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Effect of Soil Types on Growth, Survival and Abundance of Mangrove (Rhizophora racemosa) and Nypa Palm (Nypa fruticans) Seedlings in the Niger Delta, Nigeria

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The invasion of nypa palm into mangrove forest is a serious problem in the Niger Delta. It is thus hypothesized that soil will influence the growth, survival and abundance of mangrove and nypa palm seedlings. The objective was to compare the growth, survival and abundance of both species in mangroves, nypa palm and farm soils (control). The seeds were planted in polyethylene bags and monitored for one year. Seed and seedling abundance experiment was conducted in the field. The result indicates that there was significant difference in height (F 3, 162 = 4.54, P<0.001) and number of leaves (F 3, 162 = 21.52, P<0.0001) of mangrove seedlings in different soils, but there was no significant difference in diameter (F 3, 162 = 4.54, P = 0.06). Height of mangrove seedling was influenced by highly polluted soil (P = 0.027) while number of leaves was influenced by farm soil (P = 0.0001). On the other hand, mangrove seedlings planted in farm soil were taller (7.8±0.7 cm) than seedlings planted in highly polluted (7.7±0.4 cm), lowly polluted (6.3±1.4 cm) and nypa palm (6.0±0.8 cm) soils whereas Nypa palm seedlings planted in farm soil were the tallest (42±3.4 cm) followed by mangrove-high (38.8±5.8 cm), mangrove-low (34.2±cm) and nypa palm (21.1±1.0 cm) soils. Furthermore, species abundance of the different growth stages of mangrove and nypa palm seedlings were significantly different (F 1, 37 = 3.07, P = 0.04). Nypa palm seedlings outnumbered mangroves (27:1) and had higher overall survival rate (0.48) than mangroves seedlings (0.35) in all soils. This implies that nypa palm has competitive advantage over mangrove in mangrove soil.
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American Journal of Environmental Sciences
Original Research Paper
Effect of Soil Types on Growth, Survival and Abundance of
Mangrove (Rhizophora racemosa) and Nypa Palm (Nypa
fruticans) Seedlings in the Niger Delta, Nigeria
Aroloye O. Numbere
Department of Animal and Environmental Biology, University of Port Harcourt, Choba, Nigeria
Article history
Received: 27-12-2018
Revised: 08-04-2019
Accepted: 23-04-2019
Email: aroloyen@yahoo.com
Abstract: The invasion of nypa palm into mangrove forest is a serious
problem in the Niger Delta. It is thus hypothesized that soil will influence
the growth, survival and abundance of mangrove and nypa palm seedlings.
The objective was to compare the growth, survival and abundance of both
species in mangroves, nypa palm and farm soils (control). The seeds were
planted in polyethylene bags and monitored for one year. Seed and seedling
abundance experiment was conducted in the field. The result indicates that
there was significant difference in height (F3, 162 = 4.54, P<0.001) and
number of leaves (F3, 162 = 21.52, P<0.0001) of mangrove seedlings in
different soils, but there was no significant difference in diameter (F3, 162 =
4.54, P = 0.06). Height of mangrove seedling was influenced by highly
polluted soil (P = 0.027) while number of leaves was influenced by farm
soil (P = 0.0001). On the other hand, mangrove seedlings planted in farm
soil were taller (7.8±0.7 cm) than seedlings planted in highly polluted
(7.7±0.4 cm), lowly polluted (6.3±1.4 cm) and nypa palm (6.0±0.8 cm)
soils whereas Nypa palm seedlings planted in farm soil were the tallest
(42±3.4 cm) followed by mangrove-high (38.8±5.8 cm), mangrove-low
(34.2±cm) and nypa palm (21.1±1.0 cm) soils. Furthermore, species
abundance of the different growth stages of mangrove and nypa palm
seedlings were significantly different (F1, 37 = 3.07, P = 0.04). Nypa palm
seedlings outnumbered mangroves (27:1) and had higher overall survival
rate (0.48) than mangroves seedlings (0.35) in all soils. This implies that
nypa palm has competitive advantage over mangrove in mangrove soil.
