application of alos imageries for monitoring coral health in coastal waters of vietnam

This report present some experiences on the coral mapping in coastal area of Vietnam and results of application for detection of evidences of bad status of coral health due to affect by

APPLICATION OF ALOS IMAGERIES FOR MONITORING CORAL HEALTH

IN COASTAL WATERS OF VIETNAM

PI 326

Tong Phuoc Hoang Sơn

Institute of Oceanography – Viet Nam

01 Cau Da street, Vinh Nguyen, Nha Trang – Viet Nam, Phone number: 84-583590033; Facsimile Number: 84-583-590034; Email Address :

tongphuochoangson@gmai.com

1 ABSTRACT

Coral reef is one of marine habitats have high primary

production but also is high sensitive Due to comfortable

conditions in humid tropical region, coral reef in coastal

waters of Vietnam sea develop very well with their

distribution stretch along from North to South areas During

the past several decades, coral reefs in many parts of the

world have been subjected to a series of bleaching events,

including some coral reef areas in coastal waters of Vietnam

This report present some experiences on the coral mapping in

coastal area of Vietnam and results of application for

detection of evidences of bad status of coral health due to

affect by natural disasters as well as anthropogenic

interventions

2 INTRODUCTION

Vietnam lie in humid tropical area with coastal habitats

such as coral reef, sea grass bed, mangrove forest, etc,…

develop very well Coral reefs in Vietnam distribute along

coastal areas from North to South as well as in offshore

waters (Spratly and Paracell Archipelagos) Due to

importance aspect of this habitats, many projects on the

coral mapping have been carried out in coastal area of

Vietnam (Ninh Thuan, Khanh Hoa, Phu Quoc, Da Nang,

Quang Nam,…) but the assessment of natural disasters

that effect to coral reef is still few Effect of global

warming and ElNino is reasons causing coral bleaching in

Con Dao , Phu Quoc islands in July 1998 (V S Tuan et all

2005) as well as Con Dao island during October 2005 (T

P H Son et all 2006 [8] have been discussed in some

papers but how do we monitor and detect the coral

bleaching in coastal waters of Vietnam sea is opened This

report present some experiences on the coral mapping in

coastal waters of Vietnam and some evidences on affects of

natural disasters as well as human interventions to the coral

health base on the remote sensing techniques These results

were obtained from ALOS-JAXA project – PI 326 with title

“Application of ALOS and Ocean Color Imageries sources

for monitoring of Coral Health in coastal waters of South of

Viet Nam”

3 DATA AND METHODOLOGY

3.1.- Satellite images:

The remote sensing techniques is main method for detecting the distribution of coral reefs and assessment the status of coral health under affect of natural disasters and anthropogenic intervention A series of satellite imagery as well as aerial photography have been used They include

 ALOS (Japan) imagery from Project “Application of ALOS imagery for monitoring the coral health in coastal waters of Vietnam” with 18 scenes AVNIR2 (10m) and PRISM (2.5m) have been used for detection the distribution in coastal waters in Quang Tri, Quang Nam, Binh Dinh, Khanh Hoa, Ninh Thuan,

Ba Ria – Vung Tau and Kien Giang provinces

 FORMOSAT2 MS (8m) and PAN (2m): 16 scenes from SAKE Project have been used for detection the distribution in coastal waters in Quang Nam, Binh Dinh, Khanh Hoa, Ninh Thuan provinces

 Landsat ETM (30m) from USGS (2 scenes) using for detect distribution coral reef in coastal waters of Ninh Thuan province and Condao Archipelagos

 SPOT4 (20m), SPOT5 (10m) from IFREMER project, National Projects have been used for supplementing some information on the distribution of coral reef and related habitats in Con Co, Cu Lao Cham, Nam

Du archipelagos

 The color aerial photograph dataset (include 18 scenes) taking in map scale 1/5.000 that cover whole

of An Thoi Archipelagos – Phu Quoc Island

3.2.- Investigated data:

They include underwater surveyed data by difference

methods on many of coral sites in coastal waters of Vietnam (figure 1) those are:

 Surveyed data along coastal zone and surrounding the islands which obtain by manta tow method (an investigation method use for rapid assessment the distributed components of coral reefs)

