Fisheries Research Agency Japan - Wakasa-wan

Restoration Project

Fisheries Research Agency Japan - Wakasa-wan

Restoration Objective:

Researchers aimed to generate seaweed forests (particularly Sargassum) using drifting thalli and seedling production techniques, which have been developed through artificial reef construction and seaweed aquaculture.

Site Selection Criteria:

A net was set to collect drift Sargassum in a bay with drift seaweed present. 7,000 m2 of artificial reef was deployed in the same area on a sandy seabed the following year.

Cause Of Decline:

Seaweed forests have important roles in primary production and providing nursery grounds. Recently, seaweed forests have been decreasing along the coasts of Japan. On barren grounds formed after deforestation, supply of seaweed propagules is often limited due to the long distance from existing seaweed beds in the surrounding area. The dispersal ability of Sargassum embryos is rather limited compared to that of kelp, further limiting the potential for natural regeneration.

Key Reasons For Decline:


Scientific Paper

Techniques for the restoration of Sargassum beds on barren grounds

K. Yatsuya
Bull Fish Res Agen, Vol. 32.

Site Observations:

Observation Date

1st Mar 2006 – 1st Sep 2006

Action Summary:

A net was set, and the abundance and fecundity of Sargassum thalli entangled around floating ropes of the net were investigated on a bi-weekly basis from early May to late July 2005. In March of the following year, 7,000m2 of artificial reef on a sandy seabed was deployed in the same area. From April to July, floating ropes were positioned above the artificial reef to entrap drifting Sargassum thalli and supply embryos.

Lessons Learned:

Drift thalli of Sargassum have similar reproductive output to attached kelps, and can be used to generate sporophytes in aquaculture. Additionally, ropes at artificial reef sites may facilitate algal recruitment by trapping drift algae. Future studies could compare recruitment success at artificial reef sites with and without ropes to trap drift algae. This study did not include a control/reference site.

Project Outcomes:

Biomass of the entangled drifting Sargassum was the highest in late May. Drifting thalli of Sargassum patens and S. macrocarpum were found to release comparable numbers of embryos to those growing in seaweed beds. Six months following artificial reef installation, the percent cover of Sargassum on the artificial reef was higher around the floating ropes, suggesting that this setup facilitated the effective supply of Sargassum embryos by trapping drift algae.

Key Reasons For Decline:


Area of Restoration (Ha)


Indicator Data:


Ending Value:

Starting Value:

Kelp Cover