Egyptian Journal of Aquatic Research (2016) 42, 281–287

HO ST E D BYNational Institute of Oceanography and Fisheries

Egyptian Journal of Aquatic Research

http://ees.elsevier.com/ejarwww.sciencedirect.com

FULL LENGTH ARTICLE

The effects of environmental parameters

on zooplankton assemblages in tropical coastal

estuary, South-west, Nigeria

* Corresponding author. Tel.: +234 8183429107.E-mail addresses: walaxxy@gmail.com, abdulwo@funaab.edu.ng

(W.O. Abdul).

Peer review under responsibility of National Institute of Oceanography

and Fisheries.

http://dx.doi.org/10.1016/j.ejar.2016.05.0051687-4285 � 2016 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Waidi O. Abdula,*, Ezekiel O. Adekoya

a, Kehinde O. Ademolu

b,

Isaac T. Omoniyi a, Dominic O. Odulate a, Tomilola E. Akindokun a,

Akinpelu E. Olajide a

aDepartment of Aquaculture and Fisheries Management, Federal University of Agriculture, Abeokuta, Ogun State, NigeriabDepartment of Zoology, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria

Received 1 February 2016; revised 22 March 2016; accepted 30 May 2016Available online 21 June 2016

KEYWORDS

Cluster analysis;

Estuarine ecosystem;

Tropical coastal water;

Zooplankton;

Bight of Benin

Abstract The present study was carried out to examine the distribution and assemblage structure

of zooplankton in relation to environmental parameters of tropical coastal estuarine ecosystem

impounding Bight of Benin, Nigeria. The estuarine water samples were collected between January

and December, 2014 from three sampling zones (Brushpark, Open water and Wetland) then were

fixed in 4% formalin. A total of twenty-eight (28) species belonging to four (4) groups were

recorded in this study. These groups were rotifera, copepoda, cladocerans and ostracodas, and were

all widely distributed in the three investigated zones. Higher richness, dominance and abundance

indices were recorded in Zone I when compared to both Zones II and III. Cluster analysis showed

five distinct species communities. The canonical correspondence analysis (CCA) showed a distinct

smattering positive and negative correlation on the distribution of zooplankton indicating that the

relative abundance of any species was dependent on specific environmental variables.� 2016 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access

article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction

The estuarine ecosystem is a dynamic ecotype which is influ-enced by the inflow from the sea and adjacent fresh waters; this

leads to give it a unique high nutrient level at both the water

column and sediment (Jha et al., 2014). According to Kresset al. (2002), estuaries are places for human settlements andactivities (navigation, shipping, urban, industrial wastes)

which make them vulnerable to changes as a result of pollu-tion, climatic change and overfishing, which all in turn alterthe productivity of the water. The variation in the physical

and chemical processes that occur in estuaries is reflected inthe dynamics of the biological populations, particularly plank-tonic community (Marques et al., 2007).

Zooplankton play a key position in the food web and also

influence the functioning and productivity of aquatic ecosystems

282 W.O. Abdul et al.

through their impact on the nutrient dynamics (Keister et al.,2012), from pleuston to benthos (Varadharajan andSoundarapandian, 2013). According to Omori and Ikeda

(1984), the composition and abundance of zooplankton vary inaquatic environments. This makes their biomass ecologicallyvery important because of its uses formonitoring eutrophication,

pollution, global warming and environmental problems, in casesof long-term changes. Also, their abundance can be altered byspatio-temporal variations in hydrochemical parameters and

physical forces in aquatic ecosystems (Bianchi et al., 2003).Molinero et al. (2005) reported that zooplankton are

important indicators of change in aquatic systems and climatechange. However, to a certain extent the success and failure of

a fishery is dependent on the availability of plankton particu-larly zooplankton. Xuelu et al. (2011) have observed high con-centrations of fish in areas with high zooplankton production

which in turn are the areas of enrichment.Therefore, the proper knowledge of their abundance and

distribution in estuaries and response to variable ecological

abiotic components, can serve as a guide for ensuring sustain-able management of fishery resources hence, predicting theimpact of human activities on the fisheries. This study

attempted to investigate the distribution and assemblage struc-ture of zooplankton in relation to the environmental parame-ters of a tropical coastal estuary that impounds the Bight ofBenin South-west, Nigeria.

