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Title: Analysis of the Responses of Mangrove Ecosystems to
Climate Change

Abstract:

Despite the warnings against climate change since the early
century, recent human activities are still geared towards enhancing
them. Because of climate change coupled by other human activities,
natural ecosystems such as mangroves are facing difficulties in
coping with the impacts of climate change. Their natural ecological
functions, which could provide benefits to human and other species
of organisms, are disrupted. The impacts of climate change to the
mangrove ecosystem can be analyzed based on the different
environmental factors related to climate change such as sea-level
rise, wind patterns and hydrodynamic shifts, storminess,
temperature change, and availability of water from precipitation
and runoff. Responses of mangrove ecosystems to such factors and
recommendations for mangrove protection in relevance to climate
change are discussed.

I. Introduction
A. Global Climate Change

Rapid rate of emissions of greenhouse gases such as carbon
dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons from
anthropogenic sources such as burning of fossil fuels, tropical
deforestation and other human activities resulted to increase in
global temperature, otherwise known as global warming. Increased
amount of solar energy has been trapped by these gases raising the
Earth ́s surface temperature (Curry, 2005; Boesch, 2002; NRDC,
2006). Global average temperature records since 1860 showed a
continuous increasing trend (Figure 1). Since 1990, eleven of the
warmest years have occurred with the five warmest during the last
seven years namely in decreasing intensity: 2002, 1998, 2003, 2001
and 1997. Due to the recent trends, the rate of global temperature
increase accelerated from +0.6oC over the past century to an
equivalent rate of +1.0oC per century in the past two decades.

Figure 1. Recorded global rise in temperature since 1860.
(Source: Boesch, 2002) B. Threats from Global warming

The environmental factors with the greatest direct effects on
estuarine and marine ecosystems in terms of global climate change
are sea-level rise, wind patterns and hydrodynamic shifts,
storminess, temperature change, and availability of water from
precipitation and runoff. According to the report by the Third
Assessment Report of Working Group I of the Intergovernmental Panel
on Climate Change (IPCC), there is less uncertainty about predicted
changes in temperature and sea levels than about predicted changes
in precipitation, winds, and storminess (Kennedy et.al., 2002).
However, the actual impacts of these factors will depend on the
frequency and intensity coupled with human-controlled factors such
as coastal land use and management approaches (Nicholls, 2003).

[page2image14456]

1. sea level rise

Sea-level rise as a consequence of global warming is caused by
increase in seawater temperatures resulting to thermal expansion of
water and melting of glacier and polar land ice (Kennedy et. al.,
2002).

According to the report of the IPCC, the global sea-level rise
in the 20th century was between 10 and 20 cm and predicted that a
further accelerated rise of 9 to 88 cm will occur between 1990 and
2100 with a mid-estimate of 48 cm (Kennedy et.al., 2002; Nicholls,
2003).This faster rate of sea-level rise estimated at 1-2 mm per
year (Boesch, 2002) is caused by human-induced global warming.
However, the global mean sea-level rise will not be uniform around
the world since local change in sea level at any coastal location
depends on the sum of global, regional, and local factors, which is
termed as relative sea-level change (Nicholls, 2003).

Sea-level rise leads to a range of impacts including increased
flood risk and submergence, salinization of surface and ground
waters, and morphological change, such as erosion and wetland
loss.

The significant changes due to global warming particularly
sea-level rise will likely continue into the next century and
beyond despite successful efforts to curb emissions of greenhouse
gases because of the longevity of greenhouse gases in the
atmosphere and the lag in warming effects of the oceans (Boesch,
2002).

Figure 2. Sea-level rise in relation to carbon dioxide emissions
and temperature. (Source: Boesch, 2002)

[page3image13064]

2. Wind patterns and hydrodynamic shift

Modest changes in the climate cycle, particularly sea-level
conditions, short- and long-term, can alter the hydrologic balance
and tidal prism sufficient to alter habitat type and boundaries
(Doyle et.al., 2003).

The winds, which are created by the unequal heating of the Earth
́s surface, will experience weakening as polar regions experience
higher temperatures that will reduce the thermal gradient between
the poles and equator. A consequence of this is the weakening of
the overall wind-driven water circulation that could seriously
affect the structure and function of open ocean and nearshore
ecosystems (Kennedy et.al., 2002).

