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Review Paper
A review of the threat of oil exploitation to mangrove
ecosystem: Insights from Niger Delta, Nigeria
Amarachi Paschaline Onyena, Kabari Sam
*
Department of Marine Environment and Pollution Control, Faculty of Marine Environmental Management, Nigeria Maritime University,
Okerenkoko, Delta Sate, Nigeria
article info
Article history:
Received 16 October 2019
Received in revised form 8 February 2020
Accepted 9 February 2020
Keywords:
Occupational dislocation
Rural-urban drift
Artisanal refining
Environmental refugees
Climate change
abstract
Mangroves supply various goods and provide invaluable ecological services to humanity.
They serve as habitat to different species of fishes, provide a variety of plant products,
improve water quality, provide fish and shellfish for local communities, ensure coastal
stabilization, provide food chain support for near-shore fisheries, and undertake carbon
sequestration. They also serve as source of fuel, medicinal ornaments, and honey for the
local population. Despite these socio-economic and environmental benefits of mangroves,
its depletion is a continuous practice in the Niger Delta region of Nigeria. This is caused
primarily by anthropogenic activities, including over exploitation, oil spills, and crude oil
exploratory activities. These activities have destroyed livelihood structures, affected global
warming control measures, and affected the coastal system stabilization of the Niger Delta
region. This paper reviews existing literature and analysed identified gaps. The review
indicated a lack of participatory framework for mangrove conservation in coastal com-
munities in the Niger Delta despite the desperate need given the level of mangrove
degradation in the region. In addition, mangrove conservation policies exclude community
participation and negates co-management frameworks for mangrove conservation and
protection in the region. This paper reviews the impacts of land contamination on
mangrove ecosystems and socio-economic activities of local communities in the Niger
Delta region of Nigeria. A framework for mangrove conservation in the coastal commu-
nities is also proposed, with emphasis on the need to develop the capacity of a critical
mass of locals and provide low-to medium-level manpower in mangrove restoration in the
Niger Delta region.
©2020 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Mangroves are salt tolerant and sheltered intertidal forest covering most tropical and subtropical coasts with approxi-
mately 137,760 km
2
e152,360 km
2
of the world’s surface (Kainuma et al., 2013) yet are highly endangered coastal forest
ecosystem. Across 123 countries and territories around the globe, a sum of 73 mangrove species and hybrids are dispersed
(Spalding et al., 2010). On thewestern coast of Africa, mangroves extend fromthe coasts of Mauritania to Angola in the Gulf of
Guinea with about a third within the Niger Delta of Nigeria.
*Corresponding author.
E-mail address: s.kabari@yahoo.com (K. Sam).
Contents lists available at ScienceDirect
Global Ecology and Conservation
journal homepage: http://www.elsevier.com/locate/gecco
https://doi.org/10.1016/j.gecco.2020.e00961
2351-9894/©2020 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/
4.0/).
Global Ecology and Conservation 22 (2020) e0 0961
Mangroves are trees or large shrubs that have adapted to survive in harsh environmental conditions. Hence, has developed
unique survival features in the face of high salinity, anaerobic and waterlogged soils, and a challenging environment for seed
dispersal and propagation (Spalding et al., 2010). Mangrove ecosystems are a shelter for biological diversity consisting of
diverse aquatic and terrestrial flora and fauna which include mammals (monkeys, antelopes, and manatees), molluscs (bi-
valves, oysters), crustaceans, fish, reptiles and avian species.
Mangroves supply several ecosystem services that add to human wellbeing (Van Bochove et al., 2014 Friess, 2016) and may
be threatened by oil explorations and climate change. Mangroves are natural coastal habitats that buffer coastlines from
erosion and inundation, providing important protective services. Other benefits, including nursery grounds for commercially
and recreationally valued species, landing point for migratory birds, filtration of sediment, nutrients and pollutants,
enhancement of coastal fisheries, support tourism, protect coastlines (shoreline and seashore protection, stabilization of
coastal and shoreline substrate) against natural disasters such as floods and protection of coastal communities from waves
and extreme weather conditions (FAO, 2007;Mukherjee et al., 2014;Huxham et al., 2015;Barbier, 2016). Livelihoods in many
coastal communities in developing countries such as Nigeria largely depend on the productivity of mangroves and adjacent
alluvial systems. At least, 24 mangrove goods have been identified (Ackah-Baidoo, 2013). It is reported that over 60% of
commercial fishes in the Gulf of Guinea breed in the mangroves of the Niger Delta. Thus, an impact on the mangrove of the
Niger Delta affects fish distribution in the Gulf of Guinea. Additionally, cultural services (non-material benefits) of mangroves
such as recreation, spiritual enrichment and aesthetic that directly affect the people has been disproportionately impacted.
However, the Niger Delta mangroves are amongst the least studied and the worst degraded globally (Zabbey and Uyi, 2014).
Threats to the region’s mangroves include overharvesting for fuel wood, oil spill, dredging, wetland reclamation and nypa
palm invasion. A recent review ofcrude oil impact on mangrove shows that 37% of the global impact had occurred in the Niger
Delta (Duke, 2016).
