MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
https://doi.org/10.47193/mafis.3532022010908
ABSTRACT. This study was carried out from December 2018 to November 2019 to examine the
distribution and abundance of harmful algal species (HAS) in the central Bonny estuary. Seven sam-
pling stations were established with ArcGIS tool. Microalgae species were sampled with 20 μm
mesh plankton net. Nutrients were analyzed in the laboratory using the APHA 4500 Method, while
physicochemical characteristics were determined in situ. Results revealed that environmental gradi-
ents were adequate to support life in that part of the estuary except for phosphate (2.90 ±0.22-9.48
±1.06 mg l-1). A total of 31 HASs categorized into 17 genera and three classes were determined:
Bacillariophyceae (29 species), Chlorophyceae and Cyanophyceae (one species each). Navicula
amphibola had the highest density (4.713 ×103 cells l-1) while Pinnularia divergens recorded the
lowest density (0.00049 × 103cells l-1). Total density values decreased across seasons with 9.157 ×
103cells l-1 in dry season and 8.907 ×103cells l-1 in wet season. Checklist of species across stations
showed that five species were distributed across the seven stations, while two were found only in
Station 2 and 7. Diversity indices revealed Shannon’s index ranged between 3.17 and 3.25 and
species evenness ranged between 0.78 and 0.88, while Margalef range value (3.09-3.31) was con-
sidered moderately stable. Therefore, there is a need for proper management practices which could
help to reduce the level of nutrient discharge into the central Bonny estuary.
Key words: Distribution, season, abundance, HAS, environmental gradients.
Diversidad de floraciones de especies de algas nocivas en el área central del estuario del Río
Bonny, delta del Níger, Nigeria
RESUMEN. Este estudio se llevó a cabo entre diciembre de 2018 y noviembre de 2019 para
examinar la distribución y abundancia de especies de algas nocivas (HAS, por sus siglas en inglés)
en el área central del estuario del Río Bonny. Se establecieron siete estaciones de muestreo con la
herramienta ArcGIS. Las especies de microalgas se muestrearon con una red de plancton de 20 μm
de malla. Los nutrientes se analizaron en laboratorio mediante el Método APHA 4500, mientras
que las características fisicoquímicas se determinaron in situ. Los resultados revelaron que los gra-
dientes ambientales fueron adecuados para sustentar la vida en esa parte del estuario, excepto por
el fosfato (2,90 ±0,22-9,48 ±1.06 mg l-1). Se determinaron un total de 31 HAS categorizadas en
17 géneros y tres clases: Bacillariophyceae (29 especies), Chlorophyceae y Cyanophyceae (una
especie cada una). Navicula amphibola tuvo la mayor densidad (4,713 ×103células l-1) mientras
que Pinnularia divergens registró la menor densidad (0,00049 ×103células l-1). Los valores de
densidad total disminuyeron a través de las estaciones con 9,157 ×103células l-1 en la estación
seca y 8,907 ×103células l-1 en la estación húmeda. La lista de especies en las estaciones mostró
que cinco especies se distribuyeron en las siete estaciones, mientras que dos se encontraron solo
387
*Correspondence:
henry.dienye@uniport.edu.ng
Received: 30 May 2022
Accepted: 12 July 2022
ISSN 2683-7595 (print)
ISSN 2683-7951 (online)
https://ojs.inidep.edu.ar
Journal of the Instituto Nacional de
Investigación y Desarrollo Pesquero
(INIDEP)
This work is licensed under a Creative
Commons Attribution-
NonCommercial-ShareAlike 4.0
International License
Marine and
Fishery Sciences
MAFIS
ORIGINAL RESEARCH
Diversity of bloom forming harmful algal species in the central Bonny
estuary, Niger delta, Nigeria
HENRY E. DIENYE1, *, FRANCIS D. SIKOKI2, GEOFFREY N. WOKE2and OLANIYI A. OLOPADE1
1Department of Fisheries, Faculty of Agriculture, University of Port Harcourt, East/West Road, PMB 5323 - Choba, Nigeria. 2Department of
Animal and Environmental Biology, University of Port Harcourt East/West Road, PMB 5323 - Choba, Nigeria.
ORCID Henry E. Dienye https://orcid.org/0000-0001-6254-9179
INTRODUCTION
The estuarine ecosystem is an ecotype affected
by sea inflow and neighboring freshwater, which
results in high levels of nutrients in the water
body (Jha et al. 2014). According to Kress et al.
(2002), estuaries are places for human settle-
ments and activities (shipping, urban and indus-
trial waste) making them vulnerable to changes
caused by pollution, climate change and overfish-
ing, which in turn alter the water body’s produc-
tivity. Dynamics in biological populations, espe-
cially planktonic communities, represent varia-
tions in physical and chemical processes in estu-
aries (Marques et. al. 2007).
