40000

THE INFLUENCE OF SEDIMENTATION ON CORAL POPULATION IN

SEPANGGAR AREA, SABAH

HOI MENG FEI

/PERPUSTAKA~N UNIVER~ITI MALt VSIA ~AR

DISSERTATION SUBMITTED IN FULFILMENT OF THE REQlJIREMENTS

FOR THE DEGREE OF BACHELOR OF SCIENCE

(MARINE SCIENCE)

~scmNCEPROGRAMMrn

SCHOOL OF SCIENCE AND TECHNOLOGY

UNIVERSITI MALAYSIA SABAH

MARCH 2005

PERPUSTAKAAN UMS

III~III~~II~II~ 1400006373

11

DECLARATION

I declare that this thesis is my original work except for quotations and summary that

been cited in reference.

March 2005

1ll

APPROVED BY

1. SUPERVISOR

(DR SHAHBUOIN SAAD)

2. EXAMINER 1

(pROF. DR. HJ. RIDZW AN ABDUL RAHMAN)

3. EXAMINER 2

(MS. ZARINAH W AHEED)

4. DEAN

(ASSOC. PROF. DR. AMRAN AHMED)

PUMS99:1 UNIVERSITI MALAYSIA SABAH

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IV

ACKNOWLEDGEMENTS

First of all, I wish to thank my supervisor Dr. Shahbudin Saad for his guidance,

advices, criticises and helps during the study period. I would never forget his patience

for reviewing my grammar and assisted me in the preparation of the dissertation. I am

very grateful for all the chances that he has given to me.

I am truly indebted to Mr. Bujang Kadir, Mr. Ajahar Abdul Sahar, Mr. Jabdar Abdul

Sabar, Mr. Josh Pulah, Mr. Harun Mohd. Sharif and Captain Yakub Jamli for their

assistance in field work, even during fasting season. I am very grateful to Mr. Duasin

Liman and Mr. Asri Mohd. Suari for providing the logistic supports. I wish to express

my gratitude to Mr. Ismail Tajul for his assistance in both field and laboratory. I

would never forget his patience on helping me in the taxonomic works.

I am also grateful to Liew Thor Seng for his advice and guidance on experimental

design and statistic analysis. I wish to express my gratitude to Dr. Annadel Cabanban

and Madam Ejria Saleh for providing useful information. I am also thankful to Sabah

Parks for their generosity of permitting me to access their library.

Finally> I would like to express my gratitude to my parents for their understanding and

patience during the study, when negligence was inevitable. I wish to thank my sister,

Meng Wai, who has been supporting the family and let me accomplished my study. I

am also grateful to Sat Nee who has been giving me moral support and even field

assist.

v

ABSTRACT

Sediments suspended in the water column and settling on to reef surface are thought to

exert influence on coral population. This study examined the influence of

sedimentation on coral population at two locations (A and B) of reef within Sepanggar

area, Sabah. Two stations located at a reef slope were chosen for each location.

Sedimentation rates were measured using sediment tmps which were placed at two

different depths. The samples were collected once a month and further analysis was

done in the laboratory to determine the total sediment tmpped, calcium carbonate

content, organic matter content and sediment composition. Benthic covers were

determined using a 20m line intercept transect. Sedimentation rates were higher at

location A which was nearer to the source of sediment discharge. Statistical analysis

indicated significant differences in sedimentation rates between two locations. Total

algal cover was higher in location A which has higher sedimentation rates. Within

algal categories (coralline, halimeda and macro), similar patterns were observed. Live

coral cover varied significantly with location B (farther from sediment discharge)

higher than location A. Diversity of corals were not significantly different between the

two locations. Coral genus abundance showed a contrast pattern between two

locations. Differences in coral genus abundance suggests a suite of sediment tolerant