These benefits of the mangrove ecosystem, notwithstanding, the disappearances of the mangroves are having a major
impact on the vulnerability of coastal communities particularly in the developing countries (Spalding et al., 2014). This
vulnerability is a contribution of different stakeholders whose responsibility is either neglected or abandoned. While the
government has the responsibility to set policy goals for the conservation of the mangrove ecosystem, rural communities also
have a role in mangrove ecosystem conservation and this could be achieved through a participatory and co-management
mechanism.
2. Onset of oil exploration
Oil prospecting in Nigeria started in 1908 bythe German Company, Nigeria Bitumen Corporation in the Araromi area of the
present Ondo State (see Fig. 1). Their pioneering effort ended due to the outbreak of the First World War in 1914. In 1937, oil
Fig. 1. Africa showing the Niger Delta region and oil pipeline network (red lines) (Sam et al., 2017). (For interpretation of the references to colour in this figure
legend, the reader is referred to the Web version of this article.)
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e009612
prospecting resumed in Iho, Ikeduru local government area (LGA) in Imo State by Shell D’Arcy (forerunner of the present Shell
Petroleum Development Company of Nigeria) (Ijeh, 2010). The company was awarded the sole concessionary right covering
the whole territory of Nigeria. Similar to the earliereffort, their activities were again interrupted by the Second World War but
resumed in 1947 and by 1951; they discovered oil but not in commercial quantity at Akata, near Eket (Frynas, 2000). In 1956,
oil was discovered in commercial quantities at Oloibiri (Bayelsa State) in the Niger Delta Area by Shell and commercial
production began in 1958 (Nwilo and Badejo, 2007). In February 1958, Nigeria joined the league of oil producers with
approximately 6000 barrels per day. Following this feat, by 1961, other companies such as Mobil, Chevron (formally Gulf),
Agip, and Safarap (Elf) commenced oil exploration activities on-shore and off-shore areas of Nigeria, and the exploration
rights formally granted shell alone was extended to these new comers.
Today, the Niger Delta region of Nigeria has about 606 oil fields with 355 situated onshore; 251 situated offshore with 5284
drilled oil wells and 7,000 km of oil and gas pipelines (Anifowose, 2008;Onuoha, 2008). Nigeria is the largest oil producer in
Africa and the sixth largest in the world (Bello, 2017), producing an average of 2.2 million barrels per day (Pieprzyk et al.,
2009). For the past three decades and even currently Nigeria’s economy is heavily dependent on the earnings from the oil
sector. The oil sector contributes over 11% to Nigeria’s Gross Domestic Product (GDP), 95% of foreign exchange earnings and
83% of total Federal Government revenue and has therefore transformed the Nigeria’s political economy (NNPC, 2019).
2.1. The Nigerian Niger Delta
Nigeria occupies a total area of 923,768 km
2
, which consists mainly of land and water with 910,768 km
2
and 13,000 km
2
respectively and 92 million ha (Bello, 2017). Nigeria has a total population of 190 million people, with an estimated proven gas
reserve of 202 trillion cubic feet (TCF) and 37.4 billion barrels of proven oil reserves (OPEC, 2019). The Niger Delta is made of
nine states (Fig. 1) and remains the hub of oil and gas production and associated activities in Nigeria (Egwurugwu et al., 2013;
Sam et al., 2017). The Niger Delta region currently has about 13,329 settlements. Out of that number, only 98 are rated as
urban, the rest are scattered rural villages which are mostly cut off from the most basic amenities and infrastructure. The
region also hosts over 800 oil field communities with over 900 active oil wells and thousands of other oil exploitation
infrastructures.
Nigeria’s mangroves in terms of area covered are the largest in Africa with an estimated 10,515 km
2
, mostly lining the Niger
Delta coastline. The Niger River Delta is located in the southern part of Nigeria and has vegetation covering a landmass of 7.5
million ha consisting of extensive mangrove forests, brackish swamp forests, and rainforests. The region has abundant fish
resources, widespread forests, and agricultural lands for sustainable agriculture (Ana, 2011;Ukpaka, 2012). The Niger Delta
region of Nigeria has numerous oil fields situated onshore and offshore with over 123 gas flaring sites; flaring about 17.2
billion cubic metres of natural gas per year in conjunction (Ishisone, 2004), making Nigeria one of the top greenhouse gases
emitters globally (Bello, 2017). Gas flaring, exploration, drilling, extraction, transportation and refining of oil in the upstream
and downstream sectors including waste discharge, accidental spills and operational failures, as well as sabotage, oil
bunkering and artisanal refining contribute to serious environmental pollution and destruction of mangroves (Bello, 2017;
Zhang et al., 2019).
