by the physical and
chemical quality of water and immediate substrate of occupation. Water quality variables such as
temperature, dissolved oxygen, pH and nutrients have considerable effects on the life of aquatic
organisms, the physical nature of the substratum, depth, and nutritive content and degree of stability
and others. They affect species composition and distribution, diversity, stability, production and
physiological conditions of the organisms (Sharma et al., 2013). Macro-invertebrate organisms are
threatened by changes in these parameters in their habitat which are usually associated with
pollution, erosion and siltation (Lydeard et al., 2004).
Humans are adjudged to be the principal driver of change on the earth’s surface. Such impact may
shape the earth in small subtle ways and sometimes in big catastrophic ways (Karr, 2005). These
effects may result in a plethora of consequences felt by plants, animals and even humans alike. One
major natural component of the earth is the aquatic environment which is home for a vast array of
diverse organisms from those with a planktonic existence through pelagic organisms to benthic
species. Human activities also interfere with this environment.
Freshwater bodies contain diverse habitats within and around which support myriads of species of
both plants and animals and are important sources of water for human activities. In some instances
freshwaters have been dammed to provide potable water for urban settlements and the Otamiri
River is one of such freshwater bodies which are used for domestic purposes by the generality of
Nekede and Ihiagwa communities. Adeogun and Oyebamiji (2011) reported that most surface
waters in Nigeria have been used as the most expedient way of disposing wastes especially
effluents. The likely impact of human interference on freshwater bodies necessitated this present
investigation to appraise the variations in the physic-chemical parameters and likely changes that
may have occurred in the macro-benthic invertebrate community of Otamiri River.
1.2 Justification of the Study
The need for good water quality has been of growing concern in Nigeria and worldwide as
anthropogenic activities is fast degrading most water bodies. These activities which include
agricultural practices, human domestic activities and dredging, all result in pollution of the natural
habitats of aquatic organisms. The people residing close to Otamiri River are predominantly
farmers and occasional dredgers. They use poultry droppings as well as chemical fertilizers to
enrich their farmlands. These constitute pollutants which drain into the river through run-offs. In
view of this, the study attempts to evaluate the quality of the river water as well as assess the
benthic fauna diversity which is often disturbed by dredging activities. In Owerri municipal council,
Otamiri River and underground water supply from private boreholes are the main sources of water
for domestic and other uses, especially when the public water supply becomes epileptic. Otamiri
River drains areas of diverse geology, soils and land use, and like other surface waters, the river is
liable to pollution from atmospheres and also from the composition of the soils and rocks through
which the surface basin filters down into rivers. In addition, pollution of the river can result from
human activities such as dumping of solid wastes and discharge of effluents from industries into the
river. Since Owerri urban and its environs depend partly on water from Otamiri River for their
domestic uses, there is a need to assess the quality of the river water. To the best of my knowledge,
no work has been reported on the diversity of benthic fauna of Otamiri River, hence the need to
study various fauna groups and their diversity.
The findings will provide information on the water quality of the river and the diverse species of
benthos in the river. It will also provide useful information on the richness of the Otamiri River.
1.3 Objective of the Study
General objective of this study is to evaluate the water quality variables and the benthic organisms
in Otamiri River.
Specific objectives of this study were to:
i. determine the benthic organisms diversity of Otamiri River;
ii. assess the water quality of Otamiri River;
iii. determine the relationship between water quality parameters and composition of benthic
fauna in Otamiri River and
iv. determine the effect of season on physico-chemical parameters of the water and composition
of benthic organisms.
