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Spatio-temporal distribution to phytoplankton in the industrial area of Calabar River, Nigeria.


The Calabar River is the major sink of industrial and municipal wastes, but despite its hydrological importance, not much study has been carried out to investigate the distributional pattern and density of phytoplankton. Previous studies by Akpan [3], Moses [22], Ekwu and Sikoki [12] concentrated primarily on the Cross River neglecting the Calabar River which transverses human settlements, farmlands and industries. In Nigeria and elsewhere, studies have been carried out to examine the spatial distribution, abundance and diversity of phytoplankton [18,8,24,2,21,7,23,25], these studies identified different factors based primarily on the nature of anthropogenic activities predominate in the area to influence phytoplankton growth, composition and abundance. However, some of the factors reported in literature to influence phytoplankton growth, composition and abundance include dissolved oxygen, salinity, transparency, water temperature, calcium and total hardness, increase in river flow, wastes and oil pollution, silicates among others factors.

Phytoplankton is an important microscopic organism that synthesizes and sustains the majority of aquatic life forms. Phytoplankton is thus, the pioneer of an aquatic food chain; as the productivity of an aquatic ecosystem directly depends on the density of phytoplankton. The population of phytoplankton in any aquatic ecosystem constitutes a vital energy flux in the food chain. As the lowest members of the most aquatic food chain, phytoplankton is usually very numerous in numbers and of diverse shapes. Though, they constitute the starting point of energy transfer. It is however highly sensitive to allochthonously imposed changes in the environment [12,20,13] as a result of oil pollution and municipal waste disposal. Thus, the spatiotemporal distribution of the species, relative abundance and composition are an expression of the environmental health and quality of the existing water body. On this note, Forsberg [15] argued that phytoplankton diversity, distribution, abundance and variation provide vital information of energy turnover in the aquatic systems.

Indeed, in the aquatic system, Laskar and Gupta [21] reported that phytoplankton is of immense importance as a major source of organic carbon found at the base of the system (aquatic ecosystem). Therefore, the variations in the species composition give a reflection of inherent modification in the ambient condition within the aquatic ecosystem [8]. Calabar River, a major tributary of the Cross River is identified to have contributed one of the highest quotas of fish production and income for most households [3], and it forms the basis for the earliest settlement [11,12]. This study was therefore carried out to examine the spatio-temporal distribution, species abundance and diversity of phytoplankton in the Calabar River.

Materials and Methods

Study area:

The study was carried out in the Calabar River. Cross River is located on latitude 50 6' N and longitude 80 9' E enclosing Esuk Nsidung in Calabar South and Adiabo Bridge in Odukpani Local Government Area. Calabar River, a major tributary of the Cross River originates from the Oban Hills in Cross River State and flows through black shale and siltstone, clayey, sand and silt deposits before entering the estuary at Alligator Island [14]. It stretches about 25km to the north and south. The Calabar River is hydro-dynamically homogenous. The current velocity is measured to the range of 2 25 cm/sec upstream and 20cm/sec downstream [5]. The current is said to be higher during ebb tide and decreases during flood tide. Dissolved particulate materials are transported by surface current from estuary into creek and upper reaches of the Calabar River within the industrial area of Esuk Nsidung to Adiabo Bridge during semi-diurnal tides. The major occupation of peoples in the area is artisanal fisheries and trading. Rainfall is the major climatic factor that affects the hydrology of the Calabar River system and temperature in the area ranges between 180 C and 260 C [5]. Vegetation around the area is typical of tropical rainforest. The land has an undulating topography and the environment is swampy.


Phytoplankton samples were collected by trawling plankton net of 55|im mesh size of 5 knots per minutes for ten minutes across each equidistant station of 3,340.3m behind an engine boat. Plankton filtered from such catch was washed into 2 litres plastic bottles and immediately preserved with 5 drops of 4% formalin [26]. This was followed by the addition of 3 drops of lugols solution and allowed to settle for 30 minutes. All the samples were kept in ice-boxes of 400 C before taken to the laboratory for analysis.


Qualitative and quantitative analysis of phytoplankton was performed using Zeiss invented plankton microscope. Subsamples were mixed by swirling and filled into Hdro-Bios plankton sedimentation chambers. After allowing for complete sedimentation (4 hrs), microscopic analysis was then performed following UNESCO [30] using identification schemes of Edmondson [10], Prescott [27] and Sharma [29]. The numerical abundance of the phytoplankton was done by direct count method, while percentage abundance was calculated using the formula % = n/N x 100. Species diversity index was determined by the formula Shannon-Wiener's Diversity Index [28], while species evenness was calculated also using Shannon's Equitability (E).