3. Impacts of crude oil on mangroves
Mangroves are tidal wetlands and are considered to be the most highlysusceptible marine environments to large scale and
chronic oil spill (Zhang et al., 2019). Significant amount of crude oil is discharged into coastal environments and these
mangroves are extremely responsive to contamination by oil and industrial waste. For the past 60 years, there have been no
less than 238 major oil spills adjacent to mangrove-dominated shorelines worldwide. These oil spills have accounted for over
5.5 million tonnes of oil released directly, affecting up to more or less 1.94 million ha of mangrove habitat, and have killed at
least 126,000 ha of mangrove ecosystems since 1958 (Sheppard, 2000). Oil exploration in or near mangrove shorelines has
significant adverse impacts, even on the marine ecosystem (US Fish and Wildlife Services, 2013). Crude oil and their by-
products can destroy mangroves by coating aerial and submerged roots and from direct absorption (Fig. 2). Oil deposits as
marine tar residues are susceptible to mangroves which affects soil chemistry and permeability, leading to death and several
sub-lethal impacts (Duke, 2016). Once oil and marine tar residuesare deposited on or around the mangroves, they particularly
stick themselves to the plant surfaces, adsorbing to oleophilic surfaces of both flora and fauna. Oil coats breathing surfaces of
roots, stems, seedlings, and it contaminates surrounding sediments and their sessile intertidal or burrowing fauna (Zhang
et al., 2019). Also, coatings of oil on the leaves and submerged roots of the mangrove can hinder salt exchange responsible
for mediation of salt tolerance (Hoff, 2010). Crude oil is linked with toxic heavy metals most of which contaminate the soil
through underground deposits, especially Lead and Chromium. Iron is present in abundance in tropical and subtropical
aquifers and is also linked with crude oil deposits (Enujiugha and Nwanna, 2004). The damage of mangroves can also occur
through actions of mechanical abrasion, trampling, or compaction during clean-up or remedial activities can exacerbate
negative environmental impacts (US Fish and Wildlife Services, 2013;Bello, 2017;Zhang et al., 2019).
Oil spill on surface water spreads quickly, some become dissolved in water and may oxidize, and others undergo bacterial
changes and ultimately sink to the bottom. In the process, the sediment is contaminated and thus has a huge effect on biota.
Biodiversity loss and habitats destruction, largely due to top soil degradation are a main adverse effect of oil pollution. Any
region of mangroves that has been damaged by oil is vulnerable to other problems. For example, in the Niger Delta areas
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e00961 3
which are largely affected by oil pollution, mangrove forests have disappeared to the toxicity of oil spills and are being
replaced by noxious non-native Nypa fruticans, commonly known as nypa palms (Bello, 2017). These invasive species possess
a shallow root system that destabilizes the banks along the waterways, further impacting sediment distribution lower in the
delta system. Also, the process of photosynthesis is also impaired as a result of the introduction of phytotoxins into the
environment wherever oil spills occur. Oil spills can cause a variety of damage to marsh vegetation as they may reduce
growth, photosynthetic rate, stem height, density, and above ground biomass, eventually leading to plant death (Bello, 2017).
However, larger, more mature, mangroves exposed to oil only on the exposed root surfaces and sediment could have
survival duration of up to 6 months or more (Zhang et al., 2019). The degree of the impact and damage on the mangroves is
dependent on the concentration of the oil; the lighter the oils are, the more damage they cause and vice versa (Michel and
Rutherford, 2014;Duke, 2016).
Oil spill incidents caused by anthropogenic factors (e.g. activities associated with petroleum exploration, development and
production) are common place in the Niger Delta (Sam et al., 2017;Sam and Zabbey, 2018). Oil spills have detrimental impacts
on the soils and sediments, surface and groundwater, marine environment, terrestrial and aquatic ecosystems in the Niger
Delta. Discharges of petroleum hydrocarbons and petroleumederived waste streams also exacerbate impacts on biota and
widespread environmental degradation (Ite et al., 2013;Sam et al., 2017). Marine wildlife is particularly susceptible to the
toxic effects of oil and is basically far more subjected to it thanthe land-based wildlife. Many of the notable effects occur in the
intertidal zone where large volumes of oil are typically concentrated (Bodkin et al., 2003). The mostly affected are the
sedentary species and benthic organisms. Diverse species have shown different levels of biologic resistance or vulnerability to
contact with oil, with extended exposures resulting to preferential redistribution of populations, with expansion and habitat
redistribution by more resilient biota, reshaping ecosystems (Lee et al., 2015;Zhang et al., 2019).
Most marine oil explorations occur in environmentally sensitive areas, typically either in inland sea basins or offshore on
continental shelves, which are habitats to several benthic organisms in the sea (Kvenvolden and Cooper, 2003). The marine
ecosystems harbor significant bio-indicator species ranging from microbiological communities, habitat-forming species, the
indispensable mangroves, to seabirds, marine mammals, and invertebrates (TRB and NRC, 2003). Ecological impacts arise
from produced water, drilling fluids, cuttings and well treatment chemicals, wash and drainage water, sanitary and domestic
wastes and, spills and leakages.
Terrestrial impacts are caused by physical disturbance (e.g. construction of oil fields), land/soil contaminations caused by
oil spillages and leakages during drilling, and solid waste disposal.
