Phytoplankton diversity and succession in the Iyagbe ... - EuroJournals

European Journal of Scientific Research
ISSN 1450-216X Vol.43 No.1 (2010), pp.61-74
© EuroJournals Publishing, Inc. 2010
http://www.eurojournals.com/ejsr.htm
Phytoplankton diversity and succession in the
Iyagbe lagoon, Lagos
Onyema, I.C
Department of Marine Sciences, University of Lagos, Akoka, Lagos
E-mail: iconyema@gmail.com
Abstract
The phytoplankton diversity and succession in the Iyagbe lagoon was investigated
for 24 consecutive months (Oct., 2004 – Sept., 2006). Phytoplankton diversity was clearly
higher in the dry than wet season. Seven major algal groups - the Bacillariophyceae,
Cyanophyceae, Euglenophyceae, Chlorophyceae, Dinophyceae, Chrysophyceae and
Rhodophyceae were represented. The diatoms (Bacillariophyceae) were the more important
group in terms of diversity with the centric forms recording a higher number of species
than the pennate forms. Whereas dinoflagellates (Dinophyceae) recorded more species in
the dry season and at stations proximate to the Lagos habour, the euglenoids
(Euglenophyceae), chrysophytes (Chrysophyceae) and most green algae (Chlorophyceae)
were more common in the wet season and at stations further inland and away from the
Lagos habour. Notable species recorded in the dry season were Coscinodiscus radiatus,
Parabelius delognei, Coscinodiscus centralis, Coscinodiscus centralis, Skeletonema
coastatum, Coscinodiscus radiatus, Bacillaria paxillifer, Actinoptychus splendens,
Coscinodiscus marginatus and Thalassionema nizschoides, whereas Aulocoseira granulata
var. augustissima, Aulocoseura granulata, Aulocoseira granulata var. augustissima f.
spiralis, Aulocoseira varians, Microcystis aureginosa, Aulocoseira granulata var. curvata,
Gonatozygon sp., Fragillaria construens, Spirogyra africanum and Synura uvella were
reported in the wet season. Outcomes of bio-indices variations were reflections of the
degree of occurrence and abundance of species linked to seasons operating in the region.
Keywords: Microalgae, phytoplankton, diversity, Iyagbe lagoon, south-western Nigeria.
1. Introduction
The Nigerian coastal environment includes fresh, brackish and marine aquatic ecosystems. Whereas
estuaries and creeks are common in the Niger Delta area, lagoons only occur in South-western Nigeria
due to the alignment of the coastline in this region to the dominant South westerlies winds at
approximately 45 o (Hill and Webb, 1958; Onyema 2009a). Presently, there are 10 lagoons in Southwestern
Nigeria with the Apese lagoon being the more recent addition and the only true closed lagoon
in the region (Onyema, 2009b, c). These lagoons are the Yewa, Badagry, Ologe, Iyagbe, Lagos,
Kuramo, Apese, Epe, Lekki and Mahin lagoons (Onyema, 2009b).
Iyagbe lagoon until recently was not clearly familiar as a lagoon but referred to in some
literature as Badagry creek(s) (FAO, 1969; Kusemiju, 1988; Onyema, 2009a). However, Webb (1958)
recognized it as a lagoon and reported explicitly on its probable mode of formation, hydrology and
sediment type characteristics (Onyema, 2008). The formation of the Guinea coast lagoons in South-

Phytoplankton diversity and succession in the Iyagbe lagoon, Lagos 62
western Nigeria is evidently dependent on the movement of sand along the coast in a west-east
direction forming a prograding barrier (Webb, 1958; Hill and Webb, 1958; Onyema, 2008, 2009a, b,
c).
Like the Lagos lagoon, the Iyagbe lagoon receives inflow of tidal seawater via the Lagos
Harbour and this is especially prominent in the dry season. In the wet season however and as distance
from the harbour increases, fresh(er) water conditions are recorded. The area is covered largely by
luxuriant mangrove systems especially in areas of modicum or no significant noticeable human
activities. Mangrove biosystems are known to be nutrient rich, shallow, sheltered and productive
systems that serve as breeding, nursery and feeding grounds for aquatic organisms (Nwankwo and
Gaya, 1996). The phytoplankton are an important member of this comminuty especially in relation to
trophic relationship (Emmanuel and Onyema, 2007; Onyema, 2007).
At present, there is no publication on the diversity and successions of phytoplankton species in
the Iyagbe lagoon. This study aims at documenting the trends and pattern of micro-algal succession in
the lagoon.
2. Materials and Methods
2.1. Description of Study Site
Lagos State is an African megacity and is located in south-western Nigeria on the West Coast of
Africa. Lagos is located within latitudes 6° 23N and 6°41N and longitudes 2°42E and 3°42E and is
undoubtedly the commercial nerve-centre of Nigeria. Lagos has been described as the city of aquatic
splendour as a result of the significant coverage due to wetland areas (Onyema, 2009b). The Iyagbe
lagoon (Fig 1) is located in Lagos state, Nigeria and is one of the 10 lagoons in South-western Nigeria.
