Coral reef restoration

5

Coral reef restoration

Coral reef ecosystems in the world are on the declining trend mostly due to anthropogenic disturbances. When it was disturbed beyond its regenerating ability, it cannot be regenerated and will further proceed on the declining track. For coexistence with coral reefs in the future, needless to add that the top priority should be to prohibit as much disturbances and conserve the existing ecosystems, inducing its natural recovery. However, when natural recovery is considered hardly progressive or too slow without arti?cial assistance, rehabilitation measures to induce the recovery is sometimes necessary. Moreover, it is us humans that is to be responsible for the degradation itself, thus such efforts should partly be conducted if adverse effects are not caused and with careful implementation. In this chapter, restoration techniques and attempts of coral reef restorations in Japan are introduced.

Chapter

Coral Reefs of Japan 05

1381 Introduction

Coral reef ecosystems have been in decline, worldwide,

for the past 100 years. This decline has been caused by

pollution and overexploitation, and is predicted to worsen

over the next 20-30 years if appropriate measures are not

taken immediately. Added effects of the mass bleaching

and coral diseases have occurred in recent years (Pandolfi

et al. 2003). In developing countries, destructive fishing

methods, such as fishing with dynamite and poison,

have added to the damage. Coral reefs in Japan are

also declining because of repeated disturbances, such as

outbreaks of crown-of-thorns starfish (Acanthaster planci)

beginning in the 1970s, inflows of terrestrial soil, and

recent mass bleaching events.

In response to these events, a number of countries,

including Japan, the U.S., and Australia, set up the

International Coral Reef Initiative (ICRI) in 1995, and

developed a framework to discuss the conservation of coral

reefs worldwide. The ICRI considered various conservation

activities. Of these, coral restoration and regeneration

have attracted attention, and their importance has been

recognized as a management tool (ICRI 2003).

The recruitment of coral larvae on degraded reefs differs

greatly with location, due to the effects of geographic and

hydrographic conditions. Therefore, the artificial restoration

of reefs should help to regenerate coral communities where

natural recovery is limited; artificial restoration will hasten

their recovery, expand the source of larvae, create habitat for

other organisms, and recover the underwater scenery.

This section first introduces the disturbances that have

affected coral reefs in the past, and the effort that has

been exerted for their recovery, by referring to the case

of Sekisei Lagoon in the Yaeyama Archipelago, Okinawa.

It then over views the research on restoration and

current restoration/regeneration techniques, and finally

discusses future perspectives.

2 P revious efforts at coral reef

restoration in Sekisei Lagoon

Sekisei Lagoon in the Yaeyama Archipelago is the largest

coral reef in Japan; the entire area was designated as

Iriomote National Park in 1972. After establishing

the national park, the government established an

administrative office for the park in the city of Ishigaki.

In addition, the Marine Parks Center of Japan set up the

Yaeyama Marine Park Research Station at Kuroshima

Island in Sekisei Lagoon in 1975, and has been conducting

research there. Consequently, the changes in Sekisei

Lagoon since it became a national park have been

monitored relatively closely. Initially, Sekisei Lagoon

was a pristine coral reef at ‘physiognomy climax’,

unaffected by outbreaks of A. planci or anthropogenic

disturbances. This is evident from a coral distribution

map of the lagoon based on aerial photographs (in

1977, Geographical Sur vey of Japan) created by the

Environment Agency in 1980(Nature Conser vation

Bureau, Environment Agency 1981). This map suggests

that the reefs were at the stage of maximum development

and dominated by branching Acropora.

In 1980, immediately after the sur vey, an explosive

outbreak of A. planci occurred in the lagoon and most

of the corals were predated, except in the northern

part of Kohama Island (Fukuda and Miyawaki 1982).

At that time, the local residents, as well as Okinawa

Prefecture and the National Government, began a large-

scale removal of A. planci; it failed, however, to keep

pace with the scale of the outbreak. Little recovery of

the coral community occurred in the 1980s and a state of

stagnation has continued.

