1.0
INTRODUCTION
Bayelsa
State is blessed with a myriad of creeks, rivers and seas. Its people are so
intricately associated with its waters that it will be unimaginable to live
without it. These water bodies serve the people as source for fishing, domestic
uses, agriculture and transportation. Sadly, due to this dependence, most of our
waters are subjected to perennial pollution. Pollution of these waters has
resulted in the destruction and distortion of aquatic ecosystems.
Zooplanktons are important biological component in any
aquatic ecosystem. Zooplanktons are small, free-floating aquatic microorganisms
including crustaceans, rotifers, open water insect larvae and aquatic mites.
Their main function is to act as a primary and secondary links in the food chain
and they play a vital role in energy transfer of aquatic ecosystem (Rahkola-sorsa, 2008). Zooplanktons constitute the food
source for primary consumers organism and play an invaluable role in all aquatic
dynamics. Their presence is so vital and has become the most valuable indicator
of trophic status (Sanyogita et al, 2011).
Zooplankton can also be used
as bio-indicator for water pollution studies because they respond to changes
under adverse environmental condition (APHA, 2003), including being an indicator
that determines water quality, pollution and the state of eutrophication (Salar,
2004) and for understanding the health status of the water bodies.
Taylor creek is one of the
water bodies in Bayelsa State that human activities
have greatly affected its ecosystem. There is an acute need therefore to study
its zooplankton characterization in order to determine the pollution status of
the creek.
This will serve for the
protection of the creek ecosystem and its fishery.
2.0 MATERIALS AND METHOD
2.1 Description of Study Area
Taylor creek is a
lotic non-tidal fresh water environmental unit. It stretches from Besini clan to Gbarain in Yenagoa Local Government area of Bayelsa
state in Niger Delta. The creek lies between longitude 0060, 21’ E
and latitude 050
01’ to 05’ 05N. The location of the sampling sites for this study is at Ikrama-Okordia, Kalaba-Okordia, Akumoni-Okordia and Agbobiri
Community.
2.2 Sampling Sites
Four (4) sampling
sites were selected for the purpose of the study based on different land use
adjacent the creek. These stations are as follows;
2.2.1 Station 1 (Ikrama): It is located at
longitude 00 60 27’ 39.0”
E and latitude 050 09’
21.6” N. The station has an
elevation of 7m. This station has notable features such as floating aquatic
weeds and vegetation in the adjacent catchment.
2.2.2 Station 2 (Kalaba-Okordia):
It is located at longitude 006” 26’ 33.5 “E and latitude 050 08’
34.6” N. The station has an elevation of 7m. This station is characterized by
the presence of a Piggery farm. Waste from the farm wash directly into the
creek.
2.2.3 Station 3 (Akumoni-Okordia): it is
located at longitude 0060 25’ 46.9” E and latitude 050 08
14.9” N. This station has an elevation of 5m. The activities in this station are
bathing and washing. The creek is relatively small at this point.
2.2.4 Station 4 (Agbobiri Community): it is
located at longitudes 0060 25’ 11.6” E and latitude 050
07’ 10.7” N. In this
station are fishing, alongside farming, palm oil production and Garri production.
2.3.1 Water collection
Samples of
Zooplanktons were collected using plastic cans dipped 20cm below the surface of
the water. The can was held slightly dipped into the water and allowed to full.
The procedure was repeated for each sampling station. Each sample was fixed with
3ml formalin.
2.3.2. Zooplankton Analysis
Analysis for
zooplankton samples were done at the Niger Delta University
Bayelsa
State.
The samples
were allowed to stand for 46 hours before 50ml of pipetted concentrated sample
volume were obtained. A sub sample of 1ml was then taken and transferred into a
sedge-wick rafter counting chamber (Slides).
Identification and enumeration to the species level was done using a
leitzwetzlar
binocular dissecting microscope at a magnification of 20-400 for zooplankton for
each sample station using standard keys.
3.4 Data Analysis
Means were calculated
for zooplankton parameters. Their indices were used to estimate species
diversity. Shannon-Weiner diversity index given by formula
(1.1)
∑ i=1s(
) in ()
Evenness by the formula
(1.2)
E=H”/Ins
Species richness by Margalef (1951)
Formula:
(1.3 ) d = (s-1)/Inn
Where:
H” = species diversity, s = number
of families
N, = total number of animals
Ni = number of each family
T - Test statistics was employed to
determine the relationship and source of variability between stations in the
determined parameters of zooplankton.
