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Preliminary Investigation of Relationships between Bird Diversity Index and selected Physico-Chemical Parameters in Lagos Lagoon, Nigeria

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Coastal lagoons are one of the most productive ecosystems in the world, and birds are an important part of the lagoon ecosystem. In Nigeria, the Lagoon is a large water body within the Lagos metropolis. The lagoon is subject to a host of increasing anthropogenic activities due to growing urban population. Thirty-six point counts of birds were done in May, July, October 2019 and January 2020, at twelve stations in the lagoon in each study month. This was to explore how bird diversity is affected by seasonal and spatial variation as well as water quality variables. A total of 509 individuals representing 24 species and including 14 water bird species were recorded from the bird survey. Shannon-Weiner diversity index was computed for bird data per sampling trip for each station. Univariate statistical methods involving Analysis of Variance and linear regression were used to model patterns in bird diversity within the water body. From the statistical models, bird diversity in the lagoon was found to vary temporally and/or seasonally, but not spatially. Also, the diversity of birds was found to have linear relationships to a combination of water quality parameters, and a particular linear relationship to Chlorophyll a, a measure of primary productivity. This suggested that the bird diversity responded to the productivity of the water body. However, these preliminary results require more data to better understand the relationships, towards the inclusion of birds in environmental monitoring projects.
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Nosazeogie et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
103
Preliminary Investigation of Relationships between Bird Diversity Index and selected
Physico-Chemical Parameters in Lagos Lagoon, Nigeria
Nosasogie, E.O.,* Bassey, B.O., Abdullahi, I.M., Bello, B., Abiodun, S., Jolaoso, A.F., Dick, C.G., Ajani, G.,
Igbo, J., Balogun, J.K. and Yakub, A.S
Department of Biological Oceanography, Nigerian Institute for Oceanography and Marine Research, Victoria Island,
Lagos State, Nigeria
*Corresponding Email: nosazeogieesther@gmail.com; Phone: +2348031942255
ABSTRACT
Coastal lagoons are one of the most productive ecosystems in the world, and birds are an important part of the
lagoon ecosystem. In Nigeria, the Lagoon is a large water body within the Lagos metropolis. The lagoon is subject
to a host of increasing anthropogenic activities due to growing urban population. Thirty-six point counts of birds
were done in May, July, October 2019 and January 2020, at twelve stations in the lagoon in each study month. This
was to explore how bird diversity is affected by seasonal and spatial variation as well as water quality variables. A
total of 509 individuals representing 24 species and including 14 water bird species were recorded from the bird
survey. Shannon-Weiner diversity index was computed for bird data per sampling trip for each station. Univariate
statistical methods involving Analysis of Variance and linear regression were used to model patterns in bird
diversity within the water body. From the statistical models, bird diversity in the lagoon was found to vary
temporally and/or seasonally, but not spatially. Also, the diversity of birds was found to have linear relationships to
a combination of water quality parameters, and a particular linear relationship to Chlorophyll a, a measure of
primary productivity. This suggested that the bird diversity responded to the productivity of the water body.
However, these preliminary results require more data to better understand the relationships, towards the inclusion of
birds in environmental monitoring projects.
INTRODUCTION
Coastal lagoons represent an ecotone between
freshwater, marine and terrestrial ecosystems
(Christia et al., 2018). Thus, they are dynamic and
often characterized by environmental fluctuations.
Also, lagoons are among the most heterogeneous,
productive and biologically diverse systems in the
world. Usually located on the hub of urban
development, lagoons are therefore vulnerable to
pollution and over-exploitation as such are threatened
biomes (Farinós and Robledano, 2010). The Lagos
Lagoon is one of the largest water bodies in the
southwestern Nigerian coastal zone, covering an area
of about 208 km2 (Nkwoji et al., 2010). The Lagos
area typically experiences two distinct seasons: wet
and dry. Wet season is from April to September, and
dry season from October to March (Obiefuna et al.,
2012). Surrounded by a growing urban population,
the Lagos Lagoon is subject to a host of
anthropogenic activities such as sand-dredging and
waste disposal (Phillips et al., 2012). Many studies
have explored biotic groups such as plankton,
benthos and fish in the Lagos Lagoon (Nkwoji et al.,
2010; Ajagbe et al., 2012; Phillips et al., 2012). At
the very least, the species compositions of these
groups have been documented. Additionally, some of
these studies have attempted to use biodiversity as
bio-indicators of pollution. Physico-chemical
parameters in the Lagos Lagoon have been reported
to vary with the distinct seasons due to rainfall
patterns. Variations in the diversity of these biotic
groups have been explained using variability in
physico-chemical parameters and productivity.