To determine the state of decline in the reefs that has

been caused by A. planci predation, the Environment

Agency surveyed the coral reefs in Sekisei Lagoon in

1991, using the latest aerial photographs. It was apparent -1

Shuichi Fujiwara, Makoto Omori Restoration techniques

that the coral communities were in poor condition; more than half of the lagoon had coral coverage below 5% (Nature Conservation Bureau, Environment Agency 1994b).

Therefore, the Environment Agency initiated research into the recover y of coral reefs. In 1992-1994, coral restoration techniques using coral fragment transplantation were attempted (Nature Conservation Bureau, Environment Agency 1993, 1994a, 1995). At that time, a framework for the recover y of Sekisei Lagoon was developed, and the Yaeyama Coral Reef Conser vation Committee was established in April 1990, with participants representing Iriomote National Park, the Okinawa Prefecture Nature Conser vation Section, the city of Ishigaki, the town of Taketomi, local diving unions, and Yaeyama Marine Park Research Station. This conference resulted in a coral fragment transplantation pilot project, in the sea, approximately 1km south of Taketomi Island. In this project, 5,000 fragments of branching Acropora (mainly A. formosa) were transplanted within an area of 1,000m2. This was continued for several years; Misaki (1998a) has reviewed the results.

The corals in Sekisei Lagoon star ted to recover gradually in the early 1990s, and had nearly recovered to their previous state by the late 1990s when high water temperatures in 1998caused mass coral bleaching, killing corals over a wide area.

In addition, terrestrial soil runoff has also affected the coral communities in Okinawa, when construction related to land improvement enterprises started after Okinawa’s handover to Japan in 1972. The Ministr y of the Environment (the former Environment Agency) conducted research into coral tolerance of fine suspended matter in Sekisei Lagoon in fiscal 2000-2002(Fujiwara 2003). In addition, the Yaeyama Coral Reef Conservation Conference expanded its scope and monitored coral and related sedimentation, with public participation, in an attempt to get the community involved in these activities.

3 Restoration techniques

Most hermatypic corals (hereafter, corals) reproduce sexually, and colonies grow by budding polyps. When parts of a colony are broken off, such as by waves, the fragments can settle on the neighboring substrate and grow asexually to form a new colony. Using this characteristic, attempts have been made to transplant coral fragments, in order to restore coral reefs, since the 1980s overseas, and since the 1990s in Japan. This fragmentation technique can be further divided into two basic methods: the fragments are simply fixed directly

to the substrate, or they are allowed to settle on a plate, which is then transplanted once the fragment has grown

to a certain size. Other methods of restoring coral reefs have been attempted in Japan. For example, a method that involves suspending numerous ropes with attached coral fragments in the sea and letting them grow has been patented in Japan. In addition, an attempt

to promote the calcification of transplanted fragments using electrolysis has been tested in the sea off the village of Chinen, in Okinawa (Kudo and Yabiku 1988). Okubo and Omori (2001) have reviewed coral fragment transplantation techniques.

Recently developed restoration techniques include seedling production and lar vae-settlement-inducing techniques using sexual reproduction. The development

of restoration techniques using sexual reproduction has been one of the main topics of research at the Akajima Marine Science Laborator y since the beginning of the 1990s. Various basic biological studies have been conducted in cooperation with universities and private enterprises. These include inducing corals to spawn in tanks, breeding larvae and juveniles, promoting larvae settlement, and transplanting the lar val and juvenile corals to the field.

This section reviews these restoration techniques, including methods using asexual reproduction, sexual reproduction, and colony and community transplantation,

as well as transplant management.

