Nearly 80% of the species and over 90% of living coral cover were lost and some reefs were completely dead.. No coral recruitment was seen on completely dead reefs whereas there was litt
Trang 1Coral degradation and ability of rehabilitation of coral reefs
in Co To Archipelago, Quang Ninh province, Vietnam
, Nguyen Duc Cu, Dao Anh Tuyet
Institute of Marine Environment and Resources (IMER), Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet Str., Cau Giay Distr., Hanoi,
Viet Nam
a r t i c l e i n f o
Available online 25 April 2013
Keywords:
Coral degradation
Recovery
Growth rate
Transplant
a b s t r a c t
Serious degradation of coral reefs in the Co To Archipelago occurred from 2002 to 2006 Nearly 80% of the species and over 90% of living coral cover were lost and some reefs were completely dead Currently, the highest coral cover is only 7.5% where previously most of the reefs had over 50% live coral cover The cause of the reef degradation has been identified to be residues of cyanide used by local fishermen for fishing on reefs To overcome the consequences transplantation corals on natural and artificial shelters were attempted Survival rate on artificial shelters was 88.3% after 2 years and growth rate averaged 2.3 cm/year Transplanted corals on natural shelters had lower survival rate, 55.9% The natural recovery
of coral on degraded reefs was also monitored periodically in this study No coral recruitment was seen
on completely dead reefs whereas there was little new coral recruitment on reefs with some remaining live corals
&2013 Elsevier Ltd All rights reserved
1 Introduction
Serious degradation has been observed on many coral reefs
worldwide For more than a decade area, coverage and number of
species have been reduced (McClanahan, 2002; Wilkinson, 2004,
2008;Lough and Van Oppen, 2009) Many causes for this decline
have been described from different regions, e.g increasing seawater
temperature (Anthony et al., 2007), sedimentation (Hernandez et al.,
2009), freshwater runoff (Tuan et al., 2008), dynamite fishing
(McManus et al., 1997) Following these phenomena some reefs can
self-recover (Hughes et al., 2010;Sheppard et al., 2008;Halford et al.,
2004) some need help from artificial restoration and others were
unable to restore because substrate or environment was not suitable
for coral growth (Fabricius, 2005;Scheffer et al., 2001,Hughes, 1994,
Hughes et al., 2010) Application of transplanting on artificial and
natural shelters for coral restoration has been successful in many
areas of the world (Clark and Edwards, 1994;Rinkevich, 2005;Quan
and Ngai, 2008) The restoration methods included: physical,
biolo-gical, and dual restoration (combination of biological and physical
restoration) (Job et al., 2003) Depending on the specific conditions of
each area the most suitable methods for rehabilitation may be
chosen The most widely used methods are the reefball and natural
shelters (Rinkevich, 2000)
Almost all coral reefs in Co To Islands died between 2002 and
2006 In recent years, though the water seems clean, the bottom
substrate is dead coral rock and sand and very little coral has
recruited here The purpose of this study was to examine the natural recovery of coral on degraded reefs and carry out experi-ments to test for survival and growth rate of corals on natural and artificial shelters in order to develop a management plan for effective protection and restoration of coral reefs
2 Research methods
2.1 Study area
Co To Archipelago belongs to Quang Ninh province, in northern Vietnam, about 50 km from the mainland (20156′00″–21104′00″N and 107144′00″–107152′00″E), with more than 15 islands The total area of Co To Islands is 46.2 km² A population of 5195 people (in 2006) live mainly on capture fishery and agriculture This area has favorable natural conditions for reef development such as: warm and clear water, high salinity, hard substrate Therefore, coral ecosystems are developed with over 100 species of hard corals, high coverage and the biggest reef in northern Vietnam The Islands have high biodiversity including many valuable and commercial species for example reef fishes, abalone, sea cucumber, pearl oyster Additionally this area is an important fishing ground and seed is dispersed to nearby coastal areas (WWF, 1994) Therefore, Co To Islands have been considered for a list of 15 marine protected areas in Vietnam
2.2 Method of determining the status and degradation of coral
The overall status of coral reefs in the Co To was surveyed by using a small boat pulling the observer on the water surface above
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Deep-Sea Research II
0967-0645/$ - see front matter & 2013 Elsevier Ltd All rights reserved.