Harmful algal blooms (HABs) have become
the preferred scientific term instead of red tides
because these outbreaks have no connection to
the tides and may or may not color the water red
(Sverdrup et al. 2003). Additionally, some algae
species may bloom and color water, which is not
harmful. HABs are thus defined as high propaga-
tion of algae, ensuing transformation. Such algae
have the probability of producing toxins (Boesch
et al. 1997).
Approximately 300 algal species are said to
cause these blooms. It is understood that almost
one-fourth produce toxins (IOC 2015). A very
small number remains potentially harmful, which
can pollute aquatic organisms through contami-
nants resulting in health problems in human
beings, as well as multiplying and changing habi-
tats in ways that may be considered unfavorable
to them (Brand et al. 2012). Under the right con-
ditions, these groups of algal species form an
algal bloom provided that sufficient nutrients,
water column steadiness, enough light and ideal
temperatures are present (Hall et al. 2013). Nutri-
ent enrichment is the key mechanism through
which fertilizer or nutrient loads of nitrates and
phosphates are discharged into a waterbody, such
as livestock farming waste (Larsson et al. 1985)
and industrial or municipal waste (Larsson et al.
1985; Gilbert et al. 2005). Runoffs transport these
nutrients through river systems and eventually to
marine or freshwater systems. Many algal blooms
can damage aquatic species, and adverse blooms
are the result of an occasional accumulation of
toxic algae which can create hypoxic conditions,
producing damaging effects on aquatic ecosys-
tems (Gilbert et al. 2005).
Several new bloom species are assumed to fol-
low the discovery of concealed flora communities
(Smayda 1998) that had been there for years in
these lakes, but were not identified as detrimental
until more subtle toxin-revealing techniques or an
increase in the measurement and teaching of
observers were employed (Anderson et al. 1994).
The coastline is vulnerable to HABs, particularly
enclosed embayments, due to urbanization,
tourism, and industrial waste (Anderson et al.
2002; Sellner et al. 2003). Furthermore, the flow
of water, relaxation, and development of cysts are
factors in the creation of blooms (Sellner et al.
2003). There are several environmental factors
(both physical and chemical), including nutrient
availability and temperature changes, which are
being described as important drivers to harmful
algal species diversity (Giannuzzi et al. 2012).
The aim of this study was to assess the diversity
of bloom forming harmful algal species in the
central Bonny estuary of the Niger delta.
388 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
en las estaciones 2 y 7. Los índices de diversidad revelaron que el índice de Shannon osciló entre 3,17 y 3,25 y la uniformidad de las
especies osciló entre 0,78 y 0,88, mientras que el valor del rango de Margalef (3,09-3,31) se consideró moderadamente estable. Por lo
tanto, existe la necesidad de prácticas de gestión adecuadas que podrían ayudar a reducir el nivel de descarga de nutrientes en el área
central del estuario del Bonny.
Palabras clave: Distribución, estación, abundancia, HAS, gradientes ambientales.
MATERIALS AND METHODS
Study area
The Bonny estuary is among the numerous
low-land coastlines of the Niger delta complex. It
is located between 4° 25'and 4° 50'N latitude and
7° 0'and 7° 15'E longitude in Rivers State of
Nigeria (Figure 1). It extends in length to about
180 km from its mouth to the upper limits of
saline influence. It is mainly brackish and consists
of a main river channel and creek. The Bonny
estuarine channel has the highest tidal flow of all
river systems, which is influenced mostly by tidal
movements. The Bonny estuary extends from the
mouth of the estuary (lowest reach) close to the
Atlantic Ocean, where salinity is >30 in dry sea-
son and about 28 in rainy season, to the upper-
most reaches of the Iwofe area, where salinity is
<5 and <3, respectively (Dangana 1985).
Sampling stations
Seven geo-referenced stations were set up
along the estuary course using the ArcGIS tool,
through a reconnaissance preliminary survey:
Station 1 (Nembe waterside), Station 2 (Ebetu),
Station 3 (Isaka open river), Station 4 (Isaka main
town), Station 5 (Back of Ibeto cement), Station 6
(Macoba), Station 7 (NPA dockyard) (Figure 1).
Sample collection, preparation and analyses
Samplings were carried out at low tide in seven
geo-referenced stations previously described.
Surface water hauls, collected in triplicate at var-
ious sampling stations by filtering 100 l of sur-
face water over a 20 μm phytoplankton net. For
analysis and identification (Hansen 2002), they
were kept in 15 cm Nalgene storage bottles. Fifty
percent were preserved immediately using 2%
formaldehyde while the other 50% (live samples)
were stored in an insulated box to prevent rapid
389
DIENYE ET AL.: BLOOM FORMING HARMFUL ALGAL SPECIES
Figure 1. Study area indicating sampling stations in central Bonny estuary, Niger delta.
