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The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria
Egyptian Journal of Aquatic Research (2016) xxx, xxx–xxx
H O S T E D BY
National Institute of Oceanography and Fisheries
Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com
FULL LENGTH ARTICLE
The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria Waidi O. Abdul a,*, Ezekiel O. Adekoya a, Kehinde O. Ademolu b, Isaac T. Omoniyi a, Dominic O. Odulate a, Tomilola E. Akindokun a, Akinpelu E. Olajide a a b
Department of Aquaculture and Fisheries Management, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria Department of Zoology, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria
Received 1 February 2016; revised 22 March 2016; accepted 30 May 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. Ó 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 influenced by the inflow from the sea and adjacent fresh waters; this leads to give it a unique high nutrient level at both the water * Corresponding author. Tel.: +234 8183429107. E-mail addresses: [email protected], [email protected] (W.O. Abdul). Peer review under responsibility of National Institute of Oceanography and Fisheries.
column and sediment (Jha et al., 2014). According to Kress et al. (2002), estuaries are places for human settlements and activities (navigation, shipping, urban, industrial wastes) which make them vulnerable to changes as a result of pollution, climatic change and overfishing, which all in turn alter the productivity of the water. The variation in the physical and chemical processes that occur in estuaries is reflected in the dynamics of the biological populations, particularly planktonic community (Marques et al., 2007). Zooplankton play a key position in the food web and also influence the functioning and productivity of aquatic ecosystems
http://dx.doi.org/10.1016/j.ejar.2016.05.005 1687-4285 Ó 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/). Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
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through their impact on the nutrient dynamics (Keister et al., 2012), from pleuston to benthos (Varadharajan and Soundarapandian, 2013). According to Omori and Ikeda (1984), the composition and abundance of zooplankton vary in aquatic environments. This makes their biomass ecologically very important because of its uses for monitoring eutrophication, pollution, global warming and environmental problems, in cases of long-term changes. Also, their abundance can be altered by spatio-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 climate change. However, to a certain extent the success and failure of a fishery is dependent on the availability of plankton particularly zooplankton. Xuelu et al. (2011) have observed high concentrations 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 sustainable management of fishery resources hence, predicting the impact of human activities on the fisheries. This study attempted to investigate the distribution and assemblage structure of zooplankton in relation to the environmental parameters of a tropical coastal estuary that impounds the Bight of Benin 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
located between 6°200 N–6°450 N and 4°15|0 E–4°300 E and bounded by Lagos Lagoon to the south-east and to the south by the Bight of Benin (Fig. 1). The water is connected to Atlantic 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 distinct ecological characteristics. The zooplankton samples were collected at daylight hours (11.00–14.00 h) by towing a 55 lm mesh Hydrobios plankton net tied to a 25Hp engine powered canoe driven at low speed just below the water surface at a depth between 50 and 60 cm for 5 min. Collected samples were immediately transferred each time to a 250 ml labelled plastic container with screw cap. Ten samples were collected from each zone and then preserved with 4% formaldehyde prior to microscopic analysis (Yig˘it, 2006; Kolo et al., 2010) at different magnifications (50, 100 and 400). Appropriate guide (APHA, 1998) was used to aid species identification. Zooplankton community structure analysis Zooplankton community structure was analysed using three univariate indices (Shannon and Wiener diversity index, Margalef richness index and Pielou’s evenness index) to express the degree of uniformity in the distribution of individuals among taxa in the study area (Imoobe and Adeyinka, 2009). Data collected were used to establish relationship between zooplankton distribution and environmental variables using canonical correspondence analysis, a sub-routine of Paleontological
Nigeria
Zone I
Zone II
Zone III
Ogun State The study area
Figure 1
Map of tropical estuarine ecosystem around Bight of Benin, Nigeria.
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
Effects of Environmental Parameters on Zooplankton Assemblages Statistics (PAST) Package version 2.41, and cluster analysis was also carried out using the Bray–Curtis index. Environmental parameters Environmental parameters (water temperature, dissolved oxygen, 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 analysed ex-situ using standard methods for water examination (APHA, 1998). Analysis of variance (ANOVA) was used to test for significant difference (p < 0.05) of environmental parameters in the zones of the estuary. Results Spatial distribution and relative abundance of zooplankton Table 1 shows the distribution and relative abundance of zooplankton in the coastal estuary during this study. Four classes of zooplankton comprising of twenty-eight (28) species were identified during the study. These included twelve (12) species of rotifera, seven (7) species of copepoda, eight (8) species of cladocerans and a species of ostracoda. All identified samples
Table 1
3
were detected in zones I and II except Kellicottia longispina which was not detected in zone III. In all, the rotifera species, Notholca labis, Keratella cochlearis, and Ploesoma truncatum, were respectively found dominant in Zone I (61.11%), Zone II (41.18%), and Zone III (72.73%), while Ploesoma truncatum (11.76%), N. labis (11.11%) and K. cochlearis (9.09%) had the least relative abundance in Zones I, II and III respectively. In the class Rotifera, the species with the maximum and minimum number of individuals were Lecane (287 individuals/ml) and Platyias quadricornis (35individuals/ml) respectively. Only one species of the class Ostracoda (Cypridopsis sp.) was recorded in high numbers 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 relative 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 Zone II and Ceriodaphnia sp. in Zone I, with each having a relative abundance of 85.72%, 68.18% and 57.14% respectively.
