OCEANOGRAPHIC PROCESSES OF CORAL REEFS: Physical and Biological Links in the Great Barrier Reef - Chapter 7 ppsx

The Effects of Siltation
on Tropical Coastal
Ecosystems
Miguel Fortes
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Responses of Seagrass to Siltation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Effects of Siltation on Seagrass Depth Distribution and Abundance. . . . . . . . 94
Effects of Siltation on Diversity, Biomass, and Survival . . . . . . . . . . . . . . . . . 95
Effects of Siltation on Seagrass Growth and Primary Productivity . . . . . . . . . 96
Effects of Siltation on Seagrass Morphology. . . . . . . . . . . . . . . . . . . . . . . . . . 98
Responses of Corals to Siltation/Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Effects of Sedimentation on Coral Abundance,
Diversity, and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Effects of Sedimentation on Coral Growth and Productivity. . . . . . . . . . . . . 101
Modeling Reef Status and Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Responses of Mangroves to Siltation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Effects of Siltation on Seagrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Effects of Sedimentation on Coral Reefs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
Effects of Siltation on Mangroves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
INTRODUCTION
Coral reefs, seagrass beds, and mangroves are the major ecosystems in coastal
Southeast Asia. They are experiencing widespread deterioration, largely as a result of
siltation (Fortes, 1988). During the past 25 years rates of siltation in the region have
increased substantially and are among the highest in the world (Milliman & Meade,
1983; Milliman & Syvitski, 1992). These have been caused largely by human distur-
bances such as land reclamation or changes in land use (Fortes, 1988 and 1995; Short
& Wyllie-Echeverria, 1996). The rapid progression of coastal development, near and
offshore mining, agricultural land use, and deforestation have led to increasing silt

load and eutrophication. These brought about dramatic changes in the development
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of coastal plant and animal communities in both tropical and temperate waters (Orth
& Moore, 1983; Cambridge & McComb, 1984; Onuf, 1994; Terrados et al., 1998).
The aim of this chapter is to describe the changes in depth distribution, abun-
dance, growth and photosynthetic performance, and morphological changes in sea-
grasses and corals along siltation gradients. In addition, the effect of siltation on the
demography of mangrove seedlings is briefly discussed. It is hypothesized that the
reduction in light availability brought about by siltation or sedimentation is the most
operationally significant factor forcing changes in species composition and commu-
nity distribution along gradients of siltation. Hence, at less perturbed sites, a change
in species composition along a gradient should parallel a similar change with increas-
ing depth.
RESPONSES OF SEAGRASS TO SILTATION
Seagrasses are submerged angiosperms that can fulfil their entire life cycle under
water, forming extensive meadows on sandy to muddy sediments in shallow coastal
waters (den Hartog, 1970; Valiela, 1984). Among the most productive components of
coastal ecosystems (Hillman et. al., 1989), these meadows are an important link
between land and ocean (Holligan & de Boois, 1993; Hemminga et al., 1994) and
support a high primary production (Valiela, 1984; Hillman et al., 1989; Duarte,
1989). Seagrass leaves and stems add considerable three-dimensional structure to the
seabed, providing habitat, feeding, and breeding grounds as well as nurseries for a
diverse array of fauna (e.g., sirenians, birds, fish, and invertebrates: Jacobs et al.,
1981; Bell & Pollard, 1989; Howard et al., 1989; Klumpp et al., 1993). Seagrass
meadows also act as sediment traps (Bulthuis et al., 1984; Ward et al., 1984; Fonseca
& Fisher, 1986; Fonseca, 1989) and as breakwaters offering natural shoreline protec-
tion (Fonseca et al., 1982; Hemminga & Nieuwenhuize, 1990).
The effects of siltation on seagrasses are manifested in their depth distribution,

abundance, species composition, growth, primary productivity, and changes in mor-
phology. These changes are briefly discussed below.
EFFECTS OF SILTATION ON SEAGRASS DEPTH DISTRIBUTION
AND
ABUNDANCE
Seagrass beds are subject to both direct and indirect influences of man’s interference
in the coastal zone. Urbanization, large-scale reclamation and shore protection
works, increased sediment delivery by rivers draining watersheds with changing
land-use practices, eutrophication, and increased fishing pressure have severely
affected the depth distribution, density, and areal extent of seagrass meadows
(Cambridge et al., 1986; Fortes, 1988; Shepherd et al., 1989; Giesen et al., 1990;
Holligan & de Boois, 1993; Lundin & Linden, 1993).
Distribution and abundance of seagrasses are controlled by a range of environ-
mental conditions including light availability (Dennison & Alberte, 1985; Dennison,
1987), nutrient availability (Short, 1987), water motion (Fonseca & Kenworthy, 1987),
and grazing (Lanyon et al., 1989). Of these, light availability is considered one of the
94 Oceanographic Processes of Coral Reefs
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more important environmental parameters, controlling the depth to which seagrasses
can grow and excluding seagrasses from areas with low light conditions (Dennison
et al., 1993; Abal & Dennison, 1996; Bach, 1997; Bach et al., 1998; Duarte et al.,
1997). Siltation is a major factor that limits light availability for benthic organisms
The relationships between light conditions and depth distribution of temperate
seagrasses clearly document that light availability is the prime regulating factor for
plant performance (e.g., Bulthuis, 1983; Dennison, 1987; Olesen, 1996). Silt from
rivers and land reduces underwater light penetration by increasing both light absorp-
tion and scattering (Kirk, 1983; Onuf, 1994). Increase in nutrient load, similarly asso-
ciated with an increase in silt load (Malmer & Grip, 1994), favors the growth of
microalgae and epiphytes (Sand-Jensen & Borum, 1991; Duarte, 1995), thereby
reducing light availability to seagrass. In turn, reduced seagrass abundance decreases

the ability of the plants to protect surface sediments (Fonseca et al., 1982), enhanc-
ing sediment resuspension (Bulthuis et al., 1984). Deterioration of the underwater
light climate for the remaining seagrass stands results.
At Cape Bolinao, northwestern Philippines, the depth penetration of the mixed
seagrass beds declined systematically with increasing siltation (Bach, 1997 and
1998; Terrados et al., 1998). At the control site, leaf growth of Thalassia hemprichii,
Cymodocea rotunda, and Cymodocea serrulata responded clearly to artificial reduc-
tion of light. However, in natural stands of T. hemprichii, C. serrulata, and Enhalus
acoroides growing along the siltation gradient, there was no differential leaf growth
to variations in light regime. They responded only moderately to reduced light with
increasing depth.
EFFECTS OF SILTATION ON DIVERSITY, BIOMASS, AND SURVIVAL
While siltation smothers and buries benthic organisms (Duarte et al., 1997), at the same
time it increases the nutrient load in both water and the sediments (Malmer & Grip,
1994; Mitchel et al., 1997). These changes in the water and sediment conditions are
particularly detrimental for seagrasses (Giesen et al., 1990; Duarte, 1991; Sand-Jensen
& Borum, 1991; Duarte, 1995). At Cape Bolinao, the diversity of the mixed seagrass
beds was reduced with increasing silt load (Bach et al., 1998). From the most to the
least tolerant, the seagrass species could be ranked after their tolerance to siltation as:
Enhalus acoroides Ͼ Cymodocea serrulata Ͼ Halodule uninervis Ͼ Thalassia
hemprichii Ͼ Halophila ovalis Ͼ Cymodocea rotundata Ͼ Syringodium isoetifolium.
This sequential loss of species agrees well with that found in a related study among sea-
grass beds along siltation gradients in the Philippines and Thailand (Terrados et al.,
1998), suggesting that the sequence may represent a general pattern of tolerance to sil-
tation among Southeast Asian seagrass species.
At the initial phase under conditions of severe light reduction some seagrasses
exhibit a rapid loss of biomass. Leaf densities of Heterozostera tasmanica (Bulthuis,
1983) and Posidonia sinuosa (Gordon et al., 1994) decreased by 70% during the first
month of exposure to 2 and 1% of ambient light, respectively. H. pinifolia, on the
other hand, can survive long periods of light deprivation, a feature of great impor-