6.972 6.983 7.004 7.029 7.065 7.096
4.797
4.778
4.754
4.733
4.717
Isaka Town
PORT HARCOURT
Station 2 Ebetu (4.7520424, 7.0154484)
Station 3 Isaka pen iver (4.7342938, 7.0111311)or
Station 4 Isaka ain town (4.7372536, 7.0033255)m
Station 5 Back of Ibeto (4.7493771, 7.027797)
Station 6 Macoba (4.7614034, 7.0049335)
Station 7 NPA ockyard (4.7725265, 7.0085726)d
Station 1 Nembe aterside (4.7566115, 7.0254541)w
Station 7
NPA ock arddy
Station 6
Macoba
Station 5
Back f Ibetoo
Station 1
Nembe atersidew
Station 2
Ebetu
Station 4
Isaka ain ownmt
Station 3
Isaka pen iveror
N
S
WE
ò
temperature change (IOC 2015). Temperature,
salinity, Total Dissolved Solids (TDS), pH and
DO were measured in situ with a Horiba water
checker (Model Extech D0700) at each sampling
location. Triplicate surface water samples for
nutrients (phosphate PO4, nitrate NO3, nitrite
NO2, and sulphate SO4) were collected at neap
tide at a depth of 5 cm with pre-cleaned plastic
container, kept in ice-chest box and taken to the
laboratory for further nutrient analysis. Laborato-
ry determination of nutrients followed the stan-
dard procedures of water and wastewater analysis
of the American Public Health Association for
PO4, NO3, NO2and SO4(APHA 2012).
Enumeration of harmful algal species
Microalgae were counted using the Lackey
Drop Micro-transect Counting Method (APHA
1998). The sample was mixed well before sub-
sampling a drip of 0.05 ml onto a glass-slide in
triplicate with cover-slip. The processed volume
and the number of observed microalgae were
known in a given volume; their abundance was
counted with a low power objective with an
inverted microscope (Leica DMIL). Micropho-
tographs of harmful algae were taken by employ-
ing a camera fixed to the microscope. Identifica-
tion of algae was done by following references of
Taylor (1987), Hallegraeff et al. (1995), and
Tomas (1997). Density was calculated as:
Number (No) individuals ml-1 = C × TA
A × S × V
where, C =number of organisms counted; TA =
area of the cover slip, mm2 ; A =area of one strip,
mm2; S =number of strips counted; and V =vol-
ume of sample under the cover slip, ml.
Data analysis
Physicochemical and nutrient parameters of
samples were analyzed using one-way analysis of
variance of SPSS version 20. Fixed effect
ANOVAs were done in replicates. Tukey HSD
was used to separate the mean differences at a
95% confidence interval (p <0.05). Spatial vari-
ation of the various environmental parameters
and harmful algal species across the season was
done using the T-test. The diversity of HAS in the
estuary was calculated with harmful algal species
abundance, using the PRIMER software version
6.1.6 (Clarke and Gorley 2006).
Simpson’s diversity indices
The term Simpson’s diversity index is any of
three (3) closely related indices (Simpsons 1949).
- Simpson’s Diversity Index (D): it measures the
possibility of randomly picked individuals
from a sample:
D =Σ(n/N)2
D =Σn(n-1)
N (N-1)
- Simpson’s Diversity Index 1-D: here, the index
denotes possibility of entities randomly picked
in a sample.
- Simpson’s Reciprocal Index 1/D: it represents
a community of one species and a higher value.
- Shannon-Weiner Diversity Index (H’): the
level of uncertainty of forecasting a random
sample is associated to a community. Commu-
nity with one species (low diversity) (Shannon
and Wienner 1963):
H’ =-ΣpiInPi
where piis the proportion of individuals of the
ispecies.
Species richness (S) is a total number of dis-
similar species in an area. It is intensely hooked
390 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
on sample size and strength (Begon et al. 1990):
- Margalef’s Diversity Index:
Dmg =S-1
InN
- Menhinick’s Diversity Index:
DMn =S
√N
RESULTS
Results from physicochemical parameters and
seasonal variation of the surface water from the
sampled sites in the central Bonny estuary
revealed that there was a significant a difference
in pH, DO and turbidity (p <0.05), while temper-
ature, salinity, BOD, conductivity and TDS
showed no significant difference (p >0.05) across
stations. Mean values of pH, DO, salinity, BOD,
conductivity, and TDS decreased across the sea-
son (dry to wet), while temperature and turbidity
values increased across the season (dry to wet)
(Table 1).
Nutrient composition of sampled sites from the
central Bonny estuary indicated that there was a
significant difference across stations (p <0.05).
PO4and NO3decreased across seasons (dry to
wet), while NO2and SO4increased from dry to
wet season. Nitrate and sulphate showed signifi-
cant differences (p <0.01 and p <0.05, respec-
tively) across seasons (Table 2).