 Surveyed data along coastal zone and surrounding the islands which obtain by “reef check” method (an investigation method use for detail assessment the distributed components of coral reefs along the coast according to shallow and deep sections)

 Surveyed data on the coral reef distributed in the

cross section by method of “biomass frame” sections

 Surveyed data used for obtaining “homogeneous

substratum” positions (such as sand, mud, rocky,…)

for building the “Depth Invariance Index” algorithm

use for removing the “water column” in studied area

On the special term, it is called be method of “water

column correction” In some case, we re-used the

existed sediment maps instead of underwater

surveyed data (figure 2)

 Positions of key points help for clasification (coral

reef, seagrass beds, bed rock, sand, ) in Cu Lao

Cham obtain from underwater survey during May

2008, as an illustrated samples for obtaining

underwater surveyed data (figure 3)

Figure 1: The studied sites (orange circles) on coral reef

distribution in coastal waters of Vietnam by remote

sensing techniques linking with underwater surveys

1) Tran Island; 2) Co To Archipelago 3) Cat Ba

Archipelago; 4) Long Chau Archipelago; 5) Bach Long Vi

Island; 6) Me Island; 7) Nghi Son Island; 8) Con Co

Island; 9) Coastal water of Thua Thien - Hue Province;

10) Cu Lao Cham Archipelago; 11) Coastal water of

Quang Nam province; 12) Re Archipelago; 13) Xanh

Island; 14) Van Phong Bay; 15) Nha Trang Bay; 16)

Coastal Area of Ninh Thuan province Ninh Thuận; 17) Con

Dao Archipelago; 18) An Thoi Archipelago – Phu Quoc

Island; 19) Nam Du Archipelago; 20) Tho Chu

Archipelago

Figure 2: Positions of sand sites help for calculating the Depth Invariance Index in the Map of Sediment Distribution in coastal waters of Quang Nam province

Figure 3: Positions of Ground truthing site help for clasification (coral reefs, seagrass beds, bed rock, sand, ) in Cu Lao Cham Archipelago obtain from survey during May 2008

3.3.- Procedure of data processing for detection the coral reefs and relevance habitats by remote sensing technique This procedure have been carry out step by step

as following

 Geometry correction (Geo-Reference): in order to convert bitmap image co-ordinate to local geography co-ordinate (UTM project, WGS84 datum)

 Radiance correction: convert Digital Number into spectral radiance in sensor by the convert formula appear as following :

Rad = a * DN + b ; when a: gain and b: offset

 Atmospheric Correction: convert spectral radiance into reflectance in surface water and filter the atmospheric affects In this step we used “Dark Subtract” tool in ENVI software for processing

 Water Column Correction: The linear natural logarithm

relationship of water reflectance between ith band and

jth band is basic formula for calculating the Depth

Invariance Index It was showed as following

D.I.I ij = a * Ln(i) - Ln(j) + b When

- i, j : are spectral reflectance in water surface of band

pair (i,j) that obtain from atmospheric correction in 128

sand points

- a, b : are slope and intercept in regression line, they

appear strong (or not) relationship between band i and band

j by mean of Standard Deviation (r2)

The illustrated results of correlation and regression

analysis in step of “Water Column Correction” (for Cu

Lao Cham case study in ALOS - AVNIR2 date 08 June

2008) show in figure 4

y = 0.914x + 0.2349

R2 = 0.8198

2

3

4

Ln (b2)

Ln (b1)

y = 0.5245x + 1.0597

R2 = 0.8158

2

2.5

3

3.5

Ln (b3)

Ln (b2)

y = 2.9959x - 3.9647

R2 = 0.7822

3

4

5

6

Ln (b4)

Ln (b3)

Figure 4: Some linear natural logarithm relationships of

water surface reflectance between i th band and j th band,

that is basement for calculating the Depth Invariance

Index (from 128 sandy sites) in AVNIR2 image cover

Cu Lao Cham archipelago date 08 June 2008 (T.P.H

Son, 2009 [12 ])

Equation system of Depth Invariance Index of band pairs obtain from ALOS-AVNIR2 base on 128 sandy point taking in Cu Lao Cham case study have been showed as following:

D.I.I 12 = 0.914* Ln (1) - Ln (2) + 0.2349 D.I.I 13 = 0.4445 * Ln (1) - Ln (3) + 1.1215 D.I.I 14 = 1.5688* Ln (1) - Ln (4) - 0.8333 D.I.I 23 = 0.5245 * Ln (2) - Ln (3) + 1.0597 D.I.I 24 = 1.7562* Ln (2) - Ln (4) – 1.3588 D.I.I 34 = 2.9959* Ln (3) - Ln (4) - 3.9647 The correlation analysis also alow to choose only 5 new D.I.I bands (cancel D.I.I 13 for processing (r2 < 0.6) for next classification

 Mask step: allow to “hide” unstudied area i.e : land, offshore where don’t exist of coral reef and sea grass bed This step will enhance the image quality for classification

 Supervised classification: used “Mahalobich Distance” classification base on survey points in different habitats for detection the distribution of coral reefs, sea grass beds and other substratum

3.4.- The remote sensing techniques for detection the evidences causing negative affects to status of the coral health

 Detection the reasons causing phenomena of coral

bleaching:

The coral bleaching can make the mass mortality of benthos live in coral reefs This is a phenomena related strongly with climate change due to the increasing of sea water temperature, the decreasing the water salinity, the increasing the acidification processes,…

By assessment the temporal and spatial variances of sea surface temperature, water salinity and sediment flux by ocean color and multi spectral imageries as well as the finding out especial spectral color spots directly in coral sites from high resolution image allow us to detect the phenomena of coral bleaching in somewhere of coastal

water of Viet Nam

 Detection some evidences of acidification processes in

offshore water of Vietnam

Increased fossil fuel burning associated with geothermal phenomena and industrialization, cement production, land use changes associated with agricultural activities are causing atmospheric CO2 concentrations There is clear evidence that the carbonate equilibrium of the oceans is shifting in response to increasing atmospheric CO2 concentrations to rise, and at increasing rates Even small changes in CO2 concentrations in surface waters may have large negative impacts on marine calcifies and natural biogeochemical cycles of the ocean For example, decreased carbonate ion concentration significantly reduces the ability of corals to produce their calcium carbonate skeletons (Kleypas et all, 2006 [3])

In Vietnam, the studies on the acidification processes and the increasing of CO2 emission that affect to coral health are very restricted

Our study only record on some evidences of potential

geothermal phenomena in offshore Binh Thuan waters as

one of evidences of acidification processes

By visual interpretation directly in color composite image

from a scenes of ALOS-AVNIR2 (date, 18 September

2007) allow us found out this phenomena

 Detection the evidences of sediment and fresh water

plume as well as siltation processes causing the

negative effects to status of coral health

By fusion technique base on ocean color image merged to

ALOS PRISM one, we found out in some case the fresh

water and sediment from in river can be reach to offshore

waters more 40 km and they caused negative consequence

to coral health in some coral sites

A very direct approach to image enhancement is the use

of high resolution data, e.g ALOS AVNIR2 – Band 1

(10m) panchromatic images, to sharpen images of lower

spatial resolution, e.g MODIS 250 m multis-pectral data

Once a set of multi-sensor images is placed in register with

a high resolution reference image, the digital numbers

(DNs) of the various multi-spectral bands may be merged

with those for the single band (panchromatic) reference

image using techniques previously described by Cliche et al

(1985) [2] These methods may be summarized in the

following equations:

DNi' =i * DNi* DN(h) + i (1)

DNi'= i *  i* DNi   i * DN(h) + i (2)

Where:

DNi and DNi' are the DNs for the ith band of the original

and fused multi-spectral image, respectively; DN(h) is the

DN for the high resolution reference image; i, i are

scaling factors; and iand iare weighting factors

In reality condition, we used directly tool “Pan

Sharpness” in SPEAR tools of ENVI 4.4 software for

resolving this problem

 Detection the evidences of anthropogenic

interventions causing the negative effects to status of

coral health

The coastal developed activities such as building the

tourism resorts, dredging marine ports, irregular material

dumping,… can causing the negative consequences into

status of coral health

Base on spectral analysis for detecting the bottom

bathymetry, visual interpretation from color composite

images we saw a lot of cases of siltation can be badly

effected to status of coral health, destroyed and

disappearance of some coral sites in coastal waters of

Vietnam

RESULTS AND DISCUSSIONS

4.1 - Distribution of coral reefs in coastal waters of

Vietnam sea

Base on remote sensing techniques linking with underwater

surveys, the distributed scenes of coral reefs in coastal waters

of Vietnam sea have been detected

Figure 5 is illustrated results on distribution of coral reefs and related underwater habitats in Cu Lao Cham archipelagos and surrounding waters (Tong P H S, 2009 [12] )