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n Corresponding author.
E-mail addresses: ngaind@imer.ac.vn, ngaind@yahoo.com (N.D Ngai).
Trang 2the reefs to observe and record the data on living coral, dead coral,
soft coral and macro-benthos (English et al., 1997) and then select
sites to beused for specific survey by point transect method to get
data on each component of substrate, coral fishes and other
benthic communities (Hodgson et al., 2004) During the survey
we focused on the status of coral death and the cause of death
− Local fishermen were internviewed to find out the cause of
death of corals in this area Questionnaires focused on
produc-tion, the target species of exploitaproduc-tion, exploitation methods,
fishing gears, etc
− The environmental parameters were periodically monitored at
three study sites (Trau Khe, Thanh Mai, Dang Van Chau) in 2008,
2009 and 2010 Each year the three sites were monitored for three
days Measurement directly and samples for analysis were
collected at the surface and bottom 6 times/24 h Field parameters
such as salinity were measured by refractometer, temperature
and DO was measured by a DO meter, pH was measured by pH
meter OKATON, transparency was measured by secchi disk The
samples for nutrient, cyanide, pesticide and other water quality
measurements were collected at each site at both surface and
bottom layer, fixed by suitable chemicals and analyzed in the
laboratory In order to assess status of water environmental
quality, measurements were compared to promulgated standards
of Vietnam and Asian countries (Table 1)
2.3 Method of monitoring the natural recovery
− Growth of natural corals was monitored by attaching labels on
several colonies and measures them periodically A total of 12
coral colonies were marked and measured one time a year by
fiberglass ruler over colony at each site from 2008 to 2010
− The recruitment of coral juveniles was monitored and observed
on transect lines with length of 20 m at 5 reefs (Fig 1), observing
and counting the number of small coral colonies, less than 5 cm
of coral, within 2.5 m on each side of the transect The reefs were
selected for monitoring at different places (in and outside Co To
bay, on reefs with living coral and without living coral)
2.4 Transplanting coral
Two types of shelters were applied for transplanting corals
− Concrete reefballs (Reef Ball Foundation, 2008;Precht, 2006)
were designed for transplanting coral colonies with
measure-ments: 1 m in diameter, 0.8 m high, with 14–16 holes, diameter
of holes from 5 to 12 cm of which eight holes were used for
planting corals and the remaining 6–8 holes were left for
organisms to get in and out The reefball can be placed on
sand or rubble bottom Coral pieces were tied on the shelter by
fishing line and then the reefball was dropped into the sea
− Natural shelter: This kind of shelter took advantage of the dead coral rock Steel nails about 15 cm long and pointed at one end were driven 5–10 cm into coral rock, and coral fragments were tied on by plastic rope
− Coral seed was taken from donor reefs around the Co To area, most of them were massive, encrusting and laminae No branching corals were included because they were completely dead in the area Coral seed was placed in water containers with aero pump Coral colonies were then cut into small pieces with a size of 5–15 cm
3 Results and discussion
3.1 The degradation and current status of coral in Co To
Co To Archipelago has natural and environmental conditions suitable for the growth of coral A total of 114 species, 37 genera and 13 families have been found in the area (WWF, 1994) According to WWF′s experts, at that time, corals had high species richness and abundance, and the most common species belonged
to the branching coral genus Acropora, which are rapid growing
and dominant on reef Hong Van reef was the largest coral reef not only in Co To but also in the North of Vietnam with a length of
5 km and 1 km in width with high coral cover The area around the Dang Van Chau Island and southwest Thanh Lan Island had the highest coral coverage (classified as very good and excellent reef) Biological resources on the reefs were also very rich, notably sea cucumbers, cone snails, pearl oysters, and abalone
When the survey was repeated in 2003 on most reefs many newly dead corals that still retained their shape were seen, most of which were branching corals Live coral cover and species number were reduced when compared to previous results At the same time the number of species of valuable economic resources, sea cucumber and abalone were also greatly reduced