However, birds within this ecosystem have not
received much attention.
As organisms which live at an interface between
land, air and water, and are top predators, birds are an
important component of the aquatic ecosystem. They
are not only sensitive to their environment, but
conspicuous and therefore relatively easy and
inexpensive to monitor as indicators of immediate
ecosystem health. Bird diversity in aquatic
environments has been generally related to
environmental factors, such as internal environmental
gradients of water quality (Farinós and Robledano,
2010). Water quality affects the primary productivity
of any water body through its chemical
characteristics which are limiting to plant growth.
This in turn determines the amount of resources such
as available prey present to support the bird
populations, especially water-birds which are
dependent on water-bodies for food (Thapa and
Saund, 2013). Bird diversity is also affected by the
seasonal movements of the some bird species
(Mundava et al., 2012).
Understanding these relationships is vital to
establishing the role of birds as environmental
indicators, in addition to already existing indicators.
Nosazeogie et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
104
Also, information on the status of coastal bird
species, as well as the current threats facing them in
their habitat is important for the development of
sustainable management plans for coastal areas.
Determining the status of the Lagos Lagoon avifauna
is an important step towards the conservation of the
birds and thus, the ecosystem of which they are an
integral part. Thus, this study explored fundamental
relationships between bird diversity and habitat
characteristics in the Lagos Lagoon. This was
towards the inclusion of birds in an ongoing bio
monitoring project aiming at improving our
understanding of the biological characteristics of the
Lagos Lagoon in Nigeria.
METHODOLOGY
Study area
The Lagos Lagoon is located between latitude 6° 26'
N and 6° 38' N, and longitude 3° 23' E and 3° 43' E. It
is typically shallow that is, about 1.5 - 3.0m deep,
and directly connected to the Atlantic Ocean or Bight
of Benin through the Commodore Channel (Obiefuna
et al., 2012; Phillips et al., 2012). Twelve stations
were selected within the study area for sample
collection (Figure 1).
Bird survey
The Lagos Lagoon was surveyed for birds using
point-counts of observed birds within a 100m radius
around the boat, through a pair of binoculars at each
station while other samples such as water and
sediment were collected. All birds encountered either
perched or in flight, were counted by one observer
from a fiberglass boat with an outboard engine which
slowed down at each station since it could not be
completely stationary because of water movement.
Data was collected four times, between May 2019
and January 2020 from each of the selected stations.
Each sampling trip was done between 8:00h - 13:00h
during which noise was minimal within the lagoon.
Individuals of each species were identified using
Borrow and Demey, 2004 and Helms field guide to
birds of Western Africa, and then counted for 7-10
minutes at each station by one observer, depending
on the time required to collect other samples. Double
counting was avoided by noting the direction in
which individual birds flew, and by counting only
individuals in groups that were seen at a particular
time. Photographs were taken using a Nikon D5300
camera with telephoto lens to confirm species
identification.
Figure 1: Map of sampling stations along the Lagos Lagoon in Nigeria
Water Quality (Physico-chemical parameters)
Water and air temperature were recorded in-situ, with
the use of a mercury-in-glass thermometer. A Horiba
u-10 probe was used to measure pH, turbidity,
alkalinity, Total Dissolved Solids and conductivity of
water. Water samples were collected in transparent
250ml glass bottles for chlorophyll a analysis and
1000ml plastic bottles for nutrient analysis. These
samples were taken to the Biological Oceanography
laboratory of the Nigerian Institute for Oceanography
and Marine Research, Lagos, and analyzed for
Chlorophyll a and nutrient concentrations of Nitrite,
Phosphate, Silicate and Sulphate using methods
outlined in GEF, 2009.
Statistical analyses
First, Shannon-Weiner diversity index was computed
using bird data per sampling trip for each station in a
Nosazeogie et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
105
Microsoft Excel spreadsheet. Shannon diversity
index is given as: (Morris et al., 2014)
H= -Σ (pi) ln(pi),
Where ‘H’ = Shannon-Weiner’s diversity index; pi =
the proportion of individuals belonging to species ‘i’
Then, data was analyzed using the R statistical
package. The response variable, diversity was
subjected to the Shapiro-Wilk’s normality test.