Oil exploration by seismic companies involves surveying, clearing of seismic lines, and massive dynamiting for geological
excavations. The explosion of dynamite in aquatic environments leads to narcotic effects and mortality of fish and other faunal
organisms (Zabbey, 2004). The destabilization of sedimentary materials associated with dynamite shooting increases in
turbidity, blockage of filter feeding apparatuses in benthic (bottom-dwelling) fauna, and reduction of plant photosynthetic
activity due to reduced light penetration. The burying of oil and gas pipelines in the Delta fragments rich ecosystems such as
mangroves (Lonard et al., 2017). Apart from the reduction in habitat area, clearing of pipeline track segregates natural
populations, and fragments ecological systems, which may in turn distort breeding behavior of organisms. Oil coats smoother
mangroves and wetland leading to a more severe condition of hypoxia (Lonard et al., 2017). Crude oil contains toxic com-
ponents which cause outright mortality of plants and animals as well as other sub-lethal damage by interfering with the
functioning of various organ systems of plants and animals. It creates environmental conditions unfavorable for life; for
Fig. 2. Expanse of mangroves degraded by oil spills in a coastal community in the Niger Delta region (CEHRD, 2019).
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e009614
example, oil on water surface forms a layer which prevents oxygen penetration into water bodies, and this in turn leads to
suffocation of certain aquatic organisms (Useh et al., 2017). Crude oil kills plants and animals in the affected area; it also
poisons algae thereby disrupting major food chains thereby decreasing the yield of edible crustaceans. It also coats birds,
impairing their flight or reducing the insulating property of their feathers, thus making the birds more vulnerable to cold. Oil
spills in populace areas frequently wide spread, destroying crops and aquacultures through contamination of the under-
ground water and soils (Abarshi et al., 2017;Olatunji et al., 2018). Oil endangers fish hatcheries in coastal waters and as well
contaminates the flesh of commercially valuable fish (Useh et al., 2017). The decrease in dissolved oxygen by bacteria feeding
on the spilled hydrocarbons contributes to the death of fish due to lack of oxygen (Beyer et al., 2016;Useh et al., 2017).
3.1. Cultural effects
The activities of the oil industry have often resulted in a multitude of cultural problems. These include occupational
dislocation, rural-urban drift, unemployment and poor human health (Dauda, 2017;Mugisa, 2016;Matemilola et al., 2018).
The extent of these impacts is particularly important to local communities and indigenous people who may have their
traditional, communal and social values affected (Fentiman and Zabbey, 2015). There are cultural activities often practiced in
coastal communities in the Nigerian Delta that are no longer being undertaken as a result of oil spills. A classic example is the
festive bathing of community members in a river to usher in the New Year. It is a culture and also been believed that taking a
bath in that river will usher the community into a ‘new year of many good tidings’, as such, members of such community
consider the culture critical to their ‘prosperity’in a new year. This culture is continually being abolished as coastal rivers are
polluted by oil spills and cannot be used for such purposes (CEHRD, 2019). The key impacts been experienced in the Niger
Delta include seismic activities that lead to depletion of arable farm land destroys economic and crops, thus reduces farmer’s
access to land/food, which renders the areas inhabitable and lead to the exodus of man and animals. Farmers have lost their
lands and are consequently forced to emigrate to other communities in search of livelihood exerting additional pressures on
natural resources in such areas (Omofonmwan and Odia, 2009). A resultant effect is the socio-cultural changes for instance
social structure, organization, and cultural heritage, practices and beliefs, and impacts such as effects on natural resources,
rights of access, and alteration in value system influenced by foreigners (Mugisa, 2016;Zhang et al., 2019). Lack of planning
strategies may arise due to arising conflicts between development and protection, natural resource use, recreational use,
tourism and historical and cultural resource. Oil pollution results to loss of aesthetics value because of unsightly and noisy
facilities and transportation system, due to increased road, air and sea infrastructure and associated effects (e.g. noise, ac-
cident risk, increased maintenance requirements, or change in existing service) occurring in the environment.
3.2. Health effects
Human health impact can be direct effect from changes in ecological processes (e.g., consumption of seafood with bio-
accumulated oil toxins), economic stressors that can alter intermediary processes (e.g., psychological effects of community
decline), loss of major subsistence or export industries (such as through loss of fisheries), and effects of the spill causing
human harm outright (e.g., inhalation of aromatic hydrocarbons and other vaporous compounds) (Webler and Lord, 2010).
Oil pollution gives rise to the occurrence of certain ailments in areas that have suffered from oil pollution in Nigeria (Bello,
2017). Direct contact with, or exposure to oil spill material, as well as inhalation of volatile compounds, or physical contact
with crude including consumption of water and oil-contaminated seafood can have serious hazardous health effects on
humans, ranging from nausea and dizziness to carcinogenic effects, central nervous system inhibition and disruption, and
several long-term reproductive, developmental, and carcinogenic effects (Aguilera et al., 2010;Chang et al., 2014). A study of
the psychological implications of over 130 modern disaster situations revealed that technological disasters, such as oil spills,
result in more stress for affected communities than natural disasters (Picou et al., 2004). An example is the Hebei Spirit oil
spill that occurred off the Yellow Sea Coast of South Korea in 2007, releasing 12,547 kl of crude that contaminated 167 km of
shoreline and 13,978 ha of fisheries and aquaculture facilities, and which involved clean-up efforts by 563,761 people,
resulting in acute health effects. A year later, around 442 of the most affected first responders to initial effects of exposure
were analysed to assess the longevity of toxic effects. Symptoms reported include eye symptoms (average of 9.7 months),
headaches (average of 8.4 months), skin symptoms (average of 8.3 months), neurovestibular systems (average of 6.9 months),
respiratory symptoms (average2.1 months), and back pain (average 1.8 months) (Na et al., 2012) in descending order. A
number of those that came in contact with the volatile compounds during the clean-up effort still suffer from all supposed
categories of effects after 12 months, with headaches, eye symptoms, neurovestibular symptoms, respiratory symptoms, skin
symptoms, and back pain, respectively (Na et al., 2012). This is made possible given that spilled oil is reported to have
penetrated food chains and life-supporting systems such as controlled waters in the Niger Delta (Ajai, 2010;Zabbey et al.,
2017;UNEP, 2011). While there is no empirical study demonstrating the health implications of exposure to crude oil in
Nigeria (UNEP, 2011), evidence exist in other countries and this indicates a possibility of similar impacts in Nigeria.