tance for the species especially in the Southeast Gulf of Carpentaria (Australia)
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which periodically receives monsoonal rains that result in highly turbid floodwaters
covering over the seagrass beds (Shepherd et al., 1989).
In contrast to the high tolerance of H. pinifolia, H. ovalis has a low tolerance to
darkness, death occurring after only 38 days in the dark. A similar intolerance to light
deprivation has also been demonstrated for monospecific H. ovalis plants growing in
sub-tropical waters (Longstaff et al., 1999). This long-term survival strategy of
Halophila species to perturbations has also been suggested to occur elsewhere
(Kenworthy, 1992). The explanation is that seagrasses growing under reduced light
conditions allocate a lower fraction of photosynthetic products to underground tis-
sues (Madsen & Sand-Jensen, 1994) and formation of new shoots. This results in low
shoot density. For the remaining shoots, however, light becomes more available
because of a concomitant reduction in self-shading among them. Prolonged condi-
tions of improved (Williams, 1987) or reduced light availability (Zieman et al., 1989)
induce changes in shoot density and biomass.
Species loss may also result indirectly from the effect of siltation on sediment
grain size, resuspension, and resistance to oxygen diffusion (Duarte et al., 1997).
Fine-grained sediments are more readily resuspended, and therefore seagrass beds in
silted areas more often experience partial burial. The large Enhalus acoroides and
species which grow profusely via their vertical rhizomes (e.g., Cymodocea serrulata)
can comparatively tolerate both silt and burial (Vermaat et al., 1997), while smaller
species (e.g., Halodule uninervis and Syringodium isoetifolium) cannot survive bur-
ial (Duarte et al., 1997). Seagrasses also respond differently to changes in redox
potential of the sediment, depending on their morphology and ability to maintain root
oxygen supply (Smith et al., 1988). Hence, the integrated response of mixed seagrass
beds to siltation is likely to be caused by changes in both water and sediment condi-
tions it brings about.
EFFECTS OF SILTATION ON SEAGRASS GROWTH

AND
PRIMARY PRODUCTIVITY
The relationships between siltation, the light conditions it brings about, and growth
and photosynthesis of seagrasses clearly demonstrate that light is the prime factor
regulating plant performance (e.g., Bulthuis, 1983; Dennison, 1987; Olesen, 1996).
Seagrasses generally require a higher quantity of light in comparison to other marine
and terrestrial flora (Dennison et al., 1993; Duarte, 1991; Abal et al., 1994). However,
as to the actual amount of light required for long-term survival, more studies have yet
to be done. Estimates of light requirements of seagrasses differ between species (e.g.,
4.4 to 29% of surface light) and within a species (e.g., 5 to 20% of surface light)
(Dennison et al., 1993), while an average requirement of seagrasses as a group of
plants has been calculated to be 11% of surface light (Duarte, 1991).
In tropical seas, productivity of shallow seagrass stands seems to be limited
largely by the availability of nutrients (e.g., Agawin et al., 1996). However, nutrient
availability is low in fine-grained carbonate sediments (Short et al., 1985; Short,
1987) but increases in coarse-grained carbonate and terrigenous sediments
(Erftemeijer, 1994; Erftemeijer & Middelburg, 1995). These findings suggest that not
all tropical seagrass meadows might be nutrient limited (Erftemeijer et al., 1994). The
96 Oceanographic Processes of Coral Reefs
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nutrient status of seagrasses, however, may be reduced by a decrease in the availabil-
ity of light (Abal et al., 1994), thereby reducing the nutrient requirements of some
tropical seagrasses.
Three photosynthetic parameters have been found to respond strongly to both the
gradient in natural light and light deprivation, conditions which are associated with
siltation: chlorophyll a-to-b ratio, leaf amino acid concentration, and leaf
13
C value.
Decreasing chlorophyll a:b with depth has been observed in a number of seagrass
species including Zostera marina (Dennison & Alberte, 1985), H. ovalis (Longstaff

et al., 1999), Halophila spp., Halodule spp., Syringodium filiforme, and Thalassia
testudinum (Wigington & McMillan, 1979; Lee & Dunton, 1997). A decrease in the
chlorophyll a:b has been considered an adaptive response that increases the light
absorption efficiency of seagrass (Abal, 1996; Lee & Dunton, 1997).
Changes in amino acid concentrations in seagrasses are brought about by a num-
ber of environmental variables. Two of these which are associated with siltation are
water depth and nutrient addition. Depth has been shown to affect amino acid con-
centrations in Posidonia oceanica (Pirc, 1984), although this was not in the case of
Thalassodendron ciliatum (Parnik et al., 1992). Ambient sediment nutrient concen-
tration and sediment nutrient addition can also have a significant effect on amino acid
concentrations (Udy & Dennison, 1997a and b). The increase in concentration at
depth is linked to a response to reduced light availability and could be related to the
balance of nutrient against light limitation of seagrass growth, the light condition
bringing about the elevated amino acid content in the plants.
In response to shading and increased water depth, the carbon isotope ratio (
13
C)
of H. pinifolia leaves became more negative (Abal, 1996; Grice et al., 1996;
Longstaff et al., 1999). This may be due to a more rapid uptake of
12
C in relation to
13
C, the preferential rate occurring because
12
C uptake requires less energy in com-
parison to
13
C (Abal & Dennison, in press; Grice et al., 1996; Longstaff et al., 1999).
Whether reductions in light availability have significant effects on seagrass
growth and survival depends primarily on the efficiency with which light energy is

used in the autotrophic accumulation of plant biomass. These are often described
using photosynthesis-irradiance (or P-1) curves (Drew, 1979). Species that are able
to physiologically acclimate to reduced light by adjusting their P-1 curves will have
a better chance to survive severe siltation events.
Measured P-1 curves of different species revealed that in the Philippine Enhalus
acoroides and Thalassia hemprichii, variation in the compensation depth (i.e., the
depth at which daily respiratory demand and photosynthetic oxygen supply are just
in balance) with water depth and turbidity correlates well with predicted maximum
colonization depth. An important observation may then be derived from the colo-
nization depth-turbidity curve which would suggest that small reduction in water
clarity may dramatically affect seagrass performance in relatively clear waters of the
Mediterranean and the Philippines (K Ͻ0.5 m
Ϫ1
). Furthermore, it would suggest that
moderately eutrophicated waters subjected to increases in turbidity may not allow
seagrasses to colonize deeper parts.
Recent shading studies have shown that the survival period of a seagrass below
the minimum light required may be altered by adaptations in photosynthetic parame-
ters (e.g., increased chlorophyll content, changes in the chlorophyll a:b ratio,
The Effects of Siltation on Tropical Coastal Ecosystems 97
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increased canopy height and shoot thinning: Abal et al., 1994; Lee & Dunton, 1997).
This was the case with H. pinifolia which demonstrated an increased chlorophyll con-
tent, decreased chlorophyll a:b ratio, and an increased canopy height under condi-
tions of shading (Longstaff et al., 1999).
EFFECTS OF SILTATION ON SEAGRASS MORPHOLOGY
Traditionally changes in the morphology of seagrasses have been used as an indica-
tor of an adverse environmental effect on a seagrass community (e.g., Posidonia sin-
uosa, shoot density and leaf length) (Gordon et al., 1994). In the present study, the
morphological responses to siltation under consideration include decreases in bio-