Materials and methods

Study area

This study was carried out in a tropical coastal estuary that

impounds the Bight of Benin in South-west, Nigeria. It is

Zone III

Zon

Ogun State

Nigeria

Figure 1 Map of tropical estuarine ecosy

located between 6�200 N–6�450 N and 4�15|0E–4�300 E andbounded by Lagos Lagoon to the south-east and to the southby the Bight of Benin (Fig. 1). The water is connected to Atlan-

tic Ocean via Lagos lagoon. It has a regular influx of Oni,Oshun and Mosafejo rivers from Southwest Nigeria.

Sample collection and identification

Sampling was carried out between January and December,2014 (on monthly basis) at three zones (Zone I: brush park

area; Zone II: open water area; Zone III: wetland area) of dis-tinct ecological characteristics. The zooplankton samples werecollected at daylight hours (11.00–14.00 h) by towing a 55 lmmesh Hydrobios plankton net tied to a 25Hp engine poweredcanoe driven at low speed just below the water surface at adepth between 50 and 60 cm for 5 min. Collected samples wereimmediately transferred each time to a 250 ml labelled plastic

container with screw cap. Ten samples were collected fromeach zone and then preserved with 4% formaldehyde priorto microscopic analysis (Yigit, 2006; Kolo et al., 2010) at dif-

ferent magnifications (�50, �100 and �400). Appropriateguide (APHA, 1998) was used to aid species identification.

Zooplankton community structure analysis

Zooplankton community structure was analysed using threeunivariate indices (Shannon and Wiener diversity index, Mar-galef richness index and Pielou’s evenness index) to express the

degree of uniformity in the distribution of individuals amongtaxa in the study area (Imoobe and Adeyinka, 2009). Data col-lected were used to establish relationship between zooplankton

distribution and environmental variables using canonicalcorrespondence analysis, a sub-routine of Paleontological

Zone I

e II

The study area

stem around Bight of Benin, Nigeria.

Effects of Environmental Parameters on Zooplankton Assemblages 283

Statistics (PAST) Package version 2.41, and cluster analysiswas also carried out using the Bray–Curtis index.

Environmental parameters

Environmental parameters (water temperature, dissolved oxy-gen, pH, electrical conductivity), were measured in-situ with a

WTW 340i Multi-metre and transparency with a Secchi disc.Nitrate, phosphate, chlorophyll a and salinity were analysedex-situ using standard methods for water examination

(APHA, 1998). Analysis of variance (ANOVA) was used totest for significant difference (p < 0.05) of environmentalparameters in the zones of the estuary.

Results

Spatial distribution and relative abundance of zooplankton

Table 1 shows the distribution and relative abundance of zoo-plankton in the coastal estuary during this study. Four classes

of zooplankton comprising of twenty-eight (28) species wereidentified during the study. These included twelve (12) speciesof rotifera, seven (7) species of copepoda, eight (8) species of

cladocerans and a species of ostracoda. All identified samples

Table 1 Distribution and relative abundance of zooplankton species

Taxa Species Zone I number/ml

ROTIFERA Lecane sp. 147(17.07)

Filinia longiseta 84(40.00)

Branchionus sp. 84(50.00)

Platyias quadricornis 42(40.00)

Notholca labis 231(61.11)

Keratella cochlearis 42(18.18)

Trichocerca agnatha 147(58.33)

Kellicotia longispina 84(57.14)

Mytilina crassipes 168(38.09)

Ploesoma truncatum 84(11.76)

Microcondon clavus 105(14.70)

Callotheca adriatica 294(56.00)

OSTRACODA Cypridopsis sp. 147(25.93)

COPEPODA Cyclops vicinus 42(13.33)

Diaptomus sp. 63(30.00)

Copepod nauplii 168(30.76)

Canthocamptus sp. 126(46.15)

Diaphanosoma sp. 294(70.00)

Eucyclops sp. 105(62.50)

Limnocalanus sp. 210(76.92)

CLADOCERANS Macrothrix sp. 126(27.27)

Moina sp. 168(32.00)

Ceriodaphnia sp. 21(7.14)

Simocephalus sp. 42(13.33)

Ceriodaphnia sp. 252(57.14)

Alona affinis 105(17.24)

Bosmina sp. 189(37.50)

Daphnia sp. 21(8.33)

Total 3591

*Values in parenthesis are percentages of relative abundance (%) of zoop*Values are rated across zones on species basis.

were detected in zones I and II except Kellicottia longispinawhich was not detected in zone III.