(Goniopora, Fungia, Pavona, Cynarina, Porites, Pachyseris, Euphyllia, Leptoseris

and Pectinia) and sediment intolerant (Seriatopora. Pocillopora, Acropora,

Echinopora. Galaxea. Merulina. Symphyllia and Echinophyllia) genera. Alveopora,

Platygyra, Astreopora, Cycloseris, Herpolitha, Montipora, Plerogyra, Favia,

Gardineroseris, Trachyphyllia, Mycedium, Hydnophora, Haiomitra, Heliofungia,

Dipioastrea, Montastrea, Favites and Lobophyllia were intermediate between these

groups. Coral population at higher sedimented area (location A) suggesting

stabilization of coral population with a greater abundance of sediment tolerance coral

genera relative to lower sedimentation area (location B). Although some results

showed that sediment related effects on coral population are significant, but these

were not sufficient to relate sedimentation influence on coral population. Results

reported here suggest that a much more detailed study of Sepanggar area is required to

investigate further on effects of light, sediment shedding abilities of coral and

hydrodynamic factors.

PENGARUH SEDIMENTASI KE ATAS POPULASI BATU KARANG DI KAWASAN SEPANGGAR, SABAH

ABSTRAK

Vl

Kajian ini mengkaji tentang pengaruh sedimentasi ke atas populasi batu karang di dua

lokasi dalam kawasan Sepanggar, Sabah. Di setiap lokasi, dua stesen pada cerun

terumbu dipilih. Kadar sedimentasi diukur dengan menggunakan perangkap sedimen

yang dipasang pada dua kedalarnan yang berbeza di cerun terumbu. Sampel perangkap

dikumpul sebulan sekali dan dianalisis dalam makmal untuk menentukan jumlah

sedimen, kandungan kalsium karbonat, kandungan bahan-bahan organik dan

komposisi sedimen. Litupan bentik ditentukan dengan pita transek berukuran 20m. "oi

lokasi A, kadar sedimentasi adalah lebih tinggi kerana berdekatan dengan sumber

sedimen. Analisis statistik menunjukkan perbezaan yang ketara antara kadar

sedimentasi di kedua-dua lokasi. Jumlah litupan alga adalah lebih tinggi di lokasi A

yang mempunyai kadar sedimentasi yang lebih tinggi dan corak yang sarna didapati

dalarn kategori alga (coralline, halimeda dan makro). Litupan batu karang hidup

menunjukkan perbezaan antara lokasi dimana lokasi B (lebih jauh dari sumber

sediment) mempunyai litupan yang lebih tinggi berbanding dengan lokasi A Diversiti

batu karang antara dua lokasi tidak menunjukkan perbezaan yang ketara. Taburan

genera batu karang menunjukkan corak yang kontras antara dua lokasi. Perbezaan

corak ini mengasingkan sekumpulan batu karang yang toleransi kepada sedimen

(Goniopora, Fungia, Pavona, Cynarina, Porites, Pachyseris, Euphyllia, Leptoseris

dan Pectinia) dan tidak toleransi kepada sedimen (Seriatopora, Pocillopora,

Acropora, Echinopora, Galaxea, Merulina, Symphyllia dan Echinophyl/ia).

Alveopora, Platygyra, Astreopora, Cycloseris, Herpolitha. Montipora, Plerogyra,

Favia, Gardineroseris, Trachyphyllia. Mycedium, Hydnophora. Halomitra,

Heliofungia. Diploastrea. Montastrea, Favites dan Lobophyllia adalah kumpulan

sederhana. Populasi batu karang di kawasan yang mempunyai kadar sedimentasi

tinggi (lokasi A) menunjukkan keseimbangan dicapai oleh kumpulan batu karang

yang bertoleransi sedimen dengan taburan yang tinggi. Walaupun terdapat keputusan

yang menunjukkan kesan sedimen terhadap populasi batu karang yang ketara, ia

adalah tidak cukup untuk: menerangkan pengaruh sedimentasi. Kajian yang lebih

terperinci diperlukan untuk: mengkaji kesan cahaya, mekanisme pembuangan sedimen

dan faktor hidrodinamik.