mass, shoot density, and canopy height. It should be noted, however, that physiolog-
ical responses can detect declining seagrass health and impending seagrass die-off
before substantial morphological changes occur.
Sediment dynamics over a seagrass bed may range from a gradual, continuous
deposition to a sudden storm-related event (Marba et al., 1994a), and from a homo-
geneous rate over large areas to small-scale variability associated with sand ripples
or dunes (Marba et al., 1994b). Seagrasses may respond to the latter via horizontal
rhizome growth. On the other hand, the species respond to homogeneous sedimenta-
tion rates only via vertical stem elongation or re-establishment from seeds.
Vertical stem growth, even in Philippine seagrasses, has been shown to be sea-
sonal (Duarte et al., 1994; Vermaat et al., 1995): during the growing season, longer
internodes are formed and this often also occurs at a higher rate than at other, less
favorable times of the year (Duarte et al., 1994). It is probable that the capacity of sea-
grasses to respond to burial may also be seasonal, and off-season siltation may have
more dramatic effects than expected. Genera without differentiated vertical stems
may respond with a redirection of the horizontal rhizome to survive excessive silta-
tion and burial.
Shoot size is an obvious determinant of the chance to survive a burial event:
larger shoots are simply less easily buried. The largest Philippine species Enhalus
acoroides, for example, has horizontal rhizome branches that curve upward to posi-
tion the apical meristems at an average distance of 10 cm from the main rhizome,
which is generally several centimeters above the sediment. With full-grown leaves
measuring about 80 cm, the leaf canopy reaches considerably further upward
(Vermaat et al., 1995). Halophila ovalis, the smallest Philippine species, also lacks
vertical stems, but its oval leaf blades have petioles that may reach a length of 2 cm,
a height that allows a substantial short-term sediment deposition rate over the short
shoot life span of this species (1 to 2 weeks) (Duarte, 1991; Vermaat et al., 1995).
For species that do have vertical stems, considerable variation exists in annual
mean vertical growth rates, particularly among the Philippine species: 1.5 to 13 cm
shoot

Ϫ1
yr
Ϫ1
(for Cymodocea rotundata and C. serrulata, respectively). Additionally,
species differ in the height of their vertical stems. Stem lengths range between 1
and 8 cm. These vertical stems are partly buried in the sediment, but particularly in
C. serrulata, also reach above the sediment surface. Although mean annual vertical
stem growth is strictly not comparable to an instantaneous response to a short-term
98 Oceanographic Processes of Coral Reefs
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sedimentation event, the former will set the order of magnitude of the short-term
response of the seagrass shoot. Short-term responses, however, have been quantified
in a few species only.
In contrast to vertical stem growth, horizontal rhizome expansion is closely cor-
related with seagrass size and longevity. Rhizome growth is slowest (2 to 5 cm yr
Ϫ1
)
in larger and longer-lived species (Duarte et al., 1994; Vermaat et al., 1995; Duarte,
1991). This capacity may allow shorter-lived species to migrate away from or into
newly deposited sediment forms. Horizontal expansion rates at patch edges, i.e., into
newly available bare-ground, are often considerably higher than those measured in
established beds. Whereas the difference between species in mean annual vertical
stem growth amounts to about a factor of 10, horizontal rhizome growth differs by a
factor of 30, a difference present among both Mediterranean and Philippine species.
Annual horizontal growth in northern temperate Zostera species is limited, though
these species have relatively short life spans and small shoots. This is mainly caused
by the reduced length of the growing season (Marba et al., 1994a; Vermaat &
Verhagen, 1995), since rhizome internodal lengths and growth rates during the grow-
ing season are comparable to those of other small species.
The slowest-growing and longest-lived Philippine species, Enhalus acoroides,

as well as the oldest Mediterranean species, Posidonia oceanica, also have the largest
shoots and rhizomes (Duarte, 1991; Vermaat et al., 1995). In the Mediterranean, the
larger and longer-lived species showed less annual variation in photosynthetic para-
meters than the shorter-lived species, supporting the suggestion of increased seasonal
buffering with increased size and age (Duarte, 1991). This pattern, however, was not
confirmed for the three studied Philippine species, which are all rather long-lived.
Morphological adjustments may also improve light availability considerably.
Longer leaves or stems raise the photosynthetic tissue closer to the water surface, an
investment which will probably pay off in turbid, shallow waters where light is atten-
uated exponentially. The tallest tropical seagrass Enhalus acoroides is able to lift its
leaves much closer to the water surface, growing in turbid water on shallow (1 to
2 in.) mudflats close to river mouths (Nienhuis et al., 1989; Brouns & Heijs, 1991;
Erftemeijer & Herman, 1994).
In mixed meadows, form and size could be decisive and one would expect that
the smallest species in the lower leaf canopies would suffer most the impact of light
deprivation, e.g., Halophila ovalis, Halodule uninervis, and Syringodium isoeti-
folium (Vermaat et al., 1995). However, in clear waters, Halophila species have been
found to grow considerably deeper than most other seagrass species (Duarte, 1991),
and for one species Drew (1979) found a comparatively low compensation point
(9 ␮E m
Ϫ2
s
Ϫ1
for Halophila stipulacea). Hence, species from the genus Halophila
may survive longer under reduced light regimes.
In some areas, seagrasses have to cope with burial through sediment deposition
and resuspension. Burial affects seagrasses adversely by reducing light availability to
affected photosynthetic tissue, reducing diffusion of O
2
to roots and rhizomes; and

mechanically counteracting the production of new leaves by deeply buried meristems
(Duarte et al., 1997). Seagrass responses to increased sedimentation include adjust-
ments in vertical stem elongation or horizontal rhizome expansion (Duarte et al.,
The Effects of Siltation on Tropical Coastal Ecosystems 99
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1994; Marba et al., 1994 a and b), or by recolonization from seeds (Duarte et al.,
1997). Architectural differences among species result in considerable ecological
advantages for survival.
RESPONSES OF CORALS TO
SILTATION/SEDIMENTATION
Sediment deposition and suspended sediments affect coral community structure dif-
ferently. The inability of coral planulae to settle in areas where soft sediments con-
tinually cover the bottom support the observation that sediment deposition has
generally an adverse effect on living coral (Ruitenbeek et al., 1999). Adult coral
colonies of some species may survive silt cover for short periods (e.g., hours to days).
However, coverage for longer periods is lethal to virtually all species (Ruitenbeek
et al., 1999).
On the other hand, greater coral abundance may be found in many reefs with
high suspended sediment loads. Species composition in these areas may differ sub-
stantially from that in areas with low suspended sediment. This is in part due to the
differential ability of the polyps to eject sediment. Hence, coral reefs may exhibit
wide variations in species composition in areas of differing suspended sediment
loads, but coral cover may not vary significantly with suspended sediment loading
(Ruitenbeek et al., 1999).
Sedimentation patterns exert a significant control on reef development via their
influence on both sediment deposition and suspended sediment. In St. Croix, U.S.
Virgin Islands, lower transport rates of sediments permit faster reef growth (Hubbard,
1986). Annual storms (wave height ϭ 3 to 5 m), however, result in order-of-magni-
tude increases in sediment transport. They periodically flush sediments and offset the
usual imbalance between sediment import and export.

