ABUNDANCE AND DIVERSITY OF PLANKTON OF EKEREKANA …

ABUNDANCE AND DIVERSITY OF PLANKTON OF EKEREKANA

AND OKOCHIRI CREEKS IN THE UPPER BONNY ESTUARY,

NIGERIA.

PROF. EKWEOZORAND

MOSLEN M

ABSTRACTThe Ekerekana and Okochiri creeks in the upper Bonny Estuary, Rivers State, Nigeria is prone to effluent

discharge from industries located in the area. The plankton of the creeks and the adjoining river were assessed for

diversity and abundance. Twenty three stations grouped into six zones were sampled. Samples were collected in

September 2014 (wet season) and February 2015 (dry season) to reflect spatial and temporal dynamics. Twenty

three samples were collected in each season making a total of forty six samples for adequate coverage of the study

area.The abundance and diversity of phytoplankton was generally poor. Density of most species differed

significantly (p<0.05) between zone A and other zones and also between zone D and other zones, suggesting the

impact of effluent discharge on the micro algal community, as seen in the low diversity indices at zone D.

Zooplankton abundance was least at zones A (4%) and F (3%) with significant difference (p<0.01) observed

between zone D and other zones and also between zones A & F and other zones.Cluster analysis after fourth root

transformation of abundance data showed differences in similarity between zones. The differences between zones

could be due to spatial scale of impact vis-à-vis anthropogenic activities in the study area. The generally observed

poor abundance and diversity of phytoplankton and zooplankton of the Ekerekana/Okochiri creeks and the

adjoining river suggest a deteriorating aquatic system.

Keywords: Abundance, Diversity, Plankton, Ekerekana and Okochiri creeks.IntroductionWater quality affects the abundance, species composition/diversity; stability, productivity and

physiological condition of indigenous populations of aquatic organisms. Some species flourish

in highly eutrophic waters while others are very sensitive to organic and/or chemical waste

(Branco and Pereira, 2002; Vis et al., 1998). Owing to the short life cycle of plankters, they

respond quickly to environmental changes (APHA, 1975). Studies of algae, combined with

macroinvertebrate communities can provide a valuable assessment of the overall health of

aquatic systems. Phytoplankton may be floating, drifting or even suspended in the water column

and capable of little or no resistance to water current and cannot therefore escape contamination

on their own propulsion (Newell and Newell, 1977). This makes plankton a good indicator of

environmental pollution. Many characteristics of algal community structure and function can be

used to develop indicators of ecological conditions in streams (Hill et al., 1999). Algal

communities in river ecosystems are highly dynamic. Species composition changes

significantly over time at a particular spatial location in response to temporal variation in local

nutrient concentrations and herbivore levels (Hillebrand et al., 2002).Continued increase in sea

temperature due to climate change and associated changes such as ocean acidification, are likely

144

to exert major influences on plankton abundance and geographical distributions, with

implications for primary production and climate control (Bresnan et al 2008). Seasonal events

such as rainfall, monsoon winds, upwelling/downloading and the local topography and

bathymetry in the region can further complicate the nutrient dynamics in waters and affect the

resistance of waters to nutrient enrichment by the discharge and sewage effluent (Yin, 2002; Lee

et al. 2006). Despite less nutrient input from discharge in most seasons the continuous nutrient

input from local sewage provides high NH and PO for phytoplankton growth (Alvin et al 2008). 4 4

Seasonal and spatial dynamics of phytoplankton biomass is very complex and driven by a variety

of physical, chemical and biological factors (Alvin et al., 2008). In addition, the high tidal

velocity in waters and rapid flushing time in relatively open waters can suppress the

accumulation of phytoplankton biomass (Lee et al., 2006). Low water temperature may also be a

significant limiting factor for the growth of sub-tropical phytoplankton in the winter. High

zooplankton biomass in spring (Li et al., 2006) suggested that grazing might be a significant

factor controlling chlorophyll "a" biomass in most waters, especially during the initial stage of

algal blooms in spring. Favourable temperature, light and nutrient availability enhances rapid

phytoplankton growth. In shallow water systems, such as coastal lagoons, the benthic

compartment plays a crucial role in determining the functioning of the system, controlling the

main ecological processes, and changes in its structure could affect the whole system (Weslawski

et al., 2004; Tenore et al., 2006).