It is chiefly made up of the Porto-Novo and Badagry creeks. Other creeks in the immediate region
include the Tamoro, Elete, Festac, Light house and Tin can Island creeks. The Iyagbe lagoon is
centered about the town of Iyagbe (Webb, 1958) and is shallower in the Badagry than Porto-Novo
creek arm. The lagoon like the Lagos lagoon is open via the Lagos harbor enroute to the sea (Sandison,
1966).
Figure 1: Parts of lyagbe Lagoon, Porto-Novo and Badagry Creeks Showing Sampling Sites

63 Onyema, I.C
Two distinct seasons namely the wet (May – October) and the dry (November – April)
(Nwankwo, 2004b) are experienced in this region (Onyema, 2009c). In the area, dense rain forest zone
vegetation followed by littoral mangrove assemblages is the common riparine community type. Some
common organisms found in the area include amphipods, polychaetes, isopods, barnacles, oysters,
periwinkles, nematodes, fiddler crabs, sea cucumbers, mangrove crabs, mudskippers and shrimps
among others. Othe species are Rhizophora racemosa, R. harrisoni, Avicennia germinans, Phoenix
reclinata, Raphia hookeri, Elaeis guineensis, Acrotiscum aureum and Cocos nucifera. Faunal forms
associated with the stilt roots of Rhizophora include Balanus pallidus, Chthamalus (arthropods),
Mercierella enigmatica (Serpulid worm) and Gryphaea gasar (Bivalve). The mudskipper,
Periopthalmus koelreuteri, several species of crabs whish include Sesarma huzardi, Uca tangeri,
molluscs such as Tympanotonus fuscatus var. radula, Pachymelania and Littorina spp (periwinkles)
and an array of birds that feed on exposed fauna at low tide in the very shallow parts of the lagoon
system. The lagoon deposits are varied and are reflected in the pattern and type of vegetation in the
region (Webb, 1958). A similar description of study site has been provided by Onyema (2008).
Selection of stations for this study were based on their importance as confluence points and
points were the effect of anthropogenic stressors would be more likely felt. Additionally, the stations
covered the entire length of the lagoon area.
Table 1: G.P.S. location and station name of sampled areas in the Iyagbe lagoon
Station No. Station name G.P.S. locations
Station 1 Calabash Island Latitude 6 o 25 1 .987 N, Longitude 3 o 23 1 .400 E
Station 2 Tin-can Island Latitude 6 o 25 1 .833 N, Longitude 3 o 21 1 .532 E
Station 3 Ibafon Latitude 6 o 25 1 .964 N, Longitude 3 o 19 1 .244 E
Station 4 Imore Latitude 6 o 25 1 .755 N, Longitude 3 o 19 1 .915 E
Station 5 Ito-ogba Latitude 6 o 25 1 .409 N, Longitude 3 o 14 1 .624 E
Station 6 Abule-oshun Latitude 6 o 26 1 .134 N, Longitude 3 o 13 1 .224 E
Station 7 Idiagbon / Igbolobi Latitude 6 o 26 1 .214 N, Longitude 3 o 11 1 .826 E
Station 8 Iyagbe Latitude 6 o 25 1 .603 N, Longitude 3 o 11 1 .990 E
Station 9 Agbaja Latitude 6 o 24 1 .473 N, Longitude 3 o 12 1 .744 E
Station 10 Ikare Latitude 6 o 24 1 .632 N, Longitude 3 o 13 1 .705 E
Station 11 Ilashe Latitude 6 o 24 1 .676 N, Longitude 3 o 16 1 .938 E
Station 12 Idimangoro Latitude 6 o 24 1 .717 N, Longitude 3 o 19 1 .307 E
2.2. Collection of phytoplankton samples.
Phytoplankton sample were collected on each occasion and station with a 55μm mesh size standard
plankton net towed from a motorized boat for 5mins at low speed (

Phytoplankton diversity and succession in the Iyagbe lagoon, Lagos 64
Community Structure Analysis
For biological data analysis, the following diversity indices were used. Species Richness Index (d),
Menhinick’s Index (D), Shannon and Weiner diversity index (Hs), Species Equitability (j) and
Coefficient of Similarity (S) (Ogbeibu, 2005).
3. Results
3.1. The phytoplankton flora of the Iyagbe lagoon.
Seven major algal groups were represented in the micro-flora of the sampled areas within the Iyagbe
lagoon. These were the Bacillariophyceae, Cyanophyceae, Euglenophyceae, Chlorophyceae,
Dinophyceae, Chrysophyceae and Rhodophyceae. The Rhodophyceae was represented by a single
species (Batrachospermum sp.). Presented below are notable species, trends and their percentage
frequency of ocuurence for the different groups and species of algae. Table 2 shows a summary of
dominant species and their most frequent associates in the Iyagbe lagoon (Abundance per ml). Fig. 3
shows the occurrence of the most dominant species in the Iyagbe lagoon in terms of numbers.