1.4 Literature Review
1.4.1 Water quality parameters
Several studies had dealt with the relationship between the aquatic macrobenthos diversity, water
sediment and physico-chemical status of the aquatic ecosystem (Quasin et al., 2009; Garg et al.,
2009 and Edokpayi et al., 2010). Water quality plays a vital role in the distribution, abundance and
diversity of aquatic organisms. A short-term exposure of benthic organisms to water of poor quality
causes an alteration in the community structure due to the elimination of the species that are
intolerant to stress and proliferation of stress tolerant species (Woke and Wokoma 2007). The
physical and chemical characteristics of water are important parameters as they may directly or
indirectly affect its quality and consequently its suitability for the distribution and production of fish
and other aquatic organisms (Obot et al., 2014). Important physical and chemical parameters
influencing aquatic environment are temperature, rainfall, pH, salinity, dissolved oxygen,
Biological Oxygen Demand, Turbidity (Adakole and Annune 2003).
The following guide defines each variable, discusses the importance of the variable to the aquatic
environment and lists potential anthropogenic sources.
6 Temperature
This is a measurement of the intensity (not amount) of heat stored in a volume of water. Surface
water temperatures naturally range from 0°C under ice cover to 40°C in hot springs. Natural sources
of heat include: solar radiation, transfer from air, and condensation of water vapor at the water
surface, sediments, precipitation, surface runoff and groundwater. Temperature is the primary
influencing factor on water density (Integrated Land Management Bureau, 2010).
Importance: Temperature affects the solubility of many chemical compounds and can therefore
influence the effect of pollutants on aquatic life. Increased temperatures elevate the metabolic
oxygen demand, which in conjunction with reduced oxygen solubility, impacts many species.
Vertical stratification patterns that naturally occur in lakes affect the distribution of dissolved and
suspended compounds (ILMB, 2010).
Anthropogenic sources: industrial effluents, agriculture, forest harvesting, urban developments,
mining. Turbidity
This is a measurement of the suspended particulate matter in a water body which interferes with the
passage of a beam of light through the water. Materials that contribute to turbidity are silt, clay,
organic material, or micro-organisms. Turbidity values are generally reported in Nephelometric
Turbidity Units (NTU). Pure distilled water would have non-detectable turbidity (0 NTU). The
extinction depth (for lakes), measured with a Secchi disc, is an alternative means of expressing
turbidity (ILMB, 2010).
Importance: High levels of turbidity increase the total available surface area of solids in suspension
upon which bacteria can grow. High turbidity reduces light penetration; therefore, it impairs
photosynthesis of submerged vegetation and algae. In turn, the reduced plant growth may suppress
fish productivity. Turbidity interferes with the disinfection of drinking water and is aesthetically
unpleasant. (ILMB, 2010).
Anthropogenic sources: forest harvesting, road building, agriculture, urban developments, sewage
treatment plant effluents, mining, industrial effluents. pH
This is the measurement of the hydrogen-ion concentration in the water. A pH below 7 is acidic (the
lower the number, the more acidic the water, with a decrease of one full unit representing an
increase in acidity of ten times) and a pH above 7 (to a maximum of 14) is basic (the higher the
number, the more basic the water), (ILMB, 2010).
Importance: Higher pH values tend to facilitate the solubilization of ammonia, heavy metals and
salts. The precipitation of carbonate salts (marl) is encouraged when pH levels are high. Low pH
levels tend to increase carbon dioxide and carbonic acid concentrations. Lethal effects of pH on
aquatic life occur below pH 4.5 and above pH 9.5, (ILMB, 2010).
Anthropogenic sources: mining, agriculture, industrial effluents, acidic precipitation (derived from
emissions to the atmosphere from cars and industry). Dissolved oxygen (DO)
This is a measure of the amount of oxygen dissolved in water. Typically the concentration of
dissolved oxygen in surface water is less than 10 mg/L. The DO concentration is subject to diurnal
and seasonal fluctuations that are due, in part, to variations in temperature, photosynthetic activity
and river discharge. The maximum solubility of oxygen (fully saturated) ranges from approximately
15 mg/L at 0°C to 8 mg/L at 25°C (at sea level). Natural sources of dissolved oxygen are derived
from the atmosphere or through photosynthetic production by aquatic plants. Natural re-aeration of
streams can take place in areas of waterfalls and rapids, (ILMB, 2010).