Coastal currents can be affected by climate change in a number
of important ways, including increasing or decreasing the frequency
and strength of coastal upwelling, changing the properties,
including temperature and salinity, of coastal waters that are
tidally advected into estuaries thus affecting conditions at least
in the lower estuary, changing the set-up of water levels along the
coast thereby affecting relative sea-level over seasons or several
years, and changing the direction, strength or timing of long-shore
advection (Boesch, 2002).

3. Storminess

More energy is pumped into tropical storms by the warmer waters,
making them more intense. This has been partially validated by
increase in the number of category 4 and 5 storms over the past 35
years along with ocean temperature (NRDC, 2006). The IPCC, on the
other hand, was unable to find a consistent pattern of tropical and
extra- tropical storminess (frequency or intensity) due to
variability in the data but recent national and regional scenarios
in Europe suggest an increase in storminess, which will interact
unfavourably with sea-level rise and have major negative effects on
coastal ecosystems (Doyle et.al., 2003; Nicholls, 2003). The IPCC,
however, concludes that increases in the peak wind intensity of
tropical cyclones are probable as well as both mean and peak
precipitation intensities. Increased storminess may be a result of
intense latitudinal temperature gradients and increased evaporation
from tropical sea surfaces (Boesch, 2002).

4. Temperature change

An increase of 0.6oC to the average temperature near the surface
of the earth has been estimated since 1861 with most of the warming
occurring from 1910 to 1945 and from 1976 to 2000. This is
predicted to increase by 1.4 to 5.8 oC from the 1990 levels causing
an increase also in the sea-surface temperature with the greatest
warming expected to occur at high latitudes in winter (Boesch,
2002; Kennedy et.al., 2002). The greatest ecological change in
estuarine and marine ecosystems may result from the rapidity in the
temperature change (Kennedy et.al., 2002).

5. Precipitation change

Over most of the mid- to high-latitude and tropical land areas
of the Northern Hemisphere in the 20th century experienced
increased precipitation intensity and frequency, while a decrease
over sub-tropical (10o N to 30o N) land areas has been

observed. In low latitude areas, effects of climate change on
precipitation may vary (Kennedy et.al., 2002). Some areas may
experience increased precipitation while others the opposite.

C. Philippine Vulnerability

The Philippines is highly prone to storm surges and riverine
flooding due to high frequency of tropical cyclones and other
environmental degradation. An average of 20 tropical cyclones pass
yearly through the Philippines and about nine of them cross land
(Perez, no date). Heavy rains brought by monsoons frequently flood
low-lying areas in the Philippines (Figure 3). The northeast
monsoon season from November to February, brings heavy rains on the
eastern side of the country, while the western side during the
southwest monsoon season from May to September, which coincides
with the typhoon season as well. Heavy economic losses result from
the damages by tropical cyclones. Climate variability such as El
Niño causing drought and floods for La Niña also affects
variability of the amount of rainfall in the country. Rising sea
level due to climate change could aggravate the situation, as many
low-lying places in the country are usually flooded during the
monsoon seasons and tropical cyclones occurrences. With the
pressing problems of climate change, this situation is expected to
be a severe problem in the future. Since the country is comprised
of 7,108 islands, many of which are small islands, the impacts of
climate change will be further aggravated.

Figure 3. Most low-lying areas in the Philippines are flooded
during monsoon seasons or occurrence of tropical cyclones. (Source:
Perez, no date)

[page5image13280]

D. Description of mangroves

Mangrove forests, which occupy intertidal settings along the
mouths of rivers or estuaries of tropical and subtropical regions
worldwide, are universally composed of a single overstory strata of
relatively few tree species tolerant of fluctuating salinity (Doyle
et.al., 2003; Kennedy et.al., 2002). Mangroves can tolerate the
added stress of water-logging and salinity conditions that prevail
in low-lying coastal environments influenced by tides because of
their halophytic nature (Doyle et.al., 2003). They require slow
currents, no frost and plenty of fine sediment in which to set
their roots. Areas with high rainfall and upstream runoff are
associated with best-developed mangrove forests, however they grow
best in moderately saline environments. They can also keep up with
sea level rise of up to 12 cm per 100 years (Perez, no date).

E. Benefits of mangrove ecosystem

The benefits derived from the mangrove ecosystem can be divided
into four categories namely, direct use values in terms of the
goods and services they provide, indirect use values in terms of
the ecological functions which indirectly support economic
activity, optional use values or the options to directly or
indirectly use these ecosystems in the future, and non-use values,
which may arise because individuals derive satisfaction from
knowing that the ecosystems exist, and will continue to exist for
future generations (Chong, 2005).