Bacillariophyceae
The bacillariophyceae were the predominant group at all stations for the duration of the study in terms
of phytoplankton species diversity. The diversity of species were more discernable in the dry season
than in the wet season. 90 diatom species were recorded with the centric forms being more important
than the pennate forms in terms of diversity. With regard to species and their percentage frequency of
ocuurence, Coscinodiscus centralis (3.45 – 50%), Coscinodiscus eccentricus (6 - 50%), Coscinodiscus
radiatus (2 - 50%), Coscinodiscus marginatus (2.56 – 80.36%), Coscinodiscus lineatus (1.09 –
10.71%), Actinoptychus splendens (0.85 - 25%), Skeletonema coastatum (2 – 33.33%), Aulacoseira
granulata var. augustissima (2.0 - 50%), Aulocoseira granulata var. angustissima f. curvata (5.71%),
Aulacoseira granulata var. augustissima f. spiralis (1.57 – 68.75%), Odontella regia (2 – 8.57%) and
Odontella sinensis (4.26 – 10.34%) were the more abundant and frequently occurring centric species
that occurred in the lagoon. With regards to the pennate diatoms important members included Synedra
crystallina (2.13 – 64.29%), Synedra ulna (0.85 – 6.25%), Thalassionema longissima (1.21 – 26.09%),
Thalassionema fraunfeldii (2.0 – 5.98%), Thalassionema nitzschioides (2.13 – 31.25%), Parabelius
delognei (12.77 – 44.44%) and Bacillaria paxillifer (11.96 – 66.67%).
Chlorophyceae
10 species of green algae which included Akistrodesmus sp (2.86 – 24.04%), Cladophora glomerata
(0.72 - 16.67%), Gonatozygon monotaenium (2.33 - 51.35%), Gonotozygon sp. (18.92%), Microspora
flocca (6.25 - 8.97%), Straurastrum paradoxum var. cingulum (3.45%), Pediastrum simplex (0.23%),
Spirogyra africana (0.91 – 33.33%), Scenedesmus obliquus (3.49%) and Scenedesmus quadriqauda
(0.91 – 1.52%) were reported for the study lagoon.
Dinophyceae
The dinoflagellates were represented by three specie only, namely - Ceratium macroceros (1.27%),
Ceratium tripos (1.79%) and Peridinium africana (5%). Furthermore these species occurred only in the
dry season and in stations that were proximate to the Lagos habour (i.e Stations 1 and 2).

65 Onyema, I.C
Table 2: Summary of dominant species and their most frequent associates in the Iyagbe lagoon from Oct.,
2004 – Sept., 2006 (Abundance per ml).
Dominant Species Associated Species
Oct., 2004 Gonatozygon monotaenium
(285)
Aulocoseira granulata var. augustissima (125), Gonatozygon sp. (75),
Fragillaria construens (55) Spirogyra africanum (55), Synura uvella
(25)
Actinoptychus splendens (65), Coscinodiscus lineutus (45),
Nov., 2004 Aulocoseira granulata var.
augustissima (85)
Coscinodiscus centralis (15), Coscinodiscus eccentricus (15).
Dec., 2004 Aulocoseira granulata var. Actinoptychus splendens (505), Coscinodiscus marginatus (600),
augustissima (24,200) Bacillaria paxillifer (250), Pleurosigma angulatum (150).
Jan., 2005 Parabelius delognei (155) Bacillaria paxillifer (105), Cyclotella menighiniana (100), Podosira
tenobro (75), Coscinodiscus lineatus (30).
Feb., 2005 Coscinodiscus radiatus (800) Aulocoseira granulata var. augustissima (405), Parabelius delognei
(275), Thalassionema nizschoides (110).
Mar., 2005 Parabelius delognei (250) Coscinodiscus radiatus (55), Fragillaria oceanica (25), Coscinodiscus
centralis (30), Coscinodiscus eccentricus (25).
Apr., 2005 Paraelicus delognei (190) Coscinodiscus centralis (90), Coscinodiscus radiatus (85),
May, 2005 Parabelius delognei (250)
Coscinodiscus magniatum (40), Aulocoseira moniloormis (80).
Syndra crystallina (155), Coscinodiscus centralis (150), Biddulphia
leavis (125), Coscinodiscus eccentricus (65).
Jun., 2005 Aulocoseira granulata var. Actinoptychus splendens (40), Parabelieus delognei (40), Coscinodiscus
augustissima (60)
centralis (40), Anabaena constricta (30).