1. Asexual reproduction techniques

a) Transplantation of coral fragments

Okubo (2003) has brought together and described various coral fragment transplantation techniques, including the results of the author’s studies in this respect. The following is a summary of these techniques:

i) Collecting fragments: Fragments for transplantation

are collected from adult (donor) colonies. The effects

of fragmentation on the donor colony should be

minimized in the course of this operation. Although

there are insufficient physiological studies of these

effects, experience shows that if about 80% of the

adult colony is left, the donor is likely to survive and

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Chapter-5 Coral reef restoration

Coral Reefs of Japan 05

140

underwater cement

cement

flower pot

hook nylon bag with

cement inside

concrete mat

wire or

cable tie

nail bamboo skewer

bag with cement

pole

Fig. 1. The transplantation of fragmented colonies (Okubo and

Omori 2001).

will not have problems spawning eggs the following

year. It is thought that the bigger the fragment, the

higher its probability of survival, although Becker

and Muller (1999) have reported that a 2.5-cm-long

fragment is sustainable as a transplant.

ii) Transportation methods: It is preferable to transport

fragments by submerging them within a container, by

having them carried by divers to a nearby destination

(Dodge et al. 1999), or by suspending them from

a boat (Dodge et al. 1999; Munoz-Chagin 1997). It

is often convenient to carr y fragments by boat,

immersed within a bucket, but this requires attention

to temperature changes (Bowden-Kerby 1997). The

tolerance to exposure varies with the species: while

Acropora gemmifera and Favia stelligera can survive

exposure for up to about two hours, Stylophora

pistillata and Rumphella sp. should not be exposed

(Kaly 1995).

iii) Fixation on a natural platform: There are many ways

to attach fragments (Fig. 1), but underwater cement

is what is commonly used. While the chemical

influences of underwater cement on corals are not

well understood, some researchers have attempted

to reduce this influence by mixing equal amounts of

calcium carbonate with the cement. The method of

Okubo et al. (2002), in which branching fragments

are fixed to pre-fixed nails with cable ties, revealed

the benefits of underwater cement. The outcome is

generally better when a branching fragment is fixed

to the substrate vertically, as opposed to horizontally;

this may be due to the reduced accumulation of silt.

iv) Fixation on an artificial substrate: When transplanting

fragments to ar tificial structures, it is useful to

know what kinds of substrate corals attach to easily.

Comparative experiments using fer rite-added-

concrete, unglazed pottery tile, concrete block, iron,

and coral carbonate showed that coral fragments

attached best to concrete and ferrite-added concrete

(Okubo 2003). An artificial substrate made by mixing

concrete with lime ash (an industrial by-product) also

had a high fixation rate (Ikeda and Iwao 2001). These

findings suggest that coral fragments attach well to

substrates that contain concrete.

v) Environmental factors: The growth characteristics of

corals depend on the species and the environment.

Therefore, it is necessar y to sur vey the physical

characteristics of both the donor colony habitat and

the destination of transplants (e.g., waves, current,

turbidity, depth, irradiance, sedimentation level, and

salinity) before transplantation. When the two sites

have similar environments, the outcome is usually

successful, but when they differ, the survival rate is

likely to be unsatisfactory (Auberson 1982; Nature

Conser vation Bureau, Environment Agency 1993,

1994a, 1995). A study of the relationship between

the sur vival rate of transplants and temperature

and photoperiod found that the rate was inversely

correlated with temperature and directly correlated

with photoperiod (Yap and Gomez 1984; Yap et al.

1992). The mortality rate was higher during periods

of high temperature (Yap and Gomez 1984); therefore,

the season in which transplantation is conducted

should be considered. It is also necessary to avoid

sites where coral predators, such as A. planci and

coral eating gastropods (e.g., Drupella cornus), prevail.

The problems associated with fragment transplantation

include those associated with obtaining fragments by

breaking donor colonies, difficulty in standardizing

transplantation methods, lack of information about the

long-term survival rate after transplantation, and the

considerable labor and costs required for large-scale

transplantation.

b) Juvenile coral transplantation

Okamoto and Nojima (2003a) compiled data on how to

collect and transplant juvenile corals in the field, and

these are summarized here. First, juvenile corals can

be collected with the substrate in a core, using an air

drill. At the transplantation site, holes for fixation are

drilled using the same caliber drill. A small amount of

underwater cement is put in the hole, and the core with

141

Chapter-5 Coral reef restoration

the juvenile coral is inserted. If the transplantation site is affected by silt accumulation, it is desirable to drill shallow holes and insert the cores with the juvenile corals so that they are raised slightly above the sea bottom (Photo. 1). Using this method, the substrate is unified with a smooth core. Therefore, many cores can be carried in the sea or by ship, and there is less danger of hurting the juvenile corals, even if many are stored standing in a container. In addition, this method is simple, and can be used for large-scale transplantation.

