The Impacts of Shrimp Farming on Mangrove Forests
Michele Vincelli
ENVS 190A - Environmental Policy Thesis
December 14, 2015
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Table of Contents
Abstract ……………………………………………………………………………………………………………………pg. 5
Introduction ……………………………………………………………………………………………………………..pg. 5
Mangrove definitions ………………………………………………………………………………………pg. 5
Mangrove Mechanisms, Structures, and Adaptations …………………………………………pg. 6
Mangrove Forests Zones, Range, and Distribution ……………………………………...….…..pg. 8
Shrimp Farming History, Growth, and System Types ……….………………………….……pg. 10
Goal of this Review ………………………………………………………………………………………..pg. 14
Mangrove Forests; Ecological Functions and Socio-Economic Benefits ……………...………pg. 15
Habitat for species and Resources for Mankind ………….……………………………………pg. 16
Nursery Function ………………………………………………………………………………………….pg. 17
Water Purification ……………..…………………………………………………………………………pg. 19
Coastal Protection ……………………………………………………………………………….………..pg. 20
Shoreline Stabilization ……………………………………………….……………………………….…pg. 22
Land Building …………………………………………………………………….……………………..…..pg. 22
Carbon Storage …………………………………………………………….………………………………pg. 24
Shrimp farming; Ecological and Socio-Economic Impacts ………………..………………………..pg. 25
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Reduced Area of Habitat for Thousands of Species ………….……………………………….pg. 26
Reduced Availability of Land and Forest Goods ……………………………………..…………pg. 27
Nursery and Fishery Collapse …………………………………………………………………………pg. 28
Decreased Water Quality ………………………….……………………………………………………pg. 29
Loss of Protective Coastal Barrier …………….…………………………………………………….pg. 33
Decreased Shoreline Stabilization and Land Building …………………………..…………..pg. 34
Decreased Carbon Sequestration and Storage …………………………………………………pg. 35
Impacts to Coastal Communities ……………………….……………………………………………pg. 37
Solutions to Protect Forests …………………………………….………………………………………………pg. 39
Discussion ………………………………………………………………………………………………………………pg. 41
Tables and Figures ……………………………………………………..…………………………………………...pg. 46
Figure 1 ……………………….………………………………………………………………………………pg. 46
Figure 2 ……………………………………….………………………………………………………………pg. 46
Figure 3 ………………………………………………….……………………………………………………pg. 47
Table 1 ………………………………………………………..……………………………………………….pg. 47
Figure 4 ………………………………………………………...……………………………………………..pg. 48
Table 2 ………………….……………………………………………………………………………………..pg. 49
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Figure 5 …………………………………………………………………………………………………...…..pg. 49
Table 3 ……………………………..………………………………………………………………………….pg. 50
Figure 6 …………...…………………………………………………………………………………………..pg. 50
Figure 7 ……………………………………………….………………………………………………………pg. 51
Figure 8 …………………………………………………….…………………………………………………pg. 51
Figure 9 ……………………………………………………………………………………………………….pg. 52
References …………………………………………………………………………………………………………...…pg. 53
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Abstract
Mangrove forests are one of the most productive and biologically diverse
ecosystems on the planet. They occur in the tropics on shorelines and provide wildlife and
humans with resources and ecological services such as habitat, forest products, water
purification, shoreline stabilization, coastal protection, and carbon sequestration. Despite
the overwhelming importance and value of these ecosystems, many have been damaged or
destroyed by industry, with development of shrimp farms posing the greatest threat.
Current shrimp farming methods remove mangroves and alter waterways to construct
ponds to rear shrimp. The development and runoff of waste and chemicals from ponds
negatively impacts mangrove forest ecosystems, which results in loss of mangrove
resources and services. Traditional communities that depend on mangroves for sustenance
suffer from these activities and become marginalized into heavily degraded environments.
Turmoil arises between local peoples and shrimp farmers, which leads to protests, bombs,
and killings. Policies, laws, and sustainable farming methods are needed to regulate shrimp
farm development in mangrove forests and reduce negative impacts to the system. Local
communities need to be involved in the regulatory process and benefit from the industry.
Introduction
Mangrove Definitions
Mangrove forests are among the most productive, complex, and biologically diverse
ecosystems in the world. These unique systems are present on coastlines in tropical and
subtropical areas, mostly between 30 degrees North and South of the equator (McKee,
2007). Mangroves are shrubs and trees that are generally taller than a half meter and
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occur in areas where shore meets land (Kathiresan and Bingham, 2001, McKee, 2007). The
mosaic of tropical trees and shrubs combined with surrounding flora and fauna is referred
to as mangrove forest (mangal), whereas mangrove ecosystem includes all biotic and
abiotic components of the system (Kathiresan and Bingham, 2001, McKee, 2007).
Mangrove Mechanisms, Structures, and Adaptations
Mangroves have some of the most highly developed adaptations of any group of
plants due to the extreme conditions where they occur (Kathiresan and Bingham, 2001).
These plants grow in protected tropical estuaries at the mouth of rivers, meaning water is
brackish, temperatures are high (above 16 C), soils are muddy and anaerobic, winds are
strong, and plants are exposed to large fluctuations in salinity and tides (Kathiresan and
Bingham, 2001). There are 70 different mangrove species that belong to 16 families, all
displaying traits of woody halophytes (salt-tolerant plants) (McKee, 2007, Queiroz et. al.,
2013). Plants in these families display self or cross-pollination, vivipary (embryo
development while attached to parent), hydrochory (dispersal of seeds by water), and
extensive mechanisms to deal with poor, waterlogged soils and high salinity. Pollination is
completed by wind or animals; animal pollinators include insects, birds, and mammals (e.g.,
bats) (Kathiresan and Bingham, 2001, McKee, 2007). Vivipary in mangroves refers to
germination, maturation, and growth of embryo while still attached to the parent tree.
These embryos, referred to as propagules, grow on parent trees for about 4-6 months until
they are mature, reaching a size of 25-35 cm (Figure 1) (Kathiresan and Bingham, 2001,
McKee, 2007). Once mature, propagules fall off parent trees and display hydrochory; that
is, they disperse using water and tides and, for many species, can remain viable in the
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water for several months. Specific maturation time and size of propagules are highly
dependent on the type of mangrove species as well as environmental conditions
(temperature, salinity, wind, tide, etc.) (Kathiresan and Bingham, 2001, McKee, 2007).
Both vivipary and hydrochory are important adaptations since most mangroves are
inundated for at least some portion their lifetime. Yet the most impressive and highly
developed adaptations mangroves have are their many specialized roots and mechanisms
for salt-exclusion, accretion, and accumulation (Kathiresan and Bingham, 2001, McKee,
2007).
Several specialized roots may be present depending on the species of mangrove and
location of the tree. Types of roots include pneumatophores, prop roots, and buttresses.
Pneumatophores (aerial roots) are pencil like roots with large lenticels that originate
underground and grow vertically from hypoxic (anaerobic) soils to aid plants in gas
exchange (Figure 2) (Kathiresan and Bingham, 2001). Prop roots (also referred to as stilt
roots) are lateral roots that arise from stems and trunks above ground and help support
plants since underground roots are unable to penetrate deeply enough into clay soils and
sandy soils provide poor support (Kathiresan and Bingham, 2001). These roots usually
grow out from the middle section of trees and descend towards the ground, anchoring into
muddy soils to help support plants (Figure 1) (Kathiresan and Bingham, 2001). Buttress
roots also grow laterally from trunks, but are usually near the bottom of the tree and much
thicker and sturdier than prop roots. These roots help stabilize trees by providing
mechanical support (Kathiresan and Bingham, 2001, McKee, 2007).
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Mangroves need specialized mechanisms to deal with large fluctuations in salinity.
Mangroves usually display one of three traits to deal with varying levels of salt; salt
exclusion, salt excretion, and salt accumulation (Kathiresan and Bingham, 2001, McKee,
2007). Salt exclusion happens in the root systems of mangroves, where ultrafilters exclude
salts while extracting water from soils. Salt excretion is a mechanism where salt is taken in
with water, then excreted through specialized glands in leaves. Salt is then removed from
the surface of leaves by wind or rainfall (Kathiresan and Bingham, 2001). Salt
accumulation is another mechanism that involves the uptake of salty waters; however,
instead of excreting salt through specialized glands, the trees accumulate and store salts in
vacuoles of leaves, as well as twigs, wood, and bark. When the vacuoles of leaves reach
their salt-carrying capacity, they are shed from trees, which rids them of excess salts
(Kathiresan and Bingham, 2001, McKee, 2007). In addition to these highly specialized
adaptations to saline environments, most mangroves have the ability to conserve water by
regulating the amount taken in when salinity is too high. The leaves of mangroves also
have thick cuticles, which aids them in water retention by decreasing rates of
evapotranspiration (Kathiresan and Bingham, 2001, McKee, 2007). It is important to note
that the types of adaptations mangroves have are highly dependent on the species of the
tree, as well as its location (Ewel et. al., 1998, McKee, 2007).