The Bonny Estuary is one of the richest estuaries in the Niger Delta aquatic ecosystem, with a

network of creeks/tributaries linking various habitats of highly economic and ecological

importance. The estuary is open with abundant composition of flora and fauna of unique

biodiversity (Wilcox, 1980). These ecosystems are often the site where many pollution

problems exist (Saiz-Salinas and Gonzalez-Oreja, 2000) and where pollution loading caused

significant changes in abundance and species composition. The system is vulnerable to pollution

by organic, industrial and chemical pollutants/wastes from several industries and human habitats

located by the banks and water fronts, and has been the subject of much research over decades

(Chindah et.al, 1993, Moslen et al., 2006; Daka et al., 2007; Daka and Moslen, 2013; Miebaka

and Daka 2013; Moslen and Daka 2014; Moslen et al., 2015). The Ekerekana and Okochiri

creeks in the upper Bonny estuary are of ecological and economic importance. These creeks

receive industrial effluents and domestic wastes from nearby industries and squatter settlements.

This study aims to assess the abundance and diversity of plankton of the creeks and adjoining

rivers.

Materials and MethodsStudy Site The study site is the Ekerekana and Okochiri creeks and the adjoining river. The two creeks are

linked by a narrow channel and are tidal in nature with fringing mangrove vegetation. The creeks

145

Nigerian Journal Of Oil And Gas Technology

Fig. 1: Map showing study sitesSample Collection and AnalysisPlankton samples were collected in September 2014 (wet season) and February 2015 (dry

season) to reflect spatial and temporaldynamics. Twenty three samples were collected in each

season making a total of forty six samples. Plankton samples were collected by sieving fifty

Abundance And Diversity Of Plankton Of Ekerekana And Okochiri Creeks In The Upper Bonny Estuary, Nigeria.

146

located on the northern flank of the Bonny Riverreceive industrial effluent discharged by

industries located in the area particularly the Port Harcourt Refinery Company and Notori

chemicals (a fertilizer company). Other human activities along the creek and adjoining river

include sand mining/dredging, fishing, navigation by speed boat/vessels, transportation of

people and petroleum products and recreational activities. These activities can influence the

natural balance of the aquatic ecosystem and consequently its biota.For purposes of this study,

samples were collected from twenty three points which were grouped into zones (Fig. 1). ST 1, 2

& 3 (zone A), ST 4, 5, 6, 7, 8, 9, 10, 11, 12 (zone B), ST. 13, 14, 15 (zone C), ST 16, 17 (zone D),

ST 18, 19 20 (zone E) and ST 21, 22, 23 (zone F). Zones A and B were located on the Ekerekana

creek but stations in zone A were closest to the point of effluent discharge. Zone C had stations

located on the narrow channel linking the two creeks while zone D had stations located on the

Okochiri creek which also receives effluent discharge. Zones E and F were located outside the

creeks with zone F having stations close to the refinery loading jetty.

liters of water through plankton net, after which the filtrate was transferredinto a one liter open

mouth plastic container, fixedwith 5% formalin and then taken to the laboratory

foridentification. The plankton samples were kept to stand for a minimum of 24 hrs in the

laboratory and supernatantdecanted until a 50 ml concentrated residue sample was achieved.

The concentrated sample was mixed carefully by shaking and 1mL of the sub- sample was taken

and transferred into a Bogorov counting chamber using astampel pipette. Enumeration and

identificationof the organisms under the microscope was done to the lowest possible taxonomic

level.

Data analysis: The software package Plymouth Routine in Multivariate Ecological Research (PRIMER 6) was

used to analyze biological properties whichincludes the following; Abundance (N), number ofSpecies (S), Shannon-Wiener diversity index (H'), Pielou evenness index (J), Margalef richness

index (d) and Simpson domination index (ë): Both multivariate and univariate statistical

analysis was applied to the data obtained. Multivariate technique was by classification using

cluster analysis. Clustering was by hierarchical method using group average linkage of Bray-th Curtis similarities, after 4 root transformation. MINITAB R.16 was used for theAnalysis of

variance applying the General Linear Model to test for differences between zones and also

between seasons while Tukey test was used for pair-wise comparison among levels of time and

zones.

