lpha Hydraulic Engineering Consultants C - Hokkaido

Restoration Project

lpha Hydraulic Engineering Consultants C - Hokkaido

Restoration Objective:

The aim of this paper was to trial removal of sea urchins from a barren to investigate potential use as a tool for seaweed restoration.

Site Selection Criteria:

Three 50m × 50m square blocks were established on urchin barren boulder beds at depths between 4 and 8m, where kelp was not present.

Cause Of Decline:

Along the southwestern coast of Hokkaido, low-productivity urchin barrens caused by the sea urchin Strongylocentrotus nudus have persisted for ~80 years, restricting kelp beds comprised of Saccharina japonica var. religiosa and Undaria pinnatifida to shallow waters largely less than 2m in depth as a grazing refuge.

Key Reasons For Decline:


Scientific Paper

Restoration of kelp beds on an urchin barren: removal of sea urchins by citizen divers in southwestern Hokkaido

A. Watanuki, T. Aota, E. Otsuka, Iwahashi Kawai, Kuwahara H., D. Fujita
Bull. Fish. Res. Agen, Vol. 32.

Site Observations:

Observation Date

1st Sep 2005 – 1st May 2006

Action Summary:

20 citizen volunteer divers (CVD) removed urchins from an urchin barren near Kamoenai Fishing Port on the southern coast of Shakotan Peninsula in September 2005. Sea urchins were removed from two blocks (Block A and B) (50 x 50 m, 4-8m in depth) during two dives (ca. 1 hr/dive) beside the control block (Block C); and subsequent monthly removal by researchers was continued in one of the blocks (Block A). Density of kelps and urchins was measured in February and May 2006 (5 months and 8 months later).

Lessons Learned:

This study highlights the importance of continual (monthly) removal of urchins in aiding kelp regeneration, as plots where researchers removed urchins monthly following volunteer removals showed much lower urchin densities and much higher kelp densities.

Project Outcomes:

In the block where sea urchins were removed monthly, density could be reduced to almost less than 1/m2. After 5 months, seaweed had not germinated yet but diatoms and small green algae formed a mat on the hard substrata. After 8 months, the standing crop of the kelp in the blocks A (monthly removals), B (initial removal) and C (no removals) were 865g/m2, 150g/m2 and 0g/m2, while the density of sea urchins were 0.1, 3.5 and 4.2/m2, respectively.

Key Reasons For Decline:


Area of Restoration (Ha)


Indicator Data:


Ending Value:

Starting Value:

Wet Weight Kelp

g WW/m2
g WW/m2
Total Cost:800