In all, the rotifera species, Notholca labis, Keratella

cochlearis, and Ploesoma truncatum, were respectively founddominant in Zone I (61.11%), Zone II (41.18%), and ZoneIII (72.73%), while Ploesoma truncatum (11.76%), N. labis

(11.11%) and K. cochlearis (9.09%) had the least relativeabundance in Zones I, II and III respectively. In the class Roti-fera, the species with the maximum and minimum number of

individuals were Lecane (287 individuals/ml) and Platyiasquadricornis (35individuals/ml) respectively. Only one speciesof the class Ostracoda (Cypridopsis sp.) was recorded in highnumbers in Zone II (51.85%) and had the lowest number in

Zone III (22.22%).In the class Copepod, seven (7) species (including copepod

nauplii) were recorded in the three zones with Diaphanosoma

(70.00%) and Diaptomus sp. (60.00%) having the highest rela-tive abundance in all the Zones. Daphnia sp., Limnocalanus sp.and Diaphanosoms sp. had the least relative abundance of

8.33% (Zone I), 7.69% (Zone II) and 5.00% Zone III.Eight (8) species of the class Cladocerans were recorded in

this study across the three sampling zones. Ceriodaphnia sp.

predominated in Zone III followed by Macrothrix sp. in ZoneII and Ceriodaphnia sp. in Zone I, with each having a relativeabundance of 85.72%, 68.18% and 57.14% respectively.

in a tropical estuarine ecosystem around Bight of Benin, Nigeria.

Zone II number/ml Zone III number/ml Mean number/ml

441(51.22) 273(31.71) 287

84(40.00) 42(20.00) 70

63(37.50) 21(12.5) 56

42(40.00) 21(20.00) 35

42(11.11) 105(27.28) 126

168(72.73) 21(9.09) 77

42(16.67) 63(25.00) 84

63(42.85) 0(0.00) 49

147(33.33) 126(28.51) 147

336(47.05) 294(41.18) 238

378(52.94) 231(32.35) 238

147(28.00) 84(16.00) 175

294(51.85) 126(22.22) 189

189(60.00) 84(26.67) 105

21(10.00) 126(60.00) 70

126(23.07) 252(46.15) 182

84(30.77) 63(23.57) 91

105(25.00) 21(5.00) 140

42(25.00) 21(12.50) 56

21(7.69) 42(15.38) 91

315(68.18) 21(4.54) 154

189(36.00) 168(32.00) 175

21(7.14) 252((85.72) 98

105(33.33) 168(53.33) 105

63(14.28) 126(28.57) 147

210(34.48) 294(48.28) 203

42(8.33) 273(54.67) 168

168(66.67) 63(25.00) 84

3948 3381 3640

lankton species.

Table 3 Environmental parameters of Tropical Estuarine

Ecosystem around Bight of Benin, Nigeria.

Environmental

Parameters

Zone I Zone II Zone III Mean

± SE

Temperature (�C) 28.33

± 0.20a28.35

± 0.22a28.35

± 0.16a28.34

± 0.07

pH 6.52

± 0.36a6.70

± 0.24a6.550.40a 6.590.12

Electrical

conductivity (ls/cm)

483.83

± 94.52a537.17

± 86.55a489.33

± 83.07a503.44

± 33.99

Dissolved oxygen

(mg/l)

9.15

± 0.59a9.43

± 0.31a9.17

± 0.49a9.25

± 0.13

Salinity (‰) 0.43

± 0.08a0.46

± 0.11a0.47

± 0.11a0.45

± 0.04

Phosphate content

(mg/l)

0.25

± 0.02a0.27

± 0.02a0.25

± 0.04a0.26

± 0.02

Nitrate content

(mg/l)

0.20

± 0.07a0.20

± 0.07a0.19

± 0.06a0.20

± 0.02

Transparency

(cm)

31.80

± 2.46a31.63

± 2.06a30.97

± 1.45a31.47

± 0.71

Chlorophyll a

(mg/l)

0.046

± 0.00a0.039

± 0.00a0.043

± 0.00a0.033

± 0.005

*Means with similar superscript show that there were not signifi-

cantly (p> 0.05) different.

284 W.O. Abdul et al.

Meanwhile, Ceriodaphnia sp. had the least relative abundancein Zones I and II (13.33% and 33.33% respectively) andMacrothrix sp. had the least in Zone III (4.54%). Alona affinis

and Ceriodaphnia sp. had the respective maximum (203individ-uals/ml) and minimum (individuals/ml) in the class Cladocer-ans as shown in Table 1.