Mangrove Forests Zones, Range, and Distribution
Mangrove species are distributed between land and ocean, which can be split into
separate zones; the coastal (fringe) zone, the middle (riverine) zone, and the inland (basin)
zone. Environmental conditions in each of these zones are quite different in terms of
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elevation, inundation, and salinity, which influence tree morphology, anatomy,
productivity, and function (i.e., goods and services)(Table 1)(Ewel et. al., 1998, McKee,
2007). The fringe zone occurs on exposed coasts where water levels and salinity are high
and trees bear the brunt of tides, acting as a protective barrier to land. All types of roots
occur here, with pneumatophores being the most abundant to aid tree respiration (McKee,
2007). Salt secretion is the mechanism most heavily used in this zone. The riverine zone
occurs in brackish estuaries, where salinity is moderate due to water inputs from river and
tides (Figure 2a) (Ewel et. al., 1998, Kathiresan and Bingham, 2001). Trees in this zone are
the most productive and have intricate, interlocking root systems (prop roots) that work to
trap sediments that would otherwise flow into bays and oceans. Salt exclusion and
accumulation are used by trees that grow here (McKee, 2007). The basin zone occurs at
higher elevations, where inundation of trees happens occasionally with the fluctuation of
tides (Ewel et. al., 1998). Soil salinity is high due to salt accumulation through increased
evapotranspiration rates. Trees in this zone have large buttress roots and intercept water
flowing overland, which aids in filtrating toxins and sediments, therefore improving water
quality (Ewel et. al., 1998, McKee, 2007). The complexity of these forests provides habitat
to thousands of species and numerous goods and services to humans; therefore, mangrove
forests are vitally important to both wildlife and human communities worldwide (Kelly,
2012, Lee et. al., 2014, McKee, 2007).
Mangrove forests occur in large ranges across the world and have been documented
and revered by human civilizations for thousands of years (Giri et. al., 2011, Kathiresan and
Bingham, 2001). These unique forests provide habitat for thousands of species, prevent
coastal erosion, improve water quality, and trap sediments that would otherwise flow into
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bays and oceans (Islam et. al., 2005). Mangrove forests also protect wildlife and human
communities from large waves, tides, and storm surges (Paul et. al., 2010). The first
appearance of mangrove species from genera Avicennia and Rhizophora evolved around
what is now known as China some 114 million years ago (Kathiresan and Bingham, 2001).
In 2005, it was found that mangrove forests were present in 123 countries, covering an
area of approximately 18 million hectares (Figure 3) (Giri et. al., 2011, McKee, 2007,
Queiroz et. al., 2013). Historically, 75% of the world’s coastlines were dominated by
mangrove forests, with the majority occurring in areas around SE Asia and Indonesia
(Figure 4) (Giri et. al., 2011, Kathiresan and Bingham, 2001, McKee, 2007).
Due to increasing pressures from human activities and population growth, an
estimated 38% of mangrove forests have been lost over the past two decades - a rate that
exceeds the loss of both coral reefs and tropical rainforest ecosystems (Islam et. al., 2005,
Tenorio et. al., 2015, Valiela et. al., 2001), making mangrove forests the most threatened
ecosystems in the world (Kelly, 2012). Destruction of mangrove forests can be largely
attributed to the fact that most of the world’s populous (over 50%) reside in areas near
coasts, and therefore influence them greatly (Lee et. al., 2014). Human activities such as
deforestation for aquaculture and agriculture, harvesting of forest products, and coastal
development cause serious damage to and loss of these systems, with construction of
shrimp farms posing the greatest threats (Table 2) (Ewel et. al., 1998, Islam et. al., 2005,
Kelly, 2012, Lee et. al., 2014, Paul et. al., 2010, Tenorio et. al., 2015, Valiela et. al., 2001).
Shrimp Farming History, Growth, and System Types
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Shrimp farming has rapidly expanded over the last four decades as demands
increase with increasing human population size (Queiroz et. al., 2013, Stokstad, 2010).
Traditionally, global shrimp fisheries supplied most of the world’s market with wild-caught
shrimp of different species and size. However, over-fishing of the world’s oceans led to
global fishery collapses, which devastated many countries relying on export revenues for
economic stability (Islam et. al., 2005, Paez-Osuna et. al., 2003). Some regions experienced
a 30% decline in wild fish and shrimp populations (Paez-Osuna et. al., 2003). In addition to
reduction of natural populations, concerns were also being raised about ecosystem damage
caused by various fishery practices. These issues led to the creation and enforcement of
regulations by many countries, which put further pressure on fisheries since catch
limitations and use of more advanced technologies can be quite costly. As human
population and demand for shrimp and other fishery products rose, many investors started
looking for alternative ways to supply the masses, and the development of aquaculture,
especially shrimp farming, rapidly expanded in a very short period of time (Paez-Osuna et.
al., 2003).
Traditional marine shrimp farming began in Asia some 4000 years ago, but in 1970
became a global industry that now takes place in regions across the globe, a phenomenon
referred to as the Blue Revolution (Ewel et. al., 1998, Queiroz et. al., 2013, Stokstad, 2012).
About 90% of farmed shrimp come from developing countries with the three largest
exporters being Thailand, China, and Vietnam (Paul et. al., 2010). China is the leading
producer, contributing 62.3% of farmed shrimp to world production (Paul et. al., 2010)
although Thailand is the number one exporter (Kelly, 2012). Countries in Latin America
such as Ecuador, Brazil, and Mexico as well as regions in Africa have also undertaken
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shrimp farming as a way of economic stimulation and growth (Islam et. al., 2005, Queiroz
et. al., 2013). The highest demand for shrimp comes from the United States, Japan, and
Europe (Paul et. al., 2010). When fisheries worldwide began to collapse from reduced
population sizes due to overfishing, there was incentive to find alternative methods to raise
production, and shrimp farming was seen as a solution (Paez-Osuna et. al., 2003).
Conditions for shrimp farming are optimal where mangrove forests occur due to climate,
hypersaline environment, and occurrence of wild populations of shrimp larvae (Tenorio et.
al., 2015) and construction of shrimp farms in mangrove forest environments results in
high production and high profitability with low costs (Islam et. al., 2005, Tenorio et. al.,
2015). The world’s mangrove forests are mainly present in undeveloped and developing
countries and people residing in these countries saw development of shrimp farms as an
opportunity to alleviate food scarcity and poverty as well as stimulate employment and the
local economy (Queiroz et. al., 2013, Tenorio et. al., 2015). These assumptions were based
on the notion that exporting shrimp, which are the largest marine commodity in terms of
value (15% of total international trade value for fish products), would allow for economic
growth as well as decrease pressures on wild shrimp populations (Paul et. al., 2010,
Queiroz et. al., 2013, Stokstad, 2010). Beginning in the 1970’s, political and economic
support from both private and public sectors allowed regions in Asia, Africa, and Latin
America to rapidly transform mangrove forests into areas for shrimp cultivation (Queiroz
et. al., 2013). For example, in 1970, Brazil produced less than 9,000 tons of shrimp
although by 2007 production had risen to 3.2 million tons (Tenorio et. al., 2015). While a
massive jump in shrimp production was occurring worldwide (Figure 5), large portions of
mangrove forests were being cleared to make it possible. In 2015, it was estimated that
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approximately 1.5 million hectares of global mangrove forests had been converted to
shrimp farms (Tenorio et. al., 2015). Rapid conversion of mangrove forests to shrimp
farms has taken a huge toll on the once productive and biologically diverse ecosystems,
especially due to lack of laws and regulations in countries where production is the highest
(Tenorio et. al., 2015). Since most of the world’s shrimp supply comes from developing
countries, methods of shrimp farming, as well as their impacts, are an important area of
focus (Joffre et. al., 2015, Kelly, 2012).
In general, the first step to developing a shrimp farm is clearing areas near coasts
and waterways (i.e., mangrove forests) for construction of ponds to rear shrimp. Basin
mangrove areas (inland zone) are sometimes targeted for development of farms because a
constant water supply is needed to maintain water quality within ponds (Islam et. al.,
2005); however, many times ponds are built in the fringe zone of mangrove forests, which
is much more destructive to the system. The width, length, and depth of ponds depend on
the intensity of the farming system, but usually fall within a range of 1.5-3.5 meters deep
(Ewel et. al., 1998). Once dug, ponds are filled with saline water and stocked with postlarvae shrimp either from estuaries or hatcheries; next, depending on the intensity of the
system, ponds are supplemented with feed, fertilizers, and in some cases antibiotics,
disinfectants, preservatives, and pesticides (Islam et. al., 2005). Farmers that use large
amounts of feed, fertilizers, and antibiotics must abandon their ponds after approximately
five years due to severe water pollution and then either move to other areas to construct
new ponds or go out of business (Kelly, 2012). For example, in 1990, 50% of mangrove
forests in Thailand had been converted to shrimp farms and, by 1995, 24% of those farms
had been abandoned due to poor water quality and disease (Ewel et. al., 1998).