Large quantities of food and fuel, building materials and
medicines are derived from the mangrove forest. Four hundred kilos
of fish, shrimps, crabmeat, molluscs and sea cucumbers can be
derived from one hectare of mangroves in the Philippines annually.
This can also feed a further 400 kilos of fish and 75 kilos of
shrimps that mature elsewhere. The leaves of Nypa, a species of
palm, that thrives abundantly in mangrove areas is used by
Filipinos to thatch roofs while its fermented sap produces an
annual 10,000 liters of alcohol per hectare of mangroves (Perez, no
date).

The mangrove trees are also good sources of tan bark for tannin
extract industry (FAO and UNEP, 1981). The Philippines is also
deriving income from mangrove- related tourism activities such as
walk-through-the-mangrove programs, where they set- up boardwalks
for people to see the interior of the forest.

Nutrients from decaying leaves and wood are concentrated in the
muddy waters, which are home to sponges, worms, crustaceans,
molluscs and algae. Since mangrove communities are very highly
productive systems and their root systems are very intricate, they
provide valuable habitat for fisheries, shorebirds, marine mammals,
snakes and crocodiles as well as provide the basis for the
nearshore marine food web (Perez, no date). In fact, majority of
the world ́s marine species, including most fish catches depend on
coastal wetlands for part of their life cycle (Doyle et.al., 2003).
They also serve as refuges from predators (Kennedy et.al., 2002).
By harbouring large number of species, mangrove ecosystems also
support biodiversity conservation and acts as a natural gene
bank.

The root system of mangrove forests can stabilize marine and
terrestrial sediments reducing coastal erosion and supporting clear
offshore waters favourable to

coral growth. Extensive tracts of mangroves can protect the
adjacent land and human populations from storm surges of water
caused by high intensity coastal storms and hurricanes (Kennedy
et.al., 2002; Chong, 2005). A healthy mangrove forest can also
prevent salt water intrusion preventing damage of freshwater
ecosystems and agricultural areas.

F. Mangrove Communities in the Philippines

Philippine mangrove forests feature at least 40 of around 54
species in the Indo- Pacific. The main tree species are Rhizophora
apiculata, Rhizophora mucronata, Ceriops tagal, Ceriops
roxburghiana, Bruguiera gymnorrhiza, Bruguiera parviflora,
Bruguiera cylindrica and Bruguiera sexangula. Further upstream,
where the water is not so brackish, nipa palm (Nypa fruticans) may
form extensive and dense stands that are major sources of roofing
materials in coastal areas (FAO and UNEP, 1981).

The mangrove forests in the Philippines have faced massive
deforestation from about 450,000 hectares in 1918 to about 100,000
hectares at present (Primavera, 2002). This has resulted from the
indiscriminate cutting, land clearing and habitat conversion of
mangrove forests to give way to aquaculture activities largely
shrimp ponds, salt beds and human settlements. Mangrove depletion
rate of 3,700 hectares per year was observed from 1980 to 1991
mainly due to the Blue Revolution program of the government that
promoted mangrove conversion for aquaculture in order to increase
fish supply, provide livelihood and alleviate poverty. Around half
of the 279,000 ha of Philippine mangroves that disappeared between
1951 and 1988 were converted into ponds mainly for milkfish, but
also for shrimp (Primavera, 2005). Less than 20,000 hectares of
mangrove forests is considered old growth.

II. Statement of problem and objectives

Given the forecasted trends of the different environmental
factors accompanying climate change, mangrove ecosystems will be
among the most immediately threatened. Its increased vulnerability
is due to the fact that these mangrove forests are located along
the land-sea interface where most human activities are
concentrated.

The main objective of this paper is to understand the responses
of mangrove ecosystems to the different factors resulting from
global climate change.

It will specifically try to answer the following specific
objectives:

To identify various scenarios that will happen under the
different environmental

factors of climate change;

To identify human activities or interventions that aggravates
the effects of

climate change; and

To provide recommendations for future mangrove conservation
actions in the

Philippines.

III. Presentation of impacts of global warming factors to
mangrove communities

The following scenarios present the different responses of
mangrove under the varying conditions of global climate change.

A. Sea level rise

1. Encroachment upland by mangrove

Mangrove encroachment upland through freshwater marsh and swamp
environments is a possible consequent of sea-level rise in pristine
undeveloped areas with gentle slope, which could lead to increase
mangrove expanse and reduce freshwater marsh coverage (Doyle
et.al., 2003; Boesch, 2002). This is due to the fact that salinity
tolerance of mangroves will reach saturation causing encroachment
upslope (Doyle et.al., 2003).