2. Techniques using sexual reproduction

a) Seedling production

Hatta et al . (2003) devised a method of producing Acropora seedlings, which is summarized here. Gametes are either collected from slicks (Photo. 2) or by placing a funnel-like device on top of a colony ; fertilization is allowed to take place in a tank. For Acropora tenuis , about one million eggs can be collected from three colonies, about 30 cm in diameter (Shimomura et al . 2002). It is also possible to induce spawning artificially on a small scale in some species of Acropora and Montipora using hydrogen peroxide (Hayashibara et al . in press).

The larvae can be raised in a small container or a large tank (1-5 tons) containing more than 100,000 individuals (Shimomura et al . 2002). The gametes obtained from a bundle are fertilized easily, with 500,000 individuals per ton of seawater, while those obtained from slicks are susceptible to deteriorating water quality owing to the mixing of impurities and the death of unfertilized eggs, requiring breeding at lower densities. Aota et al . (2003) succeeded in producing more than two million larvae in eight floating culture ponds measuring 2 m 2 m with 1 m depth.

A chip of Hydrolithon reinboldii can induce the settlement of Acropora lar vae (Morse et al . 1996). In addition, higher rates of larvae settlement can be induced using the neuropeptide Hym-248 (Iwao et al . 2002; Hatta and Iwao 2003). Moreover, bacteria that induce the settlement of Acropora larvae have been isolated from coralline algae (Negri et al . 2001); Hatta (unpublished data) has conducted a follow-up study of this.

Larval settlement has been tested on a wide variety of substrates, including concrete, unglazed pottery tile, shell, pottery stone tile, earthenware, and slate. Generally, settlement is greater on materials that have been submerged in the sea until a layer of organisms has formed.Trials to induce lar vae settlement in the field have also been undertaken. Tetra Co., Ltd. and the Akajima Marine Science Laboratory prepared a 6.0 5.5 5.5-m enclosure and introduced larvae, allowing them to settle on concrete blocks on the bottom (Aota et al . 2003). Dr. A. Heyward who had assisted the studies in Japan at initial period, bred larvae inside a floating tank, moved the tank to the desired destination, ran tube from the bottom of the tank to a tent set up on the sea bottom, and introduced larvae into the tent from the tank using hydraulic pressure, so that the larvae could settle on the substrate under the tent (Heyward et al .

When polyps settle on a reef or a substrate in a running seawater tank, with parent colonies, zooxanthellae symbiosis is seen within one week or so. Although an initial polyp has been raised to produce a large colony in some cases (Misaki 1998b, 2002; Petersen and Tollrian 2001), there have been no reports of successful large-scale breeding of corals. Future research in this

field

Photo. 1. Juvenile coral transplantation. A core with the juvenile

coral will be cemented in the same caliber drill

(Okamoto and Nojima 2003a).

Photo. 2. A spawn slick (coral gametes and larvae) offshore.

Coral Reefs of Japan 05

142should examine how to improve the growth and survival

of juvenile corals after settlement. Measures may also be

necessary to protect corals against algae overgrowth and

coral-eating fishes.