Jul., 2005 Actinoptychus splendens (650) Aulocoseura granulata (460), Aulocoseira granulata var. augustissima
f. spiralis (225), Coscinodiscus centralis (100), Aulocoseira granulata
(66)
Aug., 2005 Aulocoseira granulata var. Aulocoseira granulata var. augustissima f. spiralis (240) Aulocoseira
augustissima f. spiralis (240) granulata var. augustissima (66), Aulocoseira varians (45),
Sept., 2005 Actinoptychus splendens (80)
Actinoptychus splendens (40), Lyngbya limnetica (20).
Aulocoseira granulata var. augustissima (70), Aulocoseira granulata
(40), Aulocoseira granulata var. augustissima f. spiralis (30),
Aulocoseira varians (25).
Oct., 2005 Aulocoseira granulata var.
augustissima (195)
Actinoptychus splendens (125), Aulocoseira granulata (55), Aulocoseira
granulata var. augustissima f. spiralis (30).
Nov., 2005 Actinoptychus splendens (525) Aulocoseira granulata var. augustissima (65), Bacillria paxillifer (60),
Aulocoseira granulata var augustissima f. spiralis (60), Coscinodiscus
maginatus (40).
Dec., 2005 Coscinodiscus centralis
(3250)
Coscinodiscus radiatus (1100), Coscinodiscus eccentricus (95),
Bacillaria paxillifer (70), Coscinodiscus gigas (60).
Jan., 2006 Coscinodiscus centralis (425) Coscinodiscus radiatus (140), Parabelius delognei (100), Bacillaria
paxillifer (60), Cyclotella meneghiniana (50).
Feb., 2006 Coscinodiscus centralis
(2315)
Parabelius delognei (300), Coscinodiscus maginatus (100), Aulocoseira
granulata var. angustissima (80), Anabaena torulosa (75).
Mar., 2006 Parabelius delognei (175) Coscinodiscus eccentricus (110), Coscinodiscus radiatus (80),
Cyclotella striata (60), Thalassionema fraunfeldii (65).
Apr., 2006 Skeletonema coastatum (450) Thalassionema fraunfeldii (226), Oscillatoria sancta (200), Aulocoseira
nummulaides (80), Asterionella jopanica (135).
May, 2006 Akistrodesmus sp. (1750) Microcystis aureginosa (200), Coscinodiscus radiatus (180), Bacillaria
paxilifer (105), Synedra crystallina (105).

Phytoplankton diversity and succession in the Iyagbe lagoon, Lagos 66
Jun., 2006 Microcystis aureginosa (105) Aulocoseira granulata var. augustissima (55), Coscinodiscus centralis
(35), Coscinodiscus eccentricus (30), Campylodiscus clypeus (15)
Jul., 2006 Actinoptychus splendens (175) Coscinodi.scus centralis (100), Coscinodiscus radiatus (60),
Aug., 2006 Actinoptychus splendens (535)
Aulocoseira granulata (70), Aulocoseira granulata var. augustissima
(40)
Bacillaria paxillifer (145), Skeletonema coastatum (105), Pleurosima
augulatum (35), Achanthes longipes (35).
Sept., 2006 Aulocoseira granulata var.
augustissima (275)
Actinoptychus splendens (210), Bacillaria paxillifer (60), Aulocoseira
granulata var. curvata (35).
Euglenophyceae
Euglena acus (2.78%), Phacus acuminatus (3.03%), Phacus curvicauda (1.92%) and Trachelomonas
hispida (0.45 - 3.02%) were the euglenoids that occurred. They were reported only in the wet season
and moreso in more inland stations of the lagoon further from the Lagos habour (especially at stations
7 and 8).
Chrysophyceae
The chrysophytes recorded two species namely Chrysoteppanoshaera globulifera (2.5 - 8.08%) and
Synura uvella (2.41 - 3.03%) for the duration of the study. Similarly, they were reported only in the
wet season and in more inland stations of the lagoon (especially at stations 7 and 8).
Rhodophyceae
Batrachospermum sp. (1.08 - 13.41%) was the only red algae recorded for the study.
3.2. Community Structure Analysis (Table 3a and b)
Values for Species Richness Index (d) varied between 0 and 0.266, Menhinick’s Index (D), 0 - 1.01,
Shannon and Wiener diversity index (Hs) 0 - 1.20, Species Equitability (j) 0 - 1.07, Species diversity
(S) 1 – 17, Abundance (N), 0 – 4400 individuals per ml, Log of Species diversity (Log S) 0.3 – 1.17
and Log of Abundance (Log N) was between1.0 and 3.37. For instance, species diversity was higher in
the second year of study than the first (Table 3a and b).

67 Onyema, I.C
Figure 2: Occurrence of the most dominant species in the lyagbe lagoon in terms of numbers (Oct., 2004-
Sept., 2006)
900
800
700
600
Abundance per ml.