EFFECTS OF SEDIMENTATION ON CORAL ABUNDANCE, DIVERSITY,
AND DISTRIBUTION
Sedimentation is among the important factors that determine coral abundance,
growth, and distribution (Hodgson, 1990; Babcock & Davies, 1991). High turbidity
and sedimentation decrease coral abundance, alter coral growth forms to a more
branching habit, and decrease species diversity (Dodge & Vaisnys, 1977). The diver-
sity of corals on all intertidal flats in the vicinity of tin dredging and smelting activi-
ties around Laem Pan Qah peninsula, Phuket, was low (six genera), the dominant
genera being Porites, Montipora, Acropora, and Platygyra (Brown & Holley, 1981).
Dodge and Vaisnys (1977) likewise reported that analysis of coral growth patterns
and populations in Bermuda reveals that living coral abundance on the reefs of Castle
Harbor, a location where extensive dredging occurred during 1941 to 1943, is much
reduced in comparison to external North–South reefs.
In Bolinao (NW Philippines), Wesseling et al. (1997) further found that
Acropora completely buried with littoral sediment (16% silt, 38% fine sand, and 38%
coarse sand) experienced high mortality. This finding suggests a reduction in coral
100 Oceanographic Processes of Coral Reefs
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composition in reefs subjected to intense sedimentation. Less sensitive taxa (e.g.,
Porites), however, were found to recover within a month of exposure.
The probable causes of these events include turbidity, physical tissue damage,
reduced larval recruitment and mortality, and their effects on coral survival. Turbidity
reduces underwater light due to scattering from sediment particles in the water col-
umn. Hence, a source of energy is virtually lost. In addition, time and energy that
could be used to capture food, grow, metabolize, and reproduce are likewise lost
(Dodge & Vaisnys, 1977).
Experimental application of sediments onto living coralline tissues has demon-
strated detrimental effects including expulsion of zooxanthellae, cellular damage,
and after complete burial, death (Babcock & Davies, 1991). On the other hand, they
found that while higher sedimentation rates reduced the number of larvae settling on

upper surfaces, total numbers of settled larvae were not significantly affected by sed-
imentation regime.
EFFECTS OF SEDIMENTATION ON CORAL GROWTH
AND
PRODUCTIVITY
At 13 sites with varying siltation levels in the Philippines, studies were conducted on
the responses of corals to sedimentation. At the level of the colony, the comparatively
fewer number of white and dark bands observed in Porites at a more silted site indicated
slower growth rate when compared to colonies with a greater number of bands observed
at a less silted site (Mamaril-Villanoy et al., 1997). Barnes and Lough (1993) found that
coral growth over a year is represented by adjacent dense and less dense bands which
may be caused by different factors, among which are turbidity and sedimentation.
At the population level, Wesseling et al. (1997) differentiated two types of
lesions in corals found along siltation gradients: Type I lesions, surrounded with liv-
ing tissue, and Type II lesions, at the edge of colonies. Colony size and density of
lesions varied among reefs, with smaller colonies and more lesions observed in more
exploited and silted areas. A relation with sedimentation rate, however, was found
only for Type II lesions where it increased significantly above a sedimentation thresh-
old rate of about 25 mg/cm
2
/day.
Sediment affects coral metabolism by decreasing photosynthetic production,
increasing relative respiration, and increasing carbon loss through greater mucus out-
put (Riegl & Brance, 1995). In nine coral species investigated under simulations of
natural sedimentation levels and light conditions, a severe reduction in productivity
and respiration was recorded under sedimented conditions. P/R ratios of all species
were above 1 in no-silt conditions. In silted conditions, on the other hand, the ratios
dropped below 1. In relation to mucus secretion, it averaged 35% of daily respiration
under the unsilted condition; the value rose to 65% under silt treatment (Riegl
& Brance, 1995).

MODELING REEF STATUS AND SEDIMENTATION
Two recent procedures are used to generate a surface dose-response model of the rela-
tionship among coral abundance and various inputs including sedimentation. These
The Effects of Siltation on Tropical Coastal Ecosystems 101
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are fuzzy logic procedures and watershed-based modeling. The first is linked to a
non-linear economic structure incorporating technical intervention (e.g., pollution
treatment) and policy interventions (e.g., taxation) (Ruitenbeek et al., 1999). The
result of the optimization process gives insights into the most cost-effective means to
protect reefs under different reef quality targets. In Montego Bay, Jamaica, for exam-
ple, appropriate policy measures costing (US) $12 million are estimated to improve
coral abundance by 10% in 25 years. At a cost of (US) $153 million, these are
expected to provide up to 20% increase.
Watershed-based modeling of sedimentation and inland pollution is a part of a
global analysis, involving 3000 watersheds in the world. It integrates data on slope,
precipitation, and land cover type to estimate “relative erosion potential” (REP) by
roughly a 2-km grid cell (Burke, L., personal communication). The results are sum-
marized by watershed to develop criteria for watersheds of low, medium, or high
mean REP. The zone of effect for sediment discharge is estimated based upon an esti-
mate of flow (discharge) for the peak rainfall month.
RESPONSES OF MANGROVES TO SILTATION
Siltation is of primary importance in the development of mangroves. In deltas along
the coasts of Southeast Asia, mangroves cover large areas. This is largely because of
high rainfall and rivers with high silt loads which combine to provide favorable con-
ditions for their development (Milliman & Meade, 1983; Milliman & Syvitski, 1992).
Highest productivity values are usually reported in mangroves associated with rivers
(Twilley et al., 1986). River flow and tides transport a large fraction of mangrove pro-
duction (on average 29.5%: Duarte & Cebrian, 1996) to nearby habitats in the form
of leaf litter and propagules (e.g., Twilley et al., 1986; Hemminga et al., 1994;
Panapitukkul et al., 1998). In addition a substantial fraction of mangrove production

is buried in the sediments (10.4% on average: Duarte & Cebrian, 1996), causing a
large fraction of the mangrove production (therefore, a large quantity of nutrients) to
be lost from the ecosystem (Boto & Bunt, 1981; Twilley et al., 1986). Primary pro-
duction of mangrove habitats therefore tends to depend on continuous nutrient sup-
ply from land or sea (Duarte et al., 1998). This nutrient dependence led to the
hypothesis that mangrove growth may be nutrient-limited, as has been shown by Boto
and Wellington (1983) and Feller (1995).
Growth of Rhizophora apiculata seedlings living at the edge of progressing man-
grove forests at the study sites in the Philippines and Thailand is directly correlated
to the nutrient and silt contents within the sediments (Duarte et al., 1998). Sites with
low nutrients and coarse sediments yielded seedlings with very low growth rates. On
the other hand, nutrient-rich, silty sediments yielded seedlings with much faster
growth rates.
The size of the watersheds drained by the rivers where mangroves grow has a
strong linkage with, among others, sediment composition and mangrove growth
(Duarte et al., 1998), while autochthonous substances are received by the mangrove
itself (Boto & Bunt, 1981; Boto, 1984; Twilley et al., 1986). However, substantial
102 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
amounts of the fine particulate material and the associated nutrients are allochtho-
nous (from land), causing sediment accretion, hence, mangrove progression (Duarte
et al., 1998). To quote the authors: “The silt plus clay content of the sediments
deposited at the mouths of large rivers, such as the Pak Phanang river in Thailand,
was very high, while sediments supporting mangroves near creeks were mainly
coarse, marine carbonates. Hence, slow-growing, nutrient-deficient mangrove stands
were associated with small rivers, while fast-growing mangroves, with a more bal-
anced nutritional status, were found in association with rivers draining watersheds
larger than 10 km
2
.”