Three classes of major groups were represented
in the samples: Bacillariophyceae, Chlorophyceae
and Cyanophyceae, with 15 genera and 31 species
(Table 3). Families Pinnulariaceae and Stephan-
odiscaceae recorded two species each; Pleurosig-
mataceae and Coscinodiscaceae recorded three
391
DIENYE ET AL.: BLOOM FORMING HARMFUL ALGAL SPECIES
Table 1. Physicochemical parameters at different stations and seasons in the central Bonny estuary. T: temperature, DO: dissolved
oxygen, BOD: biological oxygen demand, COND: conductivity, TDS: total dissolved solids.
Station pH T DO Salinity BOD COND Turbidity TDS
(°C) (mg l-1) (mg l-1) (μS cm-1) (NTU) (mg l-1)
1 6.85 ± 0.09a 29.97 ± 0.71a 4.97 ± 0.37b 15.09 ± 1.41a 2.36 ± 0.09a 21.39 ± 2.39a 7.17 ± 1.02a 19.57 ± 9.30a
2 7.11 ± 0.07b 29.48 ± 0.82a 4.64 ± 0.36ab 16.20 ± 0.98a 2.12 ± 0.19a 20.82 ± 2.32a 7.31 ± 0.57a
17.44 ± 2.33a
3 7.26 ± 0.05ab 28.97 ± 0.56a 4.46 ± 0.28ab 19.40 ± 2.40a 2.49 ± 0.18a 25.19 ± 3.51a 9.90 ± 1.07b 18.34 ± 2.24a
4 7.26 ± 0.05ab 28.95 ± 0.58a 4.39 ± 0.35ab 19.47 ± 2.29a 2.30 ± 0.21a 25.24 ± 3.46a 10.45 ± 1.02b 18.33 ± 2.31a
5 7.32 ± 0.20c 28.96 ± 0.50a 3.89 ± 0.16a 18.24 ± 2.22a 2.42 ± 0.21a 24.21 ± 3.04a 6.06 ± 0.65a 17.16 ± 2.44a
6 7.34 ± 0.05c 29.07 ± 0.53a 3.97 ± 0.17a 18.88 ± 2.04a 2.42 ± 0.13a 24.27 ± 3.11a 5.20 ± 0.63a 18.67 ± 2.24a
7 7.35 ± 0.05c 28.96 ± 0.54a 4.32 ± 0.20ab 17.81 ± 1.59a 2.34 ± 0.13a 22.84 ± 2.67a 7.20 ± 0.35a 16.87 ± 2.21a
Season
Dry 7.39 ± 0.03 28.32 ± 0.39 5.10 ± 0.20 24.10 ± 1.24 3.00 ± 0.08 29.91 ± 1.10 5.42 ± 0.29 19.20 ± 1.60
Wet 7.08 ± 0.03 29.85 ± 0.25 3.97 ± 0.77 13.20 ± 0.33 1.83 ± 0.06 14.84 ± 1.0 19.26 ± 0.50 17.20 ± 0.85
t value 6.94 3.481 6.762 9.55 11.97 13.32 6.094 1.178
p value 0.62 0.00* 0.00* 0.00* 0.00* 0.22 0.130 0.00*
Superscripts of the same alphabet are not significantly different across the column (p >0.05). Superscripts of different alphabets
are significantly different (p <0.05).
species each; Naviculaceae recorded six species;
Triceratiaceae recorded five species; and Bacillar-
iaceae recorded four species, while other families
recorded one species each. Class Bacillario-
phyceae had 29 species, while Chlorophyceae and
Cyanophyceae recorded one species each.
The Family Naviculaceae had the highest densi-
ty followed by Bacillariacea, while the Family
Microcoleaceae recorded the least density (Figure
2). Navicula spp. recorded the highest percentage
(19%) followed by Nitzschia spp. (12%), while the
lowest (1%) was recorded for Thalassiosira eccen-
trica (Figure 3). Mean cell density plotted against
species in the study area indicated that N. amphi-
bola recorded the highest mean abundance
(4,714.38 cells l-1), followed by N. dicephala
(4,603 cells l-1), while Pinnularia divergens (4.9
cells l-1) recorded the lowest abundance (Figure 4).
Abundance across seasons indicated that 17
species decreased with season (dry to wet), while
11 species increased across seasons (dry to wet).
Two species (Gyrosigma stigma and P. divergens)
recorded mean value only during the dry season,
while only one species (N. hybrida) recorded mean
values in the wet season (Figure 5). Total density
values increased across season with 9,157 cells l-1
and 8,907 cells l-1 in dry and wet seasons, respec-
tively. The Class Bacillariophyceae recorded the
highest percentage composition of harmful algal
taxa (75%), followed by the Class Chlorophyceae
(15%), and the Class Cyanophyceae (10%).
Cyclotella meneghiniana, Cymbella turgidula,
Diploneis finnica,N. amphibola and Tretraedron
tumidulum were fairly distributed across the
seven sampling stations, while two species, P.
divergens,N. hybrida were the least distributed
harmful algal species in stations 2 and 7, respec-
tively (Table 4). Diversity indices showed that the
highest taxa value (31) was recorded in Station 4
and the least taxa value (29) was recorded in Sta-
392 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
Table 2. Nutrients (phosphate PO4, nitrate NO3, nitrite NO2, and sulphate SO4) across stations and seasons in the central Bonny
estuary.
