9 Nonember 2010

Bridge Technology applied to Coral Restoration(橋梁技術をサンゴ再生に活用）

K. Kihara, Y.Hosokawa(Mitsubishi Heavy Industries Bridge & Steel Structure Engineering Co. Ltd)2. Summary(発表の要旨）
Applying anti-corrosion engineering for steel bridges
and coastal structures, we developed new coral
restoration technology.
This can help natural settlement of coral larvae onsubstrates and promote vital growth of coral juveniles.
自然のゆりかごであるサンゴ礁の再生に長年取り組み,サンゴの成長や幼生の活着（根付いて成長）を促進する技術を開発した．

Acknowledge
H.Taniguchi (Akajima Marine Science Laboratory)
Y.Koibuchi ( University of Tokyo)
S.Yamamoto (The Nippon Corrosion Engineering
Co. Ltd)
Y.Kondo (C.P.Farm Co. Ltd)1

9 Nonember 2010

3. An Engineer noticed at TAKETOMIHIGASHI pontoon (竹富東港をヒントに）① Corals growing on the pontoon surface. （浮桟橋の側壁でサンゴが成長）② No corals could not be found on the concrete seawalls nearby.
（近傍のコンクリート構造物にはサンゴが見あたらない）

Why?

Five years have passed since pontoon set（5年経過後の状況）

4. Electric field supports coral colonies.（電場があるとサンゴが育つ）
Relation between electric current density
and number of coral colonies（電流密度別単位面積毎のサンゴ着生状況）

Floating pontoon has an anticorrosion system for steelplates.
Mon tipora

Number of colonies ( /㎡ )300

concrete
steel

250

spp
Styloporaspp
Porites spp

200
150
100

anode

Cross section of the pontoon

Acropora
spp
Pocillopora

50
0
1～2.6

2.7～1010～42.5

Measured electric current density (mA/ ㎡ )Galvanic Anode System
for anti-corrosion（防食のための流電陽極システム）2

9 Nonember 2010

5. Corrosion technology should be modified in a coral friendly manner.
(電気防食は，そのままでは使えない）

R/D issues (problems to be solved)
 Damaged community of corals often found in the offshore sea.
How can we provide electricity cheaply to the offshore far fromcoast? （遠隔海域での適用）
 Too strong electric current was anticipated reverse effect forcoral growth. How much ampere is the most suitable?
(適正な条件の模索）

 How can we provide good attaching surface for promoting
formation of new coral communities? Is the electricallyformed substrate good for coral settling and growth?
（電着を応用した着床基盤の作成）

6. Galvanic anode method (No power cable method)(流電陽極法の概要)
Electriccurrent（電流）電流Galvanic system withanode needs no power
cables nor externalelectric sources.

電子
Electron（電子）

（抵抗）

＋－

陽Aluminum or
Magnesium

陽極： Mg(ﾏｸﾞﾈｼｳﾑ）
またはAl(ｱﾙﾐﾆｳﾑ）などのイオン化傾向の大き（アルミニウム又はい金属マグネシウム）

Resistor

Ca2極

Anode（陽極）

電流

陰++

M g2

－ｲｵﾝの移動＋Seawater
海水海水反応Mineral

極

電着析出物

Cathode（陰極）Fe鉄Ca2++ CO 322+

Mg + 2OH-

CaCO3
Mg(OH)2→

CaCO 3→Mg(OH) 23

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7. A field experimental device (cage)(実海域実験用棚（サンゴ増殖棚）)

Field experiment cages for checking suitableelectric current density（現地実験で適正電流を把握.）
Resistance（抵抗）

Anode(Magnesium) Cathod(Steel bar)
陰極（鉄筋））（陽極（マグネシウム））

8. Result of field experiment （現地実験結果）

The electric current of 20 100mA/m2 provided good
growth of attachedfragments of corals. ( 3年間の観測から，20-100mA/㎡の電流でサンゴが良好に成長した.）4

9 Nonember 2010

9. Laboratory experiment for larvae settling on electrically coatedsubstrate （サンゴ幼生着床基盤（電着基盤）の構築）
coating in the seawater is expected to
Flow chart(フロー） Electric
provide surface material with good affinity for① Processing of thewire netting（金網素材）②

corals and surface asperity of small scale. We
propose our treatment methodology.
①④-1②Electric chemically coating（1000～2000mA/㎡) 60days（強電流で60日電着促進）③ Weak current density(10～100mA/㎡ ）(微弱電流に切り替え）④-2⑤④ Conditioning in the sea（自然海域で養生）
1st day

2nd day

3rd day⑤ Larval settlement(サンゴ幼生着床）
1et month 2nd month 3rdmonth

10. Result of laboratory experiment（着床試験の結果）

larvaeAfter four weekｓ

Steel netting

Juveniles growth
after 15～20 monthｓ

4.50

The electrically coated wire
nettings provide better surface
than the conventional
unglazed ceramic tiles forlarvae settlement of corals.
（電着基盤の着床率が素焼きタイルに比べて多い）N u m be r o f po lyps / c m 2

4.00
3.50

Wire mesh
Unglazed ceramic tile

3.00

Unglazed ceramic tile

2.50

（素焼きタイル）

2.00
1.50
1.00
0.50
0.00

ISHGAKIAKA
Site59 Nonember 2010

11. Conclusions（結論）① In the field observation about the pontoon, reefbuilding corals grew faster on the steel surface at
actual current density of 10-50mA/㎡ than lower
electric current．

② Response to electric current may varies with species.
③ Galvanic system for substrate is proposed .
④ Weak electric current (20-100mA/㎡) seems
favorable to coral growth on the cages under the sea.
The electrochemically coated substrates were better
than the unglazed ceramic tiles as substrate.

12. Our Dream (私たちは夢を持っています）

Thank you for your kind attention.
For more information,
Please send me e-mails.

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