Keywords: Abundance, Farm Soil, Invasive Species, Mangrove, Nypa
Palm, Rhizophora
Introduction
The growth of seedlings can signify underlying
adaptation to environmental conditions. Within
different population individuals that find suitable
location not only increase their chances of survival to
maturity, but also pass on the good genes to the next
generation (Duke et al., 1997). Therefore, with time seeds
of individuals that show greater competitive ability
dominate a given locality. This adaptation by the majority
of the individuals to select a favorable soil condition is
reflected in the local pattern of seed distribution, abundance
and growth. Mangroves are amongst the most widespread
marine vascular plants along subtropical and tropical
coastlines (Sanchez, 2019). They grow in swampy soils
(Feller et al., 2010), which originates from weathered
sedimentary rocks (SPDC, 1999). The soil is a mixture of
litter at different stages of decomposition (Numbere and
Camilo, 2016) and serves as carbon sinks (Ong and Gong,
2013; Tam and Wong, 1995).
Nypa palm (Nypa fruticans) on the other hand, is
regarded as a member of the mangrove ecosystem and
from the nypoid line (Gee, 2001). However, other
studies had shown that nypa palm is not a true mangrove
(Kathiresan and Bingham, 2001). Nypa palms are
invasive species that are deliberately introduced into
the Niger Delta to curb coastal erosion (CEDA, 1997;
Keay et al., 1964). but have become a major threat to
the mangroves. They grow in mangrove soils and have
their seeds dispersed across the mangrove forest by tidal
currents, signaling readiness for full colonization. During
low tides the seeds of the palms settle down on the forest
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floor and start to grow. The growth of nypa palms
within the mangrove forest endangers the mangroves and
prevents them from attaining maturity. This is because
the palms compete for space and nutrients with the
mangroves. The palms use their tiny, permeable and
fibrous root system to absorb soil minerals. They also
produce allelochemicals, which prevents the growth of
other plants around them (Numbere, 2018). Apart from
edaphic factors, which affects soil properties,
anthropogenic factors also contribute to rapid changes in
soil composition and soil chemistry, For instance, oil and
gas exploration lead to hydrocarbon pollution (James et al.,
2007; Kathiresan and Bingham, 2001) and affects soil
chemistry (Levin et al., 2006; Alongi, 2009). In the same
vein, deforestation of mangrove trees to pave way for
exploration activity (Numbere, 2018) impact mangrove
growth (Chakraborty, 2019) leading to reduction in
species abundance. It is thus postulated that the rapid
growth of palms in mangrove forests may signify their
affinity and adaptation to mangrove soil. The purpose
of this study was to determine the growth rate of
mangrove and nypa palm seedlings in different soils and
to determine the distribution and abundance of seedlings
of both species in a deforested mangrove forest. The
objectives were (1) to compare growth of mangrove
and nypa palm seedlings in mangrove, nypa palm and
farm soils, (2) to determine the survival of mangrove
and nypa palm seedlings in different soils (3) to
determine the abundance of mangrove and nypa palm
seedlings in deforested mangrove forest.
Methods
Study Areas
Soil samples were collected at three sites in two study
locations in the Niger Delta in 2015 as follows: crop
farm in Ozuoba (4°52´N and 6°55´E), mangrove and
nypa palm forest in Okrika (04°43´N and 7°05´E)
(Fig. 1). The climate of the area is monsoonal and the
precipitation at the study location, which was
measured daily with a rain gauge from July 2015 to
June, 2016 was 1466 mm. The rain began in March and
attained its peak in May while the dry months began in
November and ended in February. The mean annual
temperature range recorded at the experimental station
was between 26-28°C. The mangrove forest near the
refinery is uniquely divided into two sections by a
connecting tarred road (~4.6 m wide) that leads from the
refinery to the jetty, where crude oil is evacuated into
ships. Ten sets of giant Nickel/Steel alloy crude oil
pipelines (i.e., 8-10 inches wide) that spans about 16 km
in length and convey crude oil and petroleum products
from the refinery to the jetty are found 1 m away from
the road. The tarred road creates an artificial partitioning
of the mangrove forest into highly (~20 m from the
pipelines) and lowly (~100 m from the pipelines)
polluted treatments. Highly polluted treatment has higher
Total Hydrocarbon Content (THC) while lowly polluted
treatment has lower THC concentration (Table 1).
Details of the study location are given in previous
studies (Numbere, 2014; Numbere and Camilo, 2017).
Fig. 1: (a) Map of study area. The map shows mangrove forest (green) and urban areas (non-green) in the Niger Delta region
6°57’30”E 7°1’0”E 7°4’30”E 7°8’0”E
4°44’0”N 4°47’30”N 4°51’0”N
Study Area 0 1.25 2.5 5km
N
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Table 1: Soil physico-chemical characteristics of different soils collected at different locations in the Niger Delta, Nigeria.