Importance: Dissolved oxygen is essential to the respiratory metabolism of most aquatic
organisms. It affects the solubility and availability of nutrients, and therefore the productivity of
aquatic ecosystems. Low levels of dissolved oxygen facilitate the release of nutrients from the
sediments. Oligotrophic (low nutrient) lakes tend to have increased concentrations of dissolved
oxygen in the hypolimnion (deeper waters) relative to the epilimnion (defined as orthograde oxygen
profiles). Eutrophic (high nutrient) lakes tend to have decreased concentrations of dissolved oxygen
in the hypolimnion relative to the epilimnion (defined as clinograde oxygen profiles), (ILMB,
Anthropogenic causes of decreased DO: forest harvesting, pulp mills, agriculture, sewage
treatment plant effluent, industrial effluents, impoundments (dams). Total hardness
The hardness of water is generally due to the presence of calcium and magnesium in the water.
Other metallic ions may also contribute to hardness. Hardness is reported in terms of calcium
carbonate and in units of milligrams per litre (mg/L). Waters with values exceeding 120 mg/L are
considered hard, while values below 60 mg/L are considered soft, (ILMB, 2010).
Importance: Harder water has the effect of reducing the toxicity of some metals (i.e., copper, lead,
zinc, etc.). Soft water may have corrosive effect on metal plumbing; while hard water may result in
scale deposits in the pipes. If the water has a hardness greater than 500 mg/L, then it is normally
unacceptable for most domestic purposes and must be treated, (ILMB, 2010).
Anthropogenic sources: mining, industrial effluents Alkalinity
This is the measurement of the water’s ability to neutralize acids. It usually indicates the presence of
carbonate, bicarbonates, or hydroxides. Alkalinity results are expressed in terms of an equivalent
amount of calcium carbonate. Note that this does not mean that calcium carbonate was found in the
sample. Natural waters rarely have levels that exceed 500 mg/L (ILMB, 2010).
Importance: Waters that have high alkalinity values are considered undesirable because of
excessive hardness and high concentrations of sodium salts. Waters with low alkalinity have little
capacity to buffer acidic inputs and are susceptible to acidification (low pH), (ILMB, 2010).
Anthropogenic sources that destroy alkalinity: mining, industrial effluents, acidic precipitation.
9 Total dissolved solids (TDS)
This is a measure of the amount of dissolved material in the water column. It is reported in mg/L
with values in fresh water naturally ranging from 0-1000 mg/L. Dissolved salts such as sodium,
chloride, magnesium and sulphate contribute to elevated filterable residue values (ILMB, 2010).
Importance: High concentrations of TDS limit the suitability of water as a drinking and livestock
watering source as well as irrigation supply. High TDS waters may interfere with the clarity, color,
and taste of manufactured products. (ILMB, 2010)
Anthropogenic sources: mining, industrial effluent, sewage treatment, agriculture, road salts. Total suspended solids (TSS)
This is a measure of the particulate matter that is suspended within the water column. Values are
reported in mg/L, (ILMB, 2010).
Importance: High concentrations of TSS increase turbidity, thereby restricting light penetration
(hindering photosynthetic activity). Suspended material can result in damage to fish gills. Settling
suspended solids can cause impairment to spawning habitat by smothering fish eggs. Suspended
solids also interfere with water treatment processes, (ILMB, 2010).
Anthropogenic sources: forest harvesting, road building, industrial effluents, urban developments,
placer mining, municipal sewage treatment plants. Conductivity
This is the measurement of the ability of water to conduct an electric current – the greater the
content of ions in the water, the more current the water can carry. Ions are dissolved metals and
other dissolved materials. Conductivity is reported in terms of microsiemens per centimeter
(μS/cm). Natural waters are found to vary between 50 and 1500 μS/cm, (ILMB, 2010).