500
400
300
200
100
Dec., 2004 Aulocoseira granulata var. angustissima **
*multiplied by 10
**multiplied by 100
0
Jan., 2005 Parabelius delognei
Feb., 2005 Coscinodiscus radiatus
Mar., 2005 Parabelius delognei
Apr., 2005 Parabelius delognei
May 2005 Parabelius delognei
Jun., 2005 Aulocoseira granulata var. angustissima
Jul., 2005 Actinoptycus splendens
Aug., 2005 Aulocoseira granulata var. angustissima
Sept., 2005 Actinoptycus splendens
Oct., 2005 Aulocoseira granulata var. angustissima
Nov. 2005 Aulocoseira granulata var. angustissima
Dec., 2005 Coscinodiscus centralis *
Jan., 2006 Coscinodiscus centralis
Feb., 2006 Coscinodiscus centralis *
Mar., 2006 Parabelius delognei
Apr., 2006 Skeletonema coastatum
May 2006 Akistrodesmus sp *
Jun., 2006 Microcystis aureginosa
Jul., 2006 Actinoptycus splendens
Aug., 2006 Actinoptycus splendens
Sept., 2006 Aulocoseira granulata var. angustissima
Oct., 2006 Gonatozygon monotaenium
Nov. 2006 Aulocoseira granulata var. angustissima

Phytoplankton diversity and succession in the Iyagbe lagoon, Lagos 68
Table 3a: Range of phytoplankton community composition parameters for the Iyagbe lagoon (Oct., 04 – Sept., 05).
Oct-04 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05 Sep-05
Species richness index (d) 0.2 - 1.09 0 - 1.65 0 - 6.12 0 - 2.33 0 - 2.0 0.26-2.13 0.33 - 1.58 0.65 - 2.66 0 - 1.74 0.51 - 2.32 0 - 1.3 0 - 0.78
Menhnick's (D) 0 - 0.75 0.25 - 0.63 0.04 - 0.48 0.16 - 0.87 0.05 - 0.64 0.26 - 1.05 0.35 – 0.8 0.29 - 0.95 0.32 - 0.96 0.3 - 1.12 0.22 - 0.68 0 - 0.65
Shannon-Wiener's Index (Hs) 0.29 - 0.65 0 - 0.89 0 - 0.56 0 - 0.84 0 - 1.0 0.22 - 0.97 0.3 - 0.88 0.3 - 1.0 0 - 0.78 0.35 - 1.20 0 - 0.73 0 - 0.61
Equitability (j) 0.48 - 0.98 0 - 1.0 0 - 0.72 0 - 1.0 0 - 0.95 0.39 - 0.98 0.59 - 1.0 0.24 - 0.93 0 - 1.0 0.37 - 1.10 0 - 0.98 0 - 1.0
Species diversity 2 - 6 1 - 11 1 - 8 1 - 10 1 - 13 2 - 11 2 - 10 4 - 17 1 - 12 3 - 13 1 - 8 0 - 5
Abundance 30 - 360 10 - 590 110 - 25280 5 - 245 80 - 930 15 - 300 20 - 295 55 - 585 5 - 175 80 - 920 5 - 320 0 - 170
Log of Species diversity 0.3 - 0.78 0 - 1.04 0 - 0.9 0 - 1.0 0 - 1.11 0.3 - 0.95 0.3 - 1.0 0.6 - 1.23 0 - 0.95 0.48 - 1.11 0 - 0.9 0 - 0.7
Log Abundance 1.48 - 2.56 1.0 - 2.77 2.04 - 4.4 0 - 2.34 1.9 - 2.97 1.18 - 2.48 1.3 - 2.47 1.74 - 2.77 0.7 - 2.24 1.7 - 2.98 0.7 - 2.51 0 - 2.51
Table 3b: Range of phytoplankton community composition parameters for the Iyagbe lagoon (Oct., 05 – Sept., 06).
Oct-05 Nov-05 Dec-05 Jan-06 Feb-06 Mar-06 Apr-06 May-06 Jun-06 Jul-06 Aug-06 Sep-06
Species richness index (d) 0.82 - 2.35 0.44 - 1.85 0.26 - .14 0.6 - 1.4 0.21 - 2.61 0.71 - 2.47 0.37 - 2.22 0.49 - 1.81 0.21 - 0.67 0.73 - 1.77 0.33 - 1.67 0.67 - 2.48
Menhnick's (D) 0.3 – 1.01 0.3 - 0.77 0.06 - .41 0.16 - 0.63 0.1 - 0.79 0.09 - 1.23 0.2 - 0.85 0.31 - 0.81 0.32 - 0.77 0.36 - 0.92 0.27 - 0.89 0.36 – 1.3
Shannon-Wiener's Index (Hs) 0.3 - 0.81 0.21 - 0.81 0.1 - 0.66 0.36 - 0.76 0.03 - 0.82 0.49 - 1.02 0.32 - 1.02 0.32 - 0.91 0.08 - 3.01 0.52 - 0.91 0.22 - 0.76 0.23 - 1.01
Equitability (j) 0.51 - 0.84 0.44 – 1.0 0.21 - 0.88 0.6 - 3.0 0.07 - 0.79 0.7 - 0.95 0.32 - 1.07 0.28 - 0.92 0.27 - 1.18 0.68 - 0.94 0.58 – 1.0 0.2 - 0.98
Species diversity 5 - 13 3 - 9 3 - 11 2 - 9 2 - 17 4 - 12 3 - 16 3 - 14 2 - 4 4 - 11 2 - 10 4 - 13
Abundance 75 - 555 15 - 180 205 - 4400 40 - 610 50 - 237 70 - 340 115 - 859 60 - 2205 10 - 110 50 - 340 15 - 885 45 - 635
Log of Species diversity 0.7 - 1.17 0.48 - 0.96 0.48 - 1.04 0.48 - 0.95 0.3 - 1.23 0.6 - 1.08 0.47 - 1.20 0.48 - 1.15 0.3 - 0.6 0.6 - 1.04 0.3 - 1.0 0.6 - 1.11
Log Abundance 1.88 - 2.74 1.18 - 2.26 2.31 - 3.64 1.81 - 2.79 1.7 - 3.37 1.85 - 2.53 2.06 - 2.93 1.78 - 3.34 1.0 - 2.04 1.7 - 2.53 1.18 - 2.95 1.65 – 2.8
Table 4: Similarity Index (j) combinations for stations in the Iyagbe lagoon (Oct., 2004 – Sept., 2006).