Figure 5: Distribution map of coral reefs and sea grass beds in Cu Lao Cham archipelago obtain from remote sensing techniques in AVNIR2 (date, 08 May 2008) [12]

Note: HC: Hard coral, SW : Sea weed: SG : Sea grass ;

RK : Rock; SD : Sand , Land Mask

The detail distribution of coral reefs in coastal water of Vietnam was recored as following

4.1.1.- Distribution of coral reefs in Northern side of Vietnam sea: include coral reefs in Tonkin Gulfs (Co To

archipelago, Tran Island, Cat ba, Bach Long Vi archipelago,…) and also coastal waters of North of Center such as Hon me (Thanh Hoa province), Nghi Son (Ha Tinh province ) and Con Co (Quang Tri)

Until now, we carried out to survey and building the distributed maps of coral reef in Co To, Bach Long Vi and Con Co (Thao N.V and Son T P H, 2007 [ ] The results present detail in figure 5, and show that:

 In Co To archipelago, live coral distribute scattered in small islands surrounding of archipelago, such as Co

To Con, Khoi, Ca Chep, Khoai Islands, and also North West of Thanh Lan Island with total area estimated about 66.1 ha Platform reef cover Death Coral in North of great Co To with area reach to 256.5 ha

 In Bach Long Vi Island, live coral existed in North and West sides with area reach to 133 ha, remained area of reefs cover the death coral, with estimated area is 491 ha

 In Con Co Island, live coral mainly existed in North side with estimated area is 72 ha The southern side cover the sandy material interpose with rocky cliffs.

4.1.2.-Distribution of coral reefs in Central of Vietnam sea: include coral reefs in Cu Lao Cham and in

coastal waters of Quang nam, Phu Yen, Khanh Hoa, Ninh

Thuan provinces

 The coral reefs in Cu Lao Cham

The live coral mainly distributed in western and

south-western sides of Lao Island and other small islets with

estimated area is 165 ha (T.P.H Son, 2008 [12] The coral

reefs in these area develop well with genus of Acropora,

Montipora and Goniopora (Nguyen Van Long et all [6 ])

The North and East of Main Island of Cu Lao Cham

cover mainly of rocky cliffs The bio resources is very

difficulty existed and developed in these areas

The southern side of Cu Lao Cham include coral reefs

with high cover level interpose with sand beaches and sea

grass beds exist in Bac, Ong, Chong, Bim, Huong and Nom

grounds

 The coral reefs in coastal waters of Quang Nam

province

Include fringing reefs and platform reefs exist

surrounding of An Hoa cape The platform reefs exist in

the front of An Hoa Gap and “great reef” bank with

predominant genus of Porites, Goniastrea, Platygyra In

An Hoa cape, the coral reefs cove mainly of “branch” coral

and soft coral with predominant of Acropora The reef is

narrow and deep

The total area of coral reefs in this area have been

estimated about 95 ha (T P Son, 2007 [11])

 The coral reefs in coastal waters of Phu Yen Province:

The coral reefs exist in the front of the mouth of Cu

Mong lagoon They have been met in Nom cape (3.5 ha),

Hoa Thanh (6.9 ha) and Vinh Hoa (4.7 ha)

The coral reefs exist in the front of the mouth of Xuan

Dai lagoon They have been met in Tu Nham Cape (32.5

ha), Vung La (5.6 ha), Hon Thung ground (10.0 ha), Tuong

ground (2.3 ha), Phu Hoi cape (12.4 ha) and Yen cape ( 3.2

ha)

In coastal waters from O Loan lagoon to An Phu

Commune is region where coral reefs develop very well and

high cover level with main component of soft coral such as

Cu Lao Mai Nha (42.3 ha), Phu Thuong (9.9 ha), Yen Cape

30.2 ha, Go ground - An Chan (39.4 ha), Chua Island – An

Chan (32.7 ha) and Dua island – An Phu (8.3 ha)