Species diversity and richness indices of zooplankton

Table 2 shows the value of species diversity, richness and even-

ness indices of zooplankton in the coastal estuary. In Zone I,the Shannon–Wienner index, Margalef richness index and Pie-lou’s evenness index for zooplankton were 3.108, 3.192 and

0.829 respectively. Also, in Zone II, the values were, 2.982,3.169 and 0.731 respectively, while, in Zone III, 2.954, 3.091and 0.737 were the respective values.

Environmental parameters

A summary of environmental parameters of the sampling zones(I, II and III) is shown in Table 3. As indicated in Table 3, anal-

ysis of variance (ANOVA) showed no significant difference(p > 0.05) in the environmental parameters of the threeinvestigated zones in the study area. The maximummean water

temperature (28.35 ± 0.16 �C) was recorded in Zones II and IIIand least (28.33 ± 0.20 �C) in Zone I. Also, the mean pH val-ues of 6.52 ± 0.36, 6.70 ± 0.24 and 6.55 ± 0.40 were recordedin Zones I, II and III respectively. The estuarine mean electrical

conductivity value, 503.44 ls/cm, was recorded in this studywith the maximum, 537.17 ls/cm, recorded in Zone II andthe minimum, 483.83 ls/cm, in Zone I. The average dissolved

oxygen concentrations were 9.15 ± 0.59 mg/l, 9.43 ± 0.31mg/l and 9.17 ± 0.49 mg/l in Zones I, II and III respectively,while the estuarine salinity value ranged between 0.43–0.47‰and 0.45 ± 0.04‰. The mean phosphate values were 0.25± 0.02 mg/l (Zone I), 0.27 ± 0.02 mg/l (Zone II) and 0.25± 0.02 mg/l (Zone III). Also, the mean nitrate concentration

of the estuary ranged between 0.19 mg/l and 0.20 mg/l, whileestuarine transparency ranged between 31.63 ± 2.06 cm and30.97 ± 1.45 cm. The chlorophyll a concentration of the estu-ary was 0.046 ± 0.00 mg/l in Zone I, 0.039 ± 0.00 mg/l in

Zone II and 0.046 ± 0.00 mg/l in Zone III.

Canonical correspondence analysis of environmental parametersand zooplankton species

The triplot of canonical correspondence analysis (CCA) forenvironmental parameters and zooplankton species in relation

Table 2 Species diversity, richness, and evenness of zooplank-

ton in tropical estuarine ecosystem around Bight of Benin,

Nigeria.

Indices Zone I Zone II Zone III

Total number of species 28 28 27

Total number of Individuals 3591 3948 3381

Shannon-Wiener Index 3.108 2.982 2.954

Pielou Evenness Index 0.829 0.731 0.737

Margalef Richness Index 3.192 3.169 3.091

to the three zones are presented in Fig. 2. Axis 1, whichaccounted for a total variance of 57.41%, was positively corre-

lated with temperature and transparency but negatively corre-lated with chlorophyll a and dissolved oxygen. Axis 2 showed42.59% variation, and it was positively correlated with salinity

and negatively correlated with phosphate, nitrate and electricalconductivity. Zooplankton species such as Branchionus sp., K.longispina, Diaptomus sp., Eucyclops sp. were all positively

influenced by salinity but negatively influenced by nitrate,phosphate and electrical conductivity. Also, species of zoo-plankton such as N. labis, Ceriodaphnia sp., Limnocalanussp., Trichocerca agnatha were all strongly and negatively influ-

enced by chlorophyll a and dissolved oxygen but impactedpositively by transparency and temperature. The cluster anal-ysis by hierarchical classification of the identified zooplankton

species revealed five distinct groups at 0.54–0.72% similaritylevel as shown in the dendrogram (Fig. 3).