The relationship between landward slope and elevation in
relation to tide range and extent, and an understanding of relative
sea-level rise are important in predicting landward transgression
of mangroves. In the modelling simulation of the mangrove
communities of the Everglades, South Florida, faster or more
extensive encroachment of mangroves into the Everglades slope
result from greater rate of sea-level rise, however, inland
penetration of saltwater conversely mangrove vegetation into
upslope marsh will occur at any rate of sea-level rise (Figure 4).
A negative impact of this is the increase loss of freshwater marsh
and swamp habitats as tidal prism increases over time as it moves
upslope (Doyle et.al., 2003). Over the next century under climate
change conditions, mangrove habitats in the Everglades will
increase while freshwater marsh/swamp will decrease.

Figure 4. Modelling simulation of mangrove Migration in South
Florida, USA under different sea-level rise scenarios. (Source:
Doyle et.al., 2003)

[page8image13888]

A consequence of this landward encroachment of mangrove forest
is enhancement of local fisheries as spawning and habitat area is
increased. However, this might be in the short term only as other
factors will have impacts on the fishery and will compromise other
wildlife benefits dependent on freshwater habitat (Doyle et.al.,
2003).

2. Mangrove loss due to coastal squeeze

The rate of sea-level rise rather than the total rise drives
more mangrove losses as they have the capacity to respond to
inundation (Nicholls, 2003). However, in areas with seaside human
development, inland migration of mangrove forests will be prevented
causing permanent submersion of the mangrove trees under high
salinity water and plant death due to salt stress (Kennedy et.al.,
2002). Presence of flood- control, navigational or other
anthropogenic structures decreases sediment inputs to the mangrove
communities preventing it from coping with sea-level rise through
normal accretion or vertical accumulation of sediment (Figure 5).
More frequent inundation stresses root metabolism due to low oxygen
concentration and sulphide, which dramatically affects the
production of organic matter needed for sufficient aggradations of
soils (Boesch, 2002). However, in some estuary catchments prone to
future increased sediment supply, inundation will be slower as
sediment build-up around the estuary margins could act to
counteract sea-level rise.

Figure 5. The figures depict changes in a mangrove forest that
inhabits a depositional terrace that is over 6000 years old (A). In
(B), sea level rises at a rate that erodes the foreshore yet allows
the forest to retrogress inland. In the presence of human attempts
to prevent sea level from inundating the land by building a
seawall, the mangrove forest will be eroded away (C and D) and the
seawall may have to be strengthened against wave action that is no
longer buffered by the mangroves. BP= before present; MSL= mean sea
level. (Source: Kennedy et.al., 2002)

[page9image16184]

Another human-activity that will increase the negative effect of
sea-level rise is too much extraction of groundwater leading to
land subsidence. Accelerated rates of subsidence and sea-level rise
may alter the depth and width of shallow estuaries, which may
increase the bottom friction of wind-driven water circulation,
thereby altering the hydrodynamics. Change in the patterns of water
movement might affect significantly the dynamics of the mangrove
ecosystem (Kennedy et.al., 2002).

B. Wind patterns and hydrodynamic shift

Coastal currents can be affected by climate change in a number
of important ways, including, increasing or decreasing the
frequency and strength of coastal upwelling, changing the
properties including temperature and salinity of coastal waters
that are tidally advected into estuaries thus affecting conditions
at least in the lower estuary, changing the set-up of water levels
along the coast thereby affecting relative sea-level over seasons
or several years, and changing the direction, strength or timing of
long-shore advection (Boesch, 2002).

Nearshore current changes may significantly affect migration of
individuals to and from the mangrove ecosystem. Such is the case of
larvae of species that spawn on the inner shelf and recruits back
into estuarine nurseries (Boesch, 2002). Alongshore wind stress and
differences in the densities and buoyancies of fresher and saltier
waters in the U.S. East Coast help produce water movements that
transport larval blue crabs, menhaden, and bluefish in the Middle
and South Atlantic Bights. Transport of these species within
estuaries and along the coast will be hindered by change in water
circulation patterns, thus lowering abundances (Kennedy et.al.,
2002; Doyle et.al., 2003).

Weakening of upwelling regions resulting from decrease of wind
speeds affects the vertical mixing of food particles and larvae
patches, thereby decreasing food supply to the larvae and
increasing mortality. At wind speeds of roughly 5 to 6 meters per
second, recruitment is maximized but lower than this poses lower
survival (Kennedy et.al., 2002).