Distribution and relative abundance of zooplankton species in a tropical estuarine ecosystem around Bight of Benin, Nigeria.
Taxa
Species
Zone I number/ml
Zone II number/ml
Zone III number/ml
Mean number/ml
ROTIFERA
Lecane sp. Filinia longiseta Branchionus sp. Platyias quadricornis Notholca labis Keratella cochlearis Trichocerca agnatha Kellicotia longispina Mytilina crassipes Ploesoma truncatum Microcondon clavus Callotheca adriatica
147(17.07) 84(40.00) 84(50.00) 42(40.00) 231(61.11) 42(18.18) 147(58.33) 84(57.14) 168(38.09) 84(11.76) 105(14.70) 294(56.00)
441(51.22) 84(40.00) 63(37.50) 42(40.00) 42(11.11) 168(72.73) 42(16.67) 63(42.85) 147(33.33) 336(47.05) 378(52.94) 147(28.00)
273(31.71) 42(20.00) 21(12.5) 21(20.00) 105(27.28) 21(9.09) 63(25.00) 0(0.00) 126(28.51) 294(41.18) 231(32.35) 84(16.00)
287 70 56 35 126 77 84 49 147 238 238 175
OSTRACODA
Cypridopsis sp.
147(25.93)
294(51.85)
126(22.22)
189
COPEPODA
Cyclops vicinus Diaptomus sp. Copepod nauplii Canthocamptus sp. Diaphanosoma sp. Eucyclops sp. Limnocalanus sp.
42(13.33) 63(30.00) 168(30.76) 126(46.15) 294(70.00) 105(62.50) 210(76.92)
189(60.00) 21(10.00) 126(23.07) 84(30.77) 105(25.00) 42(25.00) 21(7.69)
84(26.67) 126(60.00) 252(46.15) 63(23.57) 21(5.00) 21(12.50) 42(15.38)
105 70 182 91 140 56 91
CLADOCERANS
Macrothrix sp. Moina sp. Ceriodaphnia sp. Simocephalus sp. Ceriodaphnia sp. Alona affinis Bosmina sp. Daphnia sp.
126(27.27) 168(32.00) 21(7.14) 42(13.33) 252(57.14) 105(17.24) 189(37.50) 21(8.33)
315(68.18) 189(36.00) 21(7.14) 105(33.33) 63(14.28) 210(34.48) 42(8.33) 168(66.67)
21(4.54) 168(32.00) 252((85.72) 168(53.33) 126(28.57) 294(48.28) 273(54.67) 63(25.00)
154 175 98 105 147 203 168 84
3591
3948
3381
3640
Total * *
Values in parenthesis are percentages of relative abundance (%) of zooplankton species. Values are rated across zones on species basis.
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
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Meanwhile, Ceriodaphnia sp. had the least relative abundance in Zones I and II (13.33% and 33.33% respectively) and Macrothrix sp. had the least in Zone III (4.54%). Alona affinis and Ceriodaphnia sp. had the respective maximum (203individuals/ml) and minimum (individuals/ml) in the class Cladocerans as shown in Table 1.
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 ± 0.20a 6.52 ± 0.36a 483.83 ± 94.52a
28.35 ± 0.22a 6.70 ± 0.24a 537.17 ± 86.55a
28.35 ± 0.16a 6.550.40a
28.34 ± 0.07 6.590.12
489.33 ± 83.07a
503.44 ± 33.99
9.15 ± 0.59a 0.43 ± 0.08a 0.25 ± 0.02a 0.20 ± 0.07a 31.80 ± 2.46a 0.046 ± 0.00a
9.43 ± 0.31a 0.46 ± 0.11a 0.27 ± 0.02a 0.20 ± 0.07a 31.63 ± 2.06a 0.039 ± 0.00a
9.17 ± 0.49a 0.47 ± 0.11a 0.25 ± 0.04a 0.19 ± 0.06a 30.97 ± 1.45a 0.043 ± 0.00a
9.25 ± 0.13 0.45 ± 0.04 0.26 ± 0.02 0.20 ± 0.02 31.47 ± 0.71 0.033 ± 0.005
pH
Species diversity and richness indices of zooplankton Table 2 shows the value of species diversity, richness and evenness indices of zooplankton in the coastal estuary. In Zone I, the Shannon–Wienner index, Margalef richness index and Pielou’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, 3.091 and 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, analysis of variance (ANOVA) showed no significant difference (p > 0.05) in the environmental parameters of the three investigated zones in the study area. The maximum mean water temperature (28.35 ± 0.16 °C) was recorded in Zones II and III and least (28.33 ± 0.20 °C) in Zone I. Also, the mean pH values of 6.52 ± 0.36, 6.70 ± 0.24 and 6.55 ± 0.40 were recorded in Zones I, II and III respectively. The estuarine mean electrical conductivity value, 503.44 ls/cm, was recorded in this study with the maximum, 537.17 ls/cm, recorded in Zone II and the minimum, 483.83 ls/cm, in Zone I. The average dissolved oxygen concentrations were 9.15 ± 0.59 mg/l, 9.43 ± 0.31 mg/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, while estuarine transparency ranged between 31.63 ± 2.06 cm and 30.97 ± 1.45 cm. The chlorophyll a concentration of the estuary 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 parameters and zooplankton species
Electrical conductivity (ls/ cm) Dissolved oxygen (mg/l) Salinity (‰) Phosphate content (mg/l) Nitrate content (mg/l) Transparency (cm) Chlorophyll a (mg/l) *
Means with similar superscript show that there were not significantly (p > 0.05) different.