In general, high silt loads adversely affect most coastal ecosystems (e.g., coral
reefs and seagrass beds: Hodgson, 1990; Terrados et al., 1998). However, they can be
beneficial for mangrove habitat expansion. In the Philippines and Thailand, high sil-
tation in the rivers enhances seedling growth (Duarte et al., 1998), which likely helps
the seedlings to outbalance the high mortality rates encountered by newly established
unprotected seedlings (Clarke & Myerscough, 1993). It also increases sediment
accretion, forming new habitats for plant or animal community colonization
(Panapitukkul et al., 1998).
CONCLUSION
EFFECTS OF SILTATION ON SEAGRASS
The effect of siltation on seagrass is manifested primarily via its reduction of
light availability through increased water column light attenuation (Vermaat et al.,
1997), increased sedimentation and burial (Duarte et al., 1997), and, possibly,
by changing sediment conditions (Terrados et al., 1998). This is critical in mixed
seagrass beds of the tropics, where interspecific competition for space, light,
and nutrients is intense; hence, even small changes in light climate can affect
species composition and depth distribution of the communities. The gradual
decline in shoot density of individual seagrass species with depth and with
increasing siltation further suggests that suspended material, light availability, and
seagrass performance are strongly connected. The sequential loss of species along
siltation gradients in the Philippines and Thailand (Terrados et al., 1998) may repre-
sent a general pattern of tolerance to siltation among Southeast Asian seagrass
species.
Based on independent field data, a strong correlation was found between the pre-
dicted compensation depths for photosynthesis and the predicted maximum colo-
nization depth of seagrasses. This emphasizes the importance of light availability for
the depth distribution and species composition of seagrass beds. Moderate eutrophi-
cation of presently very clear coastal waters as in the Mediterranean or Philippines
will lead to only slight increases in turbidity, but may cause substantial decreases in
depth penetration of seagrasses.

Seagrass responses to increased sedimentation include adjustments in vertical
stem elongation or horizontal rhizome expansion (Duarte et al., 1994; Marba
The Effects of Siltation on Tropical Coastal Ecosystems 103
© 2001 by CRC Press LLC
et al., 1994a and b), or by recolonization from seeds (Duarte et al., 1997).
Architectural differences between species have considerable ecological advantages
for survival.
Morphological adjustments may improve considerably light use efficiency in
seagrass. Longer leaves or stems raise the photosynthetic tissue closer to the water
surface, an advantage in highly turbid waters where light is attenuated exponen-
tially. Although the effect of siltation on water column light attenuation is a key
factor, changes in sediment conditions may also play an important role for seagrass
performance.
EFFECTS OF SEDIMENTATION ON CORAL REEFS
Sedimentation controls reef development via its influence on both sediment deposi-
tion and suspended sediment. Sediment deposition and suspended sediments, in turn,
affect coral community structure differently. Adult coral colonies of some species
may survive silt cover for short periods (e.g., hours to days). However, coverage for
longer periods is lethal to virtually all species (Ruitenbeek et al., 1999).
On the other hand, greater coral abundance may be found in many reefs with
high suspended sediment loads. Hence, coral reefs may exhibit wide variations
in species composition in areas of differing suspended sediment loads, but coral
cover may not vary significantly with suspended sediment loading (Ruitenbeek
et al., 1999).
Sedimentation is among the important factors that determine coral abundance,
growth, and distribution (Hodgson, 1990; Babcock & Davies, 1991). High turbidity
and sedimentation decrease coral abundance, alter coral growth forms to a more
branching habit, and decrease species diversity (Dodge & Vaisnys, 1977). In Bolinao
(NW Philippines), Wesseling et al. (1997) further found that Acropora completely
buried with littoral sediment (16% silt, 38% fine sand, and 38% coarse sand) experi-

enced high mortality. This finding suggests a reduction in coral composition in reefs
subjected to intense sedimentation. Less sensitive taxa (e.g., Porites), however, were
found to recover within a month of exposure.
The effects of sedimentation on growth and productivity of coral reefs may be
manifested at the levels of the colony, population, and community.
Sedimentation affects coral metabolism by decreasing photosynthetic produc-
tion, increasing relative respiration, and increasing carbon loss through greater mucus
output (Riegl & Brance, 1995).
Two recent procedures are used to generate a surface dose–response model of
the relationship among coral abundance and various inputs including sedimentation.
These are fuzzy logic procedures and watershed-based modeling. The first is linked
to a non-linear economic structure incorporating technical interventions (e.g., pollu-
tion treatment) and policy interventions (e.g., taxation) (Ruitenbeek et al., 1999). The
result of the optimization process gives insights into the most cost-effective means to
protect reefs under different reef quality targets.
104 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
EFFECTS OF SILTATION ON MANGROVES
Siltation is of primary importance in the development of mangroves. Highest pro-
ductivity values are usually reported in mangroves associated with rivers (Twilley et
al., 1986). Primary production of mangrove habitats tends to depend on continuous
nutrient supply from land or sea (Duarte et al., 1998). This nutrient dependence led
to the hypothesis that mangrove growth may be nutrient-limited.
Growth of Rhizophora apiculata seedlings living at the edge of progressing man-
grove forests at the study sites in the Philippines and Thailand is directly correlated
to the nutrient and silt contents within the sediments (Duarte et al., 1998). Sites with
low nutrients and coarse sediments yielded seedlings with very low growth rates. On
the other hand, nutrient-rich, silty sediments yielded seedlings with much faster
growth rates.
In general, high silt loads adversely affect most coastal ecosystems (e.g., coral

reefs and seagrass beds: Hodgson, 1990; Terrados et al., 1998). However, they can be
beneficial for mangrove habitat expansion. In the Philippines and Thailand, high sil-
tation in the rivers enhance seedling growth (Duarte et al., 1998), which likely helps
the seedlings to outbalance the high mortality rates encountered by newly established
unprotected seedlings (Clarke & Myerscough, 1993). It also increases sediment
accretion, forming new habitats for plant or animal community colonization
(Panapitukkul et al., 1998).
The size of the watersheds drained by the rivers where mangroves grow
has a strong linkage with, among others, sediment composition and mangrove
growth. The nonlinear relationship between seedling growth performance and water-
shed size found in the study in Thailand identifies mangroves next to rivers draining
watersheds larger than 10 km
2
as the most profitable target areas in the efforts
promoting natural and artificial colonization of Rhizophora apiculata (Duarte
et al., 1998).
REFERENCES
Abal, E.G. 1996 Light, Nutrient and Water Quality Interactions with the Seagrass, Zostera
capricorni Aschers. Ph.D. thesis, Department of Botany, University of Queensland,
Brisbane, 375 pp.
Abal, E.G. & Dennison, W.C. 1996 Seagrass depth range and water quality in Southern
Moreton Bay, Queensland. Australian Journal Marine Freshwater Research 47, 763–771.
Abal, E.G. & Dennison, W.C. Stable isotope ratios, morphology and growth adaptations of
Zostera capricorni in response to in situ light reduction. Journal Experimental Marine
Biology and Ecology, in press.
Abal, E.G., Loneragan, N.R., Bowen, P., Perry, C.J., Udy, J.W., & Dennison, W.C. 1994
Physiological and morphological responses of the seagrass Zostera capricorni Aschers to
light intensity. Journal Experimental Marine Biology and Ecology 178, 113–129.
Agawin, N.S.R., Duarte, C.M., & Fortes, M.D. 1996 Nutrient limitation of Philippine sea-
grasses (Cape Bolinao, NW Philippines): in situ experimental evidence. Marine Ecology