Mangrove-high soil indicates highly polluted soil and mangrove low indicates lowly polluted soil
Soil types
--------------------------------------------------------------------------------------------------------------------------
Soil properties Mangrove-high Mangrove-low Nypa Farm F P
Ph 6.0±0.1 6.2±0.1 5.8±0.1 6.9±0.1 0.1 0.30
Organic matter (%) 1.01±0.01 1.48±0.05 1.87±0.01 1.99±0.01 0.3 0.02*
THC (mgkg1) 738.5±109.3 220±6.0 147.6±21.3 72±18.0 0.2 0.03*
Soil compaction (kg/cm2) 0.25±0.01 0.30±0.02 0.90±0.1 1.5±0.1 0.2 0.01*
Temperature (°C) 24.6±0.1 24.9±0.1 24.7±0.1 25.5±0.1 0.3 0.10
*significant
Study Species
Rhizophora racemosa (Rhizophoracea) is the
dominant species of mangroves that grows in the study
area. It grows mainly in soils that are swampy and filled
with organic material such as leave litter. It has
adventitious root system that supports survival under
anaerobic condition (Kathiresan and Bingham, 2001).
The mangrove forest supports numerous organisms and
provides some ecosystem services such as food,
medicinal herbs, fire wood and building materials
(Polidoro et al., 2010). Rhizophora propagule is torpedo-
shaped and is the longest (length: 9.4 cm) and heaviest
seed (134 g) amongst the two other prominent mangrove
species (i.e., white: Avicennia germinans; and black:
Laguncularia racemosa).
Nypa palm, Nypa fruticans (Palmae) is the second
most dominant species after the mangroves species in the
area (CEDA, 1997; Keay et al., 1964). The palms are
invasive species (Johnstone, 1996) that have colonized
vast areas of the mangrove forests in the last 20 years
(Wang et al., 2016; Numbere, 2018). They have fibrous
root system and are ubiquitous in disturbed soils that
have been infiltrated with human waste. Their seeds are
round and made up of fibrous foam-like outer covering
that makes them buoyant and scattered on forest floor.
Sample Collection
Soil samples were collected with hand-held soil
augur (Scotts, Germany) from a depth of 5 cm below
the soil surface at five randomly selected spots each in
farm, nypa palm, highly polluted mangrove (i.e.,
mangrove-high) and lowly polluted mangrove (i.e.,
mangrove-low) soils . The specific areas of soil
collection were geo-referenced with Garmin GPS
(USA). The mangrove soil is coffee brown in color,
semi-muddy and soft. The nypa palm soil is light
chocolate-brown in color, muddy, soft and filled with
organic materials while farm soil is light brown in
color, sandy-loam, porous slightly coarse and contain
plant litter. The farm soil is dark brown and was used
as the control (Fig. 2).
Soil pH was determined with a Kelway soil tester
while the soil compaction was determined with a pocket
penetrometer. Soil temperature was determined with a
digital dual sensor thermometer to a detection limit of
+/-1°C. Salinity of the surrounding water body was
determined with a salinity meter (OAKTON salt 6,
Acorn series) to a detection limit of +/-1%. Twenty seeds
each of mangrove and nypa palm were picked from the
forest floor or plucked from the trees. Those without
blemish were selected, cleaned and weighed (Ohause
model SC 2020) and their lengths measured with a
measuring tape (Keson OTR10M300). The diameter was
measured with a vernier caliper (Science ware,
Switzerland) at an accuracy of 0.1 mm.
Laboratory Analysis
Total Hydrocarbon Content (THC) and Total
Organic Content (TOC) Analysis
Total Hydrocarbon Content (THC) was determined
using colorimetric method (model: DR 890 HATCH
colorimeter) and Total Organic Content (TOC) was
determined using Walkey-Black titrimetric method. The
THC was used to determine the level of pollution of the
soil types in other to delineate the area into highly and
lowly polluted soils (Numbere and Camilo, 2016).The
TOC was used to determine the nutrient content in the
soil. This is because soil organic content influence
soil texture and composition, which affects mangrove
growth (Alongi, 2009).
Experiment 1: Seedling Growth and Survival in
Nursery
The average initial weight, diameter and length of
nypa palm (133.9 g, 4.9 mm and 9.4 cm) and mangrove
(i.e., 9.4 g, 1.1 mm and 17.4 cm) seedlings were
recorded before they were planted.