Station PO4(mg l-1) NO3(mg l-1) NO2(mg l-1) SO4(mg l-1)
1 3.14 ± 0.2a 0.72 ± 0.07a 0.0034 ± 0.0004a 1,010.43 ± 9.02c
2 2.90 ± 0.22a 2.62 ± 0.92b 0.0039 ± 0.0007a 1,026.14 ± 6.32c
3 3.70 ± 0.25a 0.53 ± 0.04a 0.0046 ± 0.0007a 967.90 ± 9.20a
4 6.71 ± 0.53b 0.66 ± 0.06a 0.0048 ± 0.0003a 978.81 ± 6.76ab
5 9.48 ± 1.06c 0.71 ± 0.06a 0.0067 ± 0.0003b 1,004.10 ± 14.03bc
6 3.73 ± 0.24a 0.54 ± 0.04a 0.0043 ± 0.0002a 1,029.62 ± 10.19c
7 5.40 ± 0.67b 0.49 ± 0.08a 0.0043 ± 0.0006a 962.381 ± 6.43a
Season
Dry 4.68 ± 0.548 1.12 ± 0.33 0.0044 ± 0.0003 974.06 ± 6.03
Wet 5.26 ± 0.32 0.73 ± 0.03 0.0047 ± 0.0002 1,014.30 ± 4.54
t value 1.059 1.371 0.601 5.439
p value 0.110 0.00** 0.130 0.02*
Superscripts of the same alphabet are not significantly different (p >0.05). Superscripts of different alphabets are significantly
different (p <0.05).
*Significant at p <0.05
**Significant at p <0.01
tion 2, while taxa values of 30 were recorded in
Stations 1, 3, 5, 6, and 7 (Table 4). The number of
individuals with the highest value (9,625) was
observed in Station 7, while the lowest value
(8,496) was reported in Station 2. The highest
value of dominance D (0.049) was reported in
Station 4, followed by 0.048 in Station 2, while
the lowest value (0.043) was reported in Stations
2 and 7. The Shannon index with the highest
value (3.25) was reported in Station 7, followed
by Stations 2 and 6 (3.23), while the lowest value
(3.17) was reported in Station 3. The highest
393
DIENYE ET AL.: BLOOM FORMING HARMFUL ALGAL SPECIES
Table 3. Harmful algal species (HAS) composition in the Central Bonny estuary.
Class Family Species
Cymbellaceae Cymbella turgidula (Grunow, 1875)
Pinnulariaceae Pinnularia undulata (Sensu Cleve, 1891)
Pinnularia divergens (W. Smith, 1853)
Bacillariophyceae Naviculaceae Navicula amphibola (Cleve, 1891)
Navicula dicephala (Ehrenberg, 1838)
Navicula oblonga (Kützing, 1844)
Gyrosigma fasciola (Griffith and Henfrey, 1856)
Gyrosigma stigma (Hassall, 1845)
Gyrosigma acuminatum (Rabenhorst, 1853)
Catenulaceae Amphora holsatica (Hustedt, 1925)
Tabellariaceae Asterionella japonica (Cleve and Möller, 1882)
Diploneidineae Diploneis finnica (Cleve, 1891)
Stephanodiscaceae Cyclotella antigua (Smith, 1853)
Cyclotella meneghiniana (Kützing, 1844)
Bacillariaceae Nitzchia hybrida (Cleve and Grunow, 1880)
Nitzchia sigma (Smith, 1853)
Nitzchia vermicularis (Hantzsch, 1860)
Bacillaria paxillifera (Muller and Hendy, 1951)
Surirellaceae Surirella robusta (Ehrenberg, 1841)
Pleurosigmataceae Pleurosigma elongatum (Smith, 1852)
Coscinodiscaceae Coscinodiscus concinnus (Smith, 1856)
Coscinodiscuss granni (Gough, 1905)
Coscinodiscuss radiatus (Ehrenberg, 1840)
Triceratiaceae Odontella aurita (Agardh, 1832)
Odontella longicruris (Hoban, 1983)
Odontella mobiliensis (Grunow, 1884)
Odontella sinensis (Grunow, 1884)
Triceratium favus (Ehrenberg, 1839)
Thalassiosiraceae Thalassiosira eccentrica (Cleve, 1904)
Chlorophyceae Clorococcaceae Tretraedron tumidulum (Hansgirg, 1889)
Cyanophyceae Microcoleaceae Microcystis aeruginosa (Kützing, 1846)
value of evenness (0.88) was registered in Station
2, followed by 0.86 in Station 7, while the least
value (0.78) was reported in Station 4. The high-
est Margalef value (3.31) was reported in Station
4, followed by 3.19 in Station 5, while the least
value of 3.09 was reported in Station 2 (Table 4).