Progress Series 138, 233–243.
The Effects of Siltation on Tropical Coastal Ecosystems 105
© 2001 by CRC Press LLC
Babcock, R. & Davies, P. 1991 Effects of sedimentation on settlement of Acropora millepora.
Coral Reefs
9, 205–208.
Bach, S.S. 1997 Havgraessers vaetkst og artssammensaening langs en siltgradient ved Kap
Bolinao, Filippineme. M.S. thesis, Freshwater Biological Laboratory, University of
Copenhagen, 56 pp.
Bach, S.S., Borum, J., Fortes, M.D., & Duarte, C.M. 1998 Species composition and plant per-
formance of mixed seagrass beds along a siltation gradient at Cape Bolinao, the
Philippines.
Marine Ecology Progress Series 174, 247–256.
Barnes, D.J. & Lough, J.K.M. 1993 On the nature and causes of density banding in massive
coral skeletons.
Journal Experimental Marine Biology Ecology 167, 91–108.
Bell, J.D. & Pollard, D.A. 1989 Ecology of fish assemblages and fisheries associated with the
Australian region. pp. 565–609 in Larkum, A.W.D., McComb, A.J., & Shepherd, S.A.
(eds)
Biology of Seagrasses: A Treatise on the Biology of Seagrasses with Special
Reference to the Australian Region, Aquatic Plant Studies,
Vol. 2. Elsevier, Amsterdam,
841 pp.
Boto, K.G. 1984 Waterlogged saline soils. pp. 20–35 in Snedaker, S.C. & Snedaker, J.G. (eds.)
The Mangrove Ecosystems: Research Methods. UNESCO, Paris, 210 pp.
Boto, K.G. & Bunt, J.S. 1981 Tidal export of particulate organic matter from a northern
Australian mangrove system. Estuarine, Coastal and Shelf Science 13, 247–255.
Boto, K.G. & Wellington, J.T. 1983 Phosphorus and nitrogen nutritional status of a northern
Australian mangrove forest.
Marine Ecology Progress Series 11, 63–69.

Brouns, J.J. & Heijs, F.M.L. 1991 Seagrass ecosystems in the tropical west Pacific.
pp. 371–390 in Mathieson, A.C. & Nienhuis, P.H. (eds) Ecosystems of the World 24,
Intertidal and Littoral Ecosystems. Elsevier, Amsterdam, 572 pp.
Brown, B.E. & Holley, M.C. 1981 The influence of tin smelting and tin dredging on the inter-
tidal reef flats of Phuket, Thailand. pp. 214 in
Proceedings Fourth International Coral
Reef Symposium, Manila, Vol. 1, 527 pp.
Bulthuis, D.A. 1983 Effects of in situ light reduction on density and growth of the seagrass
Heterozostera tasmanica (Martens ex Aschers) den Hartog in Western Port, Victoria,
Australia. Journal Experimental Marine Biology Ecology 67, 91–103.
Bulthuis, D.A., Brand, G.W., & Mobley, M.C. 1984 Suspended sediments and nutrients in
water ebbing from seagrass-covered and denuded tidal mudflats in a southern Australian
embayment.
Aquatic Botany 20, 257–266.
Cambridge, M.L. & McComb, A.J. 1984 The loss of seagrasses in Cockburn Sound, western
Australia. I. The time course and magnitude of seagrass decline in relation to industrial
development.
Aquatic Botany 20, 229–243.
Cambridge, M.L., Chiffings, A.W., Brittan, A.W., Moore, L., & McComb, A.J. 1986 The loss
of seagrasses in Cockburn Sound, Western Australia. II. Possible causes of seagrass
decline.
Aquatic Botany 24, 269–285.
Clarke, P.J. & Myerscough, P.J. 1993 The intertidal distribution of the grey mangrove
(
Avicennia marina) in Southeastern Australia: the effects of physical conditions, inter-
specific competition and predation on propagule establishment and survival. Australian
Journal Ecology 18, 307–315.
den Hartog, C. 1970 The Seagrasses of the World. North-Holland, Amsterdam, 275 pp.
Dennison, W.C. 1987 Effects of light on seagrass photosynthesis, growth and depth distribu-
tion. Aquatic Botany 27, 15–26.

Dennison, W.C. & Alberte, R.S. 1985 Role of daily light period in the depth distribution of
Zostera marina (eelgrass).
Marine Ecology Progress Series 25, 51–62.
106 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
Dennison, W.C., Orth, K.A., Moore, R.J., Stevenson, J.C., Carter, V., Kollar, S., & Batiuk, R.A.
1993 Assessing water quality with submersed aquatic vegetation. BioScience 43, 86–94.
Dodge, R.E. & Vaisnys, J.R. 1977 Coral populations and growth patterns: responses to sedi-
mentation and turbidity associated with dredging. Journal Marine Research 35 (4),
715–730.
Drew, E.A. 1979 Physiological aspects of primary production in seagrasses. Aquatic Botany 7,
139–150.
Duarte, C.M. 1989 Temporal biomass variability and production/biomass relationships of sea-
grass communities. Marine Ecology Progress Series 51, 269–276.
Duarte, C.M. 1991 Allometric scaling of seagrass form and productivity. Marine Ecology
Progress Series 77, 289–300.
Duarte, C.M. 1995 Submerged aquatic vegetation in relation to different nutrient regimes.
Ophelia 41, 87–112.
Duarte, C.M. & Cebrian, J. 1996 The fate of marine autotrophic production. Limnology
Oceanography 41, 1758–1766.
Duarte, C.M., Terrados, J., Agawin, N.S.R., Fortes, M.D., Bach, S., & Kenworthy, W.J. 1997
Response of a mixed Philippine seagrass meadow to experimental burial. Marine Ecology
Progress Series 147, 285–294.
Duarte, C.M., Geertz-Hansen, O., Thampanya, U., Terrados, J., Fortes, M.D., Kamp-Nielsen,
L., Borum, J., & Boromthanarath, S. 1998 Relationship between sediment conditions and
mangrove Rhizophora apiculata seedling growth and nutrient status. Marine Ecology
Progress Series 175, 277–283.
Duarte, C.M., Marba, N., Agawin, N.S.R., Cebrian, J., Enriquez, S., Fortes, M.D., Gallegos,
M.E., Merino, M., Olesen, B., Sand-Jensen, K., Uri, J.S., & Vermaat, J.E. 1994
Reconstruction of seagrass dynamics: age determinations and associated tools for the sea-