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Methods for shrimp farming can be classified into four different categories:
traditional, extensive, semi-intensive, and intensive (Paul et. al., 2010). These categories
are based on intensity of the operation, such as pond size, stocking densities, inputs of feed
and fertilizers, and water quality management (Paul et. al., 2010). In general, traditional
and extensive farming operations use natural water systems to maintain water quality and
recruit natural stocks of post-shrimp larvae (Table 3). Stocking densities are usually low as
are inputs of food and fertilizers. Semi-intensive and intensive operations use water
systems that are separate from the natural environment, have high stocking densities, high
amounts of chemical inputs and feed, and mechanical aeration systems (Table 3) (Joffre et.
al., 2015). Due to the cost and maintenance of supplies and technology in intensive
systems, they are used very rarely in developing countries, especially by native and local
peoples (Joffre et. al., 2015). For example, 90% of the shrimp farms in Vietnam use
traditional or extensive farming methods, with only 10% using semi-intensive or intensive
operations (Joffre et. al., 2015). Each of these methods impacts surrounding environments
(i.e., mangrove forests) differently and are, therefore, important to identify.
Goal of this Review
The ecological goods and services provided by mangrove forests have been heavily
documented (Islam et. al., 2005, Joffre et. al., 2015, Paul et. al., 2010, Queiroz et. al., 2013).
Local and native peoples living among the world’s mangrove forests have depended on
these goods and services for generations (Queiroz et. al., 2013). Starting in 1970’s, a need
for higher production of fishery products, especially shrimp, to meet demands at a time
when natural populations were in decline prompted the boom of aquaculture, and
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development of shrimp farms rapidly expanded across the globe in a very short period of
time. While fisheries and aquaculture help alleviate socio-economic hardships, such as
food insecurity and poverty, by stimulating economic growth, negative impacts from the
loss of mangrove forests have been witnessed as well (Paul et. al., 2010, Queiroz et. al.,
2013, Tenorio et. al., 2015). This review characterizes the ecological functions and socioeconomic benefits provided by mangrove forests, evaluate ecological and socio-economic
impacts that arise from removal of mangrove forests for shrimp farming, and identifies
possible solutions to protect forests. This assessment will help determine whether the
short-term benefits of shrimp farming are outweighed by the long-term benefits provided
by mangrove forests.
Mangrove Forests; Ecological Functions and Socio-Economic Benefits
The most important ecological functions (i.e., services) of mangrove forests are
providing habitat for thousands of species and goods for millions of people, providing
nursery and feeding grounds for aquatic and marine organisms, water purification (i.e.,
mechanisms to desalinize water; nutrient and sediment trapping via roots), coastal
protection from wave energy, tides, and storm surges (i.e., storm barrier), shoreline
stabilization and land building (i.e., roots prevent coastal erosion, stabilize shorelines, and
trap nutrients, sediments, and detritus), and carbon storage (Alongi, 2002, Ewel et. al.,
1998, Islam et. al., 2005, Kelly, 2012, Lee et. al., 2014, Paul et. al., 2010). Each of these
services is vital to protecting and maintaining ecological, social, and economic stability in
areas where mangrove forests occur (Islam et. al., 2005, Joffre et. al., 2015, Paul et. al., 2010,
Queiroz et. al., 2013).
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Habitat for species and Resources for Mankind
Mangrove forests provide habitat to a large number of important species, from
microbes present on prop roots in fringe zones to Bengal Tigers in basin forests (Islam et.
al., 2005, Valiela et. al., 2001). These unique ecosystems support plant and animal
populations in forests (basin zone) and offshore areas (riverine and fringe) (Ewel et. al.,
1998). For instance, in the Sundarbans (the largest continuous stretch of mangrove forest
in the world) of India and Bangladesh, mangrove forests harbor 330 plant species, 400 fish
species, 40 crustacean species, 35 reptile species, 270 bird species, and 42 mammal
species, including threatened and endangered species, such as the Estuarine Crocodile and
Royal Bengal Tiger (Islam et. al., 2005). Mangrove forests also provide habitat to many
migratory species, such as fish, birds, and mammals. For example, the vegetated tidelands
of mangrove forests (fringe and riverine zones) are important nesting and feeding sites for
many species of migratory birds (Alongi, 2002, Valiela et. al., 2001). Florida and Australia
have reported sightings of over 200 different migratory bird species in their mangrove
forests at some point every year (Ewel et. al., 1998). In addition, mangrove forests harbor
many endemic species. For example, mammals such as the Australian crab-eating rat, the
Malaysian leaf monkey, and the Proboscis monkey of Borneo (Ewel et. al., 1998).
The ability of an ecosystem to function properly and provide goods and services is
highly dependent on its composition of flora and fauna; that is, each species has its niche
(job) within each zone of the mangal and is important to the food web and ecosystem
functioning (Kathiresan and Bingham, 2001, McKee, 2007). Food webs are complex and
require different species (i.e., producers, consumers) at each stage to maintain balance of
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populations through different types of controls (i.e., bottom-up/top-down control). As a
result, species diversity and abundance within mangrove forests determines how well the
system can function and provide services to human populations (McKee, 2007).
Humans harvest several forest products that are important for sustenance and
survival as well as economic growth (Alongi, 2002, Islam et. al., 2005, Lee et. al., 2014,
Thampanya et. al. 2006, Valiela et. al., 2001). For example, in the Sundarbans of India and
Bangladesh, ten million people depend on mangrove forests for food and shelter (Islam et.
al., 2005). Timber is harvested for fuelwood, firewood, and building materials, such as
stakes for fishing, tools for agriculture, lumber for housing and household items (i.e.,
furniture), wood to build boats and bridges, and to make paper and matches (Alongi, 2002,
Ewel et. al., 1998, Islam et. al., 2005, Valiela et. al., 2001). Mangrove forests also harbor
plant species that are an important source of food, fiber, and medicine (Alongi, 2002, Ewel
et. al., 1998, Islam et. al., 2005, Valiela et. al., 2001). Tannins, honey, and wax are other
major products harvested from mangrove forests. For example, some 200 metric tons of
honey and 55 metric tons of wax are collected in coastal regions of the Sundarbans
mangrove forest every year (Islam et. al., 2005). In addition to providing sustenance to
millions of people, forestry products (timber, food, fiber, and medicine) from mangrove
forests have high commercial value, and therefore promote economic growth and viability
(Kathiresan and Bingham, 2001).
Nursery Function
Mangrove forests provide ideal conditions for nurseries and feeding grounds for
aquatic and marine organisms due to their coastal positioning, productivity, and root
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structure (Lee et. al., 2014). Most of these forests occur on coasts near mouths of rivers
and creeks, providing estuarine environments to the many species they harbor (Alongi,
2002). Crustaceans and vertebrate species utilize the fringe and riverine zones of
mangrove forests, where many prop roots are present (Ewel et. al., 1998). These zones are
crucial areas for young marine organisms and it has been found that juvenile fish actively
seek out mangrove estuaries using olfactory and other cues (Lee et. al., 2014). Shallow
waters with entanglements of aerial, prop, and buttress roots provide protection from
larger predators, and abundances of detritus, phytoplankton, and zooplankton provide
juvenile organisms with great quantities of food, allowing individuals to grow rapidly,
therefore reducing risk of predation and permitting populations to grow (Islam et. al.,
2005). Larger populations have greater genetic diversity, which reduces risks of disease,
death, and ultimately extinction (Alongi, 2002). This, in turn, provides benefits to humans
in the form of food (i.e., sustenance and commercial) and economic growth.
The nursery function of mangrove forests is one of the largest direct benefits
humans extract from them. Most of world’s mangrove forests occur along coastlines in
Asia, Latin America, and Africa (i.e., underdeveloped or developing countries); therefore,
millions of people living in rural communities near mangrove forests directly rely on them
for sustenance (Queiroz et. al., 2013). Fishing has been a big part of coastal communities’
culture for centuries, providing food and economic stimulation both locally and nationally
(Islam et. al., 2005). Large populations of crustaceans and vertebrates have been utilized
by native and foreign peoples for generations, making mangrove forests extremely valuable
to sustenance farmers, small-scale fisheries, and large-scale commercial fisheries. In fact,
90% of marine organisms that humans harvest spend some portion of their life cycle in a
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mangrove estuary, making these systems highly valuable to coastal fisheries across the
globe (Kathiresan and Bingham, 2001, McKee, 2007). In addition, a positive correlation
was made between total area of mangrove forest and commercial fish and shrimp catches
in regions of India and Bangladesh (Islam et. al., 2005). Humans depend on fishing for
sustenance and economic growth, which are dependent on population sizes, and
population sizes are directly related to size and health of nursery and feeding grounds (i.e.,
mangrove forests).
Water Purification
Mangrove forests are wetlands known to function as a water filter (Kathiresan and
Bingham, 2001, McKee, 2007). The thick, entangled aerial, prop, and buttress roots present
in different species of mangroves help maintain water quality in and around the forest
(Islam et. al., 2005, Valiela et. al., 2001). This mainly occurs in basin zones where roots
intercept and filter water-borne debris such as sediments and pollutants from inland water
systems, which keeps them from washing into estuaries and oceans (Alongi, 2002, Kelly,
2012, Valiela et. al., 2001). In addition, these systems have been shown to mitigate
eutrophication by lowering export rates of nutrients to estuaries (Valiela et. al., 2001). Salt
intrusion is also mitigated by mangroves since they have highly advanced mechanisms to
accumulate and excrete salts from water, thus reducing water salinity (Valiela et. al., 2001).