TITLE OF DISSERTATION

DECLARATION

VERIFICATION

ACKNOWLEDGEMENTS

ABSTRACT

ABSTRAK

CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

CHAPTERl

CONTENTS

INTRODUCTION

1.1 CORAL REEF ECOSYSTEM

1.2 REEF DISTURBANCE AND DEGRADATION

1.3 SEDIMENTATION

1.4 REEFS IN SABAH

1.5 AIMS OF STUDY

CHAPTER 2 LITERATURE REVIEW

Vll

Page

I

11

111

IV

V

VI

VII

x

Xl

XlI

1

1

1

2

3

3

5

2.1 REEF BUILDING CORALS 5

2.2 CORAL REEFS IN SABAH 5

2.3 THREATS ON CORAL REEFS 6

2.4 SEDIMENTATION 8

2.5 HYDRODYNAMIC CONTROL OF TERRIGENOUS SEDIMENT 9

TO CORAL REEFS

2.6 THE IMPACTS OF SEDIMENTATION ON CORAL 9

2.6.l Inhospitable substrate 9

2.6.2 Acute sediment stress 10

2.6.3 Chronic sediment stress 11

2.7 EFFECT OF WATER TRANSPARENCY 12

2.8 EXPULSION OF ZOOXANTHELLAE 12

2.9 FACTORS INDUCING MORPHOLOGICAL CHANGES IN

SCLERACTINIAN CORALS

Vlll

13

2.10 PARTIAL MORTALITY AS AN INDICATOR OF SEDIMENT 14

STRESS

2.11 INTERMEDIATE DISTURBANCE HYPOTHESIS 15

CHAPTER 3 METHODOLOGY

3.1 STUDY SITES

3.l.1 Introduction

3.1.2 Sepanggar Bay

3.1.3 Sepanggar Island

3.2 SAMPLING METHODS

3.2.1 Coral coverage

3.2.2 Suspended particulate matter

3.2.3 Sedimentation

3.2.4 Water turbidity

3.3 DATA ANALYSIS

3.3.1 Water quality

3.3.2 Sediment analyses

3.3.3 Benthic coverage

CBAPTER4 RESULTS

4.1 WATER QUALITY

4.l.1 Visibility

4.l.2 Total suspended solid

4.2 SEDIMENT ANALYSES

4.2.1 Sedimentation rate

4.2.2 Percent of calcium carbonate in sediment

4.2.3 Percent of organic matter in sediment

4.2.4 Sediment composition

4.3 BENTHIC COVERAGE

4.3.1 Percent algal cover

4.3.2 Live coral cover

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30

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34

34

36

4.3.3 Coral genus richness

4.3.4 Coral diversity

CHAPTERS DISCUSSION

5.1 WATER QUALITY

5.2 SEDIMENTATION

5.2.1 Sedimentation rate

5.2.2 Sediment characteristic

5.2.3 Sediment composition

5.3 BENTHIC COVERAGE

5.3.1 Algal cover

5.3.2 Coral cover

5.3.3 Coral diversity

5.4 IMPLICATIONS FOR IDENTIFYING SEDIMENT-RELATED

EFFECTS ON CORALS

CHAPTER 6

6.1 Conclusion

6.2 Future Studies

REFERENCES

APPENDICES

CONCLUSION AND FUTURE STUDIES

IX

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37

41

41

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x

LIST OF TABLES

Table Numbers Page

Table 2.1 Temporal changes in coral cover and species diversity within 7 the Tunku Abdul Rahman Park (T ARP), Sabah, from 1987 to 1999.

Table 4.1 T-test of visibility (in meters, Secchi disc readings) 26 between reefs (location A vs. location B).

Table 4.2 T-test of total suspended solid (in mg/I) between reefs 27 (location A vs. location B).

