Tohoku University - Nojima Island

Restoration Project

Tohoku University - Nojima Island

Restoration Objective:

The present study aims to (1) estimate the threshold density and biomass of M. nudus required to trigger the phase shift from E. bicyclis forest to a barren, (2) clarify the recovery process to adult kelp forest in relation to sea urchin abundance by continuously removing the sea urchins, and (3) estimate the sea urchin abundance required for successful recruitment of kelp juveniles and indicate the key season for successful reversion to E. bicyclis forest.

Site Selection Criteria:

Degraded site due to urchin grazing.

Cause Of Decline:

Degradation of an Eisenia bicyclis forest due to grazing by Mesocentrotus nudus had been observed (Agatsuma et al. 2019).

Key Reasons For Decline:

Overgrazing

Scientific Paper

Restricted recovery of Eisenia bicyclis kelp forest following sea urchin removal on the Pacific coast of Tohoku, Japan

Agatsuma, Y., Abe, T., Inomata, E., Takagi, S., Tanaka, K., Hirotsune, M., ... & Aoki, M. N. (2024).https://www.int-res.com/journals/meps/articles/meps14715

Organisation:

Tohoku University

Site Observations:

Observation Date

18th Jul 2015 – 20th Jun 2019

Action Summary:

Sea urchins were repeatedly removed from the study area over 3.8 years to examine how sustained reductions in sea urchin density affected both urchin abundance and the recruitment and recovery of juvenile and adult kelp.

Lessons Learned:

Reducing sea urchin density in autumn, when many invade from barrens, is crucial to ensure the survival of kelp juveniles

Project Outcomes:

As a result of continuous sea urchin removal for 3.8 yr, the kelp growth area has expanded offshore. However, increases in adult kelp following the occurrence of juveniles were restricted to the nearshore half of the experimental transects. The successful recruitment of kelp juveniles and the subsequent recovery of adult kelp forest requires M. nudus of 40 50 mm TD to be restricted to a density of 0–1 ind. m–2.

Nature of Disturbance:

Miyama et al. (2021) demonstrated that a marine heat wave occurred in the Oya shio Current region off the Pacific coast of Hokkaido and Tohoku during summers between 2010 and 2016.

Area of Restoration (Ha)

0.01

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Adult Kelp Density

2.1900
/ m2
2.5500
/ m2

Urchin Unit Area

3.0000
m2
10.6900
m2
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