Promoting recruitment of scieractinian corals using artificial substrate in the Gill Indah, Lombok Barat, Indonesia

Abstract

Coral reef destruction widespread gradually all over Indonesian waters. while available technologies in coral reef rehabilitation is impractical and very expensive. The present study is aimed to develop a new practical and inexpensive technology in coral reef rehabilitation. The technology that will be developed is to promote natural recruitment of scleractinian corals and to minimize post-settlement mortality by providing small concrete blocks. The study was carried out in a marine tourism park (TWAL) Gili Indah consisting of three small islands: Gili Air, Gili Meno and Gill Trawangan, in the Regency of Lombok Barat. Results of this study show that introducing small concrete blocks (30xl5x20 cm', LW H) can increase the abundance of coral recruits after 16 months period. The abundance of recruits in Gili Meno is lower than those in Gill Air, beside the fact that Gill Meno has higher coral cover and lower rate of sedimentation. Interaction effects between treatment and island is not significant, neither are between treatment and depth, between depth and island, and among treatment, depth and island. The results suggest that introduction of small concrete blocks can be used to promote coral reef recovery. Recruits of Acroporidae dominated the taxes of recruitment, followed by Pocilloporidae and Poritidae.

Full text

Proceedings 9'" International Coral Reef Symposium, Bali, Indonesia 23-27 October 2000,
Vol. 1
Promoting recruitment of scieractinian corals using artificial substrate in the
Gill Indah, Lombok Barat, Indonesia.
Imam Bachtiar
l
ABSTRACT
Coral reef destruction widespread gradually all over Indonesian waters. while available technologies in coral reef
rehabilitation is impractical and very expensive. The present study is aimed to develop a new practical and
inexpensive technology in coral reef rehabilitation. The technology that will be developed is to promote natural
recruitment of scleractinian corals and to minimize post-settlement mortality by providing small concrete blocks. The
study was carried out in a marine tourism park (TWAL) Gili Indah consisting of three small islands: Gili Air, Gili
Meno and Gill Trawangan, in the Regency of Lombok Barat. Results of this study show that introducing small
concrete blocks (30xl5x20 cm', LW H) can increase the abundance of coral recruits after 16 months period. The
abundance of recruits in Gili Meno is lower than those in Gill Air, beside the fact that Gill Meno has higher coral
cover and lower rate of sedimentation. Interaction effects between treatment and island is not significant, neither are
between treatment and depth, between depth and island, and among treatment, depth and island. The results suggest
that introduction of small concrete blocks can be used to promote coral reef recovery. Recruits of Acroporidae
dominated the taxes of recruitment, followed by Pocilloporidae and Poritidae.
Keywords 'Scleractinian coral, Coral reef, Recruitment,
Rehabilitation, Settlement, Lombok.
Introduction
Coral reef is one of the most important tourism assets
of Lombok Barat (Western Lombok). Coral bleaching
caused by El Nino 1998 have killed most corals in the
Lombok Strait, leaving coral reefs in very bad conditions.
Coral cover have been drastically reduced from 60-80%
down to <10% in most locations (unpublished data). At
present, however, technology developed for coral reef
rehabilitation is
not
much applicable for developing
country, like Indonesia. Coral transplantation (Harriot and
Fisk 1988), for example, is too expensive and impractical.
The degraded reefs arc far from the source reefs.
Technology of coral juvenile transplantation (Raymundo
et al. 1999) is also too complicated. Since such techno-
logy requires
marine laboratory and understanding of
spawning seasons, coral juvenile transplantation is very
unlikely to be applied in Lombok waters and many other
locations in Indonesia. Therefore, it is urgently needed to
develop a new technology that is more. practical. and
inexpensive.
The conventional method that keeping away the target
coral reef from any human disturbance is very practical,
as it does not need special expertise and equipment. In
most cases, coral recovery is
very
slow. In Indonesia,
however, this method could be very useful. In a coral reef
destroyed by lava eruption in Banda Island,
-
for example,
coral cover has returned in five years period (Tomascik et
al. 1996). Therefore, it is important to modify this natural
additional substrate method to improve coral recruitment.
Natural coral recruitment is influenced by sedimen-
tation (Hodgson 1990, Babcock and Davies 1991), type of
substrate (Harriot and Fisk 1987), algal competition
(Gleason 1996), competition with other epifauna (Harriot
and
Banks 1995, Atrigenio and Alino 1996), and
pollution (Kuhsmaro et al. 1997). Among the five factors
known influencing coral recruitment, we could reduce the
effect
of sedimentation and provide the availability of
suitable substrates, to promote (fasten)'coral recruitment.
Small-size concrete blocks may promote the rate of
coral recruitment.
The blocks may provide additional .
suitable space for planullae to settle-down and then
undergoing metamorphosis into a new colony. The blocks
may also reduce the effect of sedimentation, as the
planullae may settle down on the vertical sides whenever
the horizontal sides are badly covered by sediment. If this
hypothesis is true, the technology will be very practical,
as there is no need special expertise or special facilities
(equipment).
So far, studies on coral recruitment were to look at
recruitment pattern on natural substrate (Hughes 1985,
Smith 1997), or on artificial settlement plates (Fisk and
Harriot 1990, Banks and Harriot 1996), or natural set-
tlement plate (Wallace 1985, Sammarco 1991). Thong-
tham and Chansang (1999) studied coral recruitment both
in
natural and artificial substrates using cylinders of
concrete
modules. They found that coral settlement and
growth were relatively high in the modules than in the
natural substrate. Since the study did not use permanent
quadrates, their conclusions required further clarification.
The present study is looking at recruitment on natural
and artificial substrates, to determine the effectiveness of
introducing concrete blocks to promote coral recruitment.
The choice of simple concrete blocks in this experiment is
due to its practical in handling and building it, when this
technology to be used in a real rehabilitation purposes.
Universias Mataram, Jl. Majapahit 62. Mataram 83125, Indonesia Phone: +62+370+623873, Fax: +62+370+636918
Email address: ibachtiar@hotmail,com
425