to the three zones are presented in Fig. 2. Axis 1, which accounted for a total variance of 57.41%, was positively correlated with temperature and transparency but negatively correlated with chlorophyll a and dissolved oxygen. Axis 2 showed 42.59% variation, and it was positively correlated with salinity and negatively correlated with phosphate, nitrate and electrical conductivity. 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 zooplankton such as N. labis, Ceriodaphnia sp., Limnocalanus sp., Trichocerca agnatha were all strongly and negatively influenced by chlorophyll a and dissolved oxygen but impacted positively by transparency and temperature. The cluster analysis by hierarchical classification of the identified zooplankton species revealed five distinct groups at 0.54–0.72% similarity level as shown in the dendrogram (Fig. 3). Discussion
The triplot of canonical correspondence analysis (CCA) for environmental parameters and zooplankton species in relation
Table 2 Species diversity, richness, and evenness of zooplankton in tropical estuarine ecosystem around Bight of Benin, Nigeria. Indices
Zone I
Zone II
Zone III
Total number of species Total number of Individuals Shannon-Wiener Index Pielou Evenness Index Margalef Richness Index
28 3591 3.108 0.829 3.192
28 3948 2.982 0.731 3.169
27 3381 2.954 0.737 3.091
Four taxonomic groups of zooplankton were identified in this study and each group was widely distributed in all the sampling zones. However, rotifera group dominated the species identified, followed by cladocera, copepod, and ostracoda. Similar high dominance of rotiferas was reported by Adeyemi (2012) in Ajelo stream, Imoobe (2011) in Okhuo River and Omowaye et al. (2011) in Ojofu Lake. On the contrary, it disagrees with the study of Okorafor et al. (2013) in Calabar River where cladocerans and copepods dominated the observed zooplankton taxa. Meanwhile, the dominance of rotiferas in Nigerian aquatic ecosystems has also been documented by some other authors (Aneni and Hassan 2003; Ogbeibu and Osokpor, 2004). The dominance of rotiferas was explained to be due to predation pressure from planktivorous fishes that
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
Effects of Environmental Parameters on Zooplankton Assemblages
5
MAC
KER
1.5 DAP CYC
0.5 Zone_II
MICLEC PLO -1
-1.5
BRA Salinity
FIL PLA MYT
0.5
CAN Zone_I
SIM
1
1.5
2
2.5
LIM
TRI
-0.5 Zone_III ALO Nitrate
DIAP EUC
CAL
MOI
-0.5
Axis 2
-2
KEL
1 Transparency Temperature
Chlorophlly_a GER NOT DO
-1 NAU ECPhosphate
pH
-1.5 BOS
DIA -2 -2.5 CER
-3 Axis 1
CAL_
DIP
LIM
GER
NOT
PLA
KEL
BRA
FIL
EC
CAN
TRI
CER
DIA
SIM
DAP
CYC
KER
MAC
CRP
ALO
LEC
PLO
MIC
BOS
NAU
MOI
MYT
Figure 2 Canonical correspondence analysis between the water quality parameters and zooplankton species of a tropical estuarine ecosystem around Bight of Benin, Nigeria.
0.96
0.9
0.84
Similarity
0.78
0.72
0.66
0.6
0.54
0.48
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.
selectively prey on larger sized zooplankton and their reproductive success and short developmental rates under favourable conditions in most freshwater systems (Akin-Oriola, 2003; Imoobe and Adeyinka, 2009). Varying number of zooplankton species and populations were reported by different authors in different water bodies in Nigeria. Akin-Oriola (2003) reported 49 species comprising of 32 rotifera, 6 cladocera and protozoa and 4 copepoda in Ogunpa and Ona rivers, Imoobe and Adeyinka (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 species observed in this study may be attributed to changes in environmental parameters and the seasons of sampling.