Discussion

Four taxonomic groups of zooplankton were identified in thisstudy and each group was widely distributed in all the sampling

zones. However, rotifera group dominated the species identi-fied, followed by cladocera, copepod, and ostracoda. Similarhigh dominance of rotiferas was reported by Adeyemi (2012)

in Ajelo stream, Imoobe (2011) in Okhuo River andOmowaye et al. (2011) in Ojofu Lake. On the contrary, it dis-agrees with the study of Okorafor et al. (2013) in Calabar Riverwhere cladocerans and copepods dominated the observed zoo-

plankton taxa. Meanwhile, the dominance of rotiferas in Nige-rian aquatic ecosystems has also been documented by someother authors (Aneni and Hassan 2003; Ogbeibu and

Osokpor, 2004). The dominance of rotiferas was explained tobe due to predation pressure from planktivorous fishes that

Salinity

DO

NitratePhosphate pH

TemperatureTransparency

EC

Chlorophlly_a

LECFIL

BRAPLA

NOT

KER

TRI

KEL

MYTPLO

MIC CAL

CYC

DIA

DAP

NAU

CAN

DIAP

EUC

LIM

MAC

MOI

CER

SIM

GERALO

BOS

Zone_I

Zone_II

Zone_III

-2 -1.5 -1 -0.5 0.5 1 1.5 2 2.5

Axis 1

-3

-2.5

-2

-1.5

-1

-0.5

0.5

1

1.5

Axis

2

Figure 2 Canonical correspondence analysis between the water quality parameters and zooplankton species of a tropical estuarine

ecosystem around Bight of Benin, Nigeria.

0.48

0.54

0.6

0.66

0.72

0.78

0.84

0.9

0.96

Simi

larity

MYT

MOI

NAU

BOS

PLO

MIC

LEC

ALO

CRP

MAC

KER

CYC

DAP

DIA

SIM

CER

TRI

CAN

EC FIL

BRA

KEL

PLA

NOT

GER

LIM CAL_

DIP

Figure 3 Dendogram of cluster analysis of zooplankton of a Tropical Estuarine Ecosystem around Bight of Benin, Nigeria. LEC:

Lecane sp.; FIL: Filinia longiseta; BRA: Branchionus sp.; PLA: Platyias quadricornis; TRI: Trichocerca agnatha; KEL: Kellicotia

longispina; NOT: Notholca labis; KER: Keratella cochlearis; BOS: Bosmina sp.; ALO: Alona affinis; GER: Ceriodaphnia sp.; SIM:

Simocephalus sp.; CER: Ceriodaphnia sp.; MOI: Moina sp.; MAC: Macrothrix sp.; MYT: Mytilina crassipes; PLO: Ploesoma truncatum;

MIC: Microcondon clavus; DIP: Diaphanosoma sp.; LIM: Limnocalanus sp.; EUC: Eucyclops sp.; CAN: Canthocamptus sp.; CYC: Cyclops

vicinus; DIA: Diaptomus sp.; DIAP: Daphnia sp.; (CYP): Cypridopsis sp.; NAU: Copepod nauplii.

Effects of Environmental Parameters on Zooplankton Assemblages 285

selectively prey on larger sized zooplankton and their reproduc-tive success and short developmental rates under favourableconditions in most freshwater systems (Akin-Oriola, 2003;

Imoobe and Adeyinka, 2009). Varying number of zooplanktonspecies and populations were reported by different authors indifferent water bodies in Nigeria. Akin-Oriola (2003) reported

49 species comprising of 32 rotifera, 6 cladocera and protozoaand 4 copepoda in Ogunpa and Ona rivers, Imoobe andAdeyinka (2009) reported 40 species comprising of 16 rotiferas,

12 cladocerans, 12 copepods and 10 calanoids in a Forest River.However, the variability in the number of zooplankton speciesobserved in this study may be attributed to changes in environ-mental parameters and the seasons of sampling.

The observed zooplankton taxa during this study is higherthan the 10 species reported by Yakubu et al. (2000) from NunRiver and 24 species reported by Zabbey et al. (2008) from Imo

River, all in the Niger Delta area, but it is less than the 66 spe-cies reported by Ekwu and Sikoki (2005) in the lower Crossriver estuary. Zooplankton species identified in this study are

ideal in tropical region as Imoobe and Adeyinka (2009) earlierreported the most dominant zooplankton species in West Afri-can freshwater ecosystems to be rotiferas, copepods, clado-

ceras, ostracods and protozoan.According to Jakhar (2013), the zooplankton species type,

number and distribution in any particular aquatic habitatusually create clues on the prevailing physical and chemical

286 W.O. Abdul et al.

conditions of that habitat. Therefore, the interaction betweenvarious environmental variables can either favour the growthor mortality of zooplankton, both spatially and seasonally

