Restoration Project

Tokyo University of Marine Science and Technology - Sakibaru Beach

Restoration Objective:

This study outlines the effects of using DSCM blocks to enhance algal growth, in order to improve restoration outcomes for Sargassum beds in subtropical, shallow waters.

Site Selection Criteria:

A site was selected that was well protected, and where Sargassum alternato-pinnatum was already present. It is also a site with a history of kelp harvest and kelp restoration.

Key Reasons For Decline:


Scientific Paper

Use of fertilized molten slags to create Sargassum forests in subtropical shallow waters

D. Fujita, R. Ma, S. Akita, M. Kobayashi, Y. Hayakawa, T. Miyatani, Y. Yamahira, , Journal of Applied Phycology, Vol. 29.


Tokyo University of Marine Science and Technology

Site Observations:

Observation Date

1st Jan 2016 – 1st Apr 2016

Action Summary:

Sargassum alternato-pinnatum seedlings were attached to fertilized, molten slag blocks, by hanging fertile thalli within a cage unit (4 x 4 x 4m), deployed at a depth of 4–5m from March to April. A total of 25 units were deployed, each containing 36 blocks. Laboratory tests were also carried out comparing the growth of Sargassum alternato-pinnatum and Chondracanthus intermedius in unfertilised and fertilised seawater.

Lessons Learned:

Fertilisation did not enhance Sargassum growth in laboratory conditions, as Sargassum grew more rapidly in unfertilised treatments. There was no control treatment used in outplanting experiments, so the effect of fertiliser in the field is unclear.

Project Outcomes:

The attached germlings grew rapidly from November, and thalli of a total length >1m filled the cage by the next reproductive period the following year. S. alteronato-pinnatum germlings occasionally appeared on the coral rubble around the cages but never exceeded 5 cm in height. The fertiliser blocks exuded high concentrations of NH4-N and SiO2-Si for a period of 3 months and lower concentrations were exuded for another 3 months. Growth of S. alternato-pinnatum was higher unfertilised seawater compared to fertilised, while growth of C. intermedius was higher in the fertilised treatment. Fertilisation affected colour in both species.

Nature of Disturbance:

In spring and summer, S. alternato-pinnatum juveniles were browsed by herbivorous fish.

Key Reasons For Decline:


Indicator Data:


Ending Value:

Starting Value:

Wet Weight Kelp

g WW/m2
g WW/m2
Cost Currency:USD