Results and Discussion

A total of 35 phytoplankton species and 35 taxa representing 6 families were recorded during the study (Table 1). 35 phytoplankton taxa were recorded of which 10 (28.6%) belong to Chlorophyceae (green algae) and Bacillariophyceae (diatom) respectively, 6 (17.1%) to Euglenophyceae (green flagellates), 3 (8.6%) to Cyanophyceae (blue-green algae), Chrysophyceae and Xanthophyceae respectively. The table shows there is seasonal variation in phytoplankton taxa, as its abundance increased in the dry season than in the wet season. Across the sampling stations, the major taxa of phytoplankton in terms of diversity and abundance for the family Chlorophyceae were Eudorina spp, Chlorocoum spp, Closterium spp and Acanthosphaera spp. There were high density and abundance of Chlorophyceae in station 2, followed by station 4 and 5, while station 6 recorded the lowest abundance of Chlorophyceae in the two seasons. In addition, the Margelefs Index showed that stations 1 and 6 were the richness in terms of the number of species of the family Chlorophyceae across the seasons (Table 1).

The highest abundance of Chlorophyceae between the seasons and sequence decreased in station 2-6. For the family Euglenophyceae, Euglena spp, Cyptoglena spp, Phacus pleuroneites and Trachelomonas spp were more abundant species across the sampling stations; while stations 5, 4 and 6 recorded the highest species composition belonging to Euglenophyceae in the two seasons, while station recorded the least (2 & 3) abundance (Table 1). In addition, Nitizohia spp, Fragilaria spp, Bacillria spp and Melosira granulate were the dominant species of Bacillariophyceae across the sampling stations. There were high composition and abundance of Chlorophyceae in station 4, followed by station 5 and 2, while station 6 recorded the lowest abundance of Chlorophyceae in the two seasons (table 1). The family Chrysophycea, Pyaetharminon and Chrysapsi were the dominant or more occurring species across the sampling stations, with stations 2 recording the highest species composition and abundance of the family Chrysophycea, followed by 5 and 6, while station 3 had the least abundance of Chrysophycea in the two seasons.

For the family Cyanophyceae, Microcystic spp and Oscillatoria spp were species with high abundance across the sites, with station 5 recording the highest abundance of the family Chrysophycea, followed by station 1, while station 6 recorded the lowest. The Margalef's Index reveals that stations 2 and 3 were more diverse and richer than other stations across the seasons. The high abundance of Cyanophyceae which is noted as an estuarine species is attributable to the occasional insurgence of discharge from the estuary during tidal perturbation. For the family Xanthophyceae, Chlorocloster spp and Monocillia spp were species with high level of abundance across the sites. Station 4 had the highest abundance of the family Xanthophyceae, followed by station 6 and station 3, while station 2 recorded the lowest (Table 1). Table 2 represents the summary of the percentage composition of phytoplankton during the dry season. The information depicts that in the dry season, the family Bacillariophyceae had the highest percentage composition across the sampling stations, and this was closely followed by Chlorophyceae and Euglenophyceae respectively. Furthermore, the information in table 3 shows that during the wet season, the family Bacillariophyceae exhibited the highest density and composition followed by the families Chlorophyceae and Euglenophyceae. In all, the information in tables 2 and 3 indicates that Bacillariophyceae, Chlorophyceae and Euglenophyceae had the highest level of composition in the two seasons.


The seasonal distribution pattern of phytoplankton density reveals it to be high in the dry season than during the wet season. The high of phytoplankton in the dry season may be attributed to the increase in photic depth due to solar radiation intensity as well as the reduction in input turbid materials from other tributaries of the Calabar River. The abundance of phytoplankton density during the dry season is contrary to those of Wojciechowska et al., [32], when they observed that in the floodplain lakes of Bug river, eastern Poland, both diversity and abundance of phytoplankton were highest in summer. Similarly, Garcia de Emiliani, [17] observed high density of phytoplankton during the summer in the floodplain lakes of Argentina. The drastic reduction in the population of Euglenophyceae in dry could be attributed to the use up of essential nutrients during their boom [9]. Maximum growth of Bacillariophyceae in dry could be linked to the increased water temperature as has also been shown by Kant and Anand [19], Laskar and Gupta [21]. The high level of Bacillariophyceae may be probably due to the present of high concentration of silicates intrusion from the estuarine region during tidal incursion. Its high level could also indicate pollution in the water system. Akpan [2,3] noted that such pollution includes oxygen deficiencies leading to fish mortality, release of poisonous chemicals by toxic dinoflagellates leading to food poisoning through contaminated shellfish and reduction in aesthetic value of water. Flagellates like diatoms are proficient in their ability to reproduce. By splitting into half, a dinoflagelate can reproduce thirty three million offspring in only twenty-five divisions.