4.0 DISCUSSION
The result for the investigation of
zooplankton in Taylor Creek is represented in Table 2 and Table 3. The study
recorded high diversity in plankton communities. Some species of zooplankton
occurred across stations while others were absent in some stations. The main
groups composing zooplankton communities in the creek are the protozoans, nematoda, rotifer, annelida, insecta, porifera and crustacean.
In samples collected from four (4) stations in Taylor Creek for this study, a
total of seven (7) taxa and forty nine (49) species were identified. The largest
fraction belongs to protozoa and Annelida respectively, while insect, crustacean
and porefera have the lowest fractions respectively.
From the result, the species
richness and diversity were highest in station 2 as compared to the other
stations. All zooplankton genera of different groups were represented at least
by 1 or 2 species. Several species occurred at most stations like the protozoa
and Annelida. The total number of zooplankton species varied between a minimum
of 16 individuals in station 3 and a maximum of 55 individuals at station 2.
Protozoans were the most diverse group. And they could be considered as the
keystone which affects the total number of zooplankton species over the whole
area with 23 species across all station (Table 2).
The density of protozoa showed well
marked spatial variation and it had the highest species abundance and species
richness in station 2. The Shannon diversity index (H) was found to be the
highest at station 2 and the lowest at station 1.
Simpson dominance was found to be
the highest at station 4 and the lowest was recorded at station 3 (Table 3). The
most interesting result is the inverse correlations between the Shannon index
and evenness and the total amount of zooplankton abundance. It means that the
lowest amount of evenness shows that the abundance of zooplankton group was not
homogenous and some of them were dominant. Also the lowest amount of evenness
indicates high pollution. While the lowest Shannon’s index indicates that these
sampling areas are affected by stress. A similar trend was determined for
pelagic zooplankton of coastal waters of Malven
(Costa et al, 2012).
To explain this trend, it would be
reasonable to assume that with reduction of the total amount of zooplankton, the
relative amount of the biotope (water mass) that the species can exploit
increases leading to a reduction of inter-specific competition. Under conditions
of sufficient resources for each species, most likely evenness in their
abundance occurs (Tack et al, 2005).
The species
diversity observed in this study was impressive. This
could mean that
there is no
excessive nutrient input
which normally causes decline
in species diversity (Boaden and Seed,
1985). It is
a measure of
availability of various
ecological niches to
be occupied
by various species
of organisms within
an ecosystem (Yakub, 2004).
Connell
(1978) suggested that with small environmental stress raise, the diversity
will be increased
because of the
decreasing competition, while
if the environmental
stress increases up
to a higher
point, the diversity
starts to decrease
then. Thus, increased
eutrophication could
lead to either an increase or a decrease in diversity for a certain community.
In our study, the four
diversity indices of
protozoan communities at
station 1 were
lower than stations
2, 3 and 4,
although latter stations were
more polluted than the former.
High
levels of species richness and low abundance occur in normal water bodies (Madoni and Braghiroli, 2007). The
absence of this trend in this study shows that water suffers from pollution
inputs.
Finally,
the dearth of larger zooplanktons such as crustaceans and insect was observed in
this study. This could be as a result of the preponderance of planktivorous fishes in the creek.
Planktivorous
fish select large zooplankters and can eliminate large
cladocerans
from lakes. Preys are visually selected, in most cases, on an individual basis,
although the gill rakers of certain fishes collect
some zooplankton as water passes through the mouth and across the gills. When
size selection by fish is not in effect, and when large zooplankters are
present, smaller-sized zooplankton are generally not found to co-occur with the
larger forms. The cause is likely a result of size-selective predation of
smaller zooplankton by invertebrates (copepods, phantom midge larvae, and
predaceous Cladocera)
CONCLUSION
The result
of the study shows that station 2 has the highest number of species abundance
and richness, while station 3 had the lowest. Protozoa was the most dominant
zooplankton while insect and crustaceans were the least. The dominance of
protozoa may be connected by nutrient enrichment of the creek, while the absence
of larger zooplanktons may be connected to unfavourable
conditions and the presence of planktivorous fishes.
Therefore the creek suffers from sewage and organic pollution thus confirming
the assertion that land based activities greatly affect
aquatic integrity.
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