DISCUSSION
The pH reported in the central Bonny estuary
was well within the preferred pH range limits of
6.5 to 9.0 for optimal fish and aquatic life (Boyd
and Lichktopller 1979) recommended by the
World Health Organization (WHO 2008). Vincent-
Akpu and Nwachukwu (2016) reported a pH value
of 7.7 ±0.1 in Bonny. Valsaraj et al. (1995) report-
ed increased pH on days of extreme photosynthetic
activity. The seasonal difference in pH values
recorded was in line with results of earlier studies
conducted by Dublin-Green (1990) in the Bonny
estuary, where lower values of pH were recorded
in the rainy season. However, studies by Nweke
(2000), Ebere (2002), and Clarke (2005) registered
higher pH in the dry season than in the wet season.
394 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
Figure 2. Mean density of harmful algal family in the central Bonny estuary.
Figure 3. Percentage composition of harmful algal species (HAS) in the central Bonny estuary.
Cymbellaceae
Microcoleaceae
Pinnulariaceae
Naviculaceae
Catenulaceae
Tabellariaceae
Diploneidineae
Stephanodiscaceae
Bacillariaceae
Surirellaceae
Pleurosigmataceae
Clorococcaceae
Coscinodiscaceae
Triceratiaceae
20,000
15,000
10,000
5,000
0
Family
Mean density
cells l()
-1
Thalassiosiraceae
0
20 19.41
10.05
6.21
11.69
5.15
10.11
3.98 2.3 2.71 2.54 4.96 4.82
1.35
5.9
3.08 1.94 0.89 2.88
Percentage
Navicula spp.
Gyrosigma spp.
Cyclotella spp.
Nitzchia spp.
Coscinodiscus spp.
Odontella spp.
Pinnularia spp.
Amphora holsatica
Asterionella japonica
Bacillaria paxillifera
Cymbella turgidula
Diploneis finnica
Microcystis aeruginosa
Pleurosigma elongatum
Surirella robusta
Tretraedron tumidulum
Thalassiosira eccentrica
Triceratium favus
Species
395
DIENYE ET AL.: BLOOM FORMING HARMFUL ALGAL SPECIES
Figure 4. Abundance of harmful algal species (HAS) in the central Bonny estuary.
Figure 5. Mean density of harmful algal species (HAS) across seasons in central Bonny estuary.
1,447.48
1,704.47
1,597.18
1,267.01
703.94
1,262.52
1,670.99
2,232.72
3,316.24
3,026.62
3,058.76
2,215.62
1,040.24
847.1
4,714.38
4,603
2,879.34
2,274.27
3,157.89
1,455.15
477.27
2,709.57
2,099.23
1,067.32
2,492.66
4.9
3,707
1,937.32
1,291.76
564.91
1,812.33
Mean density ()cells l
-1
Amphora holsatica
Asterionella japonica
Bacillaria paxillifera
Coscinodiscus concinnus
Coscinodiscus granii
Coscinodiscus radiatus
Cyclotella antiqua
Cyclotella meneghiniana
Cymbella turgidula
Diploneis finnica
Gyrosigma acuminatum
Gyrosigma fasciola
Gyrosigma stigma
Microcystis aeruginosa
Navicula amphibola
Navicula dicephala
Navicula oblonga
Nitzchia hybrida
Nitzchia sigma
Nitzchia vermicularis
Odontella aurita
Odontella longicruris
Odontella mobilensis
Odontella sinensis
Pinnularia divergens
Pinnularia undulata
Pleurosigma elongatum
Surirella robusta
Thalassiosira eccentrica
Tretraedron tumidulum
Triceratium favus
Species
0
200
400
600
800
1,000
1,200
1,400
1,600
Amphora holsatica
Asterionella japonica
Bacillaria paxillifera
Coscinodiscus concinnus
Coscinodiscus granii
Coscinodiscus radiatus
Cyclotella antiqua
Cyclotella meneghiniana
Cymbella turgidula
Diploneis finnica
Gyrosigma fasciola
Gyrosigma acuminatum
Gyrosigma stigma
Microcystis aeruginosa
Navicula amphibola
Navicula dicephala
Navicula oblonga
Nitzchia vermicularis
Nitzchia sigma
Nitzchia hybrida
Odontella aurita
Odontella mobilensis
Odontella sinensis
Odontella longicruris
Pinnularia undulata
Pinnularia divergence
Pleurosigma elongatum
Surirella robusta
Tretraedron tumidulum
Thalassiosira eccentrica
Triceratium favus
Mean density ()cells l
-1
Wet Dry
Species
396 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
Table 4. Checklist and diversity of harmful algal species (HAS) in the central Bonny estuary.