2004 2005 2006
Stations Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov Dec. Jan. Feb Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov.
1 Versus 2 0.33 0.25 0.20 0.80 0.20 0.46 0.22 0.75 0.00 0.00 0.00 0.57 0.55 0.17 0.21 0.12 0.32 0.47 0.80 0.70 0.67 0.25 0.35 0.86
2 Versus 3 0.33 0.50 0.40 0.50 0.25 0.55 0.00 0.57 0.00 0.00 0.50 0.80 0.80 0.17 0.35 0.21 0.35 0.50 0.80 0.67 0.40 0.30 0.35 0.67
3 Versus 4 0.44 0.57 0.44 0.80 0.40 0.46 0.00 0.40 0.00 0.00 0.50 0.50 0.36 0.22 0.40 0.56 1.00 0.59 1.00 0.25 0.5 0.13 0.60 0.67
4 Versus 5 0.25 0.00 0.40 0.00 0.29 0.67 0.00 0.75 0.46 0.86 0.36 0.00 0.44 0.15 0.11 0.21 0.57 0.56 0.40 0.59 0.00 0.12 0.42 0.60
5 Versus 6 0.50 0.00 0.22 0.22 0.20 0.24 0.43 0.62 0.75 0.86 0.44 0.62 0.40 0.33 0.35 0.42 0.42 0.47 0.00 0.80 0.17 0.53 0.53 0.55
6 Versus 7 0.53 0.53 0.10 0.55 0.14 0.38 0.18 0.75 0.86 0.67 0.57 0.56 0.62 0.80 0.50 0.40 0.38 0.50 0.80 0.67 0.47 0.48 0.40 0.80
7 Versus 8 0.38 0.40 0.11 0.12 0.15 0.46 0.00 0.63 0.55 0.29 0.60 0.50 0.40 0.60 0.29 0.00 0.54 0.24 0.00 0.50 0.47 0.57 0.44 0.67
8 Versus 9 0.71 0.44 0.44 0.20 0.40 0.35 0.29 0.53 0.60 0.80 0.55 0.25 0.43 0.50 0.67 0.43 0.32 0.36 0.00 0.71 0.53 0.38 0.60 0.57
9 Versus 10 0.57 0.57 0.27 0.31 0.46 0.38 0.20 0.67 0.33 0.50 0.57 0.57 0.25 0.57 0.33 0.22 0.75 0.63 0.00 0.67 0.71 0.42 0.31 0.50
10 Versus 11 0.55 0.00 0.22 0.29 0.33 0.40 0.00 0.67 0.50 1.00 0.67 0.40 0.20 0.29 0.40 0.40 0.75 0.25 0.33 0.40 0.44 0.45 0.53 0.62
11 Versus 12 0.55 0.00 0.36 0.68 0.13 0.36 0.00 0.50 0.50 0.67 0.57 0.00 0.50 0.50 1.00 0.00 0.67 0.53 0.67 0.50 0.33 0.35 0.38 0.86
12 Versus 1 0.36 0.50 0.20 0.33 0.20 0.18 0.00 0.22 0.00 0.50 0.00 0.33 0.44 0.20 0.29 0.33 0.13 0.33 1.00 0.31 0.29 0.00 0.32 0.57
11 Versus 2 0.33 0.00 0.36 0.40 0.25 0.27 0.00 0.43 0.00 0.00 0.22 0.00 0.33 0.00 0.15 0.22 0.27 0.14 0.57 0.53 0.36 0.29 0.14 0.86
10 Versus 3 0.36 0.00 0.12 0.33 0.20 0.62 0.00 0.21 0.18 0.00 0.40 0.00 0.15 0.44 0.22 0.13 0.80 0.43 0.50 0.31 0.17 0.29 0.33 0.50
9 Versus 4 0.33 0.57 0.57 0.17 0.50 0.38 0.00 0.43 0.50 0.29 0.40 0.40 0.67 0.29 0.29 0.30 0.67 0.42 0.00 0.53 0.44 0.29 0.40 0.67
8 Versus 5 0.60 0.00 0.29 0.13 0.22 0.18 0.44 0.38 0.40 0.40 0.33 0.55 0.47 0.29 0.22 0.31 0.33 0.60 0.80 0.38 0.16 0.42 0.29 0.50

69 Onyema, I.C
4. Discussion
The physico-chemical parameters of the Iyagbe lagoon has been reported to exhibited seasonal changes
that were closely related to the distributive pattern of rainfall of the region (Onyema, and Nwankwo,
2009). According to Brown and Kusemiju (2002), rainfall pattern in the tropics creates the dry and wet
season experienced in West Africa. These seasonal differences determine salinity in coastal waters and
hence the distribution of aquatic species. Brown and Oyenekan (1998) are of the view that salinity
gradient in the Lagos lagoon for instance was more pronounced in the dry season than wet season.