Importance: Specific conductivity may be used to estimate the total ion concentration of the water,
and is often used as an alternative measure of dissolved solids. It is often possible to establish a
correlation between conductivity and dissolved solids for a specific body of water [dissolved solids
= conductivity x 0.55 to 0.9 (the most often used is 0.65)]. Fish diversity typically is inversely
proportional to conductivity, (ILMB, 2010).
Anthropogenic sources: mining, roads (de-icing salts), industrial & municipal effluents. High
conductivity may also be naturally occurring. Chloride
Of the halides, chloride appears in the highest concentrations in natural fresh water system, and is
reported as mg/L, (ILMB, 2010).
Importance: Chloride is important in terms of metabolic processes, as it influences osmotic salinity
balance and ion exchange. Higher chloride concentrations can reduce the toxicity of nitrite to
aquatic life. Fish diversity typically is inversely proportional to chloride concentration, (ILMB,
Anthropogenic sources: municipal water supply disinfection, sewage treatment plant effluents,
urban developments, industrial effluents, mining. Sulphate
Sulphur is commonly found as a component of sedimentary and igneous rocks in the form of
metallic sulphates. Sulphates are oxidized upon contact with aerated water, producing sulphate ions
in solution, (ILMB, 2010).
Importance: When sulphate is less than 0.5 mg/L, algal growth will not occur. On the other hand,
sulphate salts can be major contaminants in natural waters. Excessive levels in water may cause
illness, (ILMB, 2010).
Anthropogenic sources: combustion of fuel, present in soils that are oxidized through natural
processes, organic waste treatment, mine drainage, and evapourite sediments, such as anhydrite and
11 Total phosphorus
This is a measure of both inorganic and organic forms of phosphorus. Phosphorus can be present as
dissolved or particulate matter. It is an essential plant nutrient and is often the most limiting nutrient
to plant growth in fresh water. It is rarely found in significant concentrations in surface waters, and
is generally reported in μg/L or mg/L. (ILMB, 2010)
Importance: Since phosphorus is generally the most limiting nutrient, its input to fresh water
systems can cause extreme proliferations of algal growth. Inputs of phosphorus are the prime
contributing factors to eutrophication in most fresh water systems. A general guideline regarding
phosphorus and lake productivity is: <10 μg/L phosphorus yields is considered oligotrophic, 10-25
μg/L P will be found in lakes considered mesotrophic, and >25 μg/L P will be found in lakes
considered eutrophic, (ILMB, 2010).
Anthropogenic sources: sewage treatment plant effluents, agriculture, urban development
(particularly from detergents), industrial effluents. Orthophosphate (PO-3
This is a measure of the inorganic oxidized form of soluble phosphorus. It is generally reported in
μg/L or mg/L, (ILMB, 2010).
Importance: This form of phosphorus is the most readily available for uptake during
photosynthesis. High concentrations of orthophosphate generally occur in conjunction with algal
blooms, (ILMB, 2010).
Anthropogenic sources: sewage treatment plant effluent, agriculture, urban developments,
industrial effluents. Total nitrogen
This is a measure of all forms of nitrogen (organic and inorganic). Nitrogen is an essential plant
element and is often the limiting nutrient in marine waters. Total nitrogen is typically calculated by
summing up nitrate, nitrite, and Kjeldahl nitrogen values.
Importance: The importance of nitrogen in the aquatic environment varies according to the relative
amounts of the forms of nitrogen present, be it ammonia, nitrite, nitrate, or organic nitrogen (ILMB,
Anthropogenic sources: sewage treatment plant effluents, agriculture, urban developments, paper
plants, industrial effluents, recreation, mining (blasting residuals).
1.4.2 Benthic fauna
Benthic fauna refers to various organisms found on (epifauna) and in (infauna) the seabed.
Sediment-dwelling benthic fauna can be subdivided into the main groups of mussels/snails,
crustaceans, bristle worms and echinoderms. A benthic fauna survey is an ecologically relevant
parameter which, among other things, can indicate whether oxygen deficiency has occurred or not,
at a certain place. Different kinds of equipment are used for benthic fauna sampling, depending on
the water depth and the sediment type (Anon, 2015).