Annual variation in fishery recruitment may also be affected by
the timing and extent of high water conditions in the mangrove
ecosystem, since many fishes make regular movements onto flooded
marsh to feed and marsh access is apparently important to the
growth and survival of individuals. Climate change also affects
recruitment in terms of the species preference to high or low
intertidal habitats as nurseries. Sea level rise may thus act in
favour of species preferring high water level (Boesch, 2002).

C. Storminess

Estuaries are affected by storms in a number of ways including
sediment resuspension, and shoreline erosion due to high winds,
storm surges that flood wetlands and cause salinity intrusion, and
large freshets produced by intense rainfall on the watershed
(Boesch, 2002). Storm damage from wind and surge forces such as
devastating blow downs to intact but defoliated canopies are
sufficient to alter structure

and recovery of mangrove forests (Doyle et.al., 2003) In a model
projections of mangrove forests in South Florida USA, it was
suggested that as hurricane intensity increases over the next
century, average height of mangroves will be diminished and a
certain species of red mangroves will dominate. It was also
inferred based on hindcast simulation that structural composition
of modern day mangrove forests across south Florida is accounted
for by major storms with periodicity of every 30 years and with
tracks that subtended larger distribution of mangrove habitat.

Increase in hurricane intensities is projected over the next
century as a result of global climate change, which could further
alter the structure and composition of mangrove landscapes (Doyle
et.al., 2003). This can also act synergistically with sea- level
rise causing higher storm surges resulting to more destruction of
the mangrove forests. Forest elevation cannot keep pace with sea
level rise due to failure of mangrove to produce peat as a result
of excessive wind damage stresses resulting to additional plant
mortality and irreversible loss of habitat (Kennedy et.al.,
2002).

Figure 6. Modelling simulation of mangrove forest damage in
South Florida, USA from three intensities of hurricanes. (Source:
Doyle et.al., 2003)

D. Temperature change

1. Biological effects

Temperature at sub-lethal levels governs animal behaviour and
distribution patterns of organisms, influences growth and
metabolism, timing or reproduction, and controls rates of egg and
larval development. It also acts in concert with other
environmental variables such as dissolved oxygen. (Kennedy et.al.,
2002).

[page11image13448]

a. Physiological changes in organisms

Slight increases in temperature can cause appreciable impacts to
many species. A study has shown that in short-term (days)
temperature-tolerance experiments on estuarine invertebrates in the
laboratory, a temperature increase of 1oC often raised mortalities
from ~0 percent at the lower temperature to ~100 percent at the
increased temperature. However, higher than 1oC temperature
increases are expected in the coming century.

Warmer waters can cause decrease egg survival and larval
hatching and development as evidenced by the recent declines in the
abundance of winter flounder in New England. Increase in water
temperature tends to increase the metabolism of organisms, however
warm waters have less capacity to hold oxygen, which is a primary
reactant for metabolism. This imbalance of oxygen supply and demand
will cause stress to the organisms (Kennedy et.al., 2002).

b. Effects on the abundance and distribution of organisms

Population abundances and distribution of organisms are directly
or indirectly influenced by temperature changes. Higher
temperatures may result to elimination of highly mobile species
from part of its range since they can migrate to other more
suitable environments. Migration and colonization to new habitats
depend on many factors such as the number of adults available in
the original habitat and their ability to produce young, an
adequate number of potential colonizers (seeds, spores, larvae,
migrating juveniles or adults), the ability of potential colonizers
to move into the new habitat including their ability to cross
barriers, and the survival of adequate numbers of individuals in
the new habitat to ensure genetic diversity to meet environmental
challenges and to produce succeeding generations. Given such
factors are met, environmental corridor is another determining
factor for successful colonization, which link a region where a
species is at risk and a more suitable region. However, these
corridors may not be present for mangrove species that cannot
survive the high salinity marine conditions that occur between
mangrove communities resulting to the decrease in the population of
the species that have low or no dispersal capabilities such as
clams and oysters.

c. Effects on species interactions

Changes in the population of species in the mangrove communities
due to temperature change will also lead to changes in species
interactions such as predator- prey relationship. Decrease in prey
population will starve the predator population or force them to
shift to other resources thereby increasing competition for those
new resources. Another situation might be the change in the timing
of physiological events by advancing or retarding the timing of
reproduction for many species (Kennedy et.al., 2002).

d. Increase hypoxic or anoxic conditions

As stated earlier, warmer waters hold lesser amount of oxygen
than cooler water. Water column stratification will occur as the
upper layer of water is warmed

increasingly preventing oxygen from penetrating the deeper water
resulting to hypoxic or anoxic deeper waters, a condition not
suitable for benthic organisms.

e. Pathogens and Harmful Algal Bloom

Higher temperatures and salinities typically increase the
incidence of infection. This will decrease the health of the
mangrove forest and disrupts its ecological functions.