Where normal distribution is observed, parametric
tests such as Analysis of Variance and linear
regression models would be carried out. ANOVA
would be used to compare bird diversity between the
sample stations and between seasons to explore
spatial and temporal variation. In addition, Multiple
regression would be used to explore relationships
between diversity values and physico-chemical water
variables. Furthermore, we used Pearson’s correlation
coefficient for each pair of the physico-chemical
parameters to select the parameters to be included in
the multiple regression model.
RESULTS
Bird species abundance
A total of 509 individuals representing 24 species
were recorded from in and around the Lagos Lagoon.
Fourteen (58%) of these species are classified as
water birds: birds which usually forage in water.
Families, species, common names and code names
(as used in this study) as well as migratory status of
the birds are presented in Table 1.
Spatial and temporal variation in bird diversity
The result from the Analysis of Variance tests
showed that the difference in bird diversity across
stations was not significant (F1,47= 1.7237, p>0.05).
However, the average bird diversity was higher in the
dry season than in the rainy or wet season (F1,47 =
4.2032, p<0.05; Figure 3). Dry season diversity
(n=12) averaged 1.33 (SD=0.25), while wet season
diversity (n=36) averaged 1.03 (SD=0.46).
Table 1. Species recorded from Lagos Lagoon (modified from Borrow and Demey, 2004)
Family
Common name
Species name
Species code
Migratory status
Phalacrocoracidae
Long-tailed Cormorant*
Phalacrocorax
africanus
REECO
Resident
Ardeidae
Cattle Egret*
Bulbicus ibis
CATEG
Migrant (IA)
Western Reef Egret*
Egretta gularis
WEREG
Resident
Little Egret*
Egretta garzetta
LITEG
Resident
Grey Heron*
Ardea cinerea
GREHE
Migrant (P)
Green backed Heron*
Butorides striata
GRBHE
Resident
Black Heron*
Egretta ardesiaca
BLAHE
Resident
Anatidae
White-faced whistling
Duck*
Dendrocygna viduata
WHFWD
Migrant (IA)
Accipitridae
Yellow-billed Kite
Milvus migrans
YEBKI
Migrant (IA)
Falconidae
Common Kestrel
Falco tinnunculus
COMKE
Resident
Charadriidae
Spur-winged Lapwing*
Vanellus spinosus
SPWLA
Resident
Scolopacidae
Whimbrel*
Numenius phaeopus
WHIMB
Migrant (P)
Common Greenshank*
Tringa nebularia
COMGR
Migrant (P)
Common Sandpiper*
Actitis hypoleucos
COMSA
Migrant (P)
Sternidae
Common Tern*
Sterna hirundo
COMTE
Migrant (IA)
Columbidae
Laughing Dove
Streptopelia
senegalensis
LAUDO
Resident
Speckled Pigeon
Columba guinea
SPEPI
Resident
Musophagidae
Western Grey Plantain-
eater
Crinifer piscator
WEGPL
Resident
Apodidae
Little Swift
Apus affinis
LITSW
Resident
Mottled Spinetail
Telacanthura ussheri
MOTSP
Resident
Alcedinidae
Pied Kingfisher*
Ceryle rudis
PIEKI
Resident
Hirundinidae
House Martin
Delichon urbicum
HOUMA
Migrant (P)
Ethiopian Swallow
Hirundo aethipicus
ETHSW
Resident
Corvidae
Pied Crow
Corvus albus
PIECR
Resident
*Waterbirds,
IA= Intra-African
P= Palearctic
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Proceedings of 7th NSCB Biodiversity Conference, October 2020
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Figure 2: Ranking species abundance for the period May, July, October 2019 and January 2020
Figure 3: Seasonal mean bird diversity within the Lagos Lagoon;
(1=Wet season: May, July, October 2019, 2=Dry season: January 2020)
Linear Regression
The multiple regression model was initially used for
all measured physico-chemical variables such as pH,
salinity, alkalinity, Turbidity, Nitrite, Sulphate,
Silicate, Phosphate, chlorophyll a, Dissolved
Oxygen, conductivity, air temperature and water
temperature. Total Dissolved Solids was excluded
because of the high correlation with conductivity (rs =
-0.425647, p<0.05). The least significant variables
based on the p-values of the regression co-efficient
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were dropped from the model in a backward
elimination while monitoring the overall model fit
using p-values of models and adjusted R-squared
value. The regression co-efficients of the best model
are shown in Table 3. Although chlorophyll a was
one of the least significant variables, its removal
drastically reduced the model fit during the multiple
regression backward elimination. Therefore, the
relationship of chlorophyll a with Shannon-Weiner
diversity was additionally modeled using simple
linear regression and found to be significant (p<0.05,
R2 = 0.26, Figure 4).