Benthos is the community of organisms which live on, in, or near the seabed, also known as the
benthic zone. This community lives in or near marine sedimentary environments, from tidal pools
along the foreshore, out to the continental shelf, and then down to the abyssal depths (Ryan, 2007).
Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water
column. The pressure difference can be very significant (approximately one atmosphere for each 10
meters of water depth) (Ryan, 2007).
Because light does not penetrate very deep into ocean-water, the energy source for deep benthic
ecosystems is often organic matter from higher up in the water column which drifts down to the
depths. This dead and decaying matter sustains the benthic food chain; most organisms in the
benthic zone are scavengers or detritivores (Ryan, 2007).
The term benthos comes from the Greek noun βένθος “depth of the sea” (Ryan, 2007).
Benthos is also used in freshwater biology to refer to organisms at the bottom of freshwater bodies
of water, such as lakes, rivers, and streams (Ryan, 2007).
Food sources
The main food sources for the benthos are algae and organic runoff from land. The depth of water,
temperature and salinity, and type of local substrate all affect the presence of benthos. In coastal
waters and other places where light reaches the bottom, benthic photosynthesizing diatoms can
proliferate. Filter feeders, such as sponges and bivalves, dominate hard, sandy bottoms. Deposit
feeders, such as polychaetes, populate softer bottoms. Fish, such as dragonets, as well as sea stars,
snails, cephalopods, and crustaceans are important predators and scavengers (Encyclopedia
Britannica, 2008).
Benthic organisms, such as sea stars, oysters, clams, sea cucumbers, brittle stars and sea anemones,
play an important role as a food source for fish, such as the California sheephead, and humans
(Encyclopedia Britannica, 2008).
By size
Macrobenthos: Macrobenthos comprises the larger, more visible, benthic organisms that are
greater than 1 mm in size. Some examples are polychaete worms, bivalves, echinoderms, sea
anemones, corals, sponges, sea squirts, turbellarians and larger crustaceans such as crabs, lobsters
and cumaceans.
Microphotograph of typical macrobenthic animals, (from top to bottom) will include amphipods,
polychaete worms, snails, and chironomous midge larvae.
Meiobenthos: Meiobenthos comprises tiny benthic organisms that are less than 1 mm but greater
than 0.1 mm in size. Some examples are nematodes, foraminiferans, water bears, gastrotriches and
micro crustaceans such as copepods and ostracodes, (Encyclopedia Britannica, 2008).
Microbenthos: Microbenthos comprises microscopic benthic organisms that are less than 0.1 mm
in size. Some examples include bacteria, diatoms, ciliates, amoeba, and flagellates.
By type
Zoobenthos: Zoobenthos comprise the animals belonging to the benthos.
Phytobenthos: Phytobenthos comprise the plants belonging to the benthos, mainly benthic diatoms
and macroalgae (seaweed), (Encyclopedia Britannica, 2008).
By location
Endobenthos: Endobenthos live buried, or burrowing in the sediment, often in the oxygenated top
layer, i.e., a sea pen or a sand dollar, (Encyclopedia Britannica, 2008)
Epibenthos: Epibenthos lives on top of the sediments, i.e., like a sea cucumber or a sea snail
crawling about. (Encyclopedia Britannica, 2008)
Hyperbenthos: Hyperbenthos lives just above the sediment, i.e., a rock cod, (Encyclopedia
Britannica, 2008)
Fauna comes from the Latin names of what name Fauna, a Roman goddess of earth and fertility, the
Roman god Faunus, and the related forest spirits called Fauns. All three words are cognates of the
name of the Greek god Pan, and panis is the Greek equivalent of fauna. Fauna is also the word for a
book that catalogues the animals in such a manner. The term was first used by Linnaeus in the title
of his (1745) work Fauna Suecica. Subdivisions of fauna
Cryofauna: Cryofauna are animals that live in, or very close to ice.
Cryptofauna: Cryptofauna are the fauna that exist in protected or concealed microhabitats.