Station
Species 1 2 3 4 5 6 7
Bacillariophyceae
Amphora holsatica - + - + + + +
Asterionella japonica + - + + - + -
Bacillaria paxillifera + + + + - - +
Coscinodiscus concinnus + + + + + - +
Coscinodiscus granii + + - - + - +
Coscinodiscus radiatus + + + + + - +
Cyclotella antiqua + + + + + + -
Cyclotella meneghiniana + + + + + + +
Cymbella turgidula + + + + + + +
Diploneis finnica + + + + + + +
Gyrosigma fasciola - + + + + - -
Gyrosigma acuminatum + - - - + - +
Gyrosigma stigma + + - - - - -
Navicula amphibola + + + + + + +
Navicula dicephala + + + + - + -
Navicula oblonga + - + + + - +
Nitzchia vermicularis + - + + + + +
Nitzchia sigma - + + + + + -
Nitzchia hybrida - - - - - - +
Odontella aurita + - - - - - +
Odontella mobilensis + - + + - + +
Odontella sinensis + - + - + + -
Odontella longicruris - + - - - + -
Pinnularia undulata + - + + + + +
Pinnularia divergens - + - - - - -
Pleurosigma elongatum + - + + + + +
Surirella robusta + + - - + + +
Thalassiosira eccentrica + - + + + + +
Triceratium favus + - + + + + -
Chlorophyceae
Tretraedron tumidulum + + + + + + +
Cyanophyceae
Microcystis aeruginosa - - + + + - -
Temperatures across stations and seasons were
normal with reference to their location in the
Niger delta. Ansa (2005) stated between 25.9 °C
and 32.4 °C. Uedema-Naa et al. (2011) reported
a range between 28.94 °C and 29.72 °C. Vincent-
Akpu and Nwachukwu (2016) measured temper-
atures of 28.0 ±0.5 °C in Bonny. Onwugbuta-
Enyi et al. (2008) reported DO values ranged
from 4.6 to 11.8 mg l-1. These findings are in
contrast with the results of this study, which may
be due to seasons. Davies et al. (2008) also stated
reduced DO in the wet season as compared to the
dry season and attributed it to a decrease in pho-
tosynthetic events of algae, which agrees with
the result of this study. The reason for the
reduced mean DO values was attributed to the
turbidity of the water due to influxes from run-
offs and degeneration of waste in the water.
Water with DO above 6 mg l-1 will sustain fish
and desirable forms of aquatic biota, whereas
water with 2 mg l-1 DO will support mainly
decomposers.
The present salinity and conductivity records
showed a similar trend within the acceptable
range for coastal waters. Chindah and Nduaguibe
(2003) obtained salinity values from 11.5 ± 1.8 to
20.3 ± 3.0 in the lower Bonny. Clarke (2005) reg-
istered higher salinities in the dry season than in
the wet season, which is in line with the results of
this study. Dibia (2006) described conductivity
values increasing during the dry season due to
absorption of ions. Values of BOD recorded in the
study are within the tolerable range for aquatic
environments (WHO 2008). Vincent-Akpu and
Nwachukwu (2016) reported a lower value of
2.80 mg l-1 in Nembe and 2.50 mg l-1 in Bonny
estuary. Also, the observation of Braide et al.
(2004) on water quality in the Eastern Niger delta
showed that the BOD load in this study did not
pose a hazard to the aquatic environment. Boyd
(1981) reported that turbidities in natural waters
rarely go beyond 20,000 mg l-1 and even muddy
waters frequently have less than 2,000 mg l-1.
Also, the observed turbidity level in this study
corroborates the range of 2 NTU to 47 NTU stat-
ed by Asonye et al. (2007). Turbidity from plank-
ton is not harmful to fish when it is at a mild
level. Fish harvesting is made easier as they are
less suspicious (Swann 2006). Roelke et al.
(2007) reported that stability of light energy is
expected to regulate algae ecosystem structure.
Vincent-Akpu and Nwachukwu (2016) reported
TDS values of 13.1 mg l-1 in Nembe and
14.9 mg l-1 in Bonny estuary. The higher total dis-
solved organic solid concentration observed in
this study may be ascribed to high surface runoff,
overland flow, as well as higher release of organic
wastes into the river.
397
DIENYE ET AL.: BLOOM FORMING HARMFUL ALGAL SPECIES
Table 4. Continued.
Station
1 2 3 4 5 6 7
Taxa_S 30 29 30 31 30 30 30
Individuals 9,282 8,496 8,832 8,628 8,903 9,237 9,625
Dominance_D 0.046 0.043 0.048 0.049 0.045 0.044 0.043
Shannon_H 3.21 3.23 3.17 3.19 3.22 3.23 3.25
Evenness_e^H/S 0.83 0.88 0.79 0.78 0.83 0.84 0.86
Margalef 3.17 3.09 3.19 3.31 3.19 3.18 3.16
Higher phosphate values were recorded in the
wet season than in the dry season, which is in
contrast with the findings of Chinda and Braide
(2001), who reported higher phosphate in the dry
season. This may be ascribed to the higher bio-
mass of phytoplankton and epiphyton in the wet
season. Natural inputs from decay of organic mat-
ter might be a contributor to the high phosphate
levels in this estuary. Davies et al. (2009) and
Davies (2013) recorded a higher nitrate value in
the dry season than in the wet season, which is in
line with the finding of this study and might be
ascribed to high anthropogenic inputs. Nitrate
does not pose a health threat, but it is readily
reduced to nitrite by the enzyme nitrate reductase,
which is widely distributed and abundant in both
plants and microorganisms (Glidewell 1990).