In 2008 most coral reefs in this area had died completely, only a few reefs with sparse coral cover were left Generally loss was about 80% of the number of species and about 90% of the reef area (Fig 2) This is the greatest and fastest degradation recorded in the coastal areas of Vietnam On the reef only coral rock and sand was found, some covered with seaweed The Hong Van, Bac Van reef, which has been considered the biggest and most beautiful reef in the north of Vietnam was now completely dead, and the other reefs around the island Co To Lon, Dang Van Chau, Khe Trau were
in the same condition Especially, no branching corals were found
in the region—the most common species in the Co To before Some surviving corals were massive, encrusting and laminae that were scattered in the south of Khe Trau, Thanh Mai, Dang Van Chau,
Co To Con with a very low density Distance between remaining colonies was between 3 and 4 m, and colonies were small size, about 20–40 cm
The number of coral species in the Co To at present is very low,
in total 24 species of hard corals and one species of soft coral were found The distribution of species varied among reefs, most reefs had only single species In Dang Van Chau Island the only species
were Turbinaria peltata and Goniopora lobata, in Thanh Mai it was
Plesiastrea versipora The North Trau Khe was more varied, species
included Galaxea, Favia, Goniopora, Porites but Goniastrea was most
abundant At this time six reefs were surveyed for coral cover but two reefs had no living coral (Hong Van and North Khe Trau), two reefs were very sparse in living coral of small size (Dang Van Chau and Thanh Mai) Coral cover was higher south of Khe Trau and Co
To Con Island (from 3.5 to 7.5%), most colonies were small On all reefs the coverage of dead coral was high, 40–85% (Table 2,Fig 4)
Table 1
Water quality criteria for coastal environment and aquaculture.
(Source:Ministry of Environment and Resources, 2008 ).
a ASEAN
Trang 33.2 Causes of coral degradation
To find the cause of coral death, the results of field studies,
monitoring of environmental factors and information from
fisher-men on the archipelago have been combined:
Analysis of water quality in this area showed that the
tempera-ture over two seasons ranged from 21.1 to 31 1C, average 25.0 1C in
surface water and at the bottom ranged from 21.3 to 30.3 1C,
average 24.3 1C Salinity was high and relatively stable, ranging
from 30.0 to 33.0‰ for surface water and from 31.5 to 33.0‰ at the
bottom; pH ranged from 8.00 to 8.36 Dissolved oxygen
concen-tration was high, surface values ranged between 6.38 and
6.64 mgO2/L, average 6.49 mgO2/L, bottom values from 5.79 to
6.42 mgO2/L, average 6.14 mgO2/L Turbidity was low, surface layer
ranged from 1.00 to 6.61 NTU, 3.72 NTU on average, and bottom
range from 2.19 to 14.22 NTU, average 7.05 NTU
Concentrations of nutrients (ammonium, phosphate, nitrate,
nitrite), organic matter (BOD5, COD), pesticide were within
accep-table limits according to Vietnam′s water quality standards The
most notable exception was the concentration of cyanide in the water, which was very high, sometime exceeding the permitted standards (5 μg/L) Specifically, at the monitoring stations the cyanide concentration ranged from 4.13 to 5.72 μg/L, average 4.95 μg/L, bottom concentration higher than in the surface layer While cyanide concentration in water based on standard from developed countries is 1 μg/L Cyanide is one of the most poiso-nous chemicals and is highly toxic to both humans and animals, causing death even in trace amounts Cyanide does not occur in nature, but is created by technology and industry and mostly applied in large volumes for ferrous metallurgy such as gold ore and metal plating technology (Fig 3)
The information obtained from interviewing fishermen on the island show that during the years 2002–2006 about 100 diving boats would regularly exploit fishes around the islands Especially they used cyanide to catch fish on the reefs There are no monitoring data from this period, but each diver used several to
10 kg of cyanide powder per day Residue of cyanide in the water has killed high numbers of corals, particular sensitive species like
Acropora In recent years fishermen have not used cyanide to catch
fish so the trend of cyanide concentration in the water should be going down but is still high
In the survey trips we observed dead corals still retaining their shapes and unbroken unlike those killed by explosion or strong waves Combined with the above findings it can be concluded that dead coral in Co To is due to the exploitation of marine resources
by toxic cyanide in the period 2002–2006 Presently the fishermen
do not use this method because fish stocks have been depleted and coral ecosystems have been killed so the fishes have lost their habitat
3.3 Natural recovery
Results of monitoring the coral recovery through recruitment of juveniles at five reefs have been compiled inTable 3 Reefs with
Fig 1 Location of Co To Archipelago and studied sites.