Water purification provides great benefits to people in coastal communities since
clean drinking water is essential to live and thrive. Most mangrove forests are present in
underdeveloped or developing countries, which already struggle with water quality issues
due to lack of sewer systems, water treatment facilities, and/or water regulations/laws
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(Islam et. al., 2005). In addition, maintenance of water quality within the forest is
important to sustain natural balance and therefore proper system functioning (Kathiresan
and Bingham, 2001, McKee, 2007).
Coastal Protection
Mangrove forests are composed of thick stands of trees and vegetation on the
coastlines of many countries and continents worldwide (Kathiresan and Bingham, 2001,
McKee, 2007). These stands act as barriers against strong winds, waves, tides, and storms,
providing protection to inland areas (Alongi, 2008, Islam et. al., 2005, Kathiresan and
Bingham, 2001, Kelly, 2012, Lee et. al., 2014, McKee, 2007). Mangrove forests serve as sea
walls when storm surges and tsunamis reach coastlines (Kelly, 2012) and have even been
noted in the literature to attenuate energy from waves and storms more effectively than
manmade structures (Alongi, 2008, Lee et. al., 2014). This is possible because mangrove
stands are large and dense and presence of prop and buttress roots keeps them tightly
bound together. In addition, mangroves can live over 100 years and grow over 60 meters
tall, which helps protect coastlines from intense winds and precipitation (Kathiresan and
Bingham, 2001). Therefore, when strong storm surges hit coastal areas, a large portion of
energy is diffused by the thick stands, reducing the degree of impact to surrounding areas
(Lee et. al. 2014). During tropical storm events, a 100 meter area of fully grown tropical
mangrove forest can reduce energy by 20%, thereby protecting shorelines (Lee et. al.
2014). This is a very important ecological service because damage that could otherwise be
catastrophic is minimized, allowing biotic and abiotic components of the system to persist
20
and thrive. This function is also of great importance to human societies, since most of the
population resides in coastal areas worldwide (Lee et. al. 2014).
Protection from wind, waves, tides, and storms has great socio-economic benefits
(Alongi, 2008, Islam et. al., 2005, Kathiresan and Bingham, 2001, Kelly, 2012, Lee et. al.,
2014, McKee, 2007). Strong storm surges have the ability to devastate coastal communities
by flooding streets and homes and destroying structures, which can lead to death for many
humans, especially in underdeveloped or developing countries, where technological
advances are low and population numbers are high. For instance, there was a significant
reduction in the number of human deaths in areas where mangrove stands were present
compared to areas where they had been removed during a tropical cyclone event that hit
the east coast of India in 1999 (McKee, 2007). Another example of the protective role
mangroves play can be seen from the tsunami that occurred in December 2004 in the
Indian Ocean. A huge earthquake (the largest in 40 years) created the most devastating
tsunami in history, killing approximately 283,000 people. It was found that the impact of
the tsunami was significantly reduced in areas where mangrove forests were present and
intact, providing evidence of mangroves defensive role against storm surges (Alongi, 2008).
If impacts of waves, wind, and storm surges are reduced, then medical and building costs
decrease, which provides socio-economic benefits to communities in coastal areas (Alongi,
2008, Islam et. al., 2005, Kathiresan and Bingham, 2001, Kelly, 2012, Lee et. al., 2014,
McKee, 2007). In addition to coastal protection, mangrove forests help reduce erosion of
shorelines and accrete soils vertically, which increases coastal elevations over time (Alongi,
2002, Kelly, 2012, McKee, 2007, Thampanya et. al., 2006).
21
Shoreline Stabilization
The intricate entanglement of aerial, prop, and buttress roots in mangrove forests
work to preserve and stabilize existing coastlines by retaining soils and reducing rates of
erosion (Alongi, 2002, Kelly, 2012, Lee et. al., 2014, McKee, 2007, Thampanya et. al., 2006).
A study that took place Southern Thailand compared rates of erosion between coastlines
with and without mangrove forests and found that presence of mangrove forests
substantially reduced rates of erosion (Thampanya et. al., 2006). This ecological function
has been documented in mangrove forests worldwide (Alongi, 2002, Kelly, 2012, Lee et. al.,
2014, McKee, 2007). The dense, tangled roots of mangroves serve as nets that hold soils
together and in addition, these thick, woody structures reduce water flow, which helps
reduce erosion (i.e., faster water works to break soils apart more quickly) (Thampanya et.
al., 2006).
This ecological function provides a great socio-economic benefit in the form of
security. As sea levels continue to rise from global climate change, and as the human
population continues to grow, reduced erosion of shorelines can provide protection to
coastal communities worldwide (Lee et. al., 2014, Thampanya et. al., 2006). In fact, several
studies have found that in addition to stabilizing shorelines by reducing rates of erosion,
mangrove forests have the ability to accrete soils vertically, which increases coastal
elevations over time (Alongi, 2002, Kelly, 2012, Lee et. al., 2014, McKee, 2007, Thampanya
et. al., 2006, Valiela et. al., 2001).
Land Building
22
The complex root systems of mangroves in riverine and fringe zones not only retain
existing soils but form soils by trapping nutrients, sediments, and detritus (i.e., plant litter)
that either flow from inland water systems or originate in the forest (Lee et. al., 2014). Soil
accretion occurs from sediment trapping, organic matter accumulation, and compaction via
tidal energy and waves (Lee et. al., 2014, McKee, 2007). The majority of organic matter
additions come from detritus of mangrove trees in the form of leaves, twigs, branches, and
seeds (i.e., propagules), which contributes nutrients to otherwise muddy, anaerobic soils
(Kathiresan and Bingham, 2001). Since there is little oxygen present in these water-logged
soils, decomposition rates are very slow, which causes plant litter to build up; therefore,
creating peat (Kathiresan and Bingham, 2001, Lee et. al., 2014). This in-situ peat formation
leads to vertical and horizontal development of land in intertidal areas, which allows
mangrove forests to expand seaward by outcompeting other plants since they are highly
adapted to coastal environments (i.e., inundation and salinity) (Figure 6) (Lee et. al., 2014,
McKee, 2007, Thampanya et. al., 2006, Valiela et. al., 2001). Lee et. al, 2014 found that
accumulation of detritus produced within mangrove forests contributed to both soil and
peat formation, and thus vertical land development, which was supported by measured
elevation gains in both Florida and Belize. In Belize, mangrove peat accumulation was
measured to be over 10 meters thick, which was estimated to have taken around 7,000
years (Lee et. al., 2014). Mangrove forests in Southern Thailand were shown to expand
land in a seaward direction, especially near the mouths of rivers and sheltered bays
(Thampanya et. al., 2006). Another study by McKee, 2007 estimated that the roots of
mangroves in riverine and fringe zones are capable of retaining over 90% of river load
sediments, substantially contributing to vertical land development. It has been found that
23
mangrove forests add organic matter to soil and trap sediments at a rate similar to global
sea level rise (Lee et. al., 2014, Lovelock et. al., 2015). Land development is an ecological
function that helps ensure all other mangrove system services can be provided by allowing
growth and expansion of forests over time (Lee et. al., 2014, Lovelock et. al., 2015).
Vertical and horizontal land building provides great socio-economic benefits to
coastal communities since sea-level rise threatens many of the largest and most populated
cities worldwide (Lee et. al. 2014). Mangrove forests are starting to be recognized for their
land development ability, which is very important in terms of mitigating global sea-level
rise (Lee et. al., 2014, Lovelock et. al., 2015). For example, when water levels and volumes
increase near shorelines, it causes impacts from storm surges to be greater, meaning more
damage to structures and higher loss of lives. In addition, as ocean levels increase, salt
intrusion occurs, which negatively affects the system and humans (i.e., reduced amounts of
readily available freshwater). Vertical land development on tropical coastlines could be
crucial in the near future as global sea levels continue to rise (Lee et. al., 2014, Lovelock et.
al., 2015, McKee, 2007, Thampanya et. al., 2006, Valiela et. al., 2001).
Carbon Storage
Tropical mangrove forests are more productive than terrestrial forests and
therefore store more carbon (Bournazel et. al., 2015, Ewel et. al., 1998, Lee et. al., 2014).
High productivity rates are related to large amounts of insolation, nutrients, and water
availability due to climatic conditions present in the tropics (Ewel et. al., 1998). Mangrove
forests are one of the largest carbon sinks in the world due to high rates of carbon
sequestration and large carbon stocks (Bournazel et. al., 2015, Lee et. al., 2014). Carbon
24
sequestration rates are approximately 10 times greater in coastal mangrove forests than
forests that grow inland (Kelly, 2012, Lee et. al., 2014) due to dense stands of trees and
thick peat formations within mangrove forests, which both store large amounts of carbon
(Ewel et. al., 1998, Lee et. al., 2014).
This function provides socio-economic benefits in terms of climate change
mitigation (Bournazel et. al., 2015, Lee et. al., 2014). These systems take in and store
carbon at much faster rates than terrestrial systems, which helps offset anthropogenic
carbon emissions in a shorter period of time (Bournazel et. al., 2015, Ewel et. al., 1998, Lee
et. al., 2014); however, mangrove forests have not received much attention or credit for
this function (Lee et. al., 2014).