Materials and methods
Location
of
study
sites
The study was conducted at the Gill Indah Islands,
Lombok Barat (Western Lombok). The Gill Indah
consisting of three islands, i.e. Gill Air, Gill Meno and
Gili Trawangan, is a marine tourism park since 1993
(Fig. I).
FLORES SEA
Fig I. Location of study, Marine Tourism Park Gill Indah
of Lombok Barat Regency, Indonesia. Location of reefs
studied are marked with GA, GM and GT. The expe-
ri
ments in the GA2, GM2, and GT2 are omitted due to
loses of experimental and control quadrates at five meter
depth. Positions of GAI, GMI, and GT1 respectively are
S 08°20.902' E 116
0
04.808
1
,
S 08
0
20.384' E 116°03.374',
S 08°20.263' E 116
0
02.270
1
.
Study out-line
At each island, two locations were chosen: exposed
(windward) and sheltered (seaward) sides. At each
location, 24 quadrates (1x1 m
s
)
were nailed down the reef
slope in parallel direction to the coastline, 12 quadrates at
about 5 m depth and other 12 quadrates at 12 m depth.
Among the 12 quadrates, six of them have 4 concrete
blocks (size: 30x15x20. cro
s
,
LWH) and other six
quadrates without blocks are set as control. The experi-
mental (with concrete blocks) and the control quadrates
were placed alternately. Space between quadrates was
about 4 meters. The concrete block was made of cements,
gravel (small volcanic stones) and sands in the proportion
of 1:2:3.
Coral recruit
within quadrate was counted before
experiment and recounted on the eleventh months and on
the sixteenth months afterwards. Coral recruit is defined
as a single colony growing from larval settlement. It
usually can be distinguished from asexual recruit on its
basal plate. Since most corals; including recruits, are dead
during the 1998 El-Nino, the recruit from larval
settlement was obviously different from that of asexual
one. Sometimes, recruits of
Seriatophora hystrix
and S.
caliendrum
are very difficult to be decided into larval or
asexual recruits. On this occasion, the recruits are ignored
during the census. When the recruits of the two corals are
ve
ry obviously from the sexual one, such recruits were
counted. Before the experiment, 42 recruits were counted
in experimental quadrates and 13 recruits on the control
ones.
Environmental factors monitored was sedimentation,
salinity, temperature and biotic factors. Sedimentation
was monitored every month using sediment traps (English
et al. 1994). Temperature and salinity were measured in
situ using a handheld CTS (YSI type 30). Biotic factors
monitored were reef substrate and benthic coverage that
potentially affecting larval settlement and its recruitment.
Data analysis
All data are analyzed using a three factor analysis of
variance (ANOVA) type A.3 (Zar 1984). All the three
factors are fixed, i.e. treatment, depth and island. On the
sheltered (south) location, nearly all concrete blocks on
the 5 meter depth are removed by wave actions that the
position of quadrates can no longer be recognized. Recruit
data on the south location are not analyzed, therefore, and
location factor is considered not one of the factors
studied. Data randomness is found considerably low due
to the high frequency of zero (0) on the data. Data
transformation log (x+l) was carried out to improve data
randomness.
Results
There were 54 colonies counted within 72 quadrates
on the first observation (March 2000). This number
increased considerably to 124 colonies on the second
observation (August 2000). In the Gill Air (GA) and Gill
Meno (GM) the increase was high, from 14 to 59 and
from 7 to 24 colonies (within 24 quadrates) respectively.
In
the Gill
Trawangan (GT), the increase was
considerably small, from 33 to 41 colonies.
Major taxa of the recruits are Acroporidae, followed
by
Pocilloporidae
and
Poritidae.
The
Acroporidae
contribute nearly 50% of the recruit taxa. In the taxa
Acroporidae, the genus Acropora
has higher number of
recruits than the genus
Montipora.
Experimental versus control quadrates
In the first observation, February 2000, the number of
recruit was not different between the experimental and
control quadrates (Table 1).
426