Results and DiscussionThe phytoplankton taxa in the study area were very low. Ideriah et al. (2006) stated that the

growth of marine organisms depends basically on the quantity and quality of the primary

production of phytoplankton (algae). A total of 892 phytoplankton were recorded during the

study with 32 % of the organisms observed at zone A, 29 % (zone D), 23 % (zone C), 8 % (zone

B), 7 % (zone E) and 1% (zone F). Bacillariophyceae were the only group recorded with

Thalassiosirasp, Nitzsciasp, Naviculasp, Synedrasp, Gyrosigmasp, Coscinodiscussp and

Rhizosoleniasp as most abundant species in the study area (Table 1). Ogamba et al., (2004)

reported that the species with the highest self-sustaining natural mechanisms of natural increase

usually become dominant. This may account for the widespread dominance of

Bacillariophyceae in this study. The poor abundance and diversity of the phytoplankton may also

be attributed to the regular discharge of industrial effluent into the creeks which is capable of

deteriorating the water quality. This corresponds with the findings of Anaero-Nweke (2013) who

stated that phytoplankton distribution and abundance among the sampling stations in Ekerekana

area were very poor, with a total of 40 taxa represented by three families.

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PHYTOPLANKTON (Org./ml)

PERIOD

ZONE A

ZONE B

ZONE C

ZONE D

ZONE E

ZONE F

Location (F-values

Time (F-values)

Coscinodiscussp

WET 1 +

1.00 3 +

1.03 16 + 9.68

6 + 2.01

6 + 2.52

2 + 1.00

2.46* 0.01ns

DRY 1 +

0.67 7 +

2.17 7 +

1.45 5 +

2.01 6 +

2.03 1 +

0.88

Nitzsciasp

WET 10 + 1.77

4 + 1.56

12 + 12.01

13 + 1.50

6 + 1.53

1 + 0.67

3.55* 0.59ns

DRY 31 +

13.92 6 +

0.93 9 +

3.18 2 +

0.50 5 +

0.58 1 +

0.33

Synedrasp

WET 2 +

1.20 1 +

0.36 6 +

3.85 9 +

3.51 3 +

0.33 0 +

0.00 2.56* 12.86

***

DRY 15 + 6.12

9 + 1.72

5 + 2.85

9 + 4.01

4 + 0.58

0 + 0.33

Thalassiosirasp

WET 17 + 2.65

10 + 3.81

100 +

5.30

196 +

196.08

12 + 2.61

4 + 0.88

2.67* 2.13ns

DRY 63 +

24.67 3 +

0.91 20 + 7.24

8 + 0.50

10 + 2.61

1 + 0.88

Gyrosigmasp

WET 5 +

2.52 1 +

0.58 0 +

0.00 0 +

0.00 0 +

0.33 0 +

0.00 7.24**

* 6.44*

DRY

48 + 14

14.06 3 +

0.86 4 +

0.88 2 +

0.50 1 +

0.58

0 +

0.00

Naviculasp

WET 0 +

0.00 1 +

0.37 0 +

0.00 0 +

0.00 0 +

0.00

0 +

0.00

6.52**

*

12.10

***

DRY 58 + 9.34

7 + 1.42

4 + 1.33

3 + 1.50

1 + 0.33

0 +

0.00

Thalasiotrixsp WET

0 + 0.00

2 + 1.43

0 + 0.00

0 + 0.00

0 + 0.00

0 +

0.00

0.49ns 1.56ns

Asterionellasp

WET

0 + 0.00

0 + 0.11

0 + 0.33

0 + 0.00

0 + 0.33

1 + 1.00

nr nr

Pseudonitzschiasp WET

0 + 0.00

0 + 0.022

0 + 0.00

0 + 0.00

0 + 0.00

0 +

0.00

nr nr

Cyclotellasp DRY 0 + 4 + 5 + 3 + 1 + 0 +

Key: * = significant (p<0.05); ** = significant (p<0.01); *** = significant (p<0.001); ns = not significant; nr = no result