b) Inducing larval settlement by substrate processing

This is a method of inducing coral larvae settlement

on 1- to 3-cm bumps on the surface of breakwaters and

other artificial structures. These bumps are thought to

cause a vortex at the structure’s surface, increasing the

probability that larvae attach and settle. Moreover, they

are thought to decrease the risk of sea urchin grazing

after settlement. In this respect, concrete is a suitable

manufacturing material. Figure 2shows a breakwater

with wave-abating blocks in front of the bank, and root-

hardening blocks behind the bank (Fig. 2). Methods for

processing the surfaces of these concrete blocks include

i) leaving irregularities on the surface of the blocks by

omitting the smoothing process, ii) forming bumps by

a) placing wooden blocks at the top of the mold after

the concrete is poured, b) placing pieces of wood or

rubber on the inner surface of the mold, or c) attaching

secondary material, such as plates, to the blocks using

adhesives or bolts, and iii) spraying concrete on the

sur face of a block (Por t and Marine Environment

Research Institute, and Waterfront Vitalization and

Environment Research Center 1999).

Studies monitoring coral recruitment on the surface of

processed blocks have shown remarkable recruitment

on bumps produced using rough squares of wood.

Horizontal and 45-degree surfaces tended to have greater

recruitment than vertical surfaces at a depth of 20m,

while these differences did not occur at a depth of 10 m.

c) Collecting seedlings using a larvae settlement tool

Okamoto and Nojima (2003b) developed a settlement

device for collecting larvae in the sea. This small, light

device is shaped like a wooden top and consists of a

‘settlement board’, a ‘spacer’, and a ‘joint portion’; it

is designed to facilitate the settlement of larvae so that

they can be transplanted readily (Fig. 3). It is made of

potter’s clay and can be mass-produced inexpensively.

The ‘settlement board’has a hole on top for connecting

several of the devices, and grooves to increase the

settlement area. The ‘spacer’ maintains a space between

connected settlement boards, and the ‘joint portion’

functions as a guide when connecting and transplanting.

Since these devices can be connected to each other and

held in a frame, mass-transportation and mass-installation

in the sea are possible. Predators can be kept away from

the larvae by adjusting the frame interval. This device

can be transplanted on a reef substrate by drilling small

holes in the substrate, putting adhesives in the holes,

and inserting the joint portion of the device. The spacer

functions as a ‘stopper’that prevents damage to juvenile

corals growing sideways from the undersurface of the

settlement board after they have been transplanted.

The settlement of larvae is thought to be completed by

roughly ten days after spawning. After one month, when

the larvae are settled firmly on the settlement devices,

they can be transported to an appropriate calm area for

Fig. 2. T arget area for substrate processing on a breakwater to induce coral larval settlement (Port and Marine Environment Research Institute, and Waterfront Vitalization and Environment Research Center 1999).

Nojima 2003b).

growth. The frames can be transported either by divers or by using an air lifter. This method is being tested, but a large-scale project has not yet been conducted. For enough juvenile corals to settle on the devices in the sea, information is needed regarding the distribution of fertilized eggs generated by mass spawning and where the larvae settle.

3. T ransplantation of colonies and the

relocation of coral communities

Coral transplantation is generally conducted using fragments. In cases where coastal development threatens whole coral communities, as many colonies or communities as possible should be transplanted to adjacent sites. In such cases, a comprehensive environmental survey is necessary; however, there is insufficient information on this technique. There have been some trials in other countries combining clipped coral communities and artificial coral reefs, but such cases are limited, and only replacement of a community that was unavoidably removed or reclaimed during harbor construction has been carried out in Japan (Fukunishi et al. 1998).

a) Colony transplantation

Hosoya (2003) reported the transplantation of Porites lutea colonies during the construction of the Kourio-hashi Bridge on Okinawa. Massive Porites are unsuitable for transplantation, as large corals exceed 1m in diameter. Therefore, colonies 20-30cm in diameter, which were comparatively easy to handle, were used. Transplantation involved separating the colony using a chisel, transporting the colony underwater in a container to the site, and gluing the colony to the substrate using under water cement. Concrete blocks and natural carbonate rock were tested as substrates. With carbonate rock, a method that involved driving an anchor bolt into the colony base was also tested as a means of fixing the colony, and was proven effective. A follow-up survey conducted four years after transplantation showed that survival and growth were better on natural carbonate rock. Since massive Porites are usually distributed in moats, it seems appropriate to transplant them to moats. However, moats generally have sandy bottoms, which are unstable. Corals can be transplanted to a sandy bottom by installing iron piles in the bottom and attaching the corals to the piles.

