Kyushu University - Tosa Bay

Restoration Project

Kyushu University - Tosa Bay

Restoration Objective:

The aim of this study was to produce a new type of artificial reef to grow seaweeds and provide habitat for Japanese spiny lobsters, abalone and other important fishery resources.

Site Selection Criteria:

Sites with three types of bottom substrata (sandy, boulder and rocks) at 5-10m were selected.

Cause Of Decline:

Grazing by sea urchins has led to the widespread loss of kelp ('isoyake') in Japan. In this process macroalgae species such as Sargasseous and Laminariaceous species are replaced by coralline species, and consequently, fishery resources such as abalone, lobster and fish became extremely depleted.

Scientific Paper

Succession of seaweed communities on artificial reefs in Tei, Tosa Bay

M. Ohno
Japan.The Korean Journal of Phycology, Vol. 8.


Site Observations:

Observation Date

15th Mar 1987 – 15th Jun 1993

Action Summary:

60 artificial reefs were placed on the sandy bottom at 8, 10 and 13m depths in Muronohana, Japan. They were observed monthly or bimonthly from February 1999 to June 2001. Artificial reefs consisted of concrete blocks weighing 3.3 tons each that were trapezoid in shape, 2 x 1.2m at the base and 1m high. Plastic mats were attached on the sloped sides of the box. A mixture of mature Sargassum spp., Gelidium amansii and other seaweeds were transplanted during the reproductive season using the spore bag technique. Reproductive thalli were packed in mesh bags which were fixed over the artificial reef units. Slow-eluting fertilizers were placed between the units to support seaweed growth.

Lessons Learned:

Sargassum was most successfully regenerated in the sandy bottom habitat, and expanded to other areas in following years.

Project Outcomes:

After 6 years, a biomass of 5,137g wet wt m2 in the sandy area was recorded. In two other areas, i.e. boulder and rocky, a biomass of 2,666 and 2,848 g wet wt m2, respectively, were recorded. The Sargassum communities expanded from the reefs to the adjacent rocky area in following years.

Area of Restoration (Ha)


Indicator Data:


Ending Value:

Starting Value:

Wet Weight Kelp

g WW/m2
g WW/m2
Cost Year:1987