148

The findings of this study also share the views of Ogamba et al (2004) who reported that pollution affects the distribution, standing crop and chlorophyll concentration of phytoplankton. Wake (2005) in his findings also reported decreased phytoplankton number at 5.84% concentration of refinery effluent in a toxicity test while Abowei (2010) concluded that, the algal flora of refinery effluent polluted river was found to be sparse, with low species diversity and consequently low primary productivity. The density of Coscinodiscus sp differed across zones with significant difference (p<0.05) between zone C and zones A, B, D, E & F, and also between zone A and zones B, D, E & F while the density of Nitzscia sp varied significantly (p<0.05) between zone A and zones B, C, D, E & F and also between zones B & F and zones C, D & E. The density of Synedra sp and Thalassiosira sp also showed significant difference (p<0.05) between zones in the following order: D < A < C = B = E < F and D < C = A = E = F < B respectively. The density of Thalasiotrix sp did not show significant variation across zones but those of Gyrosigma sp and Navicula sp did with similar patterns (zone A < zones B, C, D, E and F). Univariate indices show the same trend for species richness, evenness and diversity with highest values obtained at zone B and lowest values at zone D while dominance showed an opposite trend with maximum value at zone D (Fig. 2). Low evenness values suggest low habitat quality across zones. Zone D on the Okochiri creek appears to be most impacted with reduced diversity indices which could be due to impact of effluent discharge into the creek.These findings also agree with Mbaneme et al. (2013) that various pollutants released into the Okrika creek affected the littoral zone, the shallow waters along the shorewhere rooted vegetation grow, and the limnetic zone, the open water that sunlight penetrates where phytoplankton (algae) live. He however stated that it is uncertain if effects in the creek were caused by eutrophication as a consequence ofnitrogen and/or COD and BOD enrichment or pH induced reactions related to acids or other pollutants discharged into the creeks but Oruibima (2004) stated that the limited ability of the creek to flush amplifies the pollution damage. Cluster analysis of abundance data showed thatzones C and D were most similar and most distant from zones F and A which were most dissimilar (Fig. 3). Zone D was located on the Okochiri creek while zone C was on the canal connecting to zone D. Zone A was located on the Ekerekana creek while zone F was located close to the refinery loading jetty on the adjoining river. Similarity between different zones suggests different responses to varying degrees of anthropogenic impacts in the study area.

Fig. 2: Phytoplankton univariate diversity indices across zones

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Fig. 3: Cluster Analysis of phytoplankton taxa based on zones

The zooplankton density (Table 2) was quite less than the phytoplankton which they prey on,

numbering 143 across the zones examined. Zone B had the highest percentage (30 %) of the total

organism while zone D and C had 27 % and 21 % respectively. Others were zone E (15%), zone

A (4 %) and zone F (3%).The poor phytoplankton number could affect the zooplankton as

observed by Joseph and Joseph (2002) that reduced productivity of phytoplankton and/or algae

will have a reduction effect on the other organisms in the environment, such as crustaceans and

fish because they serve as food to them and other zooplankton. Most abundant species recorded

included Nauplius larvae, Macrosetella sp, Calanus finmarchicus and Eurytemora sp with more

of the zooplankton found during the dry season. Significant variation (p<0.01) in the density of

nauplius larvae was observed across zones with the actual difference occurring between zone D

and zones B, E, and C and also between zones A, F and zones B, E & C. Zooplankton species

diversity, evenness and dominance were marginally different across the zones but species

richness showed significant variation with zone F having the highest value (Fig.4). The

generally lower evenness values suggesta deteriorating habitat quality traceable to the industrial

effluent and other anthropogenic activities in the area. Marcus (2014) stated that the long term

impact of refinery process wastewater amidst other activities in the study area was not really

known but believed that the complex combination of toxic substances that were simultaneously

present in refinery wastes may act synergistically and therefore impose a higher toxicity burden

on the entire ecosystem than may be predicted in laboratory studies on individual toxicants

(Mizell and Romig, 1997). Camphuysen (1989) had also observed the toxic effects of oil on

zooplanktons.