Both seeds were planted in a combination of ten
seedlings per four soil types for mangrove and nypa
palm in a combination of 10×4×2, which gives a total of
80 replications (Fig. 3a). The mangrove and nypa palm
seedlings were planted in medium-sized polyethylene
bags (32 cm×22 cm×14 cm) and placed in a 0.8 m×1.3 m
swamp box (Numbere and Camilo, 2017). The bags were
filled to the brim with four soil types up to a volume of
9856 cm3. The mangrove seedlings were planted upright
with the bottom sticking into the soil to a depth of 5 cm
while the nypa palm seedlings were buried in the soil
with the growing bud facing upward and the roots facing
downwards into the soil.
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Fig. 2: Four soil types found in the mangrove wet land areas of the Niger Delta, Nigeria: (a) Nypa palm soil (Muddy); (b) Mangrove
(chikoko-wet); (c) mangrove (Chikoko-dry) and (d) Sandy soil. It show the soil mineral particles
Semi-natural conditions were simulated in the
nursery by allowing the seedlings to grow in the open
under the elements of the weather. The seedlings were
watered daily with river water of salinity 26.4 ppt.
Height, number of leaves and diameter of seedlings
were measured between June 2015-June 2016. The
height of the mangrove seedlings was measured as the
distance between the tip of the sprouting bud and the
base of the seedling while the diameter was measured as
the circumference of the leave stalk taken 5 cm from the
bottom. Similarly, the height of the nypa palm seedlings
was measured as the length of the longest newly
sprouting leave. Mangrove started growing one month
after planting whereas nypa palm started growing 2-3
months after planting.
Survival of mangrove and nypa palm seedlings was
determined by the number of seedlings that were alive in
the different soil types at the end of one year. Survival
rate (Sx) was calculated based on the number of seedlings
alive from 0-I year (Nx) using Equation 1:
1
x
x
x
N
S
N
+
= (1)
Experiment 2: Seedling Abundance in Deforested
Mangrove Forest
Five randomly selected points were generated (Fig. 3b)
using the spa package in R Development Core Team (2014)
and the average abundance of seed and seedlings estimated
(Logan, 2010). The study area was mangrove dominated,
but because of several years of deforestation activities there
are some gaps in the forest. The experiment did not include
mature trees, but only considered seed and seedlings of
mangroves and nypa palms at different stages of growth.
A total of 354 seedlings were counted and divided into
four size classes as follows: (1) seeds (no size range), (2)
small seedlings (≤0.3 m), (3) medium seedlings (>0.3 m
or ≤0.6 m) and (4) large seedlings (>0.6 m).
2
-
7.5 mm
0.05
-
2 mm 0.002
-
0.5 mm <0.002 mm
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Fig. 3: (a) Experimental design of ( a) one unit of seedling growth experiment in polyethylene bags placed in a 1.3 m×0.8 m swamp
box (n = 80 seed and seedling samples), (b) Five randomly selected locations in a deforested forest where seedlings were
enumerated in a 20 m×20 m plot (n = 354 seed samples). Where F = farm soil, M-H = mangrove high soil. M-L = mangrove
low; N = Nypa pal soil; LAT represents latitude while LONG represent
Statistical Analysis
Normality and homoscedasticity of variance test were
conducted (Logan, 2010) (Fig. 4a). To ensure that
population group means are equal, an analysis of
variance (ANOVA) of mangrove and nypa palm growth
versus different soil types were conducted (Quinn and
Keough, 2002). Tukey’s test was performed to
investigate pair wise mean differences between groups
(Zar, 1996). Abundance experiment was analyzed with a
one-way ANOVA to test whether there was a significant
difference in seed abundance between mangrove and
nypa palm and also whether there was difference in the
abundance of the different growth stages. Here the growth
stages were regarded as the independent variables while
the number of seedlings was regarded as the dependent
variables for both species. All analyses were performed
in R statistical environment, 3.1.2 (R Development Core
Team, 2014). Bar graphs were plotted to show the
relationship of all parameters and their significance.