grass ecologist. Marine Ecology Progress Series 107, 195–209.
Erftemeijer, P.L.A. 1994 Differences in nutrient concentrations and resources between sea-
grass communities on carbonate and terrigenous sediments in South Sulawesi, Indonesia.
Bulletin Marine Science 54, 403–419.
Erftemeijer, P.L.A. & Herman, P.M.J. 1994 Seasonal changes in environmental variables, bio-
mass, production and nutrient contents in two contrasting tropical intertidal seagrass beds
in South Sulawesi, Indonesia. Oecologia 99, 45–59.
Erftemeijer, P.L.A. & Middelburg, J.J. 1995 Mass balance constraints on nutrient cycling in
tropical seagrass beds. Aquatic Botany 50, 21–36.
Erftemeijer, P.L.A., Stapel, J., Smekens, M.J.E., & Drossaert, W.M.E. 1994 The limited effect
of in situ phosphorus and nitrogen additions to seagrass beds on carbonate and terrige-
nous sediments in South Sulawesi, Indonesia. Journal Experimental Marine Biology
Ecology 182, 123–140.
Feller, I.C. 1995 Effects of nutrient enrichment on growth and herbivory of dwarf red man-
grove (Rhizophora mangle). Ecological Monographs 65, 477–505.
Fonseca, M.S. 1989 Sediment stabilization by Halophila decipiens in comparison to other sea-
grasses. Estuarine, Coastal and Shelf Science 29, 501–507.
Fonseca, M.S. & Fisher, J.S. 1986 A comparison of canopy friction and sediment movement
between four species of seagrass with reference to their ecology and restoration. Marine
Ecology Progress Series 29, 15–22.
Fonseca, M.S., Fisher, M.S., Zieman, J.C., & Thayer, G.W. 1982 Influence of the
seagrass, Zostera marina L., on current flow. Estuarine, Coastal and Shelf Science 15,
351–364.
The Effects of Siltation on Tropical Coastal Ecosystems 107
© 2001 by CRC Press LLC
Fonseca, M.S. & Kenworthy, W.J. 1987 Effects of current on photosynthesis and distribution
of seagrasses. Aquatic Botany 27, 59–78.
Fortes, M.D. 1988 Mangroves and seagrass beds of East Asia: habitats under stress. Ambio 17,
207–213.
Fortes, M.D. 1995 Seagrasses of East Asia: Environmental and Management Perspectives.

RCU/EAS Technical Report Series No. 6, United Nations Environment Programme,
Bangkok, 79 pp.
Giesen, W.B.J.T., Van Katwijk, M.M., & Den Hartog, C. 1990 Eelgrass condition and turbid-
ity in the Dutch Wadden Sea. Aquatic Botany 37, 71–85.
Gordon, D.M., Grey, K.A., Chase, S.C., & Simpson, C.J. 1994 Changes to the structure and
productivity of a Posidonia sinuosa meadow during and after imposed shading. Aquatic
Botany 47, 265–275.
Grice, A.M., Loneragan, N.R., & Dennison, W.C. 1996 Light intensity and the interactions
between physiology, morphology and stable isotope ratios in five species of seagrass.
Journal Experimental Marine Biology and Ecology 195, 91–110.
Hemminga, M.A. & Nieuwenhuize, J. 1990 Seagrass wrack-induced dune formation on a trop-
ical coast (Banc d’Arguin, Mauritania). Estuarine, Coastal and Shelf Science 31, 499–
502.
Hemminga, M.A., Slim, F.J., Kasungu, J., Ganssen, G.M., Nieuwenhuize, J., & Kruyt, N.M.
1994 Carbon outwelling from a mangrove forest with adjacent seagrass beds and coral
reefs (Gazi Bay, Kenya). Marine Ecology Progress Series 106, 291–301.
Hillman, K., Walker, D.I., Larkum, A.W.D., & McComb, A.J. 1989 Productivity and
nutrient limitation. pp. 635–685 in Larkum, A.W.D., McComb, A.J., & Shepherd, S.A.
(eds) Biology of Seagrasses: A Treatise on the Biology of Seagrasses with Special
Reference to the Australian Region, Aquatic Plant Studies, Vol. 2. Elsevier, Amsterdam,
841 pp.
Hodgson, G. 1990 The Effects of Sedimentation on Indo-Pacific Reef Corals. Ph.D. disserta-
tion, University of Hawaii, Honolulu, 338 pp.
Holligan, P.M. & de Boois, H. 1993 Land-Ocean Interactions in the Coastal Zone (LOICZ)
Science Plan. IGBP Global Change Report 25, ICSU-IGBP, Stockholm, Sweden, 50 pp.
Howard, R.K., Edgar, G.J., & Hutchings, P.A. 1989 Faunal assemblages of seagrass beds.
pp. 536–564 in Larkum, A.W.D., McComb, A.J., & Shepherd, S.A. (eds) Biology of
Seagrasses: A Treatise on the Biology of Seagrasses with Special Reference to the
Australian Region, Aquatic Plant Studies, Vol. 2. Elsevier, Amsterdam, 841 pp.
Hubbard, D.K. 1986 Sedimentation as a control of reef development: St. Croix, U.S. V.I. Coral

Reefs 5, 117–125.
Jacobs, R.P.W.M., Den Hartog, C., Braster, B.F., & Carfitre, F.C. 1981 Grazing of the seagrass
Zostera noltii by birds at Terschelling (Dutch Wadden Sea). Aquatic Botany 10, 241–259.
Kenworthy, W.J. 1992 Protecting Fish and Wildlife Habitat through a Better Understanding of
the Minimum Light Requirements of Sub-Tropical Seagrasses in the South-Eastern
United States and Caribbean Basin. Ph.D. thesis, North Carolina State University,
Raleigh, 345 pp.
Kirk, J.T.O. 1983 Light and Photosynthesis in Aquatic Ecosystems. Cambridge University
Press, Cambridge, 378 pp.
Klumpp, D.W., Salita-Espinosa, J.T., & Fortes, M.D. 1993 Feeding ecology and trophic role
of sea urchins in a tropical seagrass community. Aquatic Botany 45, 205–229.
108 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
Lanyon, J.M., Limpus, C.J., & Marsh, H. 1989 Dugongs and turtles: grazers in the seagrass
system. pp. 610–633 in Larkum, A.W.D., McComb, A.J., & Shepherd, S.A. (eds) Biology
of Seagrasses: A Treatise on the Biology of Seagrasses with Special Reference to the
Australian Region, Elsevier, Amsterdam, 841 pp.
Lee, K. & Dunton, K.H. 1997 Effects of in situ light reduction on the maintenance, growth and
partitioning of carbon resources in Thalassia testudinum Banks ex Konig. Journal
Experimental Marine Biology Ecology 210, 53–73.
Longstaff, B.J., Loneragan, N.R., O’Donohue, M., & Dennison, W.C. 1999 The effects of light
deprivation on the survival and recovery of the seagrass Halophila ovalis. Journal
Experimental Marine Biology Ecology 234, 1–27.
Lundin, C.G. & Linden, 0. 1993 Coastal ecosystems: attempts to manage a threatened
resource. Ambio 22, 46–73.
Macnae, W. 1968 A general account of the fauna and flora of mangrove swamps and forests in
the Indo-Pacific region. Advances Marine Biology 6, 73–270.
Madsen, T.V. & Sand-Jensen, K. 1994 The interactive effects of light and inorganic carbon in
aquatic plant growth. Plant Cell Environment 17, 955–962.
Malmer, A. & Grip, H. 1994 Converting tropical rainforest to forest plantation in Sabah,

