水研センター研報，第32号，61−67，平成22年
Bull. Fish. Res. Agen. No. 32, 61‑67, 2010

Different effects on seaweed succession after sea urchin removal atseveral coastal waters in Tosa Bay, southern Japan
Seiya TAINO＊1

Abstract : The effectiveness of sea urchin removal for the purpose of regenerating theseaweed bed was studied at several study areas in Tosa Bay. Marine algal succession anddensity of invaded sea urchins after sea urchin removal were examined at five stations (Kamikawaguchi, Kutsuu, Ikenoura, Tei and Sakamoto). Large perennial algae superseded coralline algae at Kamikawaguchi, Kutsuu and Ikenoura, since the inhibiting factor was removed
by sea urchin removal by scuba diving. Furthermore, spores and embryos, tided from near
seaweed beds to study area, accelerated regeneration of seaweed bed. On the other hand,seaweed beds have not regenerated after sea urchin removal by SCUBA diving at Tei andSakamoto, In these stations, it appears that both the feeding activity of sea urchin and thebrowsing activity of herbivorous fishes inhibited marine algal succession. Fishermen and students removed sea urchins by skin diving at Kamikawaguchi and Kutsuu in 2007. It should
be noted that even the skin diving removal of sea urchin have an effect on regeneration ofseaweed bed.
Key words : Isoyake, sea urchin removal,,spp.,,,

The first step to recovery of seaweed bedof invaded sea urchins after sea urchin removal
were studied at four stations (St.1, 2, 3 and St.4 orexist along theSt.4 ) by quadrat sampling from December 2002 tocoasts of Kochi Prefecture, Japan. In the IsoyakeThe barren grounds

IsoyakeFebruary 2008 (Fig. 2). According to field surveys atareas in Kochi Prefecture,

Kamikawaguchi, the deviation ofspp.

which assumed the density ofspp. in,spp. anddominate on bedrock and boulders.

preliminary survey was 0 have ranged from -9.3 to

The first approach of sea urchin removal in Kochi

0.3 ind. / m2 in St.1 and St.2 during survey period.

Prefecture started at Kamikawaguchi in 2002 (Fig. 1).

On the contrary, the density of

The experimental area was a hectare in area. It took

St.3 frequently exceeded that before removal (Fig. 2).

nine days and twenty-seven divers cumulatively to,

spp. inandgrew

remove all sea urchins in the experimental area. Seain shallow water superseded coralline algae within aurchins were crushed in the water by using ironyear of the sea urchin removal. After six years, thesticks, because there were no edible sea urchins.

coverage of

The estimated number of removed sea urchins wasapproximately 74,000 individuals. The coverages oflarge perennial algae (andbecame higher than that ofand(Fig. 3).

The second sea urchin removal carried out atIkenoura (Fig. 1) in 2006 (Taino2008). The) were examined

experimental area was half of a hectare in area. Itat thirteen stations by using a quadrat fromtook seven days and forty-two divers cumulatively

December 2002 to February 2008. Also the density

to remove all sea urchins in the experimental area.

2010年 月 日受理（Received on July 1. 2010）＊1
Kochi Prefectural Fisheries Experimental Station 1153-23 Haigata, Uranouchi, Susaki, Kochi 785-0617, JapanSeiya TAINO
The number of removed sea urchins was 150,034

anddescribed above

individuals. Sea urchins were crushed by the same

have been negative value within experimental

way as above. The density of invaded sea urchinsarea (St.1, St.2 and St.3) during the survey period.

after sea urchin removal were studied at fourOn the contrary, the density ofstations (St.1, 2, 3 and St.4) by quadrat samplingoccasionally exceeded a reference value (Fig. 4). The

from June 2006 to March 2008. The deviation ofcoverages of large perennial algae,Fig. 1. Map showing five study sites of sea urchin removal along the coast ofTosa Bay, Kochi.

Fig. 2. Seasonal variations of the deviation ofspp. at St.1-3 (December 2002
to February 2008) and St.4 (December 2002 to July 2003) and St.4 (December 2003 toJuly 2005) in Kamikawaguchi. Simplified drawing on top showing the stations of coverageobservation (open and solid circles) and quadrat sampling (solid circles).

spp.