Table 4.3 Two-way ANOV A testing the three sediment measures 28 between locations (location A vs. location B) and depth (5 m vs. 10 m).

Table 4.4 Descriptive statistics of sediment composition in three 32 categories (sand~ > 62 J.Ull, silt~ 62 - 15 J..Ull and clay; < 15 J..Illl) and result of one-way ANOV A with location as a factor.

Table 4.5 Two-way ANOV A testing on algal cover between location 34 (location A vs. location B) and depth (5 m versus 10 m).

Table 4.6 Two-way ANOV A testing on percent of coral cover with 37 location (location A vs. location B) and depth (5 m versus 10m) as factors.

Table 4.7 Two diversity indices for coral that recorded from the two 39 locations and result of one-way ANOV A.

Xl

LIST OF FIGURES

Figure Numbers Page

Figure 2.1 The possible mechanisms of zooxanthellae expulsion with 13 increasing severity of environmental stresses.

Figure 3.1 Location of the study sites in Sepanggar area. 18

Figure 3.2 The setting of sediment traps in each station 22

Figure 4.1 Spatial patterns of variation in the three sediment measures 29 (mean ± S.D.) in relation to depth (5 m; 10 m) and location (A; B).

Figure 4.2 Categorized box plot graph of sediment composition in 32 three categories between two locations.

Figure 4.3 Abundance of benthic coverage categories and coral genus 35 richness (mean ± S.D.) in the four location*depth categories-location A and location B versus 5 m depth and 10m depth.

Figure 4.4 Cumulative coral genera as a function of the number of20 m 38 transects for the two locations.

Figure 4.5 Coral genus abundance in (a) location A and (b) location B. 40

XlI

LIST OF APPENDICES

Appendix Page

Appendix A Model of zooxanthellae/coral symbiosis. 56

Appendix B Descriptive statistics of a) sedimentation rate in mg/cm2/day, 57 b) percent of calcium carbonate in the sediment and c) percent of organic matter in the sediment.

Appendix C Descriptive statistics of a) percent of sand in the sample 59 collected, b) percent of silt in the sample and c) percent of clay in the sample.

Appendix D Descriptive statistics of benthic categories in percentage. 61

Appendix E Descriptive statistics of coral genus cover in mean percentage.

62

CHAPTERl

INTRODUCTION

1.1 CORAL REEF ECOSYSTEM

Coral reefs have been categorized as highly productive ecosystems which are formed

by reef building corals that precipitate calciwn carbonate skeleton. These structures

are important habitats for diverse marine life. Coral reefs provide the basis for a

complex food web which provide sustainable food source for human. Fisheries in

coral reefs create employment for millions of fishermen and generate significant

wealth to them and the economy of their country. Besides that, reefs also play an

important role in tourism, generating billions of dollars, in some countries as crucial

income (Saxby, 2000).

1.2 REEF DISTURBANCE AND DEGRADATION

World wide coral reefs are subjected to severe anthropogenic damage which are

threatened by the economic activities they support (Wielgus et a/., 2004). There are

two main types of threats to coral reef resources: acute threats; and chronic stresses.

Acute threats cause significant damage but do not persist. There are several examples

of acute threats, examples; destructive fishing practices (blasting fishing), mechanical

2

damage (anchor damage) and crown of thorn starfish outbreaks. However, the reef

usually will recover if further assaults are minimized. Meanwhile, chronic stress,

which refers to the altering of physical or biological environment over a long term.

Examples include sewage pollution, increased sedimentation and near shore

eutrophication. Under these stresses, reefs will not recover until the stressor is

removed (Edinger et al., 1998).