Results
Effect of Soil on Growth and Survival
Mangrove propagules were the first to produce leaves
between three weeks to one month after planting, but
were the first to die within a year. Nypa palm seedlings
produced no leaf after one month. The organic content of
farm soil was the highest (1.99±0.01%) followed by
nypa palm (1.87±0.01%), mangrove-low (1.48±0.05%)
and mangrove-high (1.01±0.01%) soils (Table 1). The
Total Hydrocarbon Content (THC) was higher in
mangrove-high soil (738.5±109.3kgcm2) as compared
to farm soil (72±8 kgcm2) in line with an earlier study
(Numbere, 2014). Height of seedlings (F3,162 = 4.54,
P<0.001, Fig. 4b) and number of leaves (F3,162 = 21.52,
1.3 m
Mangrove seedlings Nypa palm seedlings
F M-H M-L N
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
F M-H M-L N
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
O O O O
Polyethylene bags
0.8 m
LONG
6.80 6.85 6.90 6.95 7.00 7.05 7.10
4.75 4.80 4.85 4.90
LAT
(a)
(b)
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P<0.0001, Fig. 4c) of mangroves in different soils were
significantly different, but diameter of seedlings were
decidedly not different (F3, 162 = 4.54, P = 0.06). Height
of mangrove seedlings were more influenced by soils
from highly polluted plot (P = 0.027) while number of
leaves were more influenced by farm soil (P = 0.0001).
Mangrove seedlings planted in farm soil were taller (7.8 ±
0.7 cm) than seedlings planted in highly polluted soil
(7.7±0.4 cm), lowly polluted soil (6.3 ± 1.4 cm) and nypa
palm soil (6.0 ± 0.8 cm). Mangrove propagules planted in
farm soils also had the highest number of leaves (6).
For nypa palms, height of seedlings (F3,157 = 9.33,
P<0.0001) and number of leaves (F3, 162 = 19.37,
P<0.0001) in different soils were significantly different.
Nypa palm seedlings planted in farm soil were decidedly
the tallest (42±3.4 cm) followed by seedlings grown in
mangrove-high (38.8±5.8 cm), mangrove-low (34.2±cm)
and nypa palm (21.1±1.0 cm) soils.
Species Distribution and Abundance
The species abundance of the different growth stages
of mangrove and nypa palm seedlings were significantly
different (F1,37 = 3.07, P = 0.04). Small to large
mangrove seedlings were obviously more than small to
large nypa palm seedlings and nypa palm seed
population was more than mangrove seed population
(Fig. 4d) in a ratio of 27:1.
Although, there was no significant difference in the
rate of survival between mangrove and nypa palm
seedlings (F1, 6 = 0.47, P>0.05); nypa palm seedlings had
higher overall survival rate (0.48) than mangroves
seedlings (0.35) in different soil types. Surprisingly,
nypa palm seedlings had higher survival rate in
mangrove soil than its own soil. But mangrove seedlings
are site specific and survived more in their own soil and
farm soil (Fig. 5).
Fig. 4: (a) Normal Q-Q graph to show that height data was normalized (b) Mean height and (c) number of leaves of mangrove
(Rhizophora racemosa) and nypa palm (Nypa fruticans) seedlings grown in different soils in the Niger River Delta, Nigeria.
M-high indicates highly polluted soil while M-low indicates lowly polluted soil (d) Abundance of seeds and different growth
stages of mangrove and nypa palms in a deforested mangrove forest in the Niger River Delta, Nigeria. Vertical lines show 1
standard error of the mean
Mangrove Nypa palm
Seedlings
Soil Types
Nypa
Farm
M-high
M-low
0 1 2 3 4 5 6 7
Number of leaves of ± sem
(c)
(a)
-1 0 1 2 3
Standard dized residuals
Normal Q-Q
Theoretical quantiles avo (high ~ soil)
-3 -2 -1 0 1 2 3
Height (cm ± sem)
0 10 20 30 40 50
Soil Types
Nypa
Farm
M-high
M-low
Species
Nypa
Mangrove
Mangrove Nypa palm
Species abundance ± sem
0 10 20 30 40 50
A
-
seed
B-small C-medium D-large
Growth stage
(b)
(d)
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Fig. 5: Graph of mean of survival rate of mangrove and nypa palm seedlings: Survival rate of mangrove and nypa palm seedlings in
farm, mangrove-high, mangrove-low and nypa palm soils in nursery
Discussion
Different soil types influenced the height and
number of leaves of mangroves and nypa palm
seedlings (Fig. 4a and 4b). But mangrove seedlings are
quick starters being viviparous while nypa palm
seedlings are slow starters based on the longer time
they take to germinate. The height of mangrove
seedling is influenced by the source of soil. Nypa palm
seedlings had better growth and survival in different
soils apart from its own soil (Fig 5). Nypa palm also has
high seedling abundance and distribution, which has
made its colonization of mangrove forest successful. The
invasion of the palms is accelerated by soil quality
change caused by human activities such as oil spillages,
waste disposal and urbanization, which had perturbed the
mangrove soil for decades. Farm and nypa palm soils are
rich in organic content than mangroves soils as a result
of the presence of manure especially during harvesting
season and disposal of municipal waste in nypa palm
forest (Table 1). This is precipitated by high human
population around mangrove forest. The increased entry
of organic waste into mangrove forest results in the
conversion of swampy soil to muddy soil. This change
affects the growth of mangroves and makes them poor
competitors to the palms. Mangrove soil is dark brown in
color because of increased litter fall and decomposition.