Shrimp farming; Ecological and Socio-Economic Impacts
Countries present in tropical areas have climatic conditions that are ideal for shrimp
farming (Joffre et. al., 2015, Paul et. al., 2010). Many of these countries are undeveloped or
developing and view shrimp farming as a means to better their quality of life (Islam et. al.,
2005). Increased quality of life in these areas refers to decreased poverty and increased
food security, as shrimp farming provides employment and economic gains can be used to
purchase food and goods (Joffre et. al., 2015, Paul et. al., 2010). However, shortly after the
Blue Revolution took off, impacts of shrimp farming on both lands (i.e., mangrove forests)
and people became apparent worldwide (Joffre et. al., 2015, Queiroz et. al., 2013). These
impacts include reduced area of habitat for thousands of species, reduced availability of
land and forest goods (i.e., agriculture, food, fuel, medicine, etc.), nursery and fishery
collapse, decreased water quality, loss of protective coastal barrier, decreased shoreline
25
stabilization and land building (i.e., increased rates of erosion), and decreased carbon
sequestration and storage (i.e., increased carbon export) (Islam et. al., 2005, Joffre et. al.,
2015, Kelly, 2012, Lee et. al., 2014, Queiroz et. al., 2013, Thampanya et. al., 2006, Valiela et.
al., 2001). In addition, local and native peoples have been greatly impacted by
development of shrimp farms and will therefore be included here (Islam et. al., 2005, Joffre
et. al., 2015, Kelly, 2012, Pierez et. al., 2003, Queiroz et. al., 2013, Tenorio et. al., 2015).
Reduced Area of Habitat for Thousands of Species
Mangrove forests are extremely complex and unique due to their tropical shoreline
locations and adaptive mechanisms, such as root structures and desalination processes;
therefore, many of the species that occur in these forests are endemic to them (Ewel et. al.,
1998). Shrimp farming requires removal of mangrove trees to build ponds to raise shrimp,
which results in reduced or fragmented habitat for animals (Lee et. al., 2014). In Thailand,
between 50-60% of original mangrove forests have been removed to construct shrimp
farms (Kelly, 2012). Rapid deforestation of mangroves has even resulted in some species
becoming threatened or endangered, such as the Bengal Tiger and Proboscis Monkey (Ewel
et. al., 1998, Lee et. al., 2014). Reduced population sizes also lower genetic diversity, which
leads to increased susceptibility to environmental hazards and diseases, placing further
pressures on already threatened species (Kathiresan and Bingham, 2001). Migratory
species that depend on these wetland habitats for food, water, and nesting sites are
decreasing in numbers, such as the Black Swan in Australia (Alongi, 2002). Biodiversity in
mangrove forests has decreased substantially, which affects the health and functioning of
the entire system (Alongi, 2002, Ewel et. al., 1998, Kathiresan and Bingham, 2001).
26
Reduced Availability of Land and Forest Goods
Loss of mangrove forests has resulted in loss of land and forest goods for millions of
people that depend on them for survival (Islam et. al., 2005, Tenorio et. al., 2015,
Thampanya et. al., 2006). Forest materials such as honey, tannins, medicine, wax,
fuelwood, and timber for building agriculture tools, fishing poles, furniture, houses,
bridges, and boats, are much more scarce, and increasing human population size places
even further pressure on the forests that remain (i.e., higher demand for goods since there
are more people, reduced availability of goods due to deforestation) (Islam et. al., 2005, Lee
et. al., 2014, Pierez et. al., 2003). In addition, traditional communities in Bangladesh
formerly used lands surrounding mangroves to grow crops and raise livestock; however,
these small farmers are displaced when investors come in and purchase land from the
government to build shrimp farms (Islam et. al., 2005). This has also happened in areas of
Brazil, especially in NE regions, where legislative permissiveness allows the rural poor to
be marginalized (Queiroz et. al., 2013, Tenorio et. al., 2015). Traditional communities in
many of the areas where shrimp farms have been developed (i.e., SE Asia and Latin
America) are being pushed out by large companies that come in and destroy mangrove
forests and surrounding land. Since small villages on shorelines depend on mangroves for
food and shelter, food scarcity increases, resulting in increased cases of malnutrition,
migration, and even death (Islam et. al., 2005, Queiroz et. al., 2013, Tenorio et. al., 2015). In
addition to forests goods and lands to grow crops and raise livestock, fishing has
historically been a large part of coastal community culture, which is also being impacted by
shrimp farming (Islam et. al., 2005, Lee et. al., 2014, Queiroz et. al., 2013, Tenorio et. al.,
2015).
27
Nursery and Fishery Collapse
Mangrove forests have been targeted for development of shrimp farms because the
tropical conditions and natural populations of shrimp larvae make production costs very
low and profitability very high (Islam et. al., 2005, Tenorio et. al., 2015). However, removal
of mangrove forests has threatened wild populations of shrimp and fish because they need
mangrove forests (fringe and riverine zones) for part of their life-cycle (i.e., larval and postlarval stages) (Paez-Osuna et. al., 2003). Riverine and fringe zones of mangrove forests
provide food (i.e., algae and plankton), protection, and breeding grounds (i.e., aerial and
prop roots) to many marine organisms (i.e., shrimp and fish), which allows populations to
grow, providing wildlife and humans with food (Ewel et. al., 1998). Removal of mangroves
results in habitat loss for marine organisms, including important commercial species,
which leads to population collapse (Islam et. al., 2005, Lee et. al., 2014, Valiela et. al., 2001).
The majority of shrimp farms (90%) are in developing countries where the most common
practices are traditional and extensive farming, which both rely on catches of wild postlarvae shrimp from mangrove estuaries to stock ponds, placing an enormous pressure on
natural populations (Table 3) (Figure 7) (Islam et. al., 2005, Joffre et. al., ,Paul et. al., 2010).
These systems connect directly to mangrove estuaries through open structures or small
canals, which transfers post-larvae shrimp directly to ponds (Paez-Osuna et. al., 2003). In
addition, many farmers use fishmeal pellets as feed in shrimp ponds, which creates even
greater fishery pressures (Islam et. al., 2005, Valiela et. al., 2001). During fry catchment, a
large number of other species are killed, reducing biodiversity and causing large
disturbances to community structure and food webs (Islam et. al., 2005). In Bangladesh,
the availability of shrimp fry in mangrove estuaries is declining each year, which has
28
resulted in abandoned farms (Islam et. al., 2005). Impacts from deforestation (i.e., habitat
loss) of mangroves to build shrimp farms and overharvesting of wild shrimp larvae to stock
ponds are so severe that shrimp farming itself is under threat (Islam et. al., 2005, Lee et. al.,
2014, Valiela et. al., 2001).
The reduction of natural shrimp and fish populations poses great threats to
sustenance fishers, family fisheries, and commercial fisheries worldwide (Islam et. al.,
2005, Lee et. al., 2014, Valiela et. al., 2001). As previously mentioned, traditional coastal
communities have relied on fishing as a food source for generations; however, shrimp
farming has reduced the amount of marine organisms available, which has created more
food insecurity among the poorest strata of society (Islam et. al., 2005, Joffre et. al., 2015,
Thampanya et. al., 2006, Queiroz et. al., 2013). In addition, many fisheries in developing
countries are in decline or have already collapsed due to reduced size of marine
populations, which creates huge economic losses and devastates many lives (Islam et. al.,
2005, Joffre et. al., 2015, Thampanya et. al., 2006, Queiroz et. al., 2013). Once wild
populations collapse, farmers abandon ponds or import shrimp from other countries and
hatcheries, which has led to the spread of many viral and bacterial diseases, such as the
White Spot Syndrome (WSS), Infectious Hypodermic Necrosis, and Taura Syndrome (PaezOsuna et. al., 2003). The ponds are then treated with antibiotics and pesticides in hopes of
reducing the spread of diseases, which has devastating affects to surrounding areas and
water systems (Islam et. al., 2005, Paez-Osuna et. al., 2003).
Decreased Water Quality
29
There are four types of shrimp farming, ranging from traditional to intensive, and
each type uses different methods to rear shrimp, creating different impacts on the
environment (Table 3) ( (Islam et. al., 2005, Paul et. al., 2010). All ponds need a constant
supply of freshwater, which is achieved through alteration of inland water systems and
extraction of groundwater (Lee et. al., 2014, Islam et. al., 2005). When shrimp farming
began to rapidly expand in the 1970’s, traditional and extensive methods used wild shrimp
larvae to stock ponds and therefore did not need pesticides and antibiotics to reduce the
spread of disease; however, with the decline of natural populations, these farms used
imported and hatchery shrimp, which carry many viral and bacterial diseases (Islam et. al.,
2005). This has led to greater usage of pellet feed, pesticides, and antibiotics among
smaller, less intensive operations, which is problematic due to the constant water exchange
with surrounding environments (Joffre et. al., 2015). In addition to pellet feed, pesticides,
and antibiotics, intensive operations use synthetic fertilizers, herbicides, preservatives, and
disinfectants that ultimately end up in the mangrove forest environment (Islam et. al.,
2005, Kelly, 2012). All farming methods eventually discharge wastewater from ponds into
surrounding waterways, which heavily pollutes systems and causes detrimental impacts,
such as eutrophication, toxicity, and spread of disease (Lee et. al., 2014, Paez-Osuna et. al.,
2003). In short, shrimp farms use large amounts of fresh water from mangrove
environments to fill and replenish ponds, then discharge polluted pond water
contaminated with feces, leftover feed, synthetic fertilizers, pesticides, herbicides,
antibiotics, and diseases, which causes eutrophication, algal blooms, reduced dissolved
oxygen (DO), spread of pathogens and disease, changes to community structure, and death
30
of biota (Ewel et. al., 1998, Islam et. al., 2005, Kelly, 2012, Lee et. al., 2014, Queiroz et. al,.