In coastal water of Ro gorge, coral reef have been seem

Dien Cape (11.6 ha), Ro Cape (18.8 ha) , Phong So (11.2

ha) và Nua Island (17.4 ha)

 The coral reefs in coastal waters of Khanh Hoa

province have been estimated about 3266 ha, (T.P.H.Son,

2007 [9] they distribute in main regions as following:

Coral reefs in Ben Goi Bay get 584.3 ha area, they main

distribute in Bip, O, Dut, Cum Meo islands, Tuong, Trao

banks Islands and also coastal waters of North West of Bay

Coral reefs in East coast get 476.6 ha area They distribute

mainly in Hon Gom penesula , Co Co channel, Great Island,

and some islets in North of Great Island

Coral reefs in South-West coast get 337.1 ha area They

distribute mainly in Du cape, Hon Khoi, My Giang, Bai Co

grounds and some underwater banks

Coral reefs in Binh Cang Bay include coral reefs in Ninh van, Hon Thi – Nha Phu Lagoon get 142.4 ha They distribute mainly in Cay Bang bay, Long beach and Chao bank

Coral reefs in Nha Trang Bay get 775.9 ha area They distribute mainly in around Hon Tre, Mun, Mot, Tam, Mieu, Vung and Cau islands as well as in Song Lo and Grand bank

Coral reefs in Cam Ranh Bay get 865.7 ha area They distribute mainly in Thuy Trieu bank, East coast in Cam Ranh penesula, Noi, Ngoai, Binh Ba Island

In coastal waters of Khanh Hoa province have been characterized by creating of platform reefs in big deep such

as Grand bank – 426 ha, Thuy Trieu Band 800 ha, (figure 6) Ninh Phuoc band 40 ha and Chao Bank – 13 ha

Figure 6 Some typical platform reefs in coastal waters

of Khanh Hoa province – Grand Bank (upper), Thuy Trieu Bank (lower)

 The coral reefs in coastal water of Ninh Thuan province: have been estimated about 1277 ha (Son T.P.H,

2005 [7], they distribute in main regions as following

 The coral reefs in coastal waters of Ninh Thuan

Province:

The narrow non-typical fringing reefs exist in main areas:

Hon Chut to Da Vach Cape - 42 ha, Vinh Hy Gorge - 28

ha , Hon Do – My Tuong – 98 ha

Thai An ground is a The typical fringing reef exist in

many grounds of coastal areas : Thai An - 252 ha, Tu

Thien (151 ha), Son Hai (182 ha)

The platform reef exist in Breda Bank with area of 84 ha

Beside in deep sea, the coral reefs also exist in 30 – 35 m

deep , exist a reef ground that cover mainly by “horn” coral

species with 168 ha area

4.1.3.- Distribution of coral reefs in Southern side of

Vietnam sea

 The coral reefs in Con Dao archipelago: The coral

reefs get a total area of 743.2 ha and sea grass beds get

a total area 480.8 ha, Son T.P.H, 2010 [13] with detail

distribution present in table 1

Table 1: The distribution of coral reefs and sea grass

bed in Con Dao archipelago

Coral reef S (ha) Sea grass bed S (ha)

Great lagoon 233.4 Great lagoon 221.8

South ConLon Isl 18.8 South ConLon Isl

Ba Island 31.1 Ba Island 10.3

Ben Dam Lagoon 167.9 Ben Dam Lagoon 78.6

Ong Dun ground 26.7 Ong Dun ground 31.2

OngCuong ground 19.7 OngCuong ground 9.0

Dam Tre Lagoon 35.2 Dam Tre Lagoon 33.8

Dam Tre cape 9.2 Dam Tre cape 14.5

Chim Chim cape 7.8 Chim Chim cape 32.4

Great Tre Island 16.4 Great Tre Island

Small Tre Island 1.5 Small Tre Island

Great Trac island 13.1 Great Trac island

Small Trac island 22.5 Small Trac island

Trac island 6.8 Trac island

Bay canh Island 112.5 Bay canh Island 49.2

Cau Island 20.6 Cau Island

 The coral reefs in An Thoi archipelago and Phu Quoc

Island include 119 ha in North West of Phu Quoc

Island (table 2), 350 ha in An Thoi Archipelagos (table

3) and 9800 ha of sea grass beds in coastal areas of Phu

Quoc (table 4), Son T.P.H, 2010 [13]