It also has low plasticity and high porosity. In contrast,
nypa soil is light brown in color, muddy and has low
litter activity. It also has high plasticity and low porosity,
which are qualities that are not conducive for mangrove
growth. Mangroves and nypa palm seedlings
performed well in farm soil because it has high
nutrient content (e.g., nitrogen and phosphorous).
Although, mangroves are poor utilizers of nitrogen,
restoration projects utilize fertilizers, which basically
contain Nitrogen, Phosphorous and Potassium (NPK)
to facilitate their growth in seed bed. This implies that
farm soil can also be used in mangrove restoration
project, if done in combination with other factors that
facilitate mangrove growth such as increased salinity,
low plasticity and high carbon content. Mangrove
seedlings introduced into nypa palm soils have poor
growth because of a deficit in nutrient content and
poor adaptation while in contrast the movement of
nypa palms seedlings into mangrove soil is
advantageous to the palms, whose root morphology
and physiology permits better nutrient absorption and
translocation as compared to the mangroves that have
hardened and less permeable root system.
Mangrove
Nypa palm
Seedlings
Mangrove_high Nypa
Mangrove_low
Farm
Soil Types
Survival Rate
0.0 0.2 0.4 0.6 0.8 1.0
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Conclusion
High abundance and distribution of nypa seeds in
deforested mangrove forest (Fig. 4d) signify early stage
of colonization, which is facilitated by propagule
pressure. This is as a result of the window of opportunity
created by the deforestation of mangroves. This situation
has been a major factor in the overall decline of
mangrove forest in the Niger Delta region. This study
therefore, suggests that since soil plays key role in
mangrove growth, there should be constant monitoring
of soil quality to forestall drastic changes that will
jeopardize the survival of the mangroves. Nypa palm
seedlings should also be physically removed from
mangrove forest to prevent colonization. In addition,
more mangrove seeds should be planted in deforested
mangrove areas to close the window of opportunity for
the palms. The outcome of this study implies that soil
quality is very significant to mangrove restoration in
deforested and polluted areas globally.
Acknowledgements
We thank our research assistants Mr. Chimezie
Brown Iwuji who assisted in sample collection. We also
thank the undergraduate mentor of the lead author,
Professor Emeritus S.N. Okiwelu, who is assistance in
proof reading the work.
Funding Information
The researchers did not receive any funds from any
funding agency for this project. The study was
independently carried out by the author at the
Department of Animal and Environmental Biology,
University of Port Harcourt, Nigeria
Author’s Contributions
Aroloye O. Numbere: Solely initiated the conceptual
and experimental design, collected data, performed the
statistical analysis and wrote the manuscript.
Conflict of Interest
The author has no conflict of interest to declare.
Ethics
This article is original and contains unpublished
material. The corresponding author confirms that all of
the other authors have read and approved the manuscript
no ethical issues involved.