2013, Valiela et. al., 2001).
Water quality is also impacted by deforestation of mangroves for construction of
shrimp farms through increased sediment loads and rates of sediment discharge, which
further reduce DO, negatively impacting aquatic and marine organisms (Islam et. al., 2005,
Lee et. al., 2014). In addition, deforestation of mangroves results in increased water
salinity from increased rates of evaporation (50%) and salt intrusion, which causes many
organisms to migrate further inland or die (Ewel et. al., 1998, Paez-Osuna et. al., 2003,
Queiroz et. al,. 2013, Valiela et. al., 2001). Decreased water quality from polluted pond
water discharges, increased sedimentation from deforestation, and increased water salinity
create negative socio-economic impacts as well (Islam et. al., 2005, Kelly, 2012).
Intensive farms are more desirable than traditional farms because their stocking
and production rates are much higher; however, so is the environmental damage they
cause (Kelly, 2012). In 2012, intensive shrimp farming operations produced 90,000 lbs. of
shrimp/acre, which is 200 times greater than production from traditional shrimp farming
(Kelly, 2012). However, ponds must be abandoned after approximately 5 years due to poor
water quality (i.e., high stocking rates leads to increased eutrophication, salinity, toxins,
and disease) (Ewel et. al., 1998, Kelly, 2012, Paez-Osuna et. al., 2003, Valiela et. al., 2001).
For instance, by 1990, 50% of mangrove forests in Thailand were converted to shrimp
farms, and by 1995, 24% of those farms had been abandoned due to high levels of water
pollution and disease, which eventually spread to India, Taiwan, Indonesia, and the
Philippines, devastating productions and thus local food security and economies (Ewel et.
31
al., 1998, Kelly, 2012). Another example of reduced production due to poor water quality
was seen in Bangladesh in 2005, when 83% of shrimp production was lost from spread of
the White Spot Syndrome disease (Islam et. al., 2005). In addition, shrimp farms in Brazil
lost 100% of their production in 2004 when the White Spot Syndrome was introduced
from imported post-larvae and spread throughout the coastal region from pond water
discharges into mangrove forest ecosystems (Queiroz et. al., 2013, Tenorio et. al., 2015).
Substantial production losses negatively impact coastal communities, as many farmers are
in debt to banks for loans they took out to construct shrimp ponds (Joffre et. al., 2015,
Queiroz et. al., 2013, Tenorio et. al., 2015). Polluted water and disease outbreaks increase
the amount of abandoned shrimp farms, since many farmers do not have the resources
they need to continue (Joffre et. al., 2015, Kelly, 2012).
Another socio-economic impact from reduced water quality is reduced fish and
shrimp populations (i.e., populations become threatened or endangered from polluted
waters and disease), which places further stress on fisheries and thus food security and
economies (Ewel et. al., 1998, Paez-Osuna et. al., 2003, Queiroz et. al,. 2013). In addition,
salination of aquifers and soils results in crop failures and livestock losses due to changes
in soil and water chemistry (i.e., reduced soil fertility), which also threatens local food
security (Islam et. al., 2005, Queiroz et. al,. 2013). Pollution discharges from shrimp farms
also reduce the amount of fresh water available to local communities, creating fresh water
crises (Islam et. al., 2005, Queiroz et. al,. 2013S).
Persistent pollutants, such as pesticides and antibiotics, that are released from
shrimp ponds work their way up the food chain, eventually reaching humans (Islam et. al.,
32
2005, Paez-Osuna et. al., 2003, Queiroz et. al,. 2013). In addition, the release of antibiotics
into mangrove forests leads to death of ecologically important bacteria and selection of
resistant bacteria, which complicates disease treatments and increases the occurrence of
infections in humans and animals (Islam et. al., 2005, Paez-Osuna et. al., 2003). Therefore,
polluted water discharges from shrimp farming negatively impact local food security and
local economies (i.e., crop and livestock loss; fishery collapse) as well as fresh water
availability and quality of life (i.e., hypersalinity and eutrophication; pathogens and
diseases) (Islam et. al., 2005, Joffre et. al., 2015, Paez-Osuna et. al., 2003, Queiroz et. al,.
2013).
Loss of Protective Coastal Barrier
Deforestation of mangrove forests for development of shrimp farms results in
reduced coastal protection from waves, tides, and storms (Alongi, 2008, Islam et. al., 2005,
Joffre et. al., 2015, Kelly, 2012, Lee et. al., 2014, McKee, 2007, Queiroz et. al., 2013). This
occurs because forests are not able to reduce energy when they are degraded, fragmented,
or absent, which results in increased damage by storms (Lee et. al., 2014). Increased
damage from storm surges has been reported in Brazil, Thailand, India, Bangladesh, and
Vietnam (Alongi, 2008, Islam et. al., 2005, Joffre et. al., 2015, Kelly, 2012, McKee, 2007,
Queiroz et. al., 2013). Ecological damage, such as loss of plants, animals, and soils, occurs
within the forests during high energy events, and damage to lands and structures occupied
by coastal communities happens as well (Alongi, 2008, Islam et. al., 2005, Joffre et. al., 2015,
Kelly, 2012, McKee, 2007, Queiroz et. al., 2013). Strong storm surges have the ability to
33
flood and damage villages and crops, which negatively impacts local food security,
economies, and lives (Joffre et. al., 2015, Kelly, 2012, Queiroz et. al., 2013).
Decreased Shoreline Stabilization and Land Building
The highly specialized and intricate root systems present in mangrove forests are
removed for development of shrimp farms (Joffre et. al., 2015, Lee et. al., 2014, Lovelock et.
al., 2015, Queiroz et. al., 2013, Thampanya et. al., 2006). Once removed, webs of thick,
interlocking roots can no longer stabilize coastlines, prevent erosion, or trap sediments,
nutrients, and detritus (Alongi, 2008, Joffre et. al., 2015, Lee et. al., 2014, Lovelock et. al.,
2015, Queiroz et. al., 2013, Thampanya et. al., 2006). Thampanya et. al., 2006, found a
positive correlation between mangrove loss and shrimp farm development, as well as
increased rates of erosion with increased area of shrimp farms. The study also found that
erosion rates were very low in areas that still had mangroves present and very high in
areas where mangroves had been removed (Thampanya et. al., 2006). Roots systems
present in mangrove forests hold soils together and trap sediments, nutrients, and detritus,
which accumulate over time, resulting in soil accretion (Lee et. al., 2014, Lovelock et. al.,
2015, Queiroz et. al., 2013, Thampanya et. al., 2006). However, this function is being lost
with removal of mangrove forests for shrimp farms and causing rates of shoreline erosion
to increase and rates of land development to decrease (Lee et. al., 2014, Lovelock et. al.,
2015, Queiroz et. al., 2013, Thampanya et. al., 2006). Rates of coastline erosion are further
accelerated by increased impact from waves, tides, and storm surges (Lee et. al., 2014,
Lovelock et. al., 2015, Queiroz et. al., 2013, Thampanya et. al., 2006). Loss of shoreline
stabilization and land building results in sea level rise (i.e., coastline elevation loss), salt
34
intrusion, eutrophication (i.e., increased levels of nutrients in the water column), and
increased sediment and carbon export (i.e., no roots present to intercept sediments and
detritus) (Lee et. al., 2014, Lovelock et. al., 2015, Queiroz et. al., 2013, Thampanya et. al.,
2006).
Sea level rise and decreased water quality from increased rates of erosion and
decreased rates of sediment trapping (i.e., soil accretion) have negative socio-economic
impacts, since most of the world’s population lives near coastlines (Joffre et. al., 2015, Islam
et. al., 2005, Lee et. al., 2014, Queiroz et. al., 2013, Thampanya et. al., 2006). These issues
are likely to intensify with global climate change, especially since mangrove forests are
carbon sinks, and are being deforested at an alarming rate (Alongi, 2002, Alongi, 2008,
Joffre et. al., 2015, Kelly, 2012, Lee et. al., 2014, Queiroz et. al., 2013, Tenorio et. al., 2015,
Thampanya et. al., 2006, Valiela et. al., 2001).
Decreased Carbon Sequestration and Storage
Mangrove forests are among the most productive ecosystems in the world
(Bournazel et. al., 2015, Ewel et. al., 1998, Joffre et. al., 2015, Kathiresan and Bingham,
2001, Kelly, 2012, Lee et. al., 2014, McKee, 2007, Tenorio et. al., 2015, Valiela et. al., 2001).