Table 1. Three factor, fixed model ANOVA on recruit abundance
in the Gili Indah
Islands.
Data were log (x+l)
transformed to homogenize the variance
and to conform
to normal distribution
(Wilk-Saphiro
test
0.67, Bartlett's
test
O2:0.04, P=0.83). df F Ratio PSource
of variation Mean
square
Trcatn€nt
D+th
Island
Tearment*Depth
Treafinentrlsland
Depth*Island
Treatnentr Deptltr
Island
Residual
0.0007
0.18329
0.36352
0.16378
0.03913
0.00434
0.12748
0.05796
n.s.
n.s.
0.003
n.s.
n.s.
n.s.
n.s,
l 0.01
l 3.16
2 6.27
I 2.83
2 2.83
2 0.68
2 0.07
55 2.2
Table 2. Three factor, fixed model ANOVA on recruit abundance
in the Gili Indah
Islands.
Data were log (x+l)
transformed
to homogenize the variance
and
to conform
to normal distribution
(Wilk-saphiro
test
0.87, Bartlett's
test
lD2=0.01,
P=0.94). Sqnceof va'iation tvtm square df FRatio P
Treafrst
D#h
Islard
Teanrnt*Depth
Treafrglt*Islard
Dflr*Island
Treatrutt*@h*Island
05wr2 I
0.01323 I
o.259l7 2
o.fitn I
0.tn37 2
0.10637 2
0.06809 2
7.59 0.0078
0.17 n$
3.35 0.OtO8
1.4 n.s.
1.59 ns.
1.38 n.s.
0.88 n.s.
At the experimental quadrates, the average of recruit
abundance (tlSE) wai about 0.8210.26 iolonies rr2,
while at the control quadr^ates recruit abundance was
about 0.79+0.31
colonies m-' (Fig. 2A).
ExperimsnLl
Fig. 2. Comparison
of recruit abundance
(tl SE) between
experimental and control quadrates in two consecutive
observations.
In the second observation, however, there was a
significant different on recruit abundance between
experimental and control quadrates (Table 2). In the
experimental quadrates,
the number of recruit is higher
than that in the control quadrates (Fig. 2 B). In the
experimental quadrates recruit abundance were about
2.25r:0,39 colonies m-2, while in the contol quadrates
recruit abundance
were about l.19+0.28 colonies
m-'.
Five
meter
versus
12
meter
depths.
In the first observation, there was no significant
difference
of coral recruits
between
in 5 and 12 meter
depths
(Table
l). At 5 meter
depth, recruit
abundance
was
about 1.12+0.37
colonies
m-2.
While at 12
meter
depth,
recruit abundance was
about
0.51+0.17
colonies
m', 1Fig.
3A)
i Ai. G Mono G Tmngan
Fig 3. Comparison of recruit
abundance
(tl SE)
between
two depths
in two consecutive
observations.
In the second observation,
August
2000,
neither
was
significant difference on recruit abundance
5 meter and
12
meter depths
(Table
2). At the 5 meter
depth,
recruit
abundance
was
about
1.81+0.35 colonies
m'2. while
at
the
E2
t
E
!z
A
o
E
2.
p1
0
GAir GMcno GTrmngm
427

