Environment Pick Up! Vol.01 Creating a Rich Seaweed Environment at Kansai International Airport

Creation of a rich seaweed bed environment

Collage image of Sorayan and underwater seaweed beds near the airport with text that reads "Pick Up! Vol. 01."

Kansai International Airport was built on an artificial island 5 kilometers off the Senshu coast in Osaka Bay to reduce aircraft noise.
We have been creating a seaweed bed environment around the airport islands since the planning phase of the airport construction to achieve harmony with the marine environment and co-existence with nature. Seaweed beds are attracting attention, not only as a habitat for sea life but also for the effect of photosynthesis on reducing CO₂ emissions.

This is the seaweed beds at KIX!

The seaweed beds in a video

Seaweed beds at KIX

Most of the airport island's seawalls extend down to the seabed in a gently sloping structure known as a sloped stone revetment. A wide variety of seaweeds and marine life inhabit this area.

Rich seaweed beds with numbers

Area of the seaweed beds at Kansai International Airport

A graph titled "Total seaweed settlement area." The seaweed bed area was 66 hectares as of March 2025, combining the first and second airport islands. It had accounted for 14% of the seaweed bed area in Osaka Bay.

Enlarge

At the seaweed beds of Kansai International Airport, we have conducted monitoring surveys to assess the condition and maintain stable seaweed bed environments. In the March 2025 survey, the seaweed bed area was confirmed to have reached 66 hectares, accounting for 14% of the total seaweed bed area in Osaka Bay.

Biodiversity conservation

An illustration of seaweed and fish. The text reads "66 species of seaweed and 31 species of fish and shellfish".

Recent surveys found 66 different seaweeds in different sizes.
We also found 31 types of reef-associated fish and shellfish that we did not see before the construction of the airport island in the muddy seabed. This shows that the seaweed bed plays an important role as a spawning ground for fish and shellfish.

  • Major seaweed: Undaria pinnatifida, Ecklonia cava, Sargassum fulvellum
  • Major creature: Epinephelus akaara, Semicossyphus reticulatus, Chromis notata

The waters around Kansai International Airport are no-fishing zones.

Absorption of CO₂ by seaweed

J Blue Credit issuance certificate.

The amount of CO₂ absorbed by seaweeds growing along the seawalls around Kansai International Airport was certified to total 280.3 tons over the three-year period from FY2022 to FY2024.

In recent years, there is a growing recognition on the importance of "blue carbon" (carbon absorbed into the marine ecosystem such as seaweed beds and shallow water) as a measure to absorb CO₂ to realize a decarbonized society. The various initiatives we have taken to create and maintain rich seaweed beds are now creating new value in contributing to the reduction of CO₂ emissions.

Seaweed beds contributing to the conservation of biodiversity in Osaka Bay

Collage image of the Nature Symbiosis Site certification logo and diverse marine life.

The seaweed beds of Kansai International Airport were highly recognized for their contribution to providing ecosystem services and conserving the biodiversity in Osaka Bay and were certified as a Nationally Certified Sustainably Managed Natural Site (areas where biodiversity is conserved by private initiatives) in October 2023 by the Ministry of the Environment.
Moreover, the seaweed beds were registered to the global database as an "Other Effective area-based Conservation Measure" (OECM: areas other than protected areas that contribute to biodiversity conservation) in August 2024, making it possible for us to make concrete contribution to the global goals for biodiversity conservation, including "30by30 target".

Creating a rich seaweed bed environment

Nurturing the environment to help the growth of seaweed

Cross section of a gently sloping stone embankment. Blocks for seaweed growth have been installed on the gently sloping seawall, creating an environment conducive to seaweed growth.

Gently sloping rubble mound seawalls

During the construction of the airport island, gently sloping rubble-mound seawalls were adopted for most of the shoreline. Unlike vertical seawalls built perpendicular to the water surface, these sloped seawalls allow sunlight to reach a wider area, creating conditions that are more favorable for seaweed growth. In addition, by actively implementing various measures to promote the settlement of seaweed—such as planting seaweed spores and installing blocks for seaweed attachment—we were able to realize the early development of large-scale seaweed beds on the artificial island.

Conservation and expansion of the rich seaweed bed environment

Since 1989, following the completion of Island 1 and the start of seedling supply, we have continued monitoring surveys to assess the condition of seaweed beds. Based on changes observed through these surveys, as well as shifts in external environmental conditions, we implement conservation measures that help maintain and further expand the seaweed bed environment, contributing to the creation of a richer and more sustainable ecosystem.

Transplanting seaweed to reinforce the function of the seawalls to protect the islands from disasters

An illustration showing the three-stage process of seaweed transplantation around the airport islands. The illustration is arranged chronologically from left to right. In the first phase (2019), Ecklonia cava was transplanted from the construction area to the second airport island. In the second phase (2020–2021), the seaweed was transplanted to environmentally friendly wave-breaking blocks installed between the first and second airport islands. The illustration depicts that in the third phase (2021-2022), a sargassum species was transplanted onto the wave-breaking blocks and seaweed beds were formed.

Following Typhoon Jebi of September 2018, we installed new wave dissipating blocks from 2019 to 2021 as a measure to reinforce the disaster preparedness of the airport islands. Large-scale planting of large seaweed, such as perennial Ecklonia, which grows on the airport islands, contributed to maintaining a stable seaweed bed environment. We are also paying attention to such physical changes in the environment when taking measures to conserve the seaweed bed.

Conservation of the seaweed bed in response to environmental changes

Ecklonia cava inside a protective net
Ecklonia cava growing inside a protective net
Recently, the marine environment has been changing significantly due to global warming and sea level rise. Damage sustained by Ecklonia cava due to Siganus fuscescens and other algae-eating fish has become one of the great environmental changes. We initiated the protection of donor algae by using nets in line with the feeing period of fish. We have also installed new substrates to promote new juvenile growth, and we monitor the situation.

Please refer to our environmental reports for other initiatives and activities.

Environmental Report