(Khanna et al., 2009). Meanwhile, zooplankton have beenunderlined as bio-indicators of aquatic environmental pertur-bation (Abowei and Sikoki, 2005) which might be because of

their easy identification during their period of high density,and high sensitivity to aquatic environmental change com-pared to other aquatic fauna. Also, the diversity, abundance

and seasonality of different zooplankton groups in aquaticecosystem affect different biotic components therein, makingthem have significant potential in assessing aquatic ecosystemhealth. Dirican et al. (2009) reported the prevalence of rotifera

species such as Brachionus and Keratella as indicators ofeutrophic condition in aquatic systems. So also, Rao andDurve (1989) and Padmanabha and Belaghi (2008) confirmed

that the occurrence of species like Filinia longiseta, Brachionusforficula and Brachionus angularis, high level of some ostracodsand cladoceras species such as Bosmina, Moina and Macro-

thrix indicate high level organic pollution as a result of highorganic matter deposit.

According to Varadharajan and Soundarapandian (2013),

the diversity of zooplankton species in aquatic ecosystems islinked to its abundance. The high diversity index recorded inZone I compared to Zones II and III reflected the abundanceof zooplankton in the brushpark area than in the wetland and

open water. High diversity index reported by Varadharajanand Soundarapandian (2013) in Mallipattinam, South eastcoast of India was linked to the presence of the seagrass and

mangrove in the environment. However, such high diversitymight indicate larger food chain, inter-specific interactionand stability among the estuarine zooplankton community.

The ordination of the zooplankton species by canonicalcorrespondence analysis (CCA) showed that the species varia-tion patterns were significantly related to the environmental

heterogeneity patterns observed in the estuary. The nine envi-ronmental significantly explained the principal variations inthe species composition of the zooplankton community. Thephysiological tolerance of zooplanktonic organisms prescribes

the environment where survival and reproduction are possible(Rougier et al., 2005). However, the variable environmentalconditions strongly affect the distribution of zooplankton spe-

cies (Dauvin et al., 1998). The canonical correspondence anal-ysis (CCA) ordination diagram revealed a clear division ofzooplankton species in accordance with their ecological

requirements. The positive correlation between Brachionussp. and salinity is similar to the findings of Silva et al. (2004)in tropical estuary. Wei and Xu (2014) also observed thatNotholca sp. had correlation with salinity and temperature.

Tankx et al. (2004) reported that copepods such as Thermocy-clops crassus, T. oithonoides, Mesocyclops leuckarti, M. gracilisand three cladocerans such as Cyclops reticulate, Leydigia

acanthocercoides and Moina brachiata in Scheldt estuary, Bel-gium were thermophilic in nature. The abundance of zoo-plankton species such as N. labis, Ceriodaphnia sp.,

Limnocalanus sp., and T. agnatha in this study was correlatedwith temperature and transparency. Soltonpour-Gargari andWellershaus (1984) observed that Eurytemora affinis which is

a typical estuarine species of the Northern Hemisphere is aeuryhaline and eurythermic copepod. The species shiftedtowards the peak of its abundance where dissolved oxygen

concentration is high (Sautour and Castel, 1995). In this study,the wide distribution and abundance of zooplankton speciessuch as Branchionus sp., K. longispina, Diaptomus sp., and

Eucyclops sp. were strongly correlated with salinity. Sousaet al. (2008) also reported that Argyrodiaptomus sp., Thermocy-clops sp. and Brachionus calyciflorus had abundance peaks in

environments with higher concentrations of chlorophyll a,whereas B. dolabratus, Kennelia tropica and Hyperthagyllamira were more associated with low transparency. According

to Imoobe and Adeyinka (2009), zooplanktonic organismsare unique bio-indicators of environmental conditions provid-ing early signs of environmental stress in aquatic ecosystemsvia their responses to certain natural or anthropogenic

disturbances.

Conclusion

The study showed that zooplankton organisms are uniqueindicators for pollution status and productivity of aquaticecosystem. The preponderance of zooplankton in the estuary

was a function of environmental parameters. The brushparkarea of the estuary favoured more diverse species of zooplank-ton than other zones, wetland and open water areas. The pres-

ence of some zooplankton in the estuary indicated that therewas a high level of anthropogenic activities in and aroundthe water body. This therefore calls for urgent checks on the

activities around the estuary to enhancing sustainable ecosys-tem health and productivity.

Conflicts of interest

The authors declare that there are no conflicts of interest.

Acknowledgements

We wish to thank the Federal University of Agriculture, Abeo-kuta for providing facilities for the study.

