Restoration Project

Nippon Tetrapod Co. - Sagami Bay

Restoration Objective:

The objective of this study was to determine if tetrapods used to protect ports and coastal structures can act as artificial substrata for seaweed restoration, and if surface roughness influences success.

Site Selection Criteria:

A site was selected near small seaweed beds of Ecklonia cava.

Cause Of Decline:

Kelp forests and Sargassum beds are not only commercially important themselves but also play an important role in spawning, in fish breeding, and as feeding grounds for many species of commercial fish, shellfish and other organisms. In Japan, grazing by sea urchins has led to an increase in the size and abundance of urchin barren grounds.

Key Reasons For Decline:

Overgrazing

Scientific Paper

Settlement of seaweeds on coastal structures

A. Watanuki, A. Yamamoto, , Hydrobiologia, Vol. 204.https://doi.org/10.1007/978-94-009-2049-1_39

Organisation:

Nippon Tetrapod Co.

Site Observations:

Observation Date

15th Sep 1981 – 15th Jan 1986

Action Summary:

Twenty 1 ton blocks (tetrapods) were placed on an almost flat bottom at a depth of approximately 14m, 300m off the coast. The blocks were placed to coincide with the maturation period of E. cava in September 1981.

Lessons Learned:

Tetrapods grew Ecklonia cava as effectively as natural substrate.

Project Outcomes:

The standing crop of nearby natural communities was 14.7kg/m2. On the blocks, it was 15.3kg/m2. Ecklonia cava samples were collected at 3.2 and 4.8 m. The average standing crop on the natural rock and blocks was 11.2 kg/m2 and 12.4 kg/m2, respectively. The standing crop of both species on the blocks was similar to that of the surrounding natural seaweed forest. The composition and growth of seaweeds on both substrata were also similar.

Key Reasons For Decline:

Overgrazing

Area of Restoration (In Square Metres)

49

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Wet Weight Kelp

15300
g WW/m2
0
g WW/m2
Costings:
Cost Currency:USD

Observation Date

15th Sep 1981 – 15th Jan 1986

Action Summary:

Twenty 1 ton blocks (tetrapods) were placed on an almost flat bottom at a depth of approximately 14m, 300m off the coast. The blocks were placed to coincide with the maturation period of E. cava in September 1981.

Lessons Learned:

Tetrapods grew Ecklonia cava as effectively as natural substrate.

Project Outcomes:

The standing crop of nearby natural communities was 14.7kg/m2. On the blocks, it was 15.3kg/m2. Ecklonia cava samples were collected at 3.2 and 4.8 m. The average standing crop on the natural rock and blocks was 11.2 kg/m2 and 12.4 kg/m2, respectively. The standing crop of both species on the blocks was similar to that of the surrounding natural seaweed forest. The composition and growth of seaweeds on both substrata were also similar.

Key Reasons For Decline:

Overgrazing

Area of Restoration (In Square Metres)

49

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Wet Weight Kelp

12400
g WW/m2
0
g WW/m2
Costings:
Cost Currency:USD