3.3. Economic effect
Given that the local economy of many coastal communities is dependent on fishing and farming, an impact on mangroves
should have economic implications on such communities. Degraded mangroves affect local fisher men and women whose
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e00961 5
economic wellbeing is dependent on a clean rivers and alluvial soil fertile soil (Zabbey et al., 2017;Ehirim et al., 2018,Fig. 3).
Low catch from fishing expedition as a result of polluted rivers (Fig. 3) could lead to economic loss and affects peasant families
whose entire livelihood are dependent on fishing.
The economic impacts of mangroves comprise of the immediate costs linked with remediating and responding to oil spill
event and prolonged societal cost incurred by population proximal and/or dependent on spill affected ecosystems (Zhang
et al., 2019). Aside the instantaneous loss of the value of the spilled contents, there is a damage connected with the spill
process (e.g., mechanical failure, ship damage/run ashore) in addition to the direct cleanup costs in attempting to remediate
the oil that was lost. The fate of the oil residue has a large effect in costs (Zhang et al., 2019); this is because oil has different
amounts of interaction with the environment and diverse rates of weathering that influences their succeeding cleanup. Hence
the volume of oil spilled and the amount of movement or dispersal going on from surface or subsurface currents and the wave
energy determines the cost of cleanups (Vanem et al., 2008). Its interaction with sediment could make it difficult to clean than
material which has remained near the spill location thereby increasing the cost of remediation. The cost of oil spill cleanup
would also depend on whether it has undergone widespread natural weathering processes or has become quickly seques-
tered or entrained within the water column or sediment. The influence on cost depends if the spills occur near-shore which
indeed have a far greater potential for economic losses and are more expensive to clean than those at sea. Examples are the
non-extended social cost to human society from the ABT Summer spill and the Atlantic Empress spill that released an excess
of 250,000 tonnes of oil in 1979 and 1991 respectively. This was due to their remote spill location was hundreds of miles
offshore (White et al., 2012). During large scale offshore spills, varying costs of US$300,000 per tonne can be used to clean for
long range cleanup as a result of distance needed to travel, compared to small near shore spills that cost US$29,000 per tonne
as at 2010 estimates (Kontovas et al., 2010). Oil spills and their effects can have devastating implications economically for
fishing and other marine industries such as tourism and have health implications for people who are tasked with aiding in
relief efforts and those that come into contact with it (Upton, 2011).
3.4. Impacts on livelihood structures
Large areas of the mangrove ecosystem have apparently been destroyed in the Nigerian coastal environment (Fig. 2). Oil
pollution results in the destruction of the Niger Delta traditional local economic support systems of fishing and farming .
Farming is the major land use system in Nigeria, especially in the Niger Delta region. The Niger Delta population is highly
reliant on the land and natural resources for their livelihoods, which includes subsistence farming and fishing (Chinweze
et al., 2012). As a result, the traditional livelihood of the region is primarily fishing and farming. Oil spills degrade most
agricultural lands in the area and has turned hitherto productive areas into wastelands. With increasing soil infertility due to
the destruction of soil micro-organisms, and dwindling agricultural productivity, farmers have been forced to abandon their
land, to seek illegitimate alternative means of livelihood. Hence, once oil spills occur, farmlands and rivers are affected (Sam
et al., 2017). Aquatic life has also been destroyed with the pollution of traditional fishing grounds, exacerbating hunger and
poverty in fishing communities (Pittock et al., 2018).
Oil spills alter the physico-chemical properties of the soil thereby resulting to loss of soil fertility and subsequent loss or/
and reduced germination and growth of plants, and reduced crop productivity (Onwurah et al., 2007;Tanee and Albert, 2015).
Reduction in crop yield and consequent productivity affects economic benefits to communities (Sam et al., 2017). The
Fig. 3. Deserted fish landing site following oil spills.
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e009616
mangroves which serve as an important source of both fuel wood for the indigenous people and a habitat for biodiversity is
now unable to survive the oil toxicity of its habitat (Jack et al., 2016). The result is substantial damage to surface water,
drinking water, fish and other fauna as well as other parts of the mangrove ecosystems which make up most of the envi-
ronment in the Niger Delta zone.