1.3 SEDIMENDATION

Sedimentation is thought to be one of the major causes of world wide coral reef

degradation (McClanahan and Obura, 1997). Main causes of sedimentation are

dredging at sea, run off resulting from clearing of vegetation and mangroves for

agriculture (Phillipp and Fabricius, 2003). An increase of sedimentation in reef waters

can affect the coral cover and diversity by: (a) reducing light availability, which is the

primary energy source for corals~ (b) increasing energy demand for self cleaning

activities and therefore hampering other vital functions like feeding, growth or

reproduction; and (c) smothering tissues if high accumulation occurs (Thomas et at .•

2003). Sediment characteristics such as tendencies to form sticky marine snow

aggregates, and differences in organic and microbial concentrations, also reduce coral

recruitment rates (Fabricius et at., 2003).

3

1.4 REEFS IN SABAH

Continuous sedimentation caused by coastal development in Sabah has led to

degradation and death of coral reefs (Rahman and Cabanban, 2001). Lim (1993; in

Spait, 2001) is the only one who conducted a study on sedimentation at Tunku Abdul

Rahman Park (T ARP). Land reclamation near Kota Kinabalu area contributed

significant amount of sediment to the sea which later spread to TARP area. Besides

that, lnanam river has drained sediment directly into Sepanggar Bay. Heavy sediment

loading has been related to the long term decline of reef in Kota Kinabalu area. (Spait,

2001).

The development of container port in Sepanggar Bay has caused severe

sedimentation on adjacent coral reefs. Although there were previous studies regarding

the coral communities in this area (Wood, 1985), the information is insufficient to

assess the impact of coastal development to the reefs. The area deserves a detailed

study on the interaction between abiotic (sediment) and biotic (coral) component in

coral reef ecosystem.

1.5 AIMS OF THIS STUDY

Since the exploitation of environment has taken place, the sustainable level has to be

achieved through management. However, sustainable management is only possible if

the scientific basis for management on environment is provided (Riegl and Riegl,

1996). The purpose of this study is to understand the influence of sedimentation on

4

coral population in Sepanggar area. The specific objectives of this study are stated

below:

1.5.1 To study the impacts of sedimentation on coral distribution.

1.5.2 To understand the impact of coastal development to the reef.

1.5.3 To conduct a baseline study of sedimentation influence on coral reefs in

Sepanggar area.

The scope of this study will focus on the impact of sedimentation on coral

distribution. Besides that, sediment tolerance and intolerance of corals will be

detennined through the study.

CHAPTER 2

LITERATURE REVIEW

2.1 REEF BUlLDING CORALS

Hermatypic corals or more commonly known as reef buildings coral. They are mainly

found on hard substratum in water with ambient temperature which rarely drops below

20 °C. The symbiotic relationship of hermatypic corals and zooxanthellae, a

unicellular dinoflagellate (e.g. Gymnodinium microadriaticum) has made corals

unique. Photosynthesis by symbiotic algae makes reef building corals deposit skeletal

calcium carbonate approximately ten times faster than non-reef building (ahermatypic)

which do not possess zooxanthellae. Therefore, reef building coral only survive where

their symbiotic algae get enough light to maintain photosynthesis and thus, coral

growth decreases with depth. In high sediment load area, suitable population only can

be found in the upper two meters while in clear blue water, reef building coral may

extend to depths exceeding 80 meters (Ditlev, 1980).

2.2 CORAL REEFS IN SABAH

Among all the oceanic reefs around the Sabah territory, Sipadan and Layang-Layang

have the best reefs which are under the informal protection of SCUBA diving resorts,

6

the Royal Malaysian Navy and the Marine Police. In the southeast of Sabah, reefs

have been degraded by over exploitation and extensive fish bombing. Reefs at Darvel

Bay have been bombed extensively except a few isolated patches with high coral

cover and fish diversity. Blast fishing also took place in the northeast and the impacts

were worsen by the practice of cyanide fishing. Since 1994, the coral coverage on the

western coast of Sabah had declined dramatically. In 1996, the landing of tropical

Greg stonn had damaged the reefs in Tunku Abdul Rahman Park. Reefs with more

than 30 percent live coral cover had been reduced to rubber fields with less than 5

percent oflive coral cover (pilcher and Cabanban, 2000).