0
10
20
30
40
50
60
70
Fig 2 Decrease of living coral cover over time.
Trang 4few live coral colonies had low settlement rate from 1–2 colonies/
year, while reefs which had more living coral had higher rates of
coral recruitment from 23–28 colonies/100 m2/year (Fig 5) Three
reefs with no living corals had no recruitment of juvenile corals after two monitoring years as seen in North Khe Trau, Thanh Mai and Dang Van Chau The most likely reason for this is that there
was no in-situ source of larvae so that they must depend on ex-situ
larvae supply and only small coral areas are available nearby On the other hand these reefs may be seriously affected by cyanide in sediment and dead coral rock and the available coral larvae may have died after settlement on bottom
The natural recovery of the coral colonies is still going on at almost all of the surveyed sites through slow growth of the surviving coral colonies Monitoring the growth rate of some coral colonies on reefs showed that growth of coral in this area was the same as in other areas and as growth of corals in general Most corals have growth rates from 2 to 3 cm/year (Table 4) The lowest
growth rate is about 1 cm/year in the genus Porites Particularly slow growth is seen in the species Pseudosiderastrea tayami which
only grows 0.5 cm/year due to the small size of this species, the largest colony having a maximum size of only about 16 cm (Veron,
2000)
Although concentration of cyanide in the water remains high the natural recovery of coral reefs through growth of remaining
0
5
10
15
20
25
30
35
Mar
2008
Jul 2008 Dec
2008 Mar 2009 Aug 2009 Dec 2009 Mar 2010 Sep 2010
0
10
20
30
40
50
60
Mar
2008
Jul 2008 Dec 2008 Mar 2009 Aug 2009 Dec2009 Mar 2010 Sep 2010
0
1
2
3
4
5
6
7
Mar
2008
Jul 2008 Dec
2008 Mar 2009 Aug 2009 Dec 2009 Mar 2010 Sep 2010
Fig 3 Concentration of environmental parameters monitored at field from
2008–2010.
Fig 4 Dead coral reef in Co To Islands.
Fig 5 Settlement of juveniles on bottom.
Fig 6 Coral colonies transplanted on reefball after 3 months.
Table 2 Coverage (%) of substrate on the reef in 2008.
Reef name Hard
coral Soft coral Dead coral Rock Sand Rubble Sponge
Northwest Khe Trau
Trang 5colonies and recruitment of new juveniles still occurs at slow
speed Unfortunately, the branching coral species which have
rapid growth rates do not exist anymore in the Co To region and
thus rehabilitation will happen slowly by massive, encrusting,
laminae corals
3.4 Artificial restoration on shelters
A total of 130 reefballs were used for transplanting coral at
3 sites (Fig 6) Survival rate and growth of corals were monitires
on 29 reefballs with 231 colonies The survival rate of corals
growing on reefballs was very high, reaching over 95% in the first
year and 88.3% after 2 years (Table 5) Coral colonies died mainly
from shock during the separation processing into smaller colonies
and some colonies were lost from the shelters due to poor
attachment in the first year In the second year the transplanted
coral had grown normally, they were adhering to shelters and covering plastic rope tightly Unfortunately, a bloom of the coral
predator, the snail Drupella sp., occurred in the Co To area They
often assemble in small groups of 5–10 individuals and eat coral tissue and therefore survival rate of coral was reduced in the second year
For coral colonies that were transplanted on coral rock by using steel nails driven into the substrate and tied by plastic rope, about
93 colonies were monitored for survival rate The fraction of surviving coral was low, the main reason being that fixation of coral pieces on to shelter was not tight enough and tying was more difficult for massive and laminae shape when tying under water
On the other hand the appearance of the snail Drupella was the
biggest threat to the new coral transplanted on this substrate because they are easy to access and the injuries of the coral colonies after the separation process attracted the snail predators The rate of survival of these corals was 55.9% after 2 years (Table 6)
Therefore, artificial coral restoration can be carried out on a large scale on the degraded reefs in the Co To archipelago both on natural and artificial shelters Growth of corals on the reefball has many advantages when compared to the natural shelter: high survival rate, easier to handle, lower rate of detachment and predation by snails When carrying out transplanting on large scale it should be noted that the donor reefs are now sparse in live corals so that transplantation may affect the donor reef, and the
Table 3
Number of juvenile coral settlement on reef.