Offshore oil drilling activities are major sources of oil pollution, mainly because of leaking pipes, accidents, ballast water
discharges, and production-water discharges. Drilling also involves the use of heavy metals such as vanadium and nickel, and
contamination of seawater with these metals is known to affect plants and animals. Oil pollution damages coastal resources
and habitats, as well as fisheries, reducing catches and incomes (UNEP, 2013). This increases poverty among indigenous
populations and may provide opportunity for local communities to take up illegitimate livelihoods (e.g. artisanal refining)
which are environmentally unsustainable (Sam and Zabbey, 2018).
The effects of oil spillage and acid rain resulting from gas flaring have been soil degradation which affects crop yield and
harvest and the migration of fishes and bottom dwelling organisms from in-shore or shallow waters into deep-sea. The result
of poor crop yield and reduction in number of seafood caught is food shortage and failure of some families to make adequate
money to meet certain basic needs. In Nigeria, agricultural sector has been rendered unprofitable with youths and women
jobless since their local economic support system of fishing and farming is no longer sustainable, moreover, this sector
supposed to be one of the largest employer of labour in Nigeria, especially in the Niger-Delta region (Bello, 2017). Considering
the condition of the Ogonis is a significant example of migration from communities and increase in environmental refugees.
The Ogoni people lived in intimately knitted communities with a subsistent economy providing them with their basic needs
before the economic considerations led to the development intervention of oil exploration which resulted in a compounded
change in the socio-economic landscape of Ogoni. Consequently, most of the Ogoni habitants have migrated to the big cities of
Port-Harcourt, Omoku, Eleme, and many others as a result of unavailability of land for farming and polluted river which
barred fishing.
The effects of oil pollution on the people and ecosystems of the Niger Delta and the apparent inability of these risks to be
sufficiently mitigated by the Government is reported to have contributed to activities of militancy in the region (Babatunde
et al., 2017;Omokhoa, 2015;Tantua and Kamruzzaman, 2016). Coastal communities in the Niger Delta region whose live-
lihoods dependent on luxuriant mangrove ecosystem and its services (e.g. fisheries), and can no longer derive such goods and
services, now engage in oil theft and militancy (Babatunde et al., 2017;Omokhoa, 2015). To earn a living, the youths would
kidnap foreign expatriates and demand huge sums of money for their release (Babatunde et al., 2017;Omokhoa, 2015;Tantua
and Kamruzzaman, 2016).
Notwithstanding such variety in the roles of mangroves, these ecosystems are still often seen as valueless wastelands
available for other uses. Such laxity toward sustaining mangroves is leading to a faster rate of destruction and disappearance
of mangroves in the Nigerian Delta. Considerable loss of the world’s mangrove cover is due to their conversion to other land
uses, such as urban area expansion, industrial development, aquaculture, agricultural development, and charcoal making
(Roma~
nach et al., 2018;Primavera et al., 2019). One of the key challenges facing mangrove conservation is inadequate un-
derstanding of their multiple roles due to poor research, particularly in the areas of climate change mitigation and adaptation
(Primavera et al., 2019).
4. Relevance of mangroves to climate change
The primary source of increasing atmospheric carbon dioxide (CO
2
) is burning of fossil fuels and thus the main contributor
to carbon dioxide concentrations, as well as emissions related to land use change. Mangroves are one of the most significant
ecosystems for sequestering carbon and reducing greenhouse gases. The capability of mangroves, sea grasses, and salt
marshes to sequester CO
2
from the atmosphere is becoming increasingly recognized at an international level (Ray and Jana,
2017;Hori et al., 2019). With the increase of atmospheric CO
2
concentration, there is a growing public and scientific concern
on the carbon sequestration potentialof various terrestrial ecosystems (Serrano et al., 2019). Mangroves are an important sink
for CO
2
. This can be enhanced by converting marginal agricultural land to non-agricultural restorative uses such as grassland,
forest or wetland. They could also provide more than 10% of essential dissolved organic carbon that is supplied to the global
ocean from land (IUCN, 2009).
Mangroves can trap not only fine sediment and organic matter but also coarse sediment driven by storm waves to form
special mangrove sediment (Allison et al., 2017). Thus, the sedimentation rate of mangrove is high (Alongi and
Mukhopadhyay, 2015). Besides, the litter productivity is high in Mangroves, which provides more carbon sequestrated in
sediments of mangrove, indicating high below ground carbon sequestration. In CO
2
sequestration, the burial of mangrove
carbon in sediments elocally or in adjacent systems are considered (Allison et al., 2017).
Mangroves, salt marshes, and sea grasses form much of the earth’s blue carbon sinks. These coastal vegetation sequester
carbon far more effectively (up to 100 times faster) and more permanently than terrestrial forests (Friess et al., 2016). Further,
studies have shown that mangrove forests store up to five times more carbon (per hectare) than most other tropical forests
around the world (Friess et al., 2016). This ability of mangroves and other coastal vegetation to store such large amounts of
carbon is, in part, due to the deep, organic rich soils in which they thrive. The entangled root systems of mangroves, which
anchor the plants into underwater sediment, slow down incoming tidal waters, allowing organic and inorganic material to
settle into the sediment surface. The sediments beneath these habitats are characterized by typically low oxygen conditions,
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e00961 7
slowing down the decay process and rates, resulting in much greater amounts of carbon accumulating in the soil. In fact,
mangroves have more carbon in their soil alone than most tropical forests have in all their biomass and soil combined.