b) Relocating coral communities

Fukunishi et al. (1998) and the Por t and Marine Environment Research Institute, and Water front Vitalization and Environment Research Center (1999) introduced a technique that involved transplanting parts

of a coral community, together with the underlying substrate; this technique is for use during harbor recla-mation or breakwater construction. In addition, a new experimental approach for advanced harbor construc-tion, one that takes coral communities into consideration, has been used in Hirara, on Miyako Island, Okinawa Prefecture, since 1998. The results have been reported

in Ishii et al. (2000, 2001) and in a pamphlet published

by the Hirara Port Construction Office, Okinawa General Bureau (2002). The following is a summary of these reports.

To relocate a coral community, it is necessary, first of all, to conduct pilot studies and select the destination carefully. After a period of trial and er ror, the transportation of a large coral community first became possible in fiscal 2000. This involved digging up the carbonate rock using a water jet system, and transporting the coral by airlift, without removing it from the water. Using this method, coral communities were relocated around the breakwater mound inside the harbor. The coral communities relocated in Januar y 1999were mostly small ones, some of which were carried away

by waves during typhoons. In contrast, all the larger, stable corals were in good condition and only a few died

as a result of the stress of relocation and environmental change. By 21months after the relocation, the coral coverage had increased at some points, according to a survey conducted in October 2000. There is presently

an application for a patent on this technique (Fig. 4).

The relocation of a coral community has advantages, as compared to fragment or colony transplantation, since the flora and fauna adhering to the substrate are also relocated and conserved; this technique can also handle massive corals, such as Porites, which are difficult to fragment.

4. Managing transplants

After transplantation, algae often overgrow the transplanted colony and sometimes kill the colony. When water temperatures are low and algae grow vigorously,

it may be necessary to remove the algae. Moreover, where coral-eating organisms, such as A. planci and D. cornus are present, they should be exterminated before transplantation, because fragmented coral releases mucus, which may attract these predators. Furthermore,

143

Chapter-5 Coral reef restoration

Coral Reefs of Japan 05

144the hooks of surfcasting fishermen and boat anchors

can destroy corals. Therefore, it is necessary to educate

fishermen about the consequences of their actions and to

place mooring buoys in areas where boats often anchor.

Transplants should be monitored to evaluate the method

used. Preferably, follow-up should last for at least five

years, since transplanted juvenile corals are thought to

take about four years to adapt to their environment. The

parameters to be monitored include coral survival and

death rates, the health of the coral, and environmental

factors such as water temperature, water flow, and

sedimentation.

A long-term rise in water temperature is fatal to

coral, and causes bleaching. Therefore, long-term

monitoring of water temperature provides useful

preliminary information. Recently, cheap, compact, self-

recording thermometers have been introduced, and

some can measure hourly data continually for about

six months (Nature Conser vation Bureau, Ministr y

of the Environment 2001). In general, more coral

species can be transplanted to locations with greater

water flow (Nature Conservation Bureau, Environment

Agency 1995). A handy method for measuring water

flow characteristics is that of methodology using

plaster balls (Komatsu and Kawai 1992; Furushima et

al. 2001). Sedimentation is especially susceptible to

human influences, especially in moats. Sedimentation

can be estimated visually, using the SPSS method (Omija

and Mitsumoto 2001), or with sediment traps (Nature

Conser vation Bureau, Ministr y of the Environment

2001). The first method is the easiest; the latter is more

difficult. All of these methods provide useful data, so the

method to be applied can be selected according to the

scale of monitoring. In addition, irradiance and nutrient

salts are also important environmental parameters, but

their long-term measurement is expensive.

In coral transplantation, the rate of growth is more

important than reproduction. However, if transplanted

corals spawn, the supply of larvae is increased, which

will further contribute to the recovery of coral reefs.