Table 2 The distribution of coral reefs and sea grass

bed in Nouth West of Phu Quoc Island

Sites S (ha) Sites S (ha)

Cua Can cape 50.0 Doi Moi Island 2.1

Ong Quoi Cape 35.0 Thay Boi Island 0.6

Ghenh dau Cape 30.9 Bang Island 0.7

Table 3 : The distributed area of coral reefs in An Thoi Archipelago

(ha)

Sites S (ha)

Dam Trong Island 12.5 Xuong Island 24.3 Dam ngoai Island 6.8 Gam Ghi Island 26.2 Dua Island 18.8 Mong tay Island 3.8 Roi Island 30.0 May Rut Ngoai Isl 29.4 Thom Island 44.2 May Rut Ngoai Bank 18.0 Trang island 5.5 May Rut Trong Island 25.6 Kho Island 4.2 Kim Quy Island 9.1 Vang island 39.0 Kim Quy Bank 52

 The coral reefs in Nam Du archipelago have been

estimated about 242 ha with detail distribution in table 4

Table 4 : The distributed area of coral reefs in Nam Du Archipelago

Sites S (ha) Sites S (ha) Nam Du Island 71.7 Bo tra island 14.5

Co Loa Island 1.6 Mau Island 17.7 Moc Island 1.3 Nom Ngoai Island 3.0 Giang Island 15.8 Nom giua island 6.9 Truoc Island 10.3 Nom Trong Island 1.5 Dau Island 24.9 Underwater Banks in

West of Nom Island

16.5

Ngang Island 33.6 Underwater Banks in

South of Nom Island

10.9

Dam Island 2.4 Underwater Banks in

South Truoc Island

10.1

 The coral reefs in Tho Chu archipelago:

Total area of coral reef have been estimated 266.1 ha and sea grass bed with 134.6 ha (table 5) , Son T.P.H, 2010 [13]

Table 5 : The distributed are of coral reefs in Tho Chu Archipelago

Coral reefs - Fringing reef

S (ha)

Coral reefs – platform

reef

S (ha) Tho Chu Isl 66.0 South of Xanh Isl 99.0

Tu Island 47.9 SW of Cai Ban Isl 12.0 Cau Island 3.1 North of Cau Island 33.6 Xanh Island 4.0

Nhan Island 14.8 Cai ban Island 2.4 Cau Cat Island 4.4 Kho Island 0.7

4.2.- The evidences making negative affects to status of the coral health: include the coral bleaching, acidification

phenomena, sediment and fresh water flux, siltation and

human intervention

4.2.1.- The coral bleaching event and mass mortality of

benthos in Condao during Mid of October of 2005

Con dao Islands lie in Southern of Vietnam sea in

geography bounders from 106o 31’ to 106045’E longitude

and 08o37’ – 08o45’N Latitude Area of coral reef in Con

Dao Island have been estimated about 1,000 ha They have

high biodiversity with 323 scleractinian species, 202

species of coral fish, 148 mollusk species, 110 crustacean

species, 44 echinoderm species and 125 polychaete species

(Vo S T et all, 2005) [15] By mean of previous studies

(Vo S.T, 2000 [14]), natural disaster is consider as one of

the best important reasons which cause the biodiversity

degradation of coral reef in Con Dao The typical examples

of effects of Lynda Typhoon (1997) and of El Nino (1998)

with high increasing of sea water temperature and causing

serious coral bleaching in Con Dao have been also recorded

(Vo Si Tuan, 2000) [14]

During Mid October of 2005 an event of mass mortality

of the corals and benthos occurred again in surround waters

of Con Dao Islands, Ben H.X et all, 2008 [1] (figure 7)

Figure 7: Some pictures of coral bleaching and mass

mortality of coral in Condao Island during October

2005 (after Hoang Xuan Ben et all, 2008 [1] )

Base on satellite data (Ocean color and Landsat ETM+) and also surveyed data from VOS-Nippon vessel,

we found out the reasons causing the coral bleaching in Con Dao Island during mid of October 2005 (figure 8)

The random coincidence of the extreme increase of sea surface temperature with lower reducing sea water salinity as well as high turbidity (mainly due to water plume from Mekong rivers) during 10-13th October 2005 is main reason causing mass mortality of corals and benthos in Con Dao Island