Ekeh and Sikoku [11] also reported abundant level of Bacillariophyceae in the lower reach of the estuary. In a similar way, Akpan [3] reported a strong correlation between silicates and diatom abundance. The present study reveals that the percentage composition of Chlorophyceae is quite high in both seasons. Despite a low percentage composition in wet season, they have a sizeable population. The boom of Chlorophyceae in dry could be attributed to high water temperature and resultant dilution of water [31]. Gabellone et al., [16] suggested that the four major regulatory factors of the ecology of the pond of floodplain ecosystem are dry season, a high and sudden increase of river flow, increase in particulate material and clear water conditions. The decrease in abundance of Chlorophyceae from stations 2 - 6 may be attributed to the prevalence of freshwater from the upstream to the downstream of the river. A study in a shallow lake in the south of Brazil identifies transparency and water temperature as environmental variables influencing the variation of phytoplankton composition [6]. Our study attributed the density of phytoplankton taxa to primarily the pollution of the water body as well as the high concentration of silicate.


The study shows the Calabar River has high diversity of phytoplankton taxa as a result of nutrient input mostly the discharge of organic wastes. The variation in phytoplankton abundance across the sampling station is attributed to oil pollution and the discharge of organic waste into the river. The presence and abundance of phytoplankton taxa is indicative of water pollution.


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(1) E.E. Ewa, (2) A.I. Iwara, (1) A.O. Alade and (2) J.A. Adeyemi

(1) Dept. of Geography & Environmental Science, University of Calabar, Nigeria

(2) Dept. of Geography, University of Ibadan, Nigeria

(3) Institute of Geosciences & Space Technology, UST, Port Harcourt, Nigeria

Corresponding Author

E.E. Ewa, Dept. of Geography & Environmental Science, University of Calabar, Nigeria Email:; Phone: +2347058219232
Table 1: Seasonal variation in the composition, diversity and
abundance of phytoplankton taxa.

Phytoplankton                Stn 1         Stn 2         Stn 3
                          Abundance     Abundance     Abundance

                         Dry    Wet    Dry    Wet    Dry    Wet


Phacus pleuroneites      4132   916    1104   904    1001   608
Trachelomonas spp        1038   832    1043   834    1073   876
Pedinipsis spp           542    248    464    219    368    109
Euglenopsis spp          586    342    828    528    738    447
Euglena acus             2504   952    2689   964    2904   448
Cyptoglena spp           1508   924    1568   108    1698   782
No. of taxa (s)           6      6      6      6      6      6
Total abundance (N)      7610   4214   7696   3575   7782   3270
Margalef's Index (d)     0.26   0.27   0.26   0.28   0.26   0.27
Species evenness (E)     0.24   0.25   0.24   0.25   0.24   0.25


Diatomella spp           692    464    752    646    634    441
Denticula thernalis sp   639    613    705    568    844    553
Coscinodiscus spp        639    481    659    369    706    407
Aulocadiscus spp         368    194    481    174    498    518
Actinocydus spp          438    278    593    505    447    316
Melosira granulate       1001   826    1934   1000   1030   841
Tribonema spp            830    617    898    448    849    216
Nitizohia spp            1670   908    1706   944    1449   908
Fraqlatia spp            1604   914    1348   905    1403   911
Bacillaria spp           1401   846    898    706    1340   941
No. of taxa (s)           10     10     10     10     10     10
Total abundance (N)      9282   6141   9974   6265   9200   6052
Margalef's Index (d)     1.0    1.0    1.0    1.0    1.0    1.0
Species evenness (E)     0.46   0.46   0.46   0.46   0.42   0.46

Phytoplankton                Stn 4         Stn 5         Stn 6
                          Abundance     Abundance     Abundance