The observed zooplankton taxa during this study is higher than the 10 species reported by Yakubu et al. (2000) from Nun River 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 species reported by Ekwu and Sikoki (2005) in the lower Cross river estuary. Zooplankton species identified in this study are ideal in tropical region as Imoobe and Adeyinka (2009) earlier reported the most dominant zooplankton species in West African freshwater ecosystems to be rotiferas, copepods, cladoceras, ostracods and protozoan. According to Jakhar (2013), the zooplankton species type, number and distribution in any particular aquatic habitat usually create clues on the prevailing physical and chemical
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
6 conditions of that habitat. Therefore, the interaction between various environmental variables can either favour the growth or mortality of zooplankton, both spatially and seasonally (Khanna et al., 2009). Meanwhile, zooplankton have been underlined as bio-indicators of aquatic environmental perturbation (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 compared to other aquatic fauna. Also, the diversity, abundance and seasonality of different zooplankton groups in aquatic ecosystem affect different biotic components therein, making them have significant potential in assessing aquatic ecosystem health. Dirican et al. (2009) reported the prevalence of rotifera species such as Brachionus and Keratella as indicators of eutrophic condition in aquatic systems. So also, Rao and Durve (1989) and Padmanabha and Belaghi (2008) confirmed that the occurrence of species like Filinia longiseta, Brachionus forficula and Brachionus angularis, high level of some ostracods and cladoceras species such as Bosmina, Moina and Macrothrix indicate high level organic pollution as a result of high organic matter deposit. According to Varadharajan and Soundarapandian (2013), the diversity of zooplankton species in aquatic ecosystems is linked to its abundance. The high diversity index recorded in Zone I compared to Zones II and III reflected the abundance of zooplankton in the brushpark area than in the wetland and open water. High diversity index reported by Varadharajan and Soundarapandian (2013) in Mallipattinam, South east coast of India was linked to the presence of the seagrass and mangrove in the environment. However, such high diversity might indicate larger food chain, inter-specific interaction and stability among the estuarine zooplankton community. The ordination of the zooplankton species by canonical correspondence analysis (CCA) showed that the species variation patterns were significantly related to the environmental heterogeneity patterns observed in the estuary. The nine environmental significantly explained the principal variations in the species composition of the zooplankton community. The physiological tolerance of zooplanktonic organisms prescribes the environment where survival and reproduction are possible (Rougier et al., 2005). However, the variable environmental conditions strongly affect the distribution of zooplankton species (Dauvin et al., 1998). The canonical correspondence analysis (CCA) ordination diagram revealed a clear division of zooplankton species in accordance with their ecological requirements. The positive correlation between Brachionus sp. and salinity is similar to the findings of Silva et al. (2004) in tropical estuary. Wei and Xu (2014) also observed that Notholca sp. had correlation with salinity and temperature. Tankx et al. (2004) reported that copepods such as Thermocyclops crassus, T. oithonoides, Mesocyclops leuckarti, M. gracilis and three cladocerans such as Cyclops reticulate, Leydigia acanthocercoides and Moina brachiata in Scheldt estuary, Belgium were thermophilic in nature. The abundance of zooplankton species such as N. labis, Ceriodaphnia sp., Limnocalanus sp., and T. agnatha in this study was correlated with temperature and transparency. Soltonpour-Gargari and Wellershaus (1984) observed that Eurytemora affinis which is a typical estuarine species of the Northern Hemisphere is a euryhaline and eurythermic copepod. The species shifted towards the peak of its abundance where dissolved oxygen
W.O. Abdul et al. concentration is high (Sautour and Castel, 1995). In this study, the wide distribution and abundance of zooplankton species such as Branchionus sp., K. longispina, Diaptomus sp., and Eucyclops sp. were strongly correlated with salinity. Sousa et al. (2008) also reported that Argyrodiaptomus sp., Thermocyclops sp. and Brachionus calyciflorus had abundance peaks in environments with higher concentrations of chlorophyll a, whereas B. dolabratus, Kennelia tropica and Hyperthagylla mira were more associated with low transparency. According to Imoobe and Adeyinka (2009), zooplanktonic organisms are unique bio-indicators of environmental conditions providing early signs of environmental stress in aquatic ecosystems via their responses to certain natural or anthropogenic disturbances. Conclusion The study showed that zooplankton organisms are unique indicators for pollution status and productivity of aquatic ecosystem. The preponderance of zooplankton in the estuary was a function of environmental parameters. The brushpark area of the estuary favoured more diverse species of zooplankton than other zones, wetland and open water areas. The presence of some zooplankton in the estuary indicated that there was a high level of anthropogenic activities in and around the water body. This therefore calls for urgent checks on the activities around the estuary to enhancing sustainable ecosystem 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, Abeokuta 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 phytoplankton community of Ajeko Stream, Iyale, North Central Nigeria. Anim. Res. Int. 9 (3), 1638–1644. Akin-Oriola, G.A., 2003. Zooplankton associations and environmental factors in Ogunpa and Ona Rivers, Nigeria. Rev. Biol. Trop. 51 (2), 391–398. American Public Health Association (APHA), 1998. Standard Methods 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., Thie´baut, 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.
