Restoration Project

The University of Tokyo - Mashike

Restoration Objective:

Researchers evaluated the continuous effects of iron fertilisation on seaweed restoration, by comparing the changes in seaweed bed distributions with analysed iron concentrations over a 5-year study period and simulated results of iron distribution in the study area.

Site Selection Criteria:

The experimental site is shallow for a considerable distance from the shore (over several hundred meters), and the seabed slope is almost 1/40. The average range of the tide is small. The shore consists of boulders ranging 20–50cm in size. A reference site was chosen 108m away from the experimental site.

Cause Of Decline:

Reduction of seaweed beds is a serious problem in coastal areas of Japan and worldwide. The lack of dissolved iron in seawater may contribute to the destruction of this ecologically important habitat.

Key Reasons For Decline:


Scientific Paper

Effectiveness of Iron Fertilization for Seaweed Bed Restoration in Coastal Areas

M. Yamamoto, T. Kato, S. Kanayama, K. Nakase, N. Tsutsumi, , Journal of Water and Environment Technology, Vol. 15.


The University of Tokyo

Site Observations:

Observation Date

1st Oct 2004 – 2nd Jun 2007

Action Summary:

39 coconut shell fibre bags (0.3m diameter and 2m length) containing a mixture of steelmaking slag and compost were buried at the shoreline of an experimental site. Changes in the seaweed bed distribution were monitored both qualitatively and quantitatively by taking photographs and using the quadrat and belt transect methods. The wet weight of seaweed per unit area was measured at 3, 5, 10, 25, and 50 m from the shoreline at both the experimental and reference sites. Additionally, the cover degree of the seaweed bed was monitored every 5 m, from 0 to 50m from the shoreline with a width of 2m.

Lessons Learned:

It is possible that changes in seaweed biomass were not caused by the installation of the slag-compost fertilizer but rather from the changes in seaweed biomass in the surrounding coastal area. It should be confirmed that the tendency of changes of seaweeds at the experimental site was different from that in the surrounding area. The difference of seaweed biomass between the experimental site and the reference site should be evaluated through statistical methods.

Project Outcomes:

This study found that the biomass of seaweeds at the fertilized (experimental) site was larger than that at the reference site. They also found that both the analysed iron concentration and the calculated iron distribution in the area corresponded to the distribution of seaweed beds.

Key Reasons For Decline:


Area of Restoration (In Square Metres)


Indicator Data:


Ending Value:

Starting Value:


Cost Currency:USD