Infauna: Infauna are benthic organisms that live within the bottom substratum of a body of water,
especially within the bottom-most oceanic sediments, rather than on its surface. Bacteria and
microalgae may also live in the interstices of bottom sediments. In general, infaunal animals
become progressively smaller and less abundant with increasing water depth and distance from
shore, whereas bacteria show more constancy in abundance, tending towards one million cells per
milliliter of interstitial seawater (Encyclopedia Britannica, 2008).
Epifauna: Epifauna, also called epibenthos, are aquatic animals that live on the bottom substratum
as opposed to within it, that is, the benthic fauna that live on top of the sediment surface at the
Macrofauna: Macrofauna are benthic or soil organisms which are retained on a 0.5mm sieve.
Studies in the deep sea define macrofauna as animals retained on a 0.3mm sieve to account for the
small size of many of the taxa (Encyclopedia Britannica, 2008).
Megafauna: Megafauna are large animals of any particular region or time. For example, Australian
megafauna (Encyclopedia Britannica, 2008).
Meiofauna: Meiofauna are small benthic invertebrates that live in both marine and fresh water
environments. The term Meiofauna loosely defines a group of organisms by their size, larger than
microfauna but smaller than macrofauna, rather than a taxonomic grouping. One environment for
meiofauna is between grains of damp sand.
In practice these are metazoan animals that can pass unharmed through a 0.5 – 1 mm mesh but will
be retained by a 30 – 45 μm mesh. The exact dimensions will vary from researcher to researcher.
Whether an organism passes through a 1 mm mesh also depends upon whether it is alive or dead at
the time of sorting ( Encyclopedia Britannica, 2008).
Mesofauna: Mesofauna are macroscopic soil invertebrates such as arthropods or nematodes.
Mesofauna are extremely diverse; considering just the springtails (Encyclopedia Britannica, 2008)
approximately 6,500 species had been identified.
Microfauna: Microfauna are microscopic or very small animals (usually including protozoans and
very small animals such as rotifers).
1.4.3 Relationship between water quality parameters and benthic fauna
Water quality plays a vital role in the distribution, abundance and diversity of aquatic organisms. A
short-term exposure of benthic organisms to water of poor quality causes an alteration in the
community structure due to the elimination of the species that are intolerant to stress and
proliferation of stress tolerant species (Woke and Wokoma, 2007). The physical and chemical
characteristics of water are important parameters as they may directly or indirectly affect its quality
and consequently its suitability for the distribution and production of fish and other aquatic
organisms (Obot et al., 2014).
The health of the ecosystem is determined by the taxonomic composition of the community as well
as its diversity. Benthic macro fauna are those organisms that live on or inside the deposit at the
bottom of a water body (Idowu and Ugwumba, 2005). They are used to detect changes in the
natural environment, monitor for the presence of pollution and its effect on the ecosystem in which
organisms’ lives and to monitor the progress of environmental cleanup (Nkwoji et al., 2010). They
are used in testing water bodies for the presence of contaminants (Nkwoji et al., 2010). Studies
have shown that there is entwining relationship between surface water quality and macro
invertebrate diversity (Teferi, et al., 2013).
The physico-chemical parameters of lakes, ponds and rivers have considerable effect on the aquatic
life. These parameters determine the productivity of a water body. Thus, a change in the physicochemical
aspect of a water body brings about a corresponding change in the relative composition
and abundance of the organisms in that water (Adeyemi et al., 2009).
Eutophication due to poor water quality has been the most challenging global threat to the quality of
water as a result of excess nutrients getting their way through run off during rainy seasons (Likens,
This process of enrichment with excess nutrients, primarily phosphorus and nitrogen, leads to
enhanced growth of algae, periphyton and/or macrophytes, as well as increased biological
productivity and decreased basin volume from the excessive addition of dissolved and particulate
inorganic and organic materials to lakes and reservoirs (Cooke et al., 2005; Likens, 2010).


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