2.3 THREATS ON CORAL REEFS

The anthropogenic activities such as clearing of forests, coastal reclamation,

agriculture and urbanization contribute a significant environmental impact on coral

reefs. These activities lead to excessive flow of freshwater, sedimentation,

eutrophication and marine pollution. Riverine systems along the western and eastern

coasts of Sabah play a great role for transporting the freshwater, sediments and

nutrients to the reefs. Continuous influx can slowly alter the community structure in

the long run (Rahman and Cabanban, 2001).

Reef decline was evident in T ARP as a result of natural and anthropogenic

effects. Tropical Greg stonn hit the Park in 1996 which reduced the live coral cover

on most reefs. On the other hand, mangrove deforestation, land clearing and

reclamation project around Kota Kinabalu areas have increased sedimentation load

7

from erosion and river discharge. Heavy sediment loading was possibly responsible

for long term decline and slow recovery of the reefs (pilcher and Cabanban, 2000).

Table 2.1 Temporal changes in coral cover and species diversity within the Tunku

Abdul Rahman Park (TARP), Sabah, from 1987 to 1999. (Adapted from Pilcher and

Cabanban, 2000)

Mtno1!is Reef 1987 1991 1994 1999 AYerage. live coml cover(%) 40.5 4'1.5 34.5 14.2

. Total nmnber of genera 42;0 52 54 -SnpiReef AveraQe livecorll l cove.r{%) 47.0 30.S 37.5 4.1 Total number of genera 46 53 53 -St8!:bom .Patch Reef Average hve coral covel (%) 30.'0 36.5 33.0 1.6

"1'otal lltrm'ber of genera 46 47 5.0 42. Manukall Red . Avemp,e live coral l~ve.r (%) 30.0 36.5 38.S "35.0 Tot al ulIltilbe.T of genera. 39 46 - 44 S ilJug- .Reef

. Average live cora 1 cover (~.'o) - 32.5 19.0 2.9 Tofa l nl1lriber of gene.ra - 50 45 44 MS.rimtik Reef A veraJ!.e Hve cora' cover C%') ~ [8.0 19.5 12.3 Total .nlllllber of genera - 41 49 50 Tluliono WokonoReef Average live coral cover (%) - -. 31 5.4' Total uumber (])f genera - - - 54

The table above shows the live coral cover status in TARP from 1987 to 1999.

Generally, the average live coral cover in most of the reefs has declined and the status

has become worse during 1999. Although tropical Greg storm during 1996 had

damaged most of the reefs, it is not a persistent disturbance and reef usually will

recover. But the average live coral cover recorded in 1999 did not show any

8

significant recovery. This may due to the increase of anthropogenic disturbance which

has caused the degradation of the reef

2.4 SEDIMENTATION

Sedimentation typically has greater impact on fringing reefs than on farther distance

reefs due to the tendency of sediment to settle near the source. Meanwhile nutrients

and other chemical compounds are being dispersed farther compared to sediment

(Cabanban el al., 2000). Major environmental changes occur when fine sediment

reaches coastal waters which alter the habitats by creating a muddy coast. It is because

mud can degrade coral reefs through a number of biological processes and the degree

of degradation is correlated with the sediment quantity and quality, sedimentation rate

and the residence time ofthe mud (Golbuu et al., 2003).

Most of the research to date has focused on assessing the changes in coral and

algae cover on disturbed reefs while quantitative data regarding quantity and quality

of suspended sediments impacting the reefs are little. Sedimentation is a major cause

of mortality in the initial life stages of hard coral which higher concentration will

affect a range of life history parameters in juvenile and adult corals (Wolanski et al.,

2003).