Increasing water temperature also facilitates eutrophication
usually resulting to proliferation of harmful algal species in a
process known as Harmful Algal Blooms. These algal species usually
contain small amount of toxins that when concentrated by
shellfishes and fishes become toxic to higher trophic organisms in
the mangrove ecosystem (Kennedy et.al., 2002).

2. Hydrodynamic change

Productivity of estuarine and marine systems is influenced by
nutrients carried from deeper waters through upwelling process.
Increases in temperature can act in two opposite ways. The first
scenario is that upwelling events will be weakened as
stratification of warm-surface water and cold-deeper water
intensifies preventing nutrients for primary production. The second
scenario expects strengthening of upwelling because there will be
more warming over land than in ocean, which will increase
low-pressure cells that typically occur over land adjacent to
offshore high- pressure cells. This will in turn enhance alongshore
winds promoting upwelling.

Coastal currents and offshore-inshore transport corridors, which
are expected to change as a result of temperature change, has
considerable effects to the distribution, recruitment, and survival
of coastal marine fish and invertebrate communities of mangrove
ecosystems (Kennedy et.al., 2002).

E. Precipitation change

Global climate change can either increase or decrease the
intensity and frequency of precipitation in coastal areas. A wide
variety of consequences results from changes in the amount and
timing of freshwater inputs to mangrove ecosystems including
shifting of the estuarine gradient up or down the estuary thereby
affecting the distribution of organisms, alteration of the flushing
rates, strengthening density stratification under higher flows and
weakening under lower flows, changes in the delivery of sediments,
nutrients, and contaminants, and modifications in the seasonal
pattern of freshwater delivery to which the life history of
migrating estuarine and anadramous organisms may be programmed
(Boesch, 2002; Doyle et.al., 2003).

1. Extreme precipitation

Extreme precipitation events, which when impounded, can cause
acute rise of water level and result to massive dieoffs. The sudden
decrease in salinity can cause severe stress to mangrove trees such
as root zone decomposition, which can further

result to rapid substrate collapse or subsidence. This has high
probability of prohibiting recolonization and promotes coastal
erosion (Doyle et.al., 2003).

Shrinking of the mangrove forest is also expected if increased
rainfall is coupled with sea-level rise because the mangrove forest
will have to compensate for the advancing high salinity water from
the sea and freshwater run-off from the land.

Water run-off is also expected to bring high amounts of
nutrients, which may lead to eutrophication of the mangrove waters.
Decomposition of plant materials will use up much of oxygen thereby
increasing water-column stratification with high nutrient
freshwater above and saline hypoxic or anoxic water at the bottom
layer (Kennedy et.al., 2002).

Catastrophic deposition of sediments can happen after extreme
rainfall causing high water turbidity, which has profound effects
to the structure and function of benthic communities.

2. Decreased rainfall

Decreased supply of freshwater from precipitation coupled with
sea-level rise would promote salinity encroachment into the tidal
freshwater reaches of the estuary. This would affect lower-salinity
communities of organisms as well as alter the food webs in
estuaries and change the residence time of nutrients and
contaminants. Increases in drought intensity or frequency would
increase the incidence of coastal hypersalinity that can lead to
reduction of valuable habitats such as mangrove forests.

Loss in productivity in the mangrove forests can be expected as
nutrient input from upstream is reduced by less water run-off.

IV. Human interventions

It is recognized that environmentally-degrading activities of
human beings have caused the rapid climate change, and further
activities are perceived to enhance the effects of these changes.
The present aggressive mitigation measures will only buy time for
highly vulnerable areas because such effects are highly probable to
occur.

A. Increased human population

With the high birth rate of the Philippines, more people are
expected to encroach into the coastal ecosystems since most of the
inner land areas are already owned and occupied. This means higher
investments will be put into building new houses and other
infrastructures in the coastal zone, which could also mean further
reduction of mangrove forests. However, present environmental laws
in the Philippines prohibit further removal of mangrove vegetation.
Thus, most planners would set aside the mangrove areas while
building constructions are allowed after the mangrove forests. If
we consider the possibility of landward encroachment of mangrove
forest in the face of sea-level rise, this measure may not be
app

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