                         Dry    Wet    Dry    Wet    Dry    Wet


Phacus pleuroneites      1507   963    1802   814    1662   824
Trachelomonas spp        1443   841    1708   922    1720   914
Pedinipsis spp           548    231    624    314    638    316
Euglenopsis spp          801    643    412    141    802    573
Euglena acus             2904   986    2801   1441   2602   1009
Cyptoglena spp           1660   914    1812   814    1443   944
No. of taxa (s)           6      6      6      6      6      6
Total abundance (N)      8863   4578   9159   4446   8867   4630
Margalef's Index (d)     0.25   0.26   0.26   0.28   0.26   0.27
Species evenness (E)     0.24   0.24   0.24   0.25   0.24   0.25


Diatomella spp           689    541    693    473    898    681
Denticula thernalis sp   809    735    938    388    848    608
Coscinodiscus spp        811    603    938    531    748    507
Aulocadiscus spp         698    517    734    273    866    404
Actinocydus spp          690    481    738    588    498    209
Melosira granulate       980    511    1007   591    1080   911
Tribonema spp            782    509    698    448    993    465
Nitizohia spp            1503   918    1630   908    1938   814
Fraqlatia spp            1433   933    802    948    950    621
Bacillaria spp           1368   914    934    994    1090   926
No. of taxa (s)           10     10     10     10     10     10
Total abundance (N)      9763   6663   1012   6142   9909   4146
Margalef's Index (d)     1.0    1.0    1.0    1.0    1.0    1.0
Species evenness (E)     0.46   0.46   0.46   0.46   0.46   0.46

Table 2: Summary of the percentage composition of phytoplankton
during the dry season.

Phytoplankton            Stn 1          Stn 2          Stn 3

                      A     %Ra      A     %Ra      A     %Ra

Bacillariophyceae   9282    28.5   9974    87.3   9200    28.4
Chrysophyceae       2620    8.1    3910    10.7   2317    7.1
Cyanophyceae        2586    8.0     258    6.9    2123    6.6
Chlorophyceae       8244    25.3   10340   3.31   8707    26.9
Euglenophyceae      7610    23.4   7696    2.07   7782     24
Xanthophyceae       2205    6.8    2086    5.71    299    7.1
Total               32547   100    36519   100    32430   99.9

Phytoplankton            Stn 4          Stn 5          Stn 6

                      A     %Ra      A     %Ra      A     %Ra

Bacillariophyceae   9763    26.6   10112   27.1   9909    28.1
Chrysophyceae       2478    6.7    3774    10.1   3620    10.3
Cyanophyceae        2892    7.8    2526    7.7    2101    6.0
Chlorophyceae       9342    25.4   9649    25.9   8342    23.7
Euglenophyceae      8863    24.1   9159    24.5   8867    25.2
Xanthophyceae       3412    9.3    2112    5.7    2418    6.9
Total               36750   100    37332   100    35254   100

Table 3: Summary of the percentage composition of phytoplankton
during the wet season.

Phytoplankton            Stn 1          Stn 2            Stn 3

                      A     %Ra      A      %Ra      A      %Ra

Bacillariophyceae   6141    29.4   6265    31.1     6055    31.8
Chrysophyceae       1400    6.7    2028    10.1     1233    6.5
Cyanophyceae        1708    8.2    1373     6.8     1268    6.7
Chlorophyceae       5795    27.7   5879    29.2     5604    29.5
Euglenophyceae      1646    7.9    1019     5.1     1591    8.4
Xanthophyceae       4214    20.2   3557    17.7     3270    17.2
Total               20904   100    20121    100    19018    100

Phytoplankton            Stn 4           Stn 5           Stn 6

                      A      %Ra      A      %Ra      A      %Ra

Bacillariophyceae   6662    28.3    6142    29.3    6146    30.1
Chrysophyceae       1723     7.3    2063     9.9    2193    10.7
Cyanophyceae        2395    10.2    1355     6.5     980     4.8
Chlorophyceae       6274    26.7    5593    26.7    4655    22.8
Euglenophyceae      1897     8.1    1341     6.4    1806     8.8
Xanthophyceae       4578    19.5    4446    21.2    4630    22.7
Total               23529    100    20940    100    20410   99.9
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Title Annotation:Original Article
Author:Ewa, E.E.; Iwara, A.I.; Alade, A.O.; Adeyemi, J.A.
Publication:Advances in Environmental Biology
Article Type:Report
Geographic Code:6NIGR
Date:Mar 1, 2013
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