Table 4
Measurement of natural coral colonies (cm).
size 8/2008
Increase 9/2009a
Increase 9/2010a
Pseudosiderastrea
tayami
a Measured by fiberglass tape over colonies.
Table 5
Ratio (%) of live coral transplanted on reefball.
Species name Number of coral
colony
Average measurement (cm) a
Growth rate/year (cm) a
Number of colony eaten by predator and detached
Survival ratio (%)
a Measured by fiberglass tape over colonies.
Table 6 Survival ratio of transplanted coral on natural shelters.
of coral colony
Average measurement (cm) a
Growth rate/
year (cm)
Number of colony eaten by predator and detached
Survival ratio (%)
Plesiastrea versipora
Echinophyllia aspera
Goniopora columna
Turbinaria peltata
Galaxea fascicularis
Goniastrea favulus
a Measured by fiberglass tape over colonies.
Trang 6outbreak of the predator snail Drupella sp is the biggest threat to
transplanted corals
4 Conclusions
The degradation of coral reefs in the Co To Archipelago was
very serious It occurred mainly in the period from 2002 to 2006
and has reduced the number of species from 127 to 25 Nearly 80%
of species, 90% of live coral cover, and 100% of some reefs were
lost Currently the highest coral coverage in the Co To area is 7.5%
whereas previously most of the reefs had coverage of at least 50%
Research results have identified the cause of coral death to be coral
fishermen using cyanide poison to catch coral fishes for a long
time Residues of cyanide also killed coral on a large scale
especially branching coral Acropora that are very sensitive to
environmental changes has been killed completely Monitoring
showed that the natural recovery of corals is taking place slowly
On the completely dead reefs there is no recovery of corals due to
no source of larvae within these reefs, whereas on some living
coral reefs the coral recruitment is high Restoration of corals by
transplanting on two types of shelters resulted in significant
differences in survival rates For corals growing on the reefballs
survival rate was higher than on natural substrates (88.3% and
55.9% respectively) because it was easier to tie the massive and
laminae corals on reefballs than on natural shelters, which
reduced the accessibility of attack of predator This opens up
prospects for artificial restoration of coral reefs in this area if we
can control the amount of predation by the snail Drupella sp.
Acknowledgments
This work is supported by KC.09.07/11-15 program (Littoral
ecosystems in the north of Vietnam Project) and People′s
Com-mittee of Quang Ninh province We are very grateful to all our
colleagues for their hard work in the field to install experiments
and monitor water environment in Co To Islands We also thank
Prof Jing Zhang, who is leader of CoReCAP Project (IOC/WESTPAC)
encouraged us to submit this paper And many thanks to Dr Kathe
Rose Jensen for editing the English language We also thank the
anonymous reviewers for their pertinent and helpful comments
References
Anthony, K.R.N., Connolly, S.R., Hoegh-Guldberg, O., 2007 Bleaching, energetics,
and coral mortality risk: effects of temperature, light, and Sediment regime.