Table 3: Multiple regression model table showing co-efficients of the parameters in the model
Estimate
Std. Error
t value
p value
(Intercept)
-1.065e+01
3.098e+00
-3.4
0.004
pH
1.579e+00
3.925e-01
4.0
0.002
salinity
-3.486e-02
2.202e-02
-1.6
0.1
alkalinity
-3.736e-02
1.012e-02
-3.7
0.003
Turbidity
1.769e-02
7.089e-03
2.5
0.03
Nitrite
-5.149e-01
2.834e-01
-1.8
0.09
Sulphate
1.868e-03
9.846e-04
1.9
0.08
Silicate
1.202e-01
3.636e-02
3.
0.0076
Phosphate
3.111e-02
2.415e-02
1.3
0.2
Chlorophyll a
8.689e-01
1.098e+00
0.8
0.4
p=0.003, R2=0.64
Figure 4: Diversity of birds and chlorophyll a concentration in the Lagos Lagoon, Nigeria
DISCUSSION
The bird species found in the Lagos Lagoon suggests
that the waterbody provides habitat for urban birds,
as well as resident and migratory water bird species.
It is worth mentioning that the most abundant species
in this study were the Speckled Pigeon, Cattle Egret,
Ethiopian Swallow and Yellow-billed Kite. These
species are typically successful within urban areas in
southern Nigeria (Efenakpo et al., 2019). Although
the Speckled Pigeon and Ethiopian Swallow land
birds were not observed to use the water directly,
they flew over the water body and rested on
structures within the water body. Additionally, the
Ethiopian Swallow and House Martin and Little
Nosazeogie et al.
Proceedings of 7th NSCB Biodiversity Conference, October 2020
109
Swift used the undersides of the Carter Bridge, a
major bridge within the lagoon for nesting. The
Cattle Egret and Yellow-billed Kite however, used
the water directly for foraging activities, as did the
other water bird species.
As shown in the species abundance curves (Figure 2),
bird diversity in the Lagos Lagoon was observed to
be higher in the dry season that is in January 2020.
This seasonal change could as a result of the presence
of migrant birds in Nigeria during the dry season
(Cresswell et al., 2009). These species leave at the
onset of the rainy season and begin to return at the
end of the rainy season. In addition, considering that
a study of Marmernor Lagoon in Spain observed bird
distribution and community structure to be a function
of water quality gradients (Farinós and Robledano,
2010), we suggest that bird diversity within the Lagos
Lagoon in this study did not differ significantly
between the stations due to the absence of spatial
gradients in physicochemical parameters. Although
water quality parameters are known to vary
seasonally in the Lagos Lagoon (Nkwoji et al., 2010),
the lagoon is homogenous in terms of spatial water
quality (Hill and Webb, 1958).
Diversity of birds in the lagoon had linear
(regression) relationships with a combination of
physico-chemical water parameters including pH,
salinity, alkalinity, Turbidity, chlorophyll a and
nutrient concentrations of Nitrite, Sulphate, Silicate
and Phosphate. While chlorophyll a is an indicator of
primary productivity, the other listed parameters are
known to influence productivity in aquatic systems
(Mannikanan et al., 2012). Moderately productive
aquatic ecosystems are expected to have higher bird
diversity because of greater prey availability,
especially for water birds (Farinós and Robledano,
2010; Thapa and Saund, 2013).
From findings, we suggests more data from bird
counts, bird prey abundance and environmental
(physico-chemical parameters, water depth and
weather) variables are required to better understand
the relationships between birds and the lagoon
ecosystem. This could promote the inclusion of birds
in environmental monitoring projects in Lagos
Lagoon and/or elsewhere.
ACKNOWLEDGEMENTS
This study was funded by the Nigerian Institute for
Oceanography and Marine Research, Lagos. We
acknoeledge Dr. Ulf Ottosson and Mr. Clive Barlow
who confirmed bird species identifications.
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Birds of Western Africa
  • Borrow
  • R Demey
Borrow, N and Demey, R. (2004). Birds of Western Africa. Christopher Helm, London. 512pp.