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Effects of Environmental Parameters on Zooplankton Assemblages 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 zooplankton 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 assessment 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, community 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.
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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. Hydrobiologia 311, 139–151. Silva, A.P., Neumann-Leita˜o, S., Schwamborn, R., Gusma˜o, 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. Yig˘it, S., 2006. Analysis of the zooplankton community by the Shannon-Weaver index in Kesikko¨pru¨ 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.
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National Institute of Oceanography and Fisheries
Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com
FULL LENGTH ARTICLE
The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria Waidi O. Abdul a,*, Ezekiel O. Adekoya a, Kehinde O. Ademolu b, Isaac T. Omoniyi a, Dominic O. Odulate a, Tomilola E. Akindokun a, Akinpelu E. Olajide a a b
Department of Aquaculture and Fisheries Management, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria Department of Zoology, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria
Received 1 February 2016; revised 22 March 2016; accepted 30 May 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. Ó 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 influenced by the inflow from the sea and adjacent fresh waters; this leads to give it a unique high nutrient level at both the water * Corresponding author. Tel.: +234 8183429107. E-mail addresses: [email protected], [email protected] (W.O. Abdul). Peer review under responsibility of National Institute of Oceanography and Fisheries.
column and sediment (Jha et al., 2014). According to Kress et al. (2002), estuaries are places for human settlements and activities (navigation, shipping, urban, industrial wastes) which make them vulnerable to changes as a result of pollution, climatic change and overfishing, which all in turn alter the productivity of the water. The variation in the physical and chemical processes that occur in estuaries is reflected in the dynamics of the biological populations, particularly planktonic community (Marques et al., 2007). Zooplankton play a key position in the food web and also influence the functioning and productivity of aquatic ecosystems
http://dx.doi.org/10.1016/j.ejar.2016.05.005 1687-4285 Ó 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/). Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
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through their impact on the nutrient dynamics (Keister et al., 2012), from pleuston to benthos (Varadharajan and Soundarapandian, 2013). According to Omori and Ikeda (1984), the composition and abundance of zooplankton vary in aquatic environments. This makes their biomass ecologically very important because of its uses for monitoring eutrophication, pollution, global warming and environmental problems, in cases of long-term changes. Also, their abundance can be altered by spatio-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 climate change. However, to a certain extent the success and failure of a fishery is dependent on the availability of plankton particularly zooplankton. Xuelu et al. (2011) have observed high concentrations 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 sustainable management of fishery resources hence, predicting the impact of human activities on the fisheries. This study attempted to investigate the distribution and assemblage structure of zooplankton in relation to the environmental parameters of a tropical coastal estuary that impounds the Bight of Benin 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
located between 6°200 N–6°450 N and 4°15|0 E–4°300 E and bounded by Lagos Lagoon to the south-east and to the south by the Bight of Benin (Fig. 1). The water is connected to Atlantic 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 distinct ecological characteristics. The zooplankton samples were collected at daylight hours (11.00–14.00 h) by towing a 55 lm mesh Hydrobios plankton net tied to a 25Hp engine powered canoe driven at low speed just below the water surface at a depth between 50 and 60 cm for 5 min. Collected samples were immediately transferred each time to a 250 ml labelled plastic container with screw cap. Ten samples were collected from each zone and then preserved with 4% formaldehyde prior to microscopic analysis (Yig˘it, 2006; Kolo et al., 2010) at different magnifications (50, 100 and 400). Appropriate guide (APHA, 1998) was used to aid species identification. Zooplankton community structure analysis Zooplankton community structure was analysed using three univariate indices (Shannon and Wiener diversity index, Margalef richness index and Pielou’s evenness index) to express the degree of uniformity in the distribution of individuals among taxa in the study area (Imoobe and Adeyinka, 2009). Data collected were used to establish relationship between zooplankton distribution and environmental variables using canonical correspondence analysis, a sub-routine of Paleontological
Nigeria
Zone I
Zone II
Zone III
Ogun State The study area
Figure 1
Map of tropical estuarine ecosystem around Bight of Benin, Nigeria.
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
Effects of Environmental Parameters on Zooplankton Assemblages Statistics (PAST) Package version 2.41, and cluster analysis was also carried out using the Bray–Curtis index. Environmental parameters Environmental parameters (water temperature, dissolved oxygen, 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 analysed ex-situ using standard methods for water examination (APHA, 1998). Analysis of variance (ANOVA) was used to test for significant difference (p < 0.05) of environmental parameters in the zones of the estuary. Results Spatial distribution and relative abundance of zooplankton Table 1 shows the distribution and relative abundance of zooplankton in the coastal estuary during this study. Four classes of zooplankton comprising of twenty-eight (28) species were identified during the study. These included twelve (12) species of rotifera, seven (7) species of copepoda, eight (8) species of cladocerans and a species of ostracoda. All identified samples
Table 1
3
were detected in zones I and II except Kellicottia longispina which was not detected in zone III. In all, the rotifera species, Notholca labis, Keratella cochlearis, and Ploesoma truncatum, were respectively found dominant in Zone I (61.11%), Zone II (41.18%), and Zone III (72.73%), while Ploesoma truncatum (11.76%), N. labis (11.11%) and K. cochlearis (9.09%) had the least relative abundance in Zones I, II and III respectively. In the class Rotifera, the species with the maximum and minimum number of individuals were Lecane (287 individuals/ml) and Platyias quadricornis (35individuals/ml) respectively. Only one species of the class Ostracoda (Cypridopsis sp.) was recorded in high numbers 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 relative 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 Zone II and Ceriodaphnia sp. in Zone I, with each having a relative abundance of 85.72%, 68.18% and 57.14% respectively.