References

Abowei, J.F.N., Sikoki, F.D., 2005. Water Pollution Management and

Control. Doubletrust Publications Company, Nigeria, 236pp.

Adeyemi, S.O., 2012. Preliminary census of zooplanktons and phyto-

plankton community of Ajeko Stream, Iyale, North Central

Nigeria. Anim. Res. Int. 9 (3), 1638–1644.

Akin-Oriola, G.A., 2003. Zooplankton associations and environmen-

tal factors in Ogunpa and Ona Rivers, Nigeria. Rev. Biol. Trop. 51

(2), 391–398.

American Public Health Association (APHA), 1998. Standard Meth-

ods for the Examination of Water and Wastewater, 20th ed.

APHA/AWWA/WEF, Washington DC.

Aneni, I.T., Hassan, A.T., 2003. Effect of pollution on seasonal

abundance of plankton in Kudeti and Onireke streams, Ibadan,

Nigeria. Zoologist 2 (2), 76–83.

Bianchi, F., Acri, F., Aubry, F.B., Berton, A., Boldrin, A., Camatti,

E., Cassin, D., Comaschi, A., 2003. Can plankton communities be

considered as bioindicators of water quality in the lagoon of

Venice? Mar. Pollut. Bull. 46, 964–971.

Dauvin, J.C., Thiebaut, E., Wang, Z., 1998. Short-term changes in the

mesozooplankton community in the Seine ROFI (Region of

Freshwater Influence) (eastern English Channel). J. Plankton Res.

20 (6), 1145–1167.

Effects of Environmental Parameters on Zooplankton Assemblages 287

Dirican, S., Haldun, M., Suleyman, C., 2009. Some physicochemical

characteristics and Rotifers of Camligoze Dam lake, Susehri, Sivas,

Turkey. J. Anim. Vet. Adv. 8 (4), 715–719.

Ekwu, O., Sikoki, F.D., 2005. Species composition and distribution of

zooplankton in the Lower Cross River Estuary. Afr. J. Appl. Zool.

Environ. Biol. 7, 5–10.

Imoobe, T.O.T., 2011. Diversity and seasonal variation of zooplank-

ton in Okhuo River, a tropical forest river in Edo State, Nigeria.

Centrepoint J. 17 (1), 37–51.

Imoobe, T.O.T., Adeyinka, M.L., 2009. Zooplankton-based assess-

ment of the trophic state of a tropical forest river. Arch. Biol. Sci.,

Belgrade 61 (4), 733–740.

Jakhar, P., 2013. Role of phytoplankton and zooplankton as health

indicators of aquatic ecosystem (a review). Int. J. Innovative Res.

Stud. 2 (12), 490–500.

Jha, B.K., Mohan, S.S., Mol, A.A., Moses, R., Babu, M.M., 2014.

Diversity and ecology of phytoplankton in Manakudy estuary,

Kanyakumari, Tamilnadu, India. Int. J. Pure Appl. Zool. 2 (4),

308–314.

Khanna, D.R., Bhutiani, R., Gagan, M., Ginh, V., Kumar, D., Ahraf,

J., 2009. A study of zooplankton with special reference to the

concentration of River Ganga at Haridwar. In: Environ. Conserv.

J. 10 (3), 15–20.

Keister, J.E., Bonnet, D., Chiba, S., Johnson, C.L., Mackas, D.L.,

Escribano, R., 2012. Zooplankton population connections, com-

munity dynamics, and climate variability. ICESJ Mar. Sci. 69, 347–

350.

Kolo, R.J., Ojutiku, R.O.,Musulmi, D.T., 2010. Plankton communities

of Tagwai Dam Minna, Nigeria. Cont. J. Fish. Aquat. Sci. 4, 1–7.

Kress, N., Coto, S.L., Brenes, C.L., Brenner, S., Arroyo, G., 2002.

Horizontal transport and seasonal distribution of nutrients,

dissolved oxygen and chlorophyll a in the Gulf of Nicoya, Costa

Rica: a tropical estuary. Cont. Shelf Res. 22, 51–66.

Marques, S.C., Azeiteiro, U.M., Martinho, F., Pardal, M.A., 2007.

Climate variability and planktonic communities: the effect of an

extreme event (severe drought) in a southern European estuary.

Estuar. Coast. Shelf Sci. 73, 725–734.

Molinero, J.C., Ibanez, F., Nival, P., Buecher, I., Souissi, S., 2005.