150

Table 2: Density of zooplankton (Mean ± Standard Error - SE) and ANOVA output

ZOOPLANKTON (Org. /ml)

PERIOD

ZONE A

ZONE B

ZONE C

ZONE D

ZONE E

ZONE F

Location (F-values

Time (F-values)

Copepoda

Nauplius larvae WET

0 ± 0.33

3 ± 1.20

0 ± 0.33

2 ± 2.01

2 ± 0.00

1 ± 0.33

3.69**

5.94*

DRY 1 ±

0.57 4 ±

0.99 3 ±

0.67 10 ± 2.01

3 ± 0.88

0 ± 0.33

Temora sp WET

0 ± 0.33

0 ± 0.00

0 ± 0.00

2 ± 1.50

0 ± 0.33

0 ± 0.33

0.65n

s 4.35

*

DRY 0 ±

0.33 4 ±

2.00 1 ±

0.58 1 ±

0.00 1 ±

0.58 0 ±

0.33

Pseudocalanus sp WET

0 ± 0.33

0 ± 0.00

0 ± 0.00

0 ± 0.00

0 ± 0.33

0 ± 0.00

1.09n

s 7.79

**

DRY 0 ±

0.33 4 ±

1.72 3 ±

0.33 1 ±

0.50 1 ±

0.33 0 ±

0.00

Macrosetella sp DRY 1 ±

0.57 2 ±

0.77 4 ±

2.19 6 ±

1.50 2 ±

0.88 0 ±

0.33 nr nr

Acartia sp DRY 0 ±

0.33 2 ±

0.46 1 ±

0.33 3 ±

0.50 2 ±

1.16 0 ±

0.33 nr nr

Pseudodiaptomus sp

DRY 0 ±

0.33 2 ±

1.07 2 ±

0.58 1 ±

0.00 1 ±

0.33

0 ±0.3

3

nr nr

Calanus finmarchicus

DRY 1 ±

0.33 4 ±

0.89 4 ±

2.03 4 ±

2.01 1 ±

0.58 0 ±

0.00 nr nr

Eurytemora sp DRY 0 ±

0.33 6 ±

2.42 1 ±

0.67 5 ±

3.51 4 ±

1.86 0 ±

0.33 nr nr

Oithoniasp DRY 0 ±

0.00 2 ±

0.70 3 ±

0.33 2 ±

0.50 1 ±

0.33 0 ±

0.33 nr nr

Paracalanus parvus

DRY 1 ±

0.67 4 ±

1.81 3 ±

1.58 3 ±

0.50 2 ±

1.16 0 ±

0.00 nr nr

Paevocalanus sp DRY 0 ±

0.33 3 ±

1.53 4 ±

0.58 1 ±

0.50 2 ±

0.88 1 ±

0.33 nr nr

Tortanus sp DRY 0 ±

0.33 3 ±

1.38 1 ±

0.58 1 ±

0.00

0 ±0.3

3 0 ±

0.33

nr nr

151


Key: * = significant (p<0.05); ** = significant (p<0.01); ns = not significant; nr = no result

Fig. 4: Zooplankton univariate diversity indices across zones

The water-soluble fractions of aromatic compounds depress phytoplankton photosynthesis,

respiration and growth, kill and cause developmental abnormalities in zooplankton and the

young stages of many aquatic organisms. Eggs andyoung ones are more sensitive than adults,

and crustaceans are more sensitive than most other groups (Nwabueze and Agbogidi, 2010).).

Cluster analysis of zooplankton abundance almost showed the same trend as the phytoplankton

structure (Fig.5). Zones A and F stood out clearly and were most dissimilar while zones B, C, D

and E showed very close relationship with themselves.

Fig. 5: Cluster Analysis of zooplankton taxa based on zonesConclusionThe abundance and diversity of plankton in Ekerekana, Okochiri creeks and the adjoining river area were generally poor. Industrial effluents and domestic wastes discharged into the creeks deteriorated the water quality and caused an extra load on the aquatic system (Moslen and Daka, 2016). This was evident by the poor abundance, composition and diversity of plankton of the study area. Opportunistic organisms may take advantage of this situation and edge out less tolerant ones. The generally low species evenness is also an indication of a poor habitat with


152

deteriorating water and sediment quality. This study has therefore, revealed the status of the abundance and diversity of the plankton community with regards to the anthropogenic activities in the study area.

Acknowledgement: We appreciate the effort of Mr. Grant Ogbe for the production of the sampling site map.

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