Abowei et al. (2012) reported algae families
including Baccillariophyceae, Dinophyceae,
Chlorophyceae, and Cyanophyceae along the shor
eline of Koluoma Creek in Bayelsa. Baccillario-
phyceae were the dominant and constituted 60%
of the phytoplankton biomass. Babu et al. (2013)
recorded 101 phytoplankton species on India’s
East-west coast, in which 76 species corresponded
to Bacillariophyceae, 17 to Dinophyceae, 5 to
Cyanophyceae, 2 to Chlorophyceae), and 1 to
Chrysophyceae.
According to Elliot (2010) the distribution pat-
tern of phytoplankton of Black Volta waters in
Ghana showed that all species, except two species
of Euglena sp. and Phacu spyrum (Eugleno-
phyceae), were fairly distributed in the four
hydrological seasons. He further stated that the
impoundment of Black Volta might, however, be
the main factor responsible for the discontinuous
seasonal distribution of Euglena sp. and P. spyrum
observed in the study. The result was similar to
other research indicating that Bacillariophyceae
were the dominant genera in water samples (Badsi
et al. 2012). Abubakar (2009) stated that in tropi-
cal regions, dry and rainy seasons showed distinct
fluctuations with an abundance of algae. Swann
(2006) reported that algae was among the reasons
for turbidity, as high turbidity during the rainy sea-
son was probably attributed to runoff. Iqbal et al.
(1990) reported that monthly variability in algal
population resulted in major seasonal disparity in
the physicochemical parameters in Hub Lake. The
higher abundance during the wet season was due
to nutrients and the water level at the time. This
finding is in contradiction to the results of this
study. Total density values decreased across sea-
sons, with 9.157 ×103cells l-1 and 8.907 ×103
cells l-1 recorded in the dry and the wet season,
respectively. Seasonal differences in algal abun-
dance in the dry season have also been reported by
Erondu and Chinda (1991) and Ogamba et al.
(2004) in the Niger delta. Indabawa and Abdullahi
(2004) also recorded higher algal cells in the dry
season than in the rainy season.
Diversity is dependent on key ecological prac-
tices such as competition, predation and succes-
sion, therefore, changes in these processes can
alter the species diversity index through modifi-
cations in evenness (Stirling and Wilsey 2001).
According to the classification of the Shannon-
Wiener index, if the diversity index is lower than
1, then biota communities would be regarded as
unstable, whereas a diversity index of 1-3 would
be considered moderately stable, and a value
higher than three would signify a stable or prime
condition (Mokoginta 2016). Shannon-Wiener
indices above three recorded in most of sampled
stations confirmed that these stations were mod-
erately stable and not under pollution stress, sug-
gesting that central Bonny estuary is relatively
vulnerable to environmental changes. Ofonmbuk
and Lawrence (2015) reported low Margalelf’s
diversity values from 2.871 to 3.513 in the Qua
Iboe estuary. This was similar to 2.93 reported by
Ogbuagu and Ayoade (2012), which is in agree-
ment with the findings of this study. This indicat-
ed that the harmful algal community was stable
among seasons in the study area. Minimal varia-
tions in the density of harmful algal species as
reflected by Shannon-Wiener, Pielous evenness,
and Margalef species richness, may be ascribed
398 MARINE AND FISHERY SCIENCES 35 (3): 387-402 (2022)
to uniform physical and chemical conditions
(Ogamba et al. 2004). The high diversity of val-
ues could be attributed to the influence of
bunkering activities, which are highly likely in
the estuary, as also reported by Adesalu and
Nwankwo (2008).
CONCLUSIONS
This study provides clear information regard-
ing the level of diversity and environmental gra-
dients in relation to species abundance and distri-
bution in the central Bonny estuary. Observed cell
densities serve as an early warning for future
bloom occurrences of potential impacts if the
density increases significantly beyond a deter-
mined threshold. In addition to effective educa-
tion, dissemination, and communication of the
available information, there is a need for an ade-
quate monitoring program warning on the forma-
tion of harmful algal blooms which requires easy
regulation of the aquatic resource in the central
Bonny estuary.
Funding
This research did not receive any specific grant
from funding agencies in the public, commercial,
or not-for-profit sectors.
Declaration of interest
The authors declare that there is no conflict of
interest.
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