North Atlantic climate and north-western Mediterranean plankton

variability. Limnol. Oceanogr. 50, 1213–1220.

Ogbeibu, A.E., Osokpor, O.R., 2004. The effect of impoundment on

the hydrology and rotifers of the Ikpoba River, Nigeria. Biosci Res.

16 (2), 132–138.

Okorafor, K.A., Effanga, E.O., Andem, A.B., George, U.U., Amos,

D.I., 2013. Spatial variation in physical and chemical parameters

and macro-invertebrates in the Intertidal Regions of Calabar River,

Nigeria. Greener J. Geol. Earth Sci. 1 (2), 063–072.

Omori, M., Ikeda, T., 1984. Methods in Marine Zooplankton Ecology.

Wiley, 330p.

Omowaye, O.S., Onimisi, M., Okpanachi, M., 2011. The zooplankton

of Ojofu Lake in Anyigba, Dekina L.G.A., Kogi State, Nigeria.

Int. Ref. Res. J. 2 (2), 114–122.

Padmanabha, B., Belaghi, S.L., 2008. Ostracods as indicators of

pollution in Lake Mysore. J. Environ. Biol. 29 (3), 415–418.

Rao, N.G., Durve, V.S., 1989. Cultural eutrophication of the lake

Rangsagar, Udaipur, Rajasthan. J. Environ. Biol. 10, 127–134.

Rougier, C., Pourriot, R., Lam-Hoai, T., Guiral, D., 2005. Ecological

patterns of the rotifer communities in the Kaw River estuary

(French Guiana). Estuar. Coast. Shelf Sci. 63, 83–91.

Sautour, B., Castel, J., 1995. Comparative spring distribution of

zooplankton in three macrotidal European estuaries. Hydrobiolo-

gia 311, 139–151.

Silva, A.P., Neumann-Leitao, S., Schwamborn, R., Gusmao, L.M.O.,

Silva, T.A., 2004. Mesozooplankton of an impacted bay in North

Eastern Brazil. Braz. Arch. Biol. Tech. 47 (3), 485–493.

Soltanpour-Gargari, A., Wellershaus, X., 1984. Eurytemora affinis –

the estuarine plankton copepod in the Weser. Vero¨ff. Inst.

Meeresforsch. Bremerh. 20, 103–117.

Sousa, W., Attayde, J.L., Rocha, E.S., Anna, E.M.E., 2008. The

response of zooplankton assemblages to variations in the water

quality of four man-made lakes in semi-aridnortheastern Brazil. J.

Plankton Res. 30, 699–708.

Tackx, M.L.M., De Pauw, N., Mieghem, R.V., Aze´mar, F., Hannouti,

A., Van-Damme, S., Fiers, F., Daro, N., Meire, P., 2004.

Zooplankton in the Schelde estuary, Belgium and The

Netherlands. Spatial and temporal patterns. J. Plankton Res. 26

(2), 133–141.

Varadharajan, D., Soundarapandian, P., 2013. Zooplankton

abundance and diversity from Pointcalimere to Manamelkudi,

South East Coast of India. J. Earth Sci. Clim. Change 4 (5),

151–161.

Wei, N., Xu, R., 2014. Distinct difference of littoral rotifer community

structure in two mangrove wetlands of Qi’ao Island, Pearl River

estuary, China. Zool. Stud. 53 (30), 1–12.

Xuelu, G.A.O., Jinming, S., Xuegang, L., 2011. Zooplankton spatial

and diurnal variations in the Changjiang River estuary before

operation of the Three Gorges Dam. Chin. J. Oceanol. Limnol. 29

(3), 591–602.

Yakubu, F., Sikoki, F.D., Abowei, J.F.N., Hart, S.A., 2000. A

comparative study of phytoplankton communities of some rivers

creeks and borrow pits in the Niger Delta Area. J. Appl. Sci.

Environ. Manage. 4 (2), 41–46.

Yigit, S., 2006. Analysis of the zooplankton community by the

Shannon-Weaver index in Kesikkopru Dam Lake, Turkey. Tarim

Bilimleri Dergisi 12 (2), 216–220.

Zabbey, N., Sikoki, F.D., Erondu, J., 2008. Plankton assemblages and

environmental gradients in the middle reach of the Imo River,

Niger Delta Nigeria. Afr. J. Aquat. Sci. 33 (2), 241–248.