Limnol Oceanogr 52 (2), 716–726
Clark, S., Edwards, A.J., 1994 Use of artificial reef structures to rehabilitate reef flats
degraded by coral mining in the Maldives Bull Mar Sci 55, 724–744
English, S., Wilkinson, C., Baker, V., 1997 Survey Manual for Tropical Marine Resources Australian Instistute of Marine Science
Fabricius, K.E., 2005 Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis Mar Pollut Bull 50, 125–146
Halford, A., Cheal, A.J., Ryan, D., Williams, D.M., 2004 Resilience to large-scale disturbance in coral and fish assemblages on the Great Barrier Reef Ecology 85, 1892–1905
Hernandez, R., Sherman, C., Weil, E., Yoshioka, P., 2009 Spatial and temporal patterns in reef sediment accumulation and composition, southwestern insular shelf of Puerto Rico Caribb J Sci 45 (2–3), 38–150
Hodgson, G., Kiene, W., Mihaly, J., Liebeler, J., Shuman, C., Maun, L., 2004 Reef Check Instruction Manual: A Guide to Reef Check Coral Reef Monitoring, Published by Reef Check, Institute of the Environment, University of California
at Los Angeles
Hughes, T.P., Graham, N.A.J., Jackson, J.B.C., Mumby, P.J., Steneck, R.S., 2010 Rising to the challenge of sustaining coral reef resilience Trends Ecol Evol 25, 633–642
Hughes, T.P., 1994 Catastrophes, phase-shifts, and large-scale degradationof a Caribbean coral-reef Science 265, 1547–1551
Job, S., Schrimm, M., Morancy, R., 2003 Reef Restoration: Practical guide for management and decision-making Carex Environnement, Ministère de l′ Écologie et du Développement Durable IFRECOR, 32p.
Lough, J.M., Van Oppen, M.J.H., 2009 Coral Bleaching: Patterns, Processes, Causes and Consequences Ecological Studies, 205 Springer178
McClanahan, T.R., 2002 The near future of coral reefs Environ Conserv 29, 460–483
McManus, J.W., Reyes, R.B., Cleto, L.N., 1997 Effects of Some destructive fishing methods on coral cover and potential rates of recovery Environ Manage 21 (1), 69–78
Ministry of Environment and Resources, 2008 National Standard on Environment Socio-Labor Publisher, Ha Noi, Vietnam
Precht, W.F., 2006 Coral Reef Restoration Handbook CRC Press Taylor & Francis Group (351p)
Quan, N.V, Ngai, N.D., 2008 The coral transplantation experiment contributes a tool for rehabilitation of degraded coral reefs in Ha Long Ba natural world heritage site, Vietnam In: Proceeding of 4 th Global Conference on Oceans, Coasts and Islands p 116–122.
Reef Ball Foundation, 2008 A Step-by-step Guide for Grassroots Efforts to Reef Rehabilitation A Publication of the Reef Ball Foundation134
Rinkevich, B., 2000 Steps towards the evaluation of coral reef restoration by using small branch fragments Mar Biol 136, 807–812
Rinkevich, B., 2005 Conservation of coral reefs through active restoration mea-sures: recent approaches and last decade progress Environ Sci Technol 39, 4333–4342
Scheffer, M., Carpenter, S., Foley, J.A., Folke, C., Walker, B., 2001 Catastrophic shifts
in ecosystems Nature 413, 591–596
Sheppard, C.R.C, Harris, A., Sheppard, A.L.S., 2008 Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean Mar Ecol Prog Ser 362, 109–117
Tuan, V.S., Ben, H.X., Hoang, P.K., 2008 Mass mortality of corals and reef living features at Con Dao archipelago (Vietnam) in October 2005 J Mar Sci Technol.
8 (1), 59–70
Veron, J E N., 2000 Corals of the World Institute of Marine Science, Australia vols.
1, 2, and 3.
Wilkinson, C., 2004 Status of Coral Reefs of the World: 2004 Vol 1,2 Global Coral Reef Monitoring Network and Reef and Rainforest Research Centre, Townsville, Australia.
Wilkinson, C., 2008 Status of Coral Reefs of the World: 2008 Global Coral Reef Monitoring Network and Reef and Rainforest Research Centre, Townsville, Australia, 296p.
WWF Vietnam Marine Conservation Northern Survey Team, 1994 Survey Report on the Biodiversity Resource Utilization and Conservation Potential of Co to Island, Quanh Ninh, North Viet Nam74