Mangroves sequester and store carbon at rates ten times higher than terrestrial forests,
making them substantial global carbon sinks (Kelly, 2012, Lee et. al., 2014). In addition to
storing carbon in woody structures (i.e., trunks and roots), mangrove forests also store
carbon as peat, which forms from accumulations of undecomposed plant matter (i.e.,
detritus) (Kathiresan and Bingham, 2001, McKee, 2007). However, deforestation of
mangroves for development of shrimp farms has substantially reduced rates of carbon
35
sequestration and storage, as well as increased rates of carbon export (Kelly, 2012, Lee et.
al., 2014). Lee et. al., (2014), found levels of carbon emissions from shrimp farms to be
much higher than any other agriculture practice in the world. In addition, Kelly, 2012,
found that farm raised shrimp have carbon footprints ten times higher than beef raised on
slash-and-burn farms in the Amazon forest. These large carbon footprints result from loss
of mangrove trees, which are no longer present to sequester carbon dioxide from the
atmosphere to store in woody structures (i.e., trunks and roots) and underground (i.e., peat
formation) (Kelly, 2012, Lee et. al., 2014). In addition, carbon exports are increased
because woody materials from deforestation (i.e., trees, roots, detritus, and sediments) are
carried offshore by waves and tides (Lee et. al., 2014). The rate of carbon exports is
dramatically increased once mangrove forests are removed because there is more carbon
available to export and greater energy from waves and tides (i.e., coastal barriers are
removed, making energy from waves, tides, and storms higher) (Bournazel et. al., 2015, Lee
et. al., 2014).
Reduced carbon sequestration and storage and increased carbon exports have
negative socio-economic impacts (Lee et. al., 2014). Global climate change affects all biotic
and abiotic elements in the world through increased average global temperatures and
unpredictable weather events (Alongi, 2008, Bournazel et. al., 2015). For instance,
increased average global temperatures increase global ocean temperatures, causing water
to expand and sea levels to rise (Alongi, 2008, Lovelock et. al., 2015). Higher sea levels
result in salt water intrusion, coastline deterioration, and increased impact from storms
(Alongi, 2008, Lee et. al., 2014, Lovelock et. al., 2015). In addition, unpredictable weather
events, such as droughts and floods, have the ability to devastate communities, especially
36
ones that depend on rain fed crops for survival (i.e., developing countries where mangroves
are being removed) (Islam et. al., 2005). Since mangrove forests are one of the largest
carbon sinks in the world, loss of sequestration and increased releases of carbon are
expected to accelerate the rate of global climate change (Alongi, 2008, Bournazel et. al.,
2015, Lee et. al., 2014, McKee, 2007). Though there is much uncertainty with this complex
issue, increased atmospheric carbon dioxide levels will most likely result in negative
impacts to societies around the world (Alongi, 2008).
Impacts to Coastal Communities
Coastal communities, especially the rural poor, are negatively impacted by
deforestation of mangrove forests for development of shrimp farms (Islam et. al., 2005,
Joffre et. al., 2015, Kelly, 2012, Queiroz et. al., 2013). Impacts stem from degraded
environments, economic losses, poor working conditions, and conflicts with large shrimp
farming industries (Islam et. al., 2005, Joffre et. al., 2015, Kelly, 2012, Queiroz et. al., 2013).
Degraded environments, such as loss of forest resources and increased water pollution,
result in food insecurity, fresh water crises, and crop failure, which also lead to economic
losses (Islam et. al., 2005, Joffre et. al., 2015, Queiroz et. al., 2013). Economic losses, such as
loss of resources (i.e., timber and fish) and agriculture (i.e., crop and livestock failure), also
stem from shrimp farms, since water pollution and disease results in low production,
forcing many farmers to stop operations after five years (Islam et. al., 2005, Kelly, 2012,
Queiroz et. al., 2013). Many of these farmers (75% in Vietnam) are in debt, so once the
farm is no longer viable, they are left in a worse position than when they started, and rates
of poverty and unemployment rise (Islam et. al., 2005, Joffre et. al., 2015, Kelly, 2012,
37
Queiroz et. al., 2013). This places heavy pressure on the rural poor, who are marginalized
into severely degraded environments with no means to survive (i.e., forests are gone, which
provided sustenance before development of shrimp farms) (Islam et. al., 2005, Joffre et. al.,
2015, Kelly, 2012, Queiroz et. al., 2013). This results in increased rates of migration out of
rural communities and into larger, developing cities, where farming operations are much
more intensive and compartmentalized (Islam et. al., 2005). Working conditions are very
poor at these large scale facilities; for example, labor is long, hard, and extensive and pay is
extremely low (Islam et. al., 2005, Kelly, 2012, Queiroz et. al., 2013). In addition, large scale
facilities in Thailand were found to use slave and child labor in shrimp processing plants
(Kelly, 2012). The monetary benefits from these intensive farms go overseas to a few
investors, which leaves local communities empty-handed and struggling, especially since
shrimp are exported too (Islam et. al., 2005, Kelly, 2012). Increased unemployment, food
insecurity, and degraded environments create turmoil between local communities and
shrimp farm owners, which is further exacerbated when local industries are outcompeted
by shrimp farmers and legislative permissiveness allows investors to occupy more land
(Islam et. al., 2005, Queiroz et. al., 2013, Tenorio et. al., 2015). These conflicts lead to
protests against expansion of shrimp farms, which results in human rights violations, such
as physical harm and death (Islam et. al., 2005, Queiroz et. al., 2013). For example, in
Bangladesh, shrimp farm owners hired professional terrorists to beat and kill protestors
and even arranged bomb attacks, which lead to the death of several local villagers (Islam et.
al., 2005). Incidents like these create anger and fear within local communities and result in
increased migration, increased violence, or acceptance of new conditions and demeaning
lifestyle (Islam et. al., 2005).
38
Solutions to Protect Forests
There is a strong need for creation and implementation of environmental laws and
regulations to protect remaining mangrove forests and control shrimp farm development
in coastal (fringe) zones (Ewel, 1998, Islam et. al., 2005, Joffre et. al., 2015, Kelly, 2012, Lee
et. al., 2014, Queiroz et. al., 2013, Tenorio et. al., 2015, Thampanya et. al., 2006). Different
mangrove zones (fringe, riverine, and basin) can be used to determine what goods and
services are most crucial and therefore which areas are most important to protect (Ewel,
1998). Areas that have not been heavily impacted by development and still connect to
surrounding habitats should be protected and restored versus isolated and degraded
mangrove stands (Lee et. al., 2014, Tenorio et. al., 2015). Restoration should include
planting many native species that work together as a mosaic of microhabitats to increase
biodiversity and ensure success of recovery (Kelly, 2012, Lee et. al., 2014). Areas chosen
for restoration should be assessed for level of impact from development and soil nutrient
levels (Kelly, 2012, Tenorio et. al., 2015). For example, in Thailand, mitigation efforts were
failing because areas selected for restoration were heavily degraded, soils lacked nitrogen,
phosphorous, and iron, and monospecific stands were planted (Kelly, 2012). Failing
restoration efforts led to the creation of the Mangrove Action Project in Thailand, which
focuses on sustainable regrowth by balancing biodiversity and economy (Kelly, 2012). This
integrated system works towards reconciliation by promoting healthy ecosystem
functioning and stable economy, since forests cannot return to their previous states and
shrimp farming has become a large source of revenue (Joffre et. al., 2015, Kelly, 2012, Lee
et. al., 2014, Tenorio et. al., 2015).
39
Similar movements have taken place in Brazil (i.e., Marine Extractive Reserves),
where monetary values were assigned to different zones to assess where conservation of
forests and development of farms should take place (Tenorio et. al., 2015). The mean
global monetary value of fringe zone forests are $37,500/hectare/year and all zones of
mangrove forests are worth $16,100/hectare/year (Tenorio et. al., 2015). These values
prompted governments in Brazil to regulate the development of shrimp farms in mangrove
forests and have construction of ponds take place in upland areas (i.e., plateaus) that
neighbor forests instead (Tenorio et. al., 2015). The idea of building farms in
inland/upland areas has become quite popular in other regions where vast amounts of
mangrove forests have been removed, as well as implementing integrated mangroveshrimp production systems where farms already exist (Lee et. al., 2014, Joffre et. al., 2015,
Kelly, 2012). In Vietnam, integrated mangrove-shrimp systems have been a successful
way to promote restoration and biodiversity while still allowing economic growth (Joffre
et. al., 2015). These systems work by planting mangroves in and around ponds on bunds
(raised beds), which helps improve water quality, habitat for shrimp, and provide
additional income (i.e., timber) for farmers (Joffre et. al., 2015).
More advanced, high-tech systems are working towards reducing environmental
damage and increasing production by developing closed-system farms inland (Figure 8)
(Stokstad, 2010). Ponds are constructed with cement and built inside greenhouses, where
water is recirculated, aerated, and shrimp are fed biofloc (Stokstad, 2010). Biofloc refers to
the use of microbes in nutrient recycling; that is, bacteria and carbon are put into systems
to allow the breakdown of ammonium in shrimp feces so it can be recycled and consumed
by shrimp (Figure 9) (Stockstad, 2010). These systems have significantly reduced
40
ecosystem damage and increased production; however, small-scale farming operations in
developing countries cannot afford advanced technology, which is where the majority of
farmed shrimp come from (Stockstad, 2010). Therefore, laws and regulations to conserve
remaining forests, as well as restoration and development of integrated mangrove-shrimp
farms, are the most promising solutions to protect the world’s mangrove forests (Ewel,
1998, Islam et. al., 2005, Joffre et. al., 2015, Kelly, 2012, Lee et. al., 2014, Queiroz et. al.,
2013, Stockstad, 2010, Tenorio et. al., 2015, Thampanya et. al., 2006).