Different effects on seaweed succession after sea urchin removal at several coastal waters in Tosa Bay, southern Japan
were examined at twenty-eight stations (Fig. 5)
by using a quadrat from June 2006 and December
2007. Our observations show that the shallow water.
population existed before sea urchinremoval colonized the Isoyake area in December
2007.
Difficult situations which show few signs of arecovery of seaweed bed
The third experimental site, Tei, is located in
the central part of Tosa Bay (Fig. 1). Extensive
population has been existed from 1980 s toearly 1990 s. A large number of researches (Ohnoand Ishikawa, 1982; Serisawa
2002a; Serisawa

2001; Serisawa
2002b; Tominaga

2004) were done in this area. The unbelievablefact that thepopulation disappeared during

1999 to 2000 at Tei was reported in 2000 and 2004
(Serisawa2000; Serisawa, 2004). The

approach of regeneration of seaweed bed started
in July 2005. There were two experimental areas
which was 49,000m2 in area respectively. It took
twenty-nine days and one hundred and twenty
divers cumulatively to remove all sea urchins in two
experimental areas. The method of removal wassame as Kamikawaguchi and Ikenoura. The numberof removed sea urchins was 304,356 individuals.
Same surveys as above were carried out at Tei
from July 2005 to February 2008. The density ofspp. has been at a low level within
experimental area during survey period. On thecontrary, the density ofexceeded areference value obtained before removal. At theseexperimental areas, the Gelidiaceae community,
which was observed before the removal of seaFig. 3. Changes in the coverage of(open circles) and(solid circles) at Kamikawaguchi.

urchins, broadened. Otherwise, large perennial algae
have never appeared during survey period. Now weare trying a spore bag method (Serisawa2005)

crushed by the same way as above. Same surveys

to regenerate large perennial algae (e.g.,described above were carried out at Sakamoto

andfrom August 2006 to February 2008. After sea).

Forth study site, Sakamoto, is located in the easternurchin removal, small annual and small perennials,

part of Tosa Bay (Fig. 1). The experimental area wasincreased here, but large perennials never appeared.

a hectare in area. It took six days and forty-three

In this station, only

divers cumulatively to remove all sea urchins inin November 2007. There are many herbivorous

the experimental area. The number of removed sea

fishes in this experimental area, and there wereurchins was 227,262 individuals. Sea urchins weremany white spots which were traces of scraping

colonized

Seiya TAINO
byfishes. It appears that both the feeding

The experimental area was a hectare in area. Theactivity of sea urchin and the browsing activity ofsea urchin removal carried out during three days

herbivorous fishes inhibited marine algal succession.

and eighty-two divers engaged cumulatively inremoval of sea urchins in the experimental area.

New approach of cooperative activity with

The sea urchins were crushed in the water. The

fishermen, students and volunteers

number of removed sea urchins was estimatedapproximately 68,000 individuals which were 40%

Fishermen and students removed sea urchins byof their total composition in the experimental area.

skin diving at Kutsuu in June and October 2007 (Fig.

After seven months, many juveniles of1, 6). After six months, many juveniles ofspp. appeared in the experimental area. It shouldhas been appeared, and then they grew
up in April 2008.

be noted that even the skin diving removal of sea
urchin have an effect on regeneration of seaweed

Thirty fishermen removed sea urchins by skin

bed.

diving at Kamikawaguchi in August 2007 (Fig. 1).

Fig. 4. Seasonal variations of the deviation ofand
Ikenoura from June 2006 to March 2008.

spp. atDifferent effects on seaweed succession after sea urchin removal at several coastal waters in Tosa Bay, southern Japan

Fig. 5. Changes in the coverage ofatIkenoura. Simplified drawing on top showing the stations of coverageobservation (open and solid circles) and quadrat sampling (solidcircles).

The case examples of marine afforestation byperennial algae colonized in the Isoyake area,sea urchin removal were reported in Hokkaido

successively. In this report, we carried out sea(Agatsuma, 2001;

urchin removal at five experimental areas. And now

Kawai, 1997; Kuwahara, 2003; Kawai and Tajima, 2003) andthere are five kinds of result. Sea urchin removal is

Nagasaki Prefecture (Yotsui and Maesako, 1993).

most effective method to regenerate seaweed bed

At Kamikawaguchi, after two weeks from removal

at Kamikawaguchi, Kutsuu and Ikenoura. Althoughof sea urchins, rocky bottoms were covered byat Tei and Sakamoto, we must develop strategies

attached diatoms in experimental area. In the next

for the browsing activity of herbivorous fishes

March,and juvenile thalli ofin addition to the feeding activity of sea urchin.

spp. appeared densely on rocky bottoms.

Furthermore, I would like to go on to develop theMaximum biomass ofbed (5.2 kg wet2wt / m ) was recorded in December 2003. Thus,attached diatoms, small annual algae and large

management of cooperative activity with fishermen,students and volunteers.

Seiya TAINOFig. 6. Photographs showing the cooperative activity with fishermen, students and volunteers. Meeting withstudents before sea urchin removal at Kutsuu (A), Skin diving removal of sea urchin at Kutsuu (B), Student
crushed sea urchins in the water by using iron stick at Kutsuu(C), Commemorative photograph of the firstcooperative activity of afforestation at Kutsuu(D).

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