10 meter depth was about 1 .63+0
.36 colonies
m
-2
.
Fig
.
3
shows that the
.rate of recruitment at 12 meters depth i
s
higher than at 5 meters depth between two observation
s
period
.
Gill Air (GA) versus Gili Meno (GM) versus Gil
l
Trawangan (GT) island
s
In .the first observation, the abundance of recruits a
t
GM was significantly lower than those at GT (Table 1)
.
While recruit abundance at GA were about the same wit
h
those at either GM or GT (Fig
. 4A )
. At GM, the averag
e
of recruit abundance was about 0
.29+0
.18 colonies
m
2
,
while at GA and GT were 0
.61+_0
.21 colonies n f
'
an
d
1
.65+0
.55 colonies
m
2
respectively
.
Environmental factors
.
Sedimentation monitoring over the period of Augus
t
1999 to February 2000 show that the lowest sedimen-
tation rate was found in the GM (Fig
. 5)
. Th
e
sedimentation rate in the GA and GT is significantl
y
higher than that in the GA (F=7
.37, df=2, P<0
.01)
.
Sedimentation rate between GT and GA is about th
e
same, 1
.87±0
.36 mg
cm
2
day
'
and 2
.02±0
.43 mg cm"
'
day
'
(± I SE) respectively, while in the GM, sedimen-
tation rate is about 0
.71±0
.21 mg cm'
2
day'
.
GAM

GMeno - GTrawangan
0
G Air

G Mono G Trawanga
n
G
ar

GMeno GTrawanaa
n
Fig 4
. Comparison of recruit abundance (±1 SE) amon
g
three islands in two consecutive observations
.
In the second observation, recruit abundance was var
y
among the three islands (Table 2)
. In the GM, recrui
t
abundance is significantly lower than that in the GA, bu
t
recruit abundance in the GT is about the same with thos
e
in the GM and GA (HSD test, Q=3
.396, df=62, P<0
.05)
.
Recruit abundance in the GA, GM and GT is abou
t
2
.46+0
.53 colonies m'
2
, 1
.0+0
.25 colonies
m
2
,
an
d
1
.71+0
.42 colonies
m
2
respectively
. Figure 4 shows tha
t
the rate of recruitment in the GA is higher than at the G
M
and GT during the period of February to August 2000
. I
n
the GT, the rate recruitment was likely the slowes
t
between the two periods
.
Interaction effects
.
There were no significant interaction effects betwee
n
treatment and depth, treatment and island, depth an
d
island, and among treatment, depth and island
. Th
e
absence of interaction effects was found either in the firs
t
or in the second observations (Table 1, Table 2)
.
Fig 5
. Comparison of sedimentation rate (±1 SE) among
'
three islands
.
Between experimental and control quadrates, th
e
proportion of benthic coverage is relatively the same
,
except the proportion of concrete blocks
. The difference
s
on benthic covers among the three islands were mainly o
n
the coverage of hard corals, algae, rubble and rock
. Gil
i
Air is high in rubble coverage, Gili Meno is high in alga
l
coverage as well as hard corals, while Gili Trawangan i
s
rich with rock coverage
. In the 5 meter depth, th
e
proportion of sand and hard corals (non-acropora) ar
e
higher than those in 12 meter depth
. Sponges and alga
l
coverages are found higher at 12 meter than at five mete r
depths
.
Discussio
n
On the first observation, recruit abundance was abou
t
the same between experimental and control quadrates . O n
the second observation, however, recruit abundance in th
e
experimental quadrates was higher than that in the contro l
one
. The first observation was carried out 11 months afte
r
the experiment
. It is likely that many settled planulla
e
have not been visible in situ
by divers at that time
. Settle
d
planullae is thought being visible after 10 months ol
d
(Clark and Edwards 1995)
. At this time, planullae tha
t
settled after May 1999 is likely not being visible yet
.
At present, data on the time of coral spawning in
-
Indonesia is very rare
. Bachtiar et al
. (1996) reported that
.
spawning time for the coral
Acropora cytherea
and
A
.
nobilis
are predicted after the full moon of January an
d
February in 1996, while the coral
Hydnophora rigida i
s
predicted spawned after the full moon of November 1996
.
428