Malaysia. II. Effects on nutrient dynamics and net losses in streamwater. Hydrology
Proceedings 8, 195–209.
Mamaril-Villanoy, M.J., Alino, P.M., Tiu-Uychiaoco, A.J., & Campos, R.T. 1997 Skeletal
Density Growth Banding in Massive Coral Porites from Bolinao, Pangasinan, Northern
Philippines. CERDS Final Report, Quezon City, 107 pp.
Marba, N., Gallegos, M.E., Merino, M., & Duarte, C.M. 1994a Vertical growth of Thalassia
testudinum: seasonal and interannual variability. Aquatic Botany 47, 1–11.
Marba, N., Cebrian, J., Enriquez, S., & Duarte, C.M. 1994b Migration of large-scale sub-
aquaeous bedforms measured with seagrasses (Cymodocea nodosa) as tracers. Limnology
Oceanography 39, 126–133.
Milliman, J.D. & Meade, R.H. 1983 World-wide delivery of river sediment to the oceans.
Journal Geology 91, 1–21.
Milliman, J.D. & Syvitski, J.P.M. 1992 Geomorphic/tectonic control of sediment discharge to
the ocean: the importance of small mountainous rivers. Journal Geology 100, 525–544.
Mitchell, A.W., Bramley, R.G.V., & Johnson, A.K.L. 1997 Export of nutrients and suspended
sediment during a cyclone-mediated flood event in the Herbert River catchment.
Australian Marine Freshwater Research 48, 79–88.
Nienhuis, P.H., Coosen, J., & Kiswara, W. 1989 Community structure and biomass distribution
of seagrasses and macrofauna in the Flores Sea, Indonesia. Netherlands Journal Sea
Research 23, 197–214.
Olesen, B. 1996 Regulation of light attenuation and eelgrass Zostera marina depth distribution
in a Danish embayment. Marine Ecology Progress Series 134, 187–194.
Onuf, C.P. 1994 Seagrasses, dredging and light in Laguna Madre, Texas, U.S.A. Estuarine,
Coastal and Shelf Science 39, 75–91.
Orth, R.J. & Moore, K.A. 1983 Chesapeake Bay: an unprecedented decline in submerged
aquatic vegetation. Science 222, 51–52.
Panapitukkul, N., Duarte, C.M., Thampanya, U., Kheowvongsri, P., Srichai, N., Geertz-
Hansen, O., Terrados, J., & Boromthanarat, S. 1998. Mangrove colonization: mangrove
progression over the growing Pak Phanang (SE Thailand) mud flat. Estuarine, Coastal
and Shelf Science 47, 51–61.

The Effects of Siltation on Tropical Coastal Ecosystems 109
© 2001 by CRC Press LLC
Parnik, T., Bil, K., Kolmakov, P., & Titlyanov, E. 1992 Photosynthesis of the seagrass Thalasso-
dendron ciliatum: leaf anatomy and carbon metabolism. Photosynthetica 26, 213–223.
Pirc, H. 1984 Growth dynamics in Posidonia oceanica (L.) Delile 1. seasonal changes of sol-
uble carbohydrates, starch, free amino acids, nitrogen and organic anions in different parts
of the plant P.S.Z.N.I. Marine Ecology 6, 141–165.
Riegl, B. & Brance, G.M. 1995 Effects of sediment on the energy budgets of four scleractin-
ian (Bourne 1900) and five alcyonarian (Lamouroux 1816) corals. Journal Experimental
Marine Biology Ecology 186, 259–275.
Ruitenbeek, J., Ridgley, M., Dollar, S., & Huber, R. 1999 Optimization of economic policies
and investment projects using a fuzzy logic based cost-effectiveness model of coral reef
quality: empirical results for Montego Bay, Jamaica. Coral Reefs 18, 381–392.
Sand-Jensen, K. & Borum, J. 1991 Interactions among phytoplankton, periphyton and macro-
phytes in temperate freshwaters and estuaries. Aquatic Botany 41, 137–175.
Shepherd, S.A., McComb, A.J., Bulthuis, D.A., Neverauskas, V., Steffensen, D.A., & West, R.
1989 Decline of seagrasses. pp. 346–393 in Larkum, A.W.D., McComb, A.J.,
& Shepherd, S.A. (eds)
Biology of Seagrasses: A Treatise on the Biology of Seagrasses
with Special Reference to the Australian Region, Aquatic Plant Studies Vol. 2. Elsevier,
Amsterdam, 841 pp.
Short, F.T. 1987 Effects of sediment nutrients on seagrasses: literature review and mesocosm
experiment. Aquatic Botany 27, 41–57.
Short, F.T. & Wyllie-Echeverria, S. 1996 Natural and human induced disturbance of sea-
grasses. Environment Conservation 23, 17–27.
Short, F.T., Davies, M.W., Gibson, R.A., & Zimmerimann, C.F. 1985 Evidence for phospho-
rus limitation in carbonate sediments of the seagrass Syringodium filiforme. Estuarine,
Coastal and Shelf Science 20, 419–430.
Smith, R.D., Pregnall, A.M., & Alberte, R.S. 1988 Effects of anaerobiosis on root metabolism
of Zostera marina (eelgrass): implications for survival in reducing sediments. Marine

Biology 98, 131–141.
Terrados, J., Duarte, C.M., Fortes, M.D., Borum, J., Agawin, N.S.R., Bach, S., Thampanya, U.,
Kamp-Nielsen, L., Kenworthy, J., Geertz-Hansen, O., & Vermaat, J. 1998 Changes in
community structure and biomass of seagrass communities along gradients of siltation in
SE Asia. Estuarine, Coastal and Shelf Science 46, 757–768.
Twilley, R.R., Lugo, A.E., & Patterson-Zucca, C. 1986 Litter production and turnover in basin
mangrove forests in southwest Florida. Ecology 67, 670–683.
Udy, J.W. & Dennison, W.C. 1997a Growth and physiological responses of three seagrass
species to elevated sediment nutrients in Moreton Bay, Australia. Journal Experimental
Marine Biology Ecology
217, 253–277.
Udy, J.W. & Dennison, W.C. 1997b Physiological responses of seagrasses used to identify
anthropogenic nutrient inputs.
Marine Freshwater Research 48, 605–614.
Valiela, I. 1984 Marine Ecological Processes. Springer-Verlag, Berlin, 305 pp.
Vermaat, J.E. & Verhagen, F.C.A. 1995 Freezer-independent preservation of carbohydrate
samples from water plants: a methodological test. Aquatic Botany 51, 155–161.
Vermaat, J.E., Agawin, N.S.R., Duarte, C.M., Fortes, M.D., Marba, N., & Uri, J.S. 1995
Meadow maintenance, growth and productivity of a mixed Philippine seagrass bed.
Marine Ecology Progress Series 124, 215–225.
Vermaat, J.E., Agawin, N.S.R., Duarte, C.M., Enriquez, S., Fortes, M.D., Marba, N., Uri, J.S.,
& van Vierssen, W. 1997 The capacity of seagrasses to survive increased turbidity and sil-
tation: the significance of growth form and light use. Ambio 26, 499–594.
110 Oceanographic Processes of Coral Reefs
© 2001 by CRC Press LLC
Ward, L.G., Boynton, W.R., & Kemp, W.M. 1984 The influence of waves and seagrass com-
munities on suspended particulates in an estuarine embayment. Marine Geology 59,
85–103.
Wesseling, I., Uychiaoco, A.J., Alino, P.M., & Vermaat, J.E. 1997 Partial Mortality in Porites
spp.: Variation among Philippine Populations and the Potential for Rapid Assessment of

Sediment Effects. CERDS Final Report, Quezon City, 107 pp.
Wigington, J.R. & McMillan, C. 1979 Chlorophyll composition under controlled light condi-
tions as related to the distribution of seagrasses in Texas and the U.S. Virgin Islands.
Aquatic Botany, 6, 171–184.
Williams, S.L. 1987 Competition between the seagrasses Thalassia testudinum and
Syringodium filiforme in a Caribbean lagoon. Marine Ecology Progress Series 35, 91–98.
Zieman, J.C., Fourqurean, J.W., & Iverson, R.L. 1989 Distribution, abundance and productiv-
ity of seagrasses and macroalgae in Florida Bay. Bulletin Marine Science 4, 292–311.
The Effects of Siltation on Tropical Coastal Ecosystems 111
© 2001 by CRC Press LLC