Environmental gradients linked to seasons were similar in the Iyagbe and Lagos lagoons (Onyema and
Nwankwo, 2009). Furthermore, hydrological conditions and plankton spectrum in the Lagos lagoon
has been reported to be governed by the salinity and associated environmental gradients (Akpata et al.
1993; Onyema et al. 2003). Similarly for the Iyagbe lagoon, Onyema and Nwankwo (2009) reported
the effect of a continuum of variations linked to rainfall events in the wet season and tidal seawater
incursion from the Lagos habour which is prominent in the dry season.
The phytoplankton of the Iyagbe lagoon was dominated by diatoms throughout the study.
Similar findings have been reported by Nwankwo (1988, 1996a), Nwankwo and Akinsoji (1989),
Onyema et al. (2003, 2007, 2008) for the Lagos lagoon and environs. Erondo and Chindah also (1991)
also recorded a phytoplankton community dominated by diatoms which constituted more than 85% of
the total phytoplankton population. In the Iyagbe lagoon phytoplankton diversity was generally higher
during the dry season than the wet (rainy) season and vise versa with regard to phytoplankton densities.
Specifically, blooms of Aulacosiera granulata var. angustissima was reported in the wet season.
Moreso micro-algal dynamics differed measurably in the two annual cycles probably in response to
variations in the water chemistry regime during the two years of study. Hence, the effect of
meteorological forcings cannot be dispensed with as controlling factors in the availability of nutrients
and flood situations that significantly determine phytoplankton diversity and succession (Onyema,
2008).
The reason for an observed reduced diversity in the phytoplankton spectrum of the Iyabge
lagoon as compared to the Lagos lagoon (Nwankwo, 1988; Nwankwo et al., 2003, Onyema et al.,
2003) may be as a result of the high levels of chemicals and toxic contaminants that continually find
their way in to the lagoon system in this area hence reducing diversity. Habour related chemical and oil
related input are known to have deleterious effects on aquatic biota in the region (Chukwu, 2002;
Onyema et. al., 2006). The Lagos lagoon is arguably more impacted by organic pollution than the
Iyagbe lagoon area (Onyema et al., 2003), even though other waste types impact both lagoons.
According to Nwankwo (1984), the occurrence of pennate forms during the rainy season in the
Lagos lagoon suggests their dislodgement from the substratum probably during high water discharge,
while tidal inflow probably accounted for the appearance of some marine forms in the plankton at the
same period. The reports of Suriella ovata, S. striatula, S. splendida, Cymbella affinis, and Amphora
ovalis during the survey may be slight reflections of possible stirring of the lagoon phytobenthic
community into the plankton. According to Onyema et. al. (2003) frequently occurring pennate forms
in the plankton samples from the Lagos lagoon was a likely reflection of the mixing of the shallow
lagoon and phytobenthic community by tides and flood waters at different seasons. Nwankwo and
Akinsoji (1989), Onyema and Nwankwo (2006) and Onyema et. al. (2007) are also of similar views in
there study of shallow coastal water bodies in south-western Nigeria. The presence of known marine
forms like Amphora alata, Asterionella japonica, Ditylum brightwellii, Melosira moniliformis, M.
nummuloides, Triceratium favus and the various species of Coscinodiscus, Odontella, Chaetoceros,
Rhizosolenia, Leptocylindricus, Thalassosira and Thalassionema further confirms the incursion of
seawater to the lagoon. These species are commonly found in the sea area of Lagos lagoon (Nwankwo
and Onyema, 2003; Nwankwo et al., 2004). This inflow is more discernable in the dry season as
further reflected by the phytoplankton spectrum and water chemistry characteristics (Nwankwo, 1988,
1996a, 1998b, 2004a, Nwankwo and Akinsoji, 1992, Onyema et. al. 2003).