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Article
Full-text available
The Niger Delta mangrove is the third largest in the world and the largest in Africa. Since the 1960s oil and gas exploration has become an important economic activity, resulting in significant alteration of the landscape via pollution, urbanization and invasion. Landsat images of six different years (1984, 1986, 2000, 2003, 2005 and 2007) were used to determine land cover across 3, 700 km2. Landscape was segregated between areas with oil and gas exploration and those without. Two forest types were identified namely mangrove and mixed, which were further decomposed into high (Mang 1) and low (Mang 2) density mangroves and palms. A total of 145 landscape square samples, each 6.76 km2 were randomly selected in each map and statistically analyzed and modeled. The results showed that the kappa coefficient for the six years were all >0.9, (i.e., 0.93, 0.07, 0.94, 0.93, 0.90 and 0.94) indicating high classification accuracy. Also great change in mangrove landscape occurred in the last decade. Locations with increased oil and gas activities had significantly decreased amount of mangrove and palm forests. Also mixed forests increased over time and had a significant negative relationship with mangrove, Mang 1 and Mang 2. Even though the total area of mangrove forest did not change significantly (p>0.05), the total biomass of mangrove decreased (p<0.01). Nypa palm abundances increased over time, yet, it is negatively affected by the exploration. Increase in mixed forest and urban region has negatively affected the mangrove forest in the Niger’s delta landscape. High density mangrove forest withstood better the impacts of oil and gas exploration compared to mixed forest, but low density mangrove forest was the opposite. This suggests complex landscape level effects among different forest types.
Article
Full-text available
Nutrient cycling often moves between litter fall and decomposition. It is hypothesized that hydrocarbon pollution will slow down mangrove litter decomposition because of the reduction in microbial activities. We studied decomposition rates at different levels of pollution (i.e. high and low) and amongst different mangrove species (i.e. red, white and black). For the first experiment, fresh leaves of Rhizophora racemosa were collected, sealed in a litter bag and placed on the mangrove floor for 1.24 years at which all the leaves had completely decomposed to humus and were oven-dried and weighed to calculate the decomposition rate constant (k) of mass loss. Although there was no significant difference in the rate of decomposition (P > 0.05), leaves at the highly polluted plot had lower rate of decomposition (6.58 × 10⁻⁴) when compared to leaves at the lowly polluted plot (1.75 × 10⁻³). In the second experiment, there was a significant difference in decomposition rates amongst species (P < 0.05). Red mangrove leaves (0.41) decomposed more than white (0.28) and black (0.28) mangrove leaves. This implies that hydrocarbon pollution slowed, but did not stop the decomposition of mangrove leaves.
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Full-text available
This study was carried out with the primary aim of understanding how the mangrove ecosystem in the Niger Delta has been altered recently. Specifically, we determined the spatial extent of the mangrove forest in the Niger Delta using remotely sensed satellite data and estimated changes in the spatial extent of the forest from the mid-1980s through 2003. Overall, about 21,340 hectares of Mangrove forest was lost over the study period. Fieldwork confirmed that these losses were primarily due to urbanization, dredging activities, activities of the oil and gas industries, and the spread of Nypa Palm (Nypa frutican) plant species.
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Numerous ideas have emerged on the definitions, consequences of introduction, causes of damage, population dynamics and mode of propagation, prevention, and adaptibility of invasive species along with their impact on native species directly or indirectly by way of alteration of ecosystem dynamics. An Invasive species is defined as a species having been introduced outside its native range through human activities which are likely to cause economic or ecological harm. Estuaries and Coastal-Estuarine –Mangrove ecosystems being the most productive and sensitive ecosystems in the world, have appeared to be very much susceptible to introductions of non-native species because of lot of possibilities out of different ecological and people oriented activities in and around these eco-regions such as shipping and boating, ecotourism, fisheries, aquaculture etc. Alongside, several ecological perturbations such as eutrophication, global warming, biomagnification and biotransformation of persistent pollutants, etc. along with the negative impacts of introduced species on marine estuarine flora and fauna by outcompeting them for basic life support resources, human health risk associated with transmission of pathogens, and higher bioaccumulation capabilities of invasive species than native species have threatened this ecologically sensitive region considerably.
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R - the statistical and graphical environment is rapidly emerging as an important set of teaching and research tools for biologists. This book draws upon the popularity and free availability of R to couple the theory and practice of biostatistics into a single treatment, so as to provide a textbook for biologists learning statistics, R, or both. An abridged description of biostatistical principles and analysis sequence keys are combined together with worked examples of the practical use of R into a complete practical guide to designing and analyzing real biological research. Topics covered include: simple hypothesis testing, graphing. exploratory data analysis and graphical summaries. regression (linear, multi and non-linear). simple and complex ANOVA and ANCOVA designs (including nested, factorial, blocking, spit-plot and repeated measures). frequency analysis and generalized linear models. Linear mixed effects modeling is also incorporated extensively throughout as an alternative to traditional modeling techniques. The book is accompanied by a companion website www.wiley.com/go/logan/r with an extensive set of resources comprising all R scripts and data sets used in the book, additional worked examples, the biology package, and other instructional materials and links.
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