Carbon offsets based on the protection and restoration of coastalvegetation could therefore be far more cost effective than
current approaches focused on terrestrial and peat forests, even before taking into consideration the enormous additional
benefits to fisheries, coastal protection, and the livelihoods of coastal inhabitants. Therefore, deforestation of mangroves
means releasing larger amounts of carbon into the atmosphere. This in turn causes the wet soil to dry up, leading to the
release of even more stored carbon into the atmosphere. Estimates suggest a range of between 150 million to 1 billion tonnes
of CO
2
that is emitted annually due to the destruction of mangrove forests globally. Thus, at the global scale, coastal wetland
destruction could account for 1e3% of industrial emissions; a number that is on the rise as more and more coastal wetlands
are destroyed every year around the world.
Currently, climatic change coupled with oil exploration activities in the region have negatively impacted on the envi-
ronment. This has resulted in the alteration of habitats, biodiversity loss and pollution of water bodies. Climate change
impacts on the mangroves negatively reducing their quality and thus affect livelihood pattern of households in affected
communities (Primavera et al., 2019).
5. What is needed for effective mangrove conservation regime?
In order for mangroves to be managed effectively, critical frameworks or enabling conditions should be established. Given
the Niger Delta context, we recommend the development of frameworks for mangrove conservation. The framework should
introduce a participatory mechanism that would allow a broad-spectrum of stakeholders contribute to a robust conservation
framework. With this approach to designing a framework, stakeholders at the community level will own the initiative,
support it and participate in the implementation of same, as it will deliver net profit to respective communities. A partici-
patory and co-management approach has been practiced in India, where the government, rural communities and other
stakeholders including the regulators undertake complementary functions for mangrove conservation and protection
(DasGupta and Shaw, 2013).
Fig. 4. Proposed co-management model for mangrove conservation in the Niger Delta region of Nigeria. The framework outlines the roles of different stake-
holders in mangrove conservation. Primarily, coastal communities (the custodians of the mangrove ecosystem), have a responsibility to engage in mangrove
planting, restoration/revegetation of degraded areas, and initiation of local norms that would encourage sustainable management of mangrove ecosystem
particularly mapped protected areas.
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e009618
We also recommend a co-management approach to mangrove conservation. Given that the livelihood of coastal com-
munities largely depends on the mangrove ecosystem, a co-management regime will allow communities to contribute to
effective maintenance of the mangrove ecosystem (Fig. 4). This system has been practiced in the Sundarbans, which
constitute the world’s largest continuous mangrove forest (10,000 km
2
) located within the river delta system between India
and Bangladesh. The co-management approach provides specific roles and responsibility for different stakeholders, including
coastal communities, in mangrove conservation. The framework ensures coastal communities are principally involved and
allowed to participate in mangrove conservation decision-making processes. Once this is established in Niger Delta coastal
communities as a policy, communities will actively participate in mangrove conservation activities. This has been reported to
achieve a participatory governance system and reduced conflicts associated with mangrove forest protection between reg-
ulators and communities (German Cooperation, 2017).
Also necessary is a stringent legal framework that supports and incorporates mangrove management strategies into a
wider planning and policy framework (Ayanlade and Proske, 2016;Babatunde et al., 2017;Udoh, 2016). Such frameworks
need to involve all relevant agencies and stakeholders and extend across all adjacent and connected ecosystems, watersheds
and adjacent waters. If restoration of mangrove is to be achieved, the access and use of mangrove forests and land must be
clearly stated (Babatunde et al., 2017). Where local communities and institutions do not have any legal title to the land other
than traditional de facto rights, local masses are frequently displaced by centralized decisions that lead to the development,
reclamation and clearing of mangrove habitats. Establishments of framework policy and legislation established at national
levels can prevent bit by bit loss and degradation (Ayanlade and Proske, 2016;Udoh, 2016). There should be a total removal of
perverse incentives alongside ‘enabling’policies and legislation (Babatunde et al., 2017). Extremely low-cost purchase of
mangrove areas for development purposes, tax breaks for the establishment of new aquaculture, and subsidies for shrimp
farmers need to be removed or counterbalanced by introducing positive incentives for restoration and maintenance of
mangrove habitat, and legislation to encourage more sustainable low impact aquaculture, including the rehabilitation of
abandoned ponds. Involving local communities in mangrove conservation efforts is vital to the achievement of any resto-
ration intervention (Sam et al., 2017b;Babatunde et al., 2017). Aquaculture provides economic benefits and food security in
many mangrove regions (Numbere, 2018). To attain sustainable aquaculture, a complete accounting of the costs and benefits
of the forest itself, its removal and replacement by ponds, and the benefits derived from aquaculture during the life of those
ponds should be applied (Ayanlade and Proske, 2016;Udoh, 2016).