Distribution and relative abundance of zooplankton species in a tropical estuarine ecosystem around Bight of Benin, Nigeria.
Taxa
Species
Zone I number/ml
Zone II number/ml
Zone III number/ml
Mean number/ml
ROTIFERA
Lecane sp. Filinia longiseta Branchionus sp. Platyias quadricornis Notholca labis Keratella cochlearis Trichocerca agnatha Kellicotia longispina Mytilina crassipes Ploesoma truncatum Microcondon clavus Callotheca adriatica
147(17.07) 84(40.00) 84(50.00) 42(40.00) 231(61.11) 42(18.18) 147(58.33) 84(57.14) 168(38.09) 84(11.76) 105(14.70) 294(56.00)
441(51.22) 84(40.00) 63(37.50) 42(40.00) 42(11.11) 168(72.73) 42(16.67) 63(42.85) 147(33.33) 336(47.05) 378(52.94) 147(28.00)
273(31.71) 42(20.00) 21(12.5) 21(20.00) 105(27.28) 21(9.09) 63(25.00) 0(0.00) 126(28.51) 294(41.18) 231(32.35) 84(16.00)
287 70 56 35 126 77 84 49 147 238 238 175
OSTRACODA
Cypridopsis sp.
147(25.93)
294(51.85)
126(22.22)
189
COPEPODA
Cyclops vicinus Diaptomus sp. Copepod nauplii Canthocamptus sp. Diaphanosoma sp. Eucyclops sp. Limnocalanus sp.
42(13.33) 63(30.00) 168(30.76) 126(46.15) 294(70.00) 105(62.50) 210(76.92)
189(60.00) 21(10.00) 126(23.07) 84(30.77) 105(25.00) 42(25.00) 21(7.69)
84(26.67) 126(60.00) 252(46.15) 63(23.57) 21(5.00) 21(12.50) 42(15.38)
105 70 182 91 140 56 91
CLADOCERANS
Macrothrix sp. Moina sp. Ceriodaphnia sp. Simocephalus sp. Ceriodaphnia sp. Alona affinis Bosmina sp. Daphnia sp.
126(27.27) 168(32.00) 21(7.14) 42(13.33) 252(57.14) 105(17.24) 189(37.50) 21(8.33)
315(68.18) 189(36.00) 21(7.14) 105(33.33) 63(14.28) 210(34.48) 42(8.33) 168(66.67)
21(4.54) 168(32.00) 252((85.72) 168(53.33) 126(28.57) 294(48.28) 273(54.67) 63(25.00)
154 175 98 105 147 203 168 84
3591
3948
3381
3640
Total * *
Values in parenthesis are percentages of relative abundance (%) of zooplankton species. Values are rated across zones on species basis.
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
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Meanwhile, Ceriodaphnia sp. had the least relative abundance in Zones I and II (13.33% and 33.33% respectively) and Macrothrix sp. had the least in Zone III (4.54%). Alona affinis and Ceriodaphnia sp. had the respective maximum (203individuals/ml) and minimum (individuals/ml) in the class Cladocerans as shown in Table 1.