Figure 8 The terrestrial, warmer fresh water plume with high turbid reach more 200 km (from river mouth) are main reasons causing coral bleaching and mass mortality of benthos in Condao island (T.P.H Son, et al,

2006 [8]

During March – April of 2010, from survey data we also recorded the extreme increasing of sea water temperature and decreasing of water salinity in some places (Van Phong Bay, Con Dao Island, Tho Chu and Nam Du archipelagos, )

These results show clearly two periods with extreme anomaly of highest sea temperature and lowest salinity occur during October 2005 (light purple line) and second period of March to June (dot pink line) of 2010 (figure 9) Latupov and his colleagues [5] by SCUBA surveys from cooperation Viet – Russian investigation on Oparin Researcher Vessel during March of 2010 also found out the coral bleaching in Nam Du and Tho Chu archipelago with strong rate

Regret, by ALOS and any satellite imagery sources we have

not found out this phenomena yet

24

26

28

30

32

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12

2002 2003 2004 2005 2006

2007 2008 2009 2010

SST ( ° C)

24

25

26

27

28

29

30

31

32

33

34

35

T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12

2002 2003 2004 2005 2006

2007 2008 2009 2010

S ‰

Figure 9 The monthly variance of Sea Surface

Temperature (upper) and Sea Surface Salinity (lower)

in offshore of Con Dao Island, show that 2005 and 2010

can causing the coral bleaching due to highest water

temperature and lowest sea water salinity

4.2.2.- The oil seep process in geothermal center and

acidification process in Phu Quy Island:

Phu Quy Island or Cu lao Thu island place in center

coordinate about 109 o 58’ E and 10o 30’ N where exist

many ancient volcanoes

According to French authors, on 2nd March 1923, there

was an eruption at Tro island (10o16 N, 109o 01 E) which

produced scoriaceous basalt The eruption stopped on 13th

May 1923, and this island were eroded below sea level (the

recorded material is missing)

The studied results of Pham Van Thom (personal

information) also recognized that, this area is biggest

geothermal center of Vietnam

When we consider the reason that causing the oil slick

attack on many tourism resorts of Vietnam during 2007, we

searched a lot of AVNIR2 and found out a yellow trace

appear in Phu Quy Island in scene of ALOS - AVNIR2 date

27 July 2007 (figure 10)

Combination all of existed data, we suggest on

phenomena of oil seep in Eastern side of Phu Quy island

This phenomena will expand the acidification process in here and effect directly to coral reefs in Phu Quy island

Figure 10 The yellow track from RGB321 color composite image (AVNIR2 date 17 July 2007) allow to suggest on formation of natural oil seep and acidification processes in Phu Quy island

4.2.3.- The sediment and fresh water plume from river after flood events affect badly to status of coral health

As presented, in section 4.2.1, the terrestrial, warmer fresh water plume with high turbid from river can cause serious damage to coral reefs However, not all of time, we can search a suitable satellite image with high resolution (e.g, AVNIR2, SPOT5, Landsat ) for detection the sediment and fresh water plume after flood events (especial the cloud cover level in these periods is very high)

By combination between ocean color images and high resolution satellite images sometime we can overcome above disadvantage (figure 11)

Figure 11 Inundation area in downstream of Thu Bon River and sediment plume after Sangsane typhoon reach to CulaoCham island by fusion techniques between MODIS (250m) and Band 1 - AVNIR2 (10m)

The processed data show that the fresh water and sediment

plume from river Thu Bon can reach to North side of Cu

Lao Cham Island (108o30 E, 15o57’ N) and badly affect to

coral reefs in this area

4.2.4 The coastal development activities and their

affect to status of coral health

The coastal developed activities such as building the

tourism resorts, dredging marine ports, irregular dredged

material dumping,… can causing the negative consequences

into status of coral health

For instance, Nha Trang Bay is not only Marine

Protection Area but also is one of famous tourism sites of

Vietnam There are a lot of tourism constructors were built

in coastal area where exist coral reef and they destroyed a

part or make disappearance completely coral reefs and

related habitats in these areas

The Dam Gia ground in North West of Tre Island (Nha

Trang bay) existence a coral reef (21 ha) lie mixing with

sea grass bed (12 ha) in surrounding Before 2005, this was

an ideal site for snorkeling activities and an excursion site

for tourist but after that VinaPernLand resort was formed

and this reef was destroyed step by step and disappeared

completely during 2008 (figure 12)