Protected areas are a generally used management tool that can help prevent mangrove loss and degradation in specific
locations. They can supply social, economic and environmental benefits, through a more sustainable management of re-
sources or indirectly comprehensive protection of ecosystem services (Table 1). Restoration and afforestation are viable and
widely used management options to recover lost or establish new mangrove forest. While avoiding loss remains the lowest
cost and highest benefit route to mangrove conservation and sustainable use, mangrove restorationhas been widely practiced
around the world. Incentives need to be created that promote more environmentally responsible behavior and enhance local
livelihoods. This may be particularly important in the near future while perverse incentives are still distorting markets and
payments for ecosystem services are still under development. Mangrove conservation for poverty alleviation may require
Table 1
Mangrove ecosystem goods and services. This Table outlines benefits that could be derived mangrove conservation management mechanisms
(Adapted from Ronnback et al., 2007;Brander et al., 2012).
Ecosystem services Ecosystem goods References
Carbon sequestration Fish Ronnback et al. (2007)
Brander et al. (2012)
Fentiman and Zabbey (2015)
Shore protection Shrimps
Water quality regulation Honey
Erosion control Molluscs
Climate regulation Birds and eggs
Habitat and nursery ground Tea
Link to other marine systems Vinegar
Cultural and religious values Firewood
Recreation and tourism Charcoal
Information function Poles, beams, paneling
Boat building
Timber
Dye for cloth and nets
Furniture
Glue
Tannis for net preservation
Traditional medicine
Fodder
Fishing bait (worms)
Raw materials for handicrafts
Fishing boats
Fertilizers
Lime from mollusc shells
Insect control
A.P. Onyena, K. Sam / Global Ecology and Conservation 22 (2020) e00961 9
Governments to recognize the strong link between mangrove ecosystem degradation and the persistence of poverty in many
rural coastal communities. The destruction and degradation of mangroves has strong socio-economic impacts (Babatunde
et al., 2017). Improved appreciation of the range of values of mangroves may prove useful in making appropriate decisions
for more efficient and sustainable use. Community based poverty reduction programmes are needed where restoration and
management of mangroves is implemented while providing communities with suitable alternatives to mangroves de-
pendency (for domestic consumption and commerce). Successfully applied, these efforts can succeed in improving the
ecological conditions of mangroves as well as the livelihoods of local communities (Ayanlade and Proske, 2016;Udoh, 2016).
5.1. Knowledge gaps and research needs
There are many studies outlining the impacts of mangrove degradation (Fentiman and Zabbey, 2015;Duke, 2016;
Numbere, 2018;Onwurah et al., 2007;Tanee and Albert, 2015), but there is limited explanation on how the impacted
communities could participate in mangrove conservation, even as their livelihoods depend on it.
More pertinent is the poor knowledge of rural community members on the dangers of anthropogenic activities on the
maintenance and sustainability of the mangrove ecosystem. Awareness of the risks posed by some activities (e.g. clearing the
mangrove forest) could enhance communities’active participation in the conservation and protection of mangrove forests
(Fentiman and Zabbey, 2015). There is also limited knowledge that socio-cultural aspect of mangrove services should be
considered by policy-makers as an indispensable criterion for confronting the key challenges in mangrove ecosystems
conservation (Fentiman and Zabbey, 2015;Tanee and Albert, 2015). With the increase in the disappearance of mangroves and
destruction of livelihood structures in the Nigerian Niger Delta, there is need for the establishment of community vanguards
to develop a sustainable platform for mangrove revegetation and the stabilization of aquatic ecosystem (Onwuteaka and
Uwagbae, 2016;Vaughn, 2017;Numbere, 2018). Where mangrove conservation strategy is lacking, it will be difficult to
harness the diverse benefits of the mangrove ecosystem in the Niger Delta and its global implications, given the nature of
mangrove depletion (Numbere, 2018), without a mangrove ecosystem conservation framework.
6. Conclusion
As the world’s mangroves continue to disappear as a result of human population, development pressures, and oil ex-
plorations in the Niger Delta, it becomes even more important to assess the values of these important systems. Oil spills at
marine ecosystems will have many effects on the mangroves, environment and its ecology which are ultimately dependent on
the type and volume of oil. Understanding the various services mangrove ecosystems provide which include attenuation of
waves and buffer winds, storm protection, maintenance of fisheries, nutrient cycling, tourism, recreation, education and
research would trigger us developing better methods of assessing the protective benefits of these ecosystems. It is worthy of
note that its disappearance due to human development and oil pollution could have deleterious effects on the ecosystem,
cultural, health and socio-economic values of the affected ecosystem and man. The key to dealing with future oil spill events
in the environment that might in turn affect mangroves include prevention, understanding the effects of oil once it is released
into the environment and the effects of oil on marine biota and ecosystems, as well as structural features such as coastlines
and seafloors.
Therefore, mangrove forest should not be seen as useless areas of vegetation to be cut down indiscriminately for agri-
culture, housing and industrial development but as viable resources to be developed in a suitable manner. In order to raise
awareness of the multiple benefits of mangrove ecosystems, there is an opportunity to conduct more research and also focus
more on expanding mangrove areas in participation with local communities and other key stakeholders. Improving the
valuation of the protective service of mangroves, and the other benefits provided by these essential habitats, may prove
significant in these future coastal management decisions and sustainability.
Declaration of competing interest
None of the authors declare any competing or conflict of interest.
Acknowledgement
The authors appreciate the efforts of the anonymous reviews that provided comments and inputs that refined the paper.
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