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 ± 0.20a 6.52 ± 0.36a 483.83 ± 94.52a
28.35 ± 0.22a 6.70 ± 0.24a 537.17 ± 86.55a
28.35 ± 0.16a 6.550.40a
28.34 ± 0.07 6.590.12
489.33 ± 83.07a
503.44 ± 33.99
9.15 ± 0.59a 0.43 ± 0.08a 0.25 ± 0.02a 0.20 ± 0.07a 31.80 ± 2.46a 0.046 ± 0.00a
9.43 ± 0.31a 0.46 ± 0.11a 0.27 ± 0.02a 0.20 ± 0.07a 31.63 ± 2.06a 0.039 ± 0.00a
9.17 ± 0.49a 0.47 ± 0.11a 0.25 ± 0.04a 0.19 ± 0.06a 30.97 ± 1.45a 0.043 ± 0.00a
9.25 ± 0.13 0.45 ± 0.04 0.26 ± 0.02 0.20 ± 0.02 31.47 ± 0.71 0.033 ± 0.005
pH
Species diversity and richness indices of zooplankton Table 2 shows the value of species diversity, richness and evenness indices of zooplankton in the coastal estuary. In Zone I, the Shannon–Wienner index, Margalef richness index and Pielou’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, 3.091 and 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, analysis of variance (ANOVA) showed no significant difference (p > 0.05) in the environmental parameters of the three investigated zones in the study area. The maximum mean water temperature (28.35 ± 0.16 °C) was recorded in Zones II and III and least (28.33 ± 0.20 °C) in Zone I. Also, the mean pH values of 6.52 ± 0.36, 6.70 ± 0.24 and 6.55 ± 0.40 were recorded in Zones I, II and III respectively. The estuarine mean electrical conductivity value, 503.44 ls/cm, was recorded in this study with the maximum, 537.17 ls/cm, recorded in Zone II and the minimum, 483.83 ls/cm, in Zone I. The average dissolved oxygen concentrations were 9.15 ± 0.59 mg/l, 9.43 ± 0.31 mg/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, while estuarine transparency ranged between 31.63 ± 2.06 cm and 30.97 ± 1.45 cm. The chlorophyll a concentration of the estuary 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 parameters and zooplankton species
Electrical conductivity (ls/ cm) Dissolved oxygen (mg/l) Salinity (‰) Phosphate content (mg/l) Nitrate content (mg/l) Transparency (cm) Chlorophyll a (mg/l) *
Means with similar superscript show that there were not significantly (p > 0.05) different.
to the three zones are presented in Fig. 2. Axis 1, which accounted for a total variance of 57.41%, was positively correlated with temperature and transparency but negatively correlated with chlorophyll a and dissolved oxygen. Axis 2 showed 42.59% variation, and it was positively correlated with salinity and negatively correlated with phosphate, nitrate and electrical conductivity. 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 zooplankton such as N. labis, Ceriodaphnia sp., Limnocalanus sp., Trichocerca agnatha were all strongly and negatively influenced by chlorophyll a and dissolved oxygen but impacted positively by transparency and temperature. The cluster analysis by hierarchical classification of the identified zooplankton species revealed five distinct groups at 0.54–0.72% similarity level as shown in the dendrogram (Fig. 3). Discussion
The triplot of canonical correspondence analysis (CCA) for environmental parameters and zooplankton species in relation
Table 2 Species diversity, richness, and evenness of zooplankton in tropical estuarine ecosystem around Bight of Benin, Nigeria. Indices
Zone I
Zone II
Zone III
Total number of species Total number of Individuals Shannon-Wiener Index Pielou Evenness Index Margalef Richness Index
28 3591 3.108 0.829 3.192
28 3948 2.982 0.731 3.169
27 3381 2.954 0.737 3.091
Four taxonomic groups of zooplankton were identified in this study and each group was widely distributed in all the sampling zones. However, rotifera group dominated the species identified, followed by cladocera, copepod, and ostracoda. Similar high dominance of rotiferas was reported by Adeyemi (2012) in Ajelo stream, Imoobe (2011) in Okhuo River and Omowaye et al. (2011) in Ojofu Lake. On the contrary, it disagrees with the study of Okorafor et al. (2013) in Calabar River where cladocerans and copepods dominated the observed zooplankton taxa. Meanwhile, the dominance of rotiferas in Nigerian aquatic ecosystems has also been documented by some other authors (Aneni and Hassan 2003; Ogbeibu and Osokpor, 2004). The dominance of rotiferas was explained to be due to predation pressure from planktivorous fishes that
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
Effects of Environmental Parameters on Zooplankton Assemblages
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MAC
KER
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CAN Zone_I
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Chlorophlly_a GER NOT DO
-1 NAU ECPhosphate
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CAL_
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CRP
ALO
LEC
PLO
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Figure 2 Canonical correspondence analysis between the water quality parameters and zooplankton species of a tropical estuarine ecosystem around Bight of Benin, Nigeria.
0.96
0.9
0.84
Similarity
0.78
0.72
0.66
0.6
0.54
0.48
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.
selectively prey on larger sized zooplankton and their reproductive success and short developmental rates under favourable conditions in most freshwater systems (Akin-Oriola, 2003; Imoobe and Adeyinka, 2009). Varying number of zooplankton species and populations were reported by different authors in different water bodies in Nigeria. Akin-Oriola (2003) reported 49 species comprising of 32 rotifera, 6 cladocera and protozoa and 4 copepoda in Ogunpa and Ona rivers, Imoobe and Adeyinka (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 species observed in this study may be attributed to changes in environmental parameters and the seasons of sampling.