Figure 12: Dam Gia Gorge in Nha Trang Bay before

(4/2004) and after (7/2007) build VinaPear Resort It

make to disappear 50 ha of coral reefs and 12 ha of sea

grass beds (after, T.P.H Son, et all 2007 [9])

Some coral sites in coastal waters of Vietnam such as Bai Tien – Duong De, Tam Island (Nha Trang Bay), My Giang (Van Phong Bay),… also lie in similar circumstance The dredging activities in marine ports and dredged material dumping can also cause the negative effects to coral reefs in coastal water

By mean of spectral analysis in an AVNIR2 scenes (date

17 July 2007) for extracting the bottom bathymetry in South of Nha Trang Bay (T.P.H.Son, et all 2007), we also fount simultaneously out the underwater “hills” (figure 13) They appear suddenly (July 2006) and were disappeared

in next year (19 May 2008)

Figure 13 The appearance of underwater “hills” in South of Nha Trang that formed from dredged material dumping (extract from AVNIR2 image)

They cause the siltation and server affect directly to fringing coral reefs in Mun, Mot, Tam Islands and also platform reef – Thuy Trieu Bank lie on Southern side The surveys from sediment traps in Nha Trang Bay (Latupov, Malyutin, 2006, [4], N.V.Long (cite from Son.T.P.H 2007 [9] also recorgnized these events

4 CONCLUSIONS

Base on the abundance satellite images include AVNIR2 mainly from JAXA – ALOS project and other sources such

as SPOT4-5, Formosat2, Landsat ETM+ as well as aerial photographs, the area and distributed maps of almost coral sites in coastal waters of Vietnam have been detected

In North side, include coral reefs in Coto archipelago (256 ha), Bach Long Vi ( 133 ha) and Con Co (72 ha)

In Central region, include the coral reefs in Cu lao Cham

archipelagos (165 ha), the coastal waters of Quang nam

province (95 ha), the coastal waters of Phu Yen province

(303 ha), the coastal waters of Khanh Hoa province (3266

ha) , the coastal waters of Ninh Thuan province (1000 ha)

In southern side and in Thailand Gulf (only in

Vietnamese territory), include coral reefs in Con Dao

archipelago (743 ha), An Thoi archipelago and Phu Quoc

Island (469 ha), Nam Du archipelago (242 ha) Tho Chu

archipelago (134 ha)

By mean of the remote sensing techniques, we also

detected the series of the evidences causing negative affects

to status of the coral health, those are:

The coral bleaching event and mass mortality of benthos

in Condao archipelago during Mid of October of 2005 and

also at March to June of 2010

The oil seep process in geothermal center and

acidification process in Phu Quy Island

The sediment and fresh water plume from river after big

flood event affect badly to status of coral health

The coastal development activities and their affect to

status of coral health

The reason causing above phenomenon related to

natural disaster, global climate change as well as

anthropogenic intervention

This report showed big potential for application of ALOS

imagery for monitoring the status of coral health in coastal

waters of Vietnam sea

6 REFERENCES

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corals and reef living features at Con Dao archipelago

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and P Teillet, 1985 Integration of the SPOT Panchromatic

Channel into its Multispectral Mode for Image Sharpness

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[3] Kleypas, J.A., R.A Feely, V.J Fabry, C Langdon, C.L

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[8] T.P.H Son, Lau Va Khin, Hoang Xuan Ben, Tan Chun Knee, Joji Ishizaka, Varis Ransi, Sarat Tripathy (2006) Discuss on the main reasons causing mass mortality of coral and benthos in Con Dao Island during October 2005 In Proceeding of 2006 NAGISA conference – Kobe – Japan [9] T.P.H Son, et all 2007, The status on distribution and biodiversity on coral reef in coastal water of Khanh Hoa province The final report of provincial project, Nha Trang,

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Acknowledgments

The authors thank Japan Aerospace Exploration Agency (JAXA) for supporting the ALOS-AVNIR2 satellite imageries under ALOS-PI 326 project; the United State Geological Survey (USGS) for LandSat ETM+ imagery and the National Aeronautics and Space Administration (NASA) for the MODIS imageries which contributed in this study