Personal observation around the full moon of February
1998, reconfirmed that coral
A.
nobilis
contained
ripe
eggs. Five days after the full moon the ripe eggs had not
yet disappear. It seems that the spawning may be delayed
one lunar month, since the full moon occurred in the first
week of February 1998, as this also happened in the Great
Barrier Reef (Willis et al. 1985).
Results of the second observation show that the
introduction of artificial substrate can promote recruit
abundance. It is likely that availability of hard substrate is
responsible for the higher number of recruit in experi-
mental quadrates. The role of concrete blocks to minimize
sedimentation impact is not obvious in the present study.
On the two consecutive observations, recruit abundance
of the GM is consistently the lowest, beside the fact it has
the lowest sedimentation rate. There have been reported
that sedimentation can reduce the number of recruits by
preventing planullae
settlement
and reduce recruit
survivorship (Hodgson 1990, Babcock and Davies 1991).
In the present study, the high rate of sedimentation found
in the GA and GT are relatively low compared to those
reported on the previous study (Babcock and Davies
1991). It is likely that the impact of sedimentation on the
present study is not large enough to reduce coral
recruitment.
Therefore, the high recruit abundance on the
experimental quadrates is likely owing to its higher
available space for larval settlement than in the control
quadrates.
This finding demonstrate that simple concrete blocks
can be used for coral reef rehabilitation in future. As long
as larvae supply is not a problem, the concrete blocks
could be used effectively. Several factors, however, needs
to
be studied: such as recruit survivorship and its
contribution for coral coverage. If this result is consistent
in the next following years, cheaper artificial substrates
should be studied in promoting coral recruitment, for
example volcanic stones. In the present study, wave
action in the south locations removed most of the blocks.
This suggests that the size or form of the concrete block
was not heavy enough to encounter the wave energy. The
size and form of the concrete blocks may also be studied
in future.
On the first observation, GT has higher number of
recruits than GM, while GA has about the same number
of recruits
with either GM or GT. On the second
observation, however, the number of recruits in GT about
the same as in GM, while GA is higher than GM. These
results
show that each island has different rate of
recruitment between the two consecutive observations.
At present, sedimentation rate on the three islands is
lower than that had been reported to affect the rate of
coral recruitment (Hodgson 1990, Babcock and Davies
1991).
Therefore, sedimentation rate is not obviously
affecting 7coral recruitment on this study, neither are
benthic coverage factors. Further observation is required
to examine the role of benthic coverage in shaping coral
community in the artificial substrate.
In summary, introduction of small concrete blocks can
promote recruit abundance. Therefore, it is suggested that
this
method will be a very practical and "cheap" method
in coral reef rehabilitation. Coral transplantation methods
needs divers to carry it out (Harriot and Fisk 1988),
juvenile transplantation also need divers and
.
marine
laboratory (Raymundo et al. 1999), while artificial
substrate introduction method in this study does not need
any of those obstacles. The artificial substrate used in this
study is simpler than artificial substrate used in Thailand
(Thontham and Chansang 1999). Therefore, the like-
lihood involving local community to participate in coral
reef rehabilitation is high. Even any boatman could carry
out coral reef rehabilitation using this method.
Acknowledgement This study was funded by the
Government of Indonesia through the Riset Unggulan
Terpadu VII, contract number: 77/SP/RUT/1999. I wish
to
extend
my gratitude to Muhlis, Budianto, Taufik
Hidayal, Bambang Arwono and Totok Sasbiyanto, for
their supports during the study.
My thanks are also
extended Dr. Dharma Arief and Dr. Suharsono (LII) for
their suggestions and discussions on the study.
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