Ishinomaki Senshu University - Ogatsu Bay

Restoration Project

Ishinomaki Senshu University - Ogatsu Bay

Restoration Objective:

The objective of this study was to reduce grazing pressure of sea urchins in barrens to allow U. pinnatifida restoration.

Site Selection Criteria:

Sites were selected that previously hosted Undaria kelp beds.

Cause Of Decline:

U. pinnatifida had inhabited in the inner areas of Ogatsu Bay, Japan, but declined during the 1990s due to grazing by the sea urchin sea urchin Strongylocentrotus nudus, resulting in the formation of barren grounds.

Key Reasons For Decline:


Scientific Paper

Undaria pinnatifida habitat loss in relation to sea urchin grazing and water flow conditions, and their restoration effort in Ogatsu Bay, Japan

H. Tamaki, Fukuda K., Arai M., S. Arai, D. Muraoka
Journal of Water and Environment Technology, Vol. 7.

Site Observations:

Observation Date

10th Dec 2004 – 8th Jun 2005

Action Summary:

Two sets of artificial buoyed reefs were moored in the middle depth of water using ropes and weights in December 2004. The reefs were designed to prevent the migration of sea urchins and allow the recovery of U. pinnatifida and other non-encrusting macroalgae. Both buoyed reefs were made of wood and were 1.0 m x 1.0 m x 16cm. Another reef was installed on the bottom to allow the migration of sea urchins, stacking blocks as the control treatment within the restoration area (1.0m x 0.4m x 36cm). U. pinnatifida cultivated in the laboratory with the average height of 46.7 ± 17.5cm, were tied onto each reef (approximately 50 plants), and their coverage was monitored monthly.

Lessons Learned:

The target species of kelp (Undaria) was overgrown by Saccharina.

Project Outcomes:

Buoyed artificial reefs allowed the recovery of U. pinnatifida and other macroalgae. There were some losses of transplanted U. pinnatifida partly caused by withering after the reproductive maturation period, but S. japonica and other macroalgae species were naturally recruited and increased on the buoyed beds. In contrast, the barren habitat remained at the area grounded to the bottom in the inner bay. Overall, restoration efforts using the artificial buoyed reef resulted in the success of the recovery of macroalgal habitats in the sea urchin dominated barren grounds by the reduction of grazing pressure of sea urchins.

Key Reasons For Decline:


Area of Restoration (Ha)


Indicator Data:


Ending Value:

Starting Value:

Dry Weight Kelp

g DW/m2
g DW/m2