The observed zooplankton taxa during this study is higher than the 10 species reported by Yakubu et al. (2000) from Nun River 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 species reported by Ekwu and Sikoki (2005) in the lower Cross river estuary. Zooplankton species identified in this study are ideal in tropical region as Imoobe and Adeyinka (2009) earlier reported the most dominant zooplankton species in West African freshwater ecosystems to be rotiferas, copepods, cladoceras, ostracods and protozoan. According to Jakhar (2013), the zooplankton species type, number and distribution in any particular aquatic habitat usually create clues on the prevailing physical and chemical
Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005
6 conditions of that habitat. Therefore, the interaction between various environmental variables can either favour the growth or mortality of zooplankton, both spatially and seasonally (Khanna et al., 2009). Meanwhile, zooplankton have been underlined as bio-indicators of aquatic environmental perturbation (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 compared to other aquatic fauna. Also, the diversity, abundance and seasonality of different zooplankton groups in aquatic ecosystem affect different biotic components therein, making them have significant potential in assessing aquatic ecosystem health. Dirican et al. (2009) reported the prevalence of rotifera species such as Brachionus and Keratella as indicators of eutrophic condition in aquatic systems. So also, Rao and Durve (1989) and Padmanabha and Belaghi (2008) confirmed that the occurrence of species like Filinia longiseta, Brachionus forficula and Brachionus angularis, high level of some ostracods and cladoceras species such as Bosmina, Moina and Macrothrix indicate high level organic pollution as a result of high organic matter deposit. According to Varadharajan and Soundarapandian (2013), the diversity of zooplankton species in aquatic ecosystems is linked to its abundance. The high diversity index recorded in Zone I compared to Zones II and III reflected the abundance of zooplankton in the brushpark area than in the wetland and open water. High diversity index reported by Varadharajan and Soundarapandian (2013) in Mallipattinam, South east coast of India was linked to the presence of the seagrass and mangrove in the environment. However, such high diversity might indicate larger food chain, inter-specific interaction and stability among the estuarine zooplankton community. The ordination of the zooplankton species by canonical correspondence analysis (CCA) showed that the species variation patterns were significantly related to the environmental heterogeneity patterns observed in the estuary. The nine environmental significantly explained the principal variations in the species composition of the zooplankton community. The physiological tolerance of zooplanktonic organisms prescribes the environment where survival and reproduction are possible (Rougier et al., 2005). However, the variable environmental conditions strongly affect the distribution of zooplankton species (Dauvin et al., 1998). The canonical correspondence analysis (CCA) ordination diagram revealed a clear division of zooplankton species in accordance with their ecological requirements. The positive correlation between Brachionus sp. and salinity is similar to the findings of Silva et al. (2004) in tropical estuary. Wei and Xu (2014) also observed that Notholca sp. had correlation with salinity and temperature. Tankx et al. (2004) reported that copepods such as Thermocyclops crassus, T. oithonoides, Mesocyclops leuckarti, M. gracilis and three cladocerans such as Cyclops reticulate, Leydigia acanthocercoides and Moina brachiata in Scheldt estuary, Belgium were thermophilic in nature. The abundance of zooplankton species such as N. labis, Ceriodaphnia sp., Limnocalanus sp., and T. agnatha in this study was correlated with temperature and transparency. Soltonpour-Gargari and Wellershaus (1984) observed that Eurytemora affinis which is a typical estuarine species of the Northern Hemisphere is a euryhaline and eurythermic copepod. The species shifted towards the peak of its abundance where dissolved oxygen
W.O. Abdul et al. concentration is high (Sautour and Castel, 1995). In this study, the wide distribution and abundance of zooplankton species such as Branchionus sp., K. longispina, Diaptomus sp., and Eucyclops sp. were strongly correlated with salinity. Sousa et al. (2008) also reported that Argyrodiaptomus sp., Thermocyclops sp. and Brachionus calyciflorus had abundance peaks in environments with higher concentrations of chlorophyll a, whereas B. dolabratus, Kennelia tropica and Hyperthagylla mira were more associated with low transparency. According to Imoobe and Adeyinka (2009), zooplanktonic organisms are unique bio-indicators of environmental conditions providing early signs of environmental stress in aquatic ecosystems via their responses to certain natural or anthropogenic disturbances. Conclusion The study showed that zooplankton organisms are unique indicators for pollution status and productivity of aquatic ecosystem. The preponderance of zooplankton in the estuary was a function of environmental parameters. The brushpark area of the estuary favoured more diverse species of zooplankton than other zones, wetland and open water areas. The presence of some zooplankton in the estuary indicated that there was a high level of anthropogenic activities in and around the water body. This therefore calls for urgent checks on the activities around the estuary to enhancing sustainable ecosystem 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, Abeokuta 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 phytoplankton community of Ajeko Stream, Iyale, North Central Nigeria. Anim. Res. Int. 9 (3), 1638–1644. Akin-Oriola, G.A., 2003. Zooplankton associations and environmental factors in Ogunpa and Ona Rivers, Nigeria. Rev. Biol. Trop. 51 (2), 391–398. American Public Health Association (APHA), 1998. Standard Methods 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., Thie´baut, 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.
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Please cite this article in press as: Abdul, W.O. et al., The effects of environmental parameters on zooplankton assemblages in tropical coastal estuary, South-west, Nigeria. Egyptian Journal of Aquatic Research (2016), http://dx.doi.org/10.1016/j.ejar.2016.05.005