Discussion
Mangrove forests are among the most productive, complex, and biologically diverse
ecosystems in the world (Ewel et. al., 1998, Kathiresan and Bingham, 2001, McKee, 2007).
These unique forests occur on coastlines in tropical and subtropical areas and provide
habitat for thousands of species, including nursery grounds for marine organisms (i.e., fish
and shrimp), and specialized environments for many threatened and endangered animals
(Ewel et. al., 1998, Kathiresan and Bingham, 2001, McKee, 2007). Traditional coastal
communities rely on mangrove forests for many goods, such as food (i.e., fish) and forest
products (i.e., fuelwood and building materials) (Islam et. al., 2005, Quieroz et. al. 2013,
Tenorio et. al., 2015). The roots of mangrove trees create intricate webs, which stabilize
coastlines by preventing erosion, and improve water quality by filtering contaminants and
trapping sediments and detritus that would otherwise flow into bays and oceans (Ewel et.
al., 1998, Kathiresan and Bingham, 2001, McKee, 2007). Sediments and detritus that get
trapped by root systems accumulate and build land over time, which helps mitigate sea
level rise (Lee et. al, 2014, Lovelock et. al., 2015). In addition, mangrove forests sequester
41
and store carbon at rates ten times higher than terrestrial forests, which helps mitigate
global climate change (Kelly, 2012, Lee et. al, 2014). However, despite the overwhelming
importance and value of these ecosystems, many have been damaged or destroyed by
industry, with development of shrimp farms posing the greatest threat (Ewel et. al., 1998,
Kelly, 2012, Lee et. al, 2014).
The majority of shrimp farms are in developing countries, where lack of laws,
regulations, and permits have led to devastating and irreversible ecological damage (Islam
et. al., 2005, Quieroz et. al. 2013, Tenorio et. al., 2015). When global fisheries collapsed in
the 1970’s from overharvesting, large-scale fishing industries turned to farming as a way to
meet world demands for seafood (Islam et. al., 2005, Joffre et. al., 2015, Quieroz et. al. 2013,
Tenorio et. al., 2015). Large investors went to governments in countries with mangrove
forests and promised financial redemption through economic gains from shrimp farming.
Top-down decision making in undeveloped and developing countries resulted in selling
land to investors, who rapidly transformed mangrove forests into intensive, destructive
shrimp farms, which marginalized the coastal communities who relied on them the most
(Islam et. al., 2005, Tenorio et. al., 2015). Indeed, short-term profits were high with
production rates up to 90,000 pounds/acre; however, the rural poor were unable to build
such advanced operations, and therefore practiced traditional and extensive farming
methods, which are unsustainable due to lack of resources and education (Islam et. al.,
2005, Kelly, 2012). Traditional and extensive farms construct ponds within mangrove
forests by deforesting trees, shrubs, and roots, and by building dikes and canals to get
access to water and wild post-larvae shrimp from mangrove estuaries (Joffre et. al., 2015).
Local farmers built farms in an attempt to improve their quality of life through increased
42
food security and personal. However, 90% of rural farmers must get loans to start
operations, and lack of scientific management results in collapse of ponds, which leaves
them empty-handed and in debt (Joffre et. al., 2015). Farmers must abandon the once
viable ponds after approximately five years due to poor water quality and sometimes
spread of disease, which leaves traditional communities and mangrove forests in ruins
(Kelly, 2012).
By removing mangroves, goods and services are lost, such as habitat for terrestrial,
aquatic, and marine species, which results in local fishery collapse and decreases local food
security (Islam et. al., 2005). In addition, endemic species become threatened or
endangered, forest products are lost (i.e., honey, wax, fuelwood, building materials), rates
of coastal erosion increase, land building decreases, carbon sequestration and storage
decrease, and the once protective coastal barrier is gone (Lee et. al., 2014). In addition,
water availability and quality are severely decreased, as ponds need constant supplies of
fresh water to maintain water quality, and release polluted waters into the ecosystem after
harvest (Islam et. al., 2005, Quieroz et. al. 2013, Tenorio et. al., 2015). The loss of these
ecological goods and services has devastating impacts on traditional coastal communities
that have been relying on mangrove forests for generations (Islam et. al., 2005, Quieroz et.
al. 2013, Tenorio et. al., 2015). Rates of poverty increase, food security decreases,
unemployment increases, and quality of life is reduced (Islam et. al., 2005, Quieroz et. al.
2013, Tenorio et. al., 2015). In addition to food insecurity and economic losses, traditional
coastal communities are negatively impacted through poor working conditions, heavily
degraded environments, and loss of land (Islam et. al., 2005, Quieroz et. al. 2013, Tenorio
et. al., 2015. Large-scale operations continue to occupy land and push traditional
43
industries out, such as local agriculture and livestock farms, which creates turmoil between
local communities and shrimp farm owners (Islam et. al., 2005). This occurs due to great
differences in perceptions and values between traditional coastal communities and shrimp
farm investors, such as reciprocity and connectedness versus competition and
individualism (Queiroz et. al., 2013). These differences lead to exploitation of both people
and mangrove ecosystems, which creates turmoil and violence between the two distinctive
groups (Islam et. al., 2005, Quieroz et. al. 2013, Tenorio et. al., 2015). Reconciliation is
greatly needed to reduce the rate of ecological and socio-economic damage, as well as keep
shrimp farming viable through sustainable practices and management, since the industry is
completely dependent on the services mangrove ecosystems provide (Islam et. al., 2005,
Joffre et. al., 2015, Quieroz et. al. 2013, Tenorio et. al., 2015, Stokstad, 2010).
Protection and restoration of mangrove forests is happening in many countries,
including Brazil, Thailand, and Vietnam. Creation and implementation of laws and
regulations is crucial to protect remaining forests. Assessments of mangrove degradation
are needed to determine what areas to protect and restore, and which to develop, though
most governments now recognize that construction of shrimp farms should occur inland.
Restoration, mitigation, and management need to be scientific and community based to
ensure successful recovery and sustainability of forests. In addition, traditional coastal
populations need to benefit from these efforts socio-economically by restoring human
rights and quality of life (Islam et. al., 2005, Joffre et. al., 2015, Lee et. al., 2014, Quieroz et.
al. 2013, Tenorio et. al., 2015).
44
Many global issues are directly or indirectly connected to the loss of mangrove
forests. Wildlife and human populations worldwide heavily depend on goods and services
provided by mangrove forests. The perceived benefits of mangrove forest removal for
shrimp farm development are far surpassed by the ecological and economic benefits they
provide. Large portions of the world’s human population directly depend on mangrove
forests for resources and services; therefore, degraded and over-exploited systems result
in extreme impacts to societies and economies worldwide. Services such as coastal
protection, soil accretion, and carbon sequestration are very difficult to quantify
monetarily; however, I believe their overall value far outweighs any benefits gained
through farming of shrimp. Innovation and ingenuity can reduce impacts to mangrove
forests by finding alternative ways to farm shrimp. Implementation of regulations and
sustainable practices is needed to protect the forests that still remain. A global policy to
protect traditional villages and communities from exploitation by large investors is also
greatly needed.
45
Tables and Figures
Figure 1: (A) Prop roots in mangrove forest. (B) Prop roots of an individual mangrove tree.
(C) Propagules of a mangrove (Kathiresan and Bingham, 2001).
Figure 2: (A) Riverine zone of a mangrove forest. (B) Aerial roots (pneumatophores) of a
mangrove tree. (C) Close up view of pneumatophores (Kathiresan and Bingham, 2001).
46
Figure 3: Distributions of the world’s mangrove forests in 2000 (Giri et. al., 2011).
Table 1: Different zones of mangrove forests provide different goods and services. 1=most
significant zone for that good or service (Ewel et. al., 1998).
47
Figure 4: (A) Global mangrove forest distribution and abundance. (B) Mangrove forest
distribution and abundance in Asia (Islam et. al., 2005).
48
Table 2: Loss of worlds mangrove forests, separated by human use and continent (Valiela
et. al., 2001).
Figure 5: Graph representing increase in global shrimp production 1981-1999 (Islam et. al.,
2005).
49
Table 3: Characterizations of different types of shrimp farms (Paul et. al., 2010).
Figure 6: Model displaying mechanisms for land development within mangrove forests
(Lee et. al., 2014).
50
Figure 7: Photograph of extensive shrimp farm showing development of ponds in basin
zones of mangrove forests (Valiela et. al., 2001).
Figure 8: High-tech, closed-system farm inside of a greenhouse (Stokstad, 2010).
51
.
Figure 9: Shrimp consuming biofloc (converted shrimp feces) in a closed-system farm
(Stokstad, 2010).
52
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