9

2.5 HYDRODYNAMIC CONTROL OF TERRIGENOUS SEDIMENT TO

CORAL REEFS

The hydrologic cycle and associated terrigenous sediment fluxes are among the

environmental factors that have been extensively altered by human activities.

Sediment inputs to the coastal zone have heterogeneous distributions depending on

climate, topography and land use (McLaughlin et al., 2003). The main forces

responsible for the coastal flows that disperse coastal and alluvial sediments include

tide and weather (Hoitink and Hoekstra, 2003). Resuspension from the sea floor and

sediment input from river determine concentration of suspended solids in the water

column. If the wave energy is low, the suspended sediment settles out of the water

column and is deposited on the sea floor and upon sea floor-inhabiting organisms

(Philipp and Fabricius, 2003). However, high variation of suspended sediment

concentration has to depend on various factors such as changes in sediment

availability and variable critical shear stresses for erosion and deposition (Hoitink,

2004).

2.6 THE IMPACTS OF SEDIMENTATION ON CORAL

2.6.1 Inhospitable substrate

Sediment characteristics such as tendencies to form sticky marine snow aggregates

and differences in organic and microbial concentrations will alter the effect of

sedimentation on coral recruits (Fabricius et al., 2003). Unconsolidated sediment is an

unstable substrate for reef formation and these conditions may persist over geologic

10

time scales regardless to additional sediment deposition stresses (McLaughlin et al .•

2003).

Coral larvae will start to settle on suitable substratum after a few days or weeks

after the mass spawning of reef building event They metamorphose to primary polyps

which soon start depositing their calciwn carbonate skeleton and add new polyps by

budding. The ability of young coral recruits to survive sedimentation or other

environmental disturbance has to depend on the capacity of coral reef communities to

recover from the disturbance events (Fabricius et al .• 2003).

2.6.2 Acute sediment stress

Settlement of suspended sediment from the water column onto reefs can affect control

the distributions and abundance of coral species through lethal and sublethal effects.

Settlement of particles onto live coral surfaces can cause tissue necrosis and death

because ofthe combined effects of smothering and microbial action (Gleason, 1998).

Some species are able to clean off deposits efficiently and show no damage due

to sedimentation (philipp and Fabricius, 2003). Given the multiple ways of sediments

disturbance on reef building corals, it is not surprising that these animals have evolved

various mechanisms to clean their tissue surfaces of sediment Sediment shedding

mechanisms include passive rejection (particles slide off by gravitational flow due to

convexity of colony surface), distension of polyp by uptake of water (creates a steep

side for gravitational flow to proceed), ciliary transport of mucus entrapped particles

and manipulation of grains off the colony by the use of tentacles. However, most of

11

the reef building corals use one or more of these mechanisms. The variation of

methods used in providing the most effective sediment shedding depends on the

differences in overall colony and polyp architecture (Gleason, 1998).

Energy spend in shedding sediments will decrease colony fitness by limiting

energy for other processes such as food capture, growth, tissue maintenance and

reproduction (Gleason, 1998). In a longer term, heavy sediment loading can influence

coral cover as well as the species composition in communities due to differences in

sediment tolerances between species (Philipp and Fabricius, 2003).

2.6.3 Chronic sediment stress

High concentration of suspended sediments can impact corals by reducing the water

clarity and light levels which is a potential stressor of photosynthesis dependent coral

reefs (McLaughlin, 2003). Zooxanthellae serve as primary producers and supply their

coral host with up to 95 percents of their photosynthetic products, such as sugar,

amino acids, carbohydrates and small peptides. All these compounds provide the coral

energy for respiration, growth and the deposition of its calcium carbonate skeleton

(Saxby, 2000) (Appendix A). Deposition of calcium carbonates in corals is dependent

on photosynthetic rates of the zooxanthellae and therefore, reductions in light intensity

resulted by increases in suspended sediment loads can lead to significantly reduced

rates of colony growth (Gleason, 1998).

50

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