Phytoplankton diversity and succession in the Iyagbe lagoon, Lagos 70
The more frequently occurring species encountered throughout a study by Kadiri (1999) of
phytoplankton in coastal water of Nigeria was Actinoptychus splendens. Kadiri (2007) has also
reported taxonomic details of this species in the region. This species had a good distribution in the
Iyagbe lagoon. According to Kadiri (1999) Actinoptychus splendens, Aulacoseira granulata and
Aulacoseira granulata var. angustissima f. curvata had a wide distribution in the area studied.
According to the same author, the prominence of A. granulata in all the coastal states studied, add to
the impressive array of evidence attesting to the cosmopolitan nature of the species. Its prevalence has
been reported in other coastal waters in Nigeria – (Lagos lagoon Fox 1957, Nwankwo, 1988, 1996a,
Kadiri, 1999; Onyema et al. 2003; Eleiyele reservoir, Imevbore, 1968; River Niger Eaton, 1966; River
Oshun, Egborge, 1973, 1974; Warri River, Opute, 1990).
The record of Trichodesmium thiebautii, the only true marine cyanobacteria (Desikachary,
1959) is noteworthy. According to Nwankwo et al., (2003) Trichodesmium thiebautii bloom off the
coastal waters of south-western Nigeria and is not an annual event and seems to be favoured by high
surface water temperatures and low nutrient levels. Further to this, Dugale et. al. (1964) has reported
massive blooms of T. thiebautii clogging fishing nets and reducing fish catch for the Arabian sea.
According to Siver (2003), with regards to the chrysophytes, the synurophyceae are
euplanktonic in nature and occur almost exclusively in freshwater habitat. Furthermore, the authors are
of the opinion that the most diverse floras of scaled chrysophytes are typically found in slightly acidic
condition. Wujek et al. (2004) have recently listed new records of chrysophytes for Nigeria from the
Lekki lagoon and this included Synura uvella encounted in this study but not Chrysoteppanoshaera
globulifera.
Aulacoseira granulata var. angustissima and Microcystis aeruginosa bloom in the wet season
may be indication of a number of situations. Nwankwo (1998) and Onyema et al. (2003) are of the
view that high densities of Aulacoseira granulata and Aulacoseira granulata var. augustissima
recorded for instance in the Lagos lagoon in the wet season were possibly recruited from the eastern
extremes of the Lagos lagoon system known to be fresh all through the year. It is also possible that for
the Iyagbe lagoon these species are recruited from the Ologe lagoon through the Elete creek and the
Yewa and Badadry lagoons that are located to the west of the Iyagbe lagoon.
It was also possible that reduced phytoplankton diversity and counts at some points especially
in the dry season may be due to grazing effects of phytoplankton elements by shoals of planktivorous
fishes in the coastal waters. Subrahmanyan (1959) suggested a similar situation in studies of the
phytoplankton of the West Coast of India. It is possible to infere from this study that variations in the
intensity of the main peak of production of phytoplankton of the Iyagbe lagoon vary from year to year.
A similar feature has been recorded by Nwankwo (1984) for the Lagos lagoon, Wimpenny (1966) for
the Yorkshire and Dogger Bank and Subrahmanyan (1959) for the West Coast of India.
With regard to the biotic distribution and community structure of phytoplankton species of the
Iyagbe lagoon, it is also possible that these quantitative fluctuations are due likely to blooming and
dominance of different species of diatoms during periods concerned. With regard to similarity index
(d), stations close to each other were more similar and this semblance was more especially after a
change in season (rainy or dry) has set in. Within the Iyagbe lagoon, stations were also very dissimilar
at the start and peak of the rainy season. Higher similarities in stations were more ovoius at periods
around November and December for the dry season and July and August for the wet season in the
annual cycle.
Some very low indices values at the beginning and end of the rainy season may be as a result of
sharp drop or rise in salinity which could have eliminated some species. For instance according to
Nwankwo (1996, 2004b) there are four ecologically important periods in in the Nigeria coastal waters
owing to the distributive pattern of rainfall. The preponderance of very few species primarily
Aulocoseira and Microcystis species in the wet season and Coscinodiscus, Actinoptycus, Odontella and
Parabelius species in the dry season probably accounted for low equitability values (j) in some months.
In the phytoplankton spectrum, periods of low diversity indices usually had strong dominance by a few
species. Stations close together recorded higher similarity index values than stations further apart.

71 Onyema, I.C
There were differences in the assemblages that existed between the phytoplankton spectra of
the seaward part of the lagoon and those further inland. Whereas a typical marine flora existed for most
months in the stations closer to the harbour (sea) especially in the dry season a low brackish /
freshwater community existed in areas more inland from the harbour especially in the wet season.
Acknowledgement
The author is grateful to the department of Marine Sciences, University of Lagos for logistics support
and use of its facilities.
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