The spawning of transplants also indicates that the

colony is stable, so monitoring the formation of gametes

and spawning may be necessary.

4 Deployment and future issues

1. P rogress and comparison of restoration

techniques

The first case of coral transplantation in Japan was

probably in 1970, when the Kushimoto Marine Park

Center in Wakayama Prefecture constr ucted an

underwater observatory and transplanted coral colonies

to restore the surrounding underwater landscape. This

area contains corals that are typically distributed in

Honshu (mainland Japan), and a large tabular Acropora

hyacinthus community. In transplantation experiments

with this species, the corals grew to a size showing

typical colony features within 1-2 years (Tatsuki 1977).

As already stated, the development of restoration

techniques has recently shifted to seedling production

and lar vae-settlement-inducing techniques, using

sexual reproduction. Such advances should eliminate

the necessity of manipulating an existing community.

Advances in coral restoration techniques are not only

effective in restoring coral reefs and creating artificial

reefs but will also reduce the damage caused by the

collection of existing colonies once ornamental corals

can be cultured in aquaria. If full-scale ‘coral farming’

becomes possible, Japanese aquaculture technologies,

which lead the world, should suppor t progress in

projects that transfer such restoration techniques to

tropical countries, and contribute to the conservation of

the marine environment worldwide. Table 1 summarizes

the progress, thus far, of research and development in

coral reef restoration techniques; future advances are

expected.

2. Future research

In the future, the main coral reef restoration techniques

Fig. 4. General description of the relocation procedure used for

coral communities in an ‘environmentally friendly

breakwater’ (Ishii et al. 2001).

are expected to make use of larvae. For that purpose, forecasting the destination of slicks in the open sea is indispensable. However, oceanographic information is presently insufficient for such forecasts, and research in this field is anticipated.

The selection of a proper site is very important when transplanting colonies and releasing larvae. Restoration cannot be considered successful unless the corals introduced to a new environment grow, reproduce, and expand their range. In this respect, it is necessary to clarify the detailed relationships at each stage in coral life histories with in situ factors, such as interspecies competition, the effects of predation by coral-eating organisms, and the kinds of substrate that larvae are most likely to settle on. As stated previously, there has been insufficient research undertaken on micro- or medium-scale physical factors (e.g., the water flow regime) in coral reef regions; this will be an important future research topic.

Lastly, the possibility of altered genetics within a taxonomic unit, owing to hybridization or a decrease in gene diversity resulting from a restoration program, should be mentioned. If corals are transplanted within the area where eggs are distributed under natural conditions, these factors should not be problematic. However, the transportation of corals to remote regions, outside their natural range, might alter the regional gene composition. Moreover, because corals have high genetic diversity and easily hybridize (Hatta et al. 1999; Willis et al. 1997), it is necessary to use eggs and fragments obtained from many colonies that are widely distributed. If the number of donor colonies is limited or the genetic diversity is lost, corals that are extremely susceptible to environmental change and disease will result. The Hawaiian Porites compressa has greater genetic diversity where environmental disturbance is frequent and lower diversity where disturbance is infrequent (Hunter 1993). It is necessary to determine the level of gene diversity of existing coral communities, using molecular techniques, before cross-fertilization or transplantation of fragmented colonies takes place.

5 Conclusions

The Ministr y of the Environment established the International Coral Reef Research and Monitoring Center at Ishigaki Island in 1998as a base for monitoring coral reef communities. It is the focus of the activities of the ICRI, and conducts conservation activities in Sekisei Lagoon. The ministr y also enacted the Law for the Promotion of Nature Restoration in 2002, and selected Sekisei Lagoon as the site of a nature restoration project, in cooperation with various local agencies; work is currently being undertaken on coral reef restoration. The techniques introduced in this chapter should prove useful for restoring coral reefs, and the results will be applied to other coral reefs in Japan and overseas. But, needless to say, the development of such techniques should not merely assume that the destruction of the coral reefs from the growth of human activities is inevitable.

145 Chapter-5 Coral reef restoration