[Held on Sunday, November 15] Horseshoe Crab Environmental Festival ～ Free admission, come and go as you please. Think about the future of Kasaoka’s sea through horseshoe crabs. There will also be LEGO building and LEGO science.

Many people in Okayama Prefecture probably think of Kasaoka when they hear the word horseshoe crab.

And for good reason: in Kasaoka City, the “Horseshoe Crab Breeding Ground” is designated a National Natural Monument. The city is also home to the world’s only museum dedicated to horseshoe crabs, the Kasaoka Municipal Horseshoe Crab Museum.

Meanwhile, changes in the marine environment have become increasingly noticeable in recent years, and catches have reportedly declined significantly.
In Kasaoka City, the “Horseshoe Crab Environmental Festival,” an event that uses the horseshoe crab as a symbol to consider the marine environment, will be held for the first time on Sunday, November 15, 2026.

This article introduces how the festival came about and what to look forward to on the day, based on an interview with the staff member in charge at the Kasaoka City Environment Division, which is organizing the event.

What Is the “Horseshoe Crab Environmental Festival”?

The Horseshoe Crab Environmental Festival is an event organized by Kasaoka City that uses the horseshoe crab as a symbol to consider the environment.

The venue is HAGIHARA Blue Sea Hall (Kasaoka Civic Hall), and the event runs from 10 a.m. to 2 p.m. Admission is free, and visitors may come and go as they please.

The event’s centerpiece is a stage where Kasaoka City will announce its “Kasaoka Nature Positive Declaration.” A “Horseshoe Crab Environmental Summit” will also be held, where the four cities of Saijo (Ehime Prefecture), Imari (Saga Prefecture), Kitsuki (Oita Prefecture), and Kasaoka, all home to horseshoe crabs, will share their initiatives.

In addition to the stage program, there will be activities for everyone from children to adults, including a workshop to build horseshoe crabs with LEGO bricks, a horseshoe crab quiz, a horseshoe crab product contest, and food trucks.

See the images below for details.

Main Hall Program

The following program is planned for the main hall.

1. Kasaoka Junior Chamber, a general incorporated association: “Kabutoganix”
2. Opening and welcome remarks
3. Presentations by participants in the workshop on considering the environment through LEGO horseshoe crabs
4. Presentation on activities by Kasaoka Municipal Jinai Elementary School
5. Presentation by the Nature Positive Official Ambassadors
6. Lecture by Tomohiko Hidetа, Biodiversity Conservation Planning Officer, Chugoku-Shikoku Regional Environment Office, Ministry of the Environment: “Our Lives and the Story of Living Things”
7. Horseshoe Crab Environmental Summit
8. Horseshoe Crab Environmental Partnership Declaration and Kasaoka Nature Positive Declaration
9. Announcement of the results of the horseshoe crab quiz and product contest

Programs Requiring Reservations

With so much on offer, some programs require advance reservations.

• LEGO Building (Let’s Build a Horseshoe Crab)
  40 minutes per session, 20 participants, ages 5 and up, participation fee: ¥1,000
• LEGO Science (Let’s Move a Horseshoe Crab)
  40 minutes per session, 16 participants, elementary and junior high school students
• Horseshoe Crab Quiz [Beginner Level]
  Prizes for participants and those who pass

Interview with a Staff Member of the Kasaoka City Environment Division

We spoke with Kentaro Ikeda, a staff member of the Kasaoka City Environment Division, which is organizing the Horseshoe Crab Environmental Festival, about how the festival was planned and what visitors can look forward to.

How the Event Came About

Could you tell us how the Horseshoe Crab Environmental Festival came about?

Ikeda (honorific omitted)

It was prompted by the increasingly noticeable changes in the marine environment.
In the fishing industry, one of the primary industries, catches have declined significantly. A lack of successors is cited as one cause, but environmental changes due to global warming and other factors, as well as the loss of seaweed beds, are also said to be major contributors.

Kasaoka City includes the inhabited islands of the Kasaoka Islands, which lie within the Setonaikai National Park area.
We thought that everyone needed to do a little more to protect the marine environment.

And since Kasaoka City’s “Horseshoe Crab Breeding Ground” is designated a National Natural Monument, we decided to promote environmental conservation using the horseshoe crab as a symbol, and began our efforts last year (2025), led by Mayor Kurio.

In fiscal 2025, we recruited official Nature Positive Ambassadors and developed a vision for community-building centered on the horseshoe crab through an intensive four-month program. Our goal is to advance Nature Positive.

Nature Positive, translated into Japanese as “shizen saiko” (“nature recovery”), refers to “halting and reversing the loss of biodiversity in order to put nature on a path to recovery.”

Source: Nature Positive | ecojin: Ministry of the Environment

We also have a project implementation plan that brings together the environmental conservation activities, environmental surveys, economic activities, and awareness-raising and educational activities we will pursue. For each resident’s awareness to change, people need to gather and take part. We thought an event could be one way to make that happen.

Kasaoka City has previously held cleanup activities and released young horseshoe crabs, among other initiatives. We decided to add to these efforts by holding the Horseshoe Crab Environmental Festival.

Festival Highlights

What are the highlights of this festival?

Ikeda

The biggest highlight is the chance to take part in LEGO Building and LEGO Science, two of LEGO’s educational programs. We’ve made special arrangements for them to come to Kasaoka City this time.

For something fun, there will be food trucks.
There will also be panel displays by partner organizations and workshops at the venue. In addition to LEGO, Chugoku Electric Power plans to hold a workshop for elementary and junior high school students.

And there’s the Horseshoe Crab Environmental Summit in the main hall.
The mayors of Saijo, Imari, and Kitsuki, where horseshoe crabs live, will join us and introduce horseshoe crab conservation and environmental protection activities in their respective regions.

We also plan to make the Horseshoe Crab Environmental Partnership Declaration at the summit.

A Message to Residents

What would you like residents to take away from the festival?

Ikeda

In addition to the work we have done so far, environmental conservation needs to involve economic organizations and others, and become a sustained effort.

I hope residents will also raise their awareness of environmental conservation and use this as an opportunity to consider changing their behavior—for example, in their consumer choices.

Finally, could you share a message for our readers?

Ikeda

People in Kasaoka City live surrounded by abundant nature, so they may feel that this is simply the way things are.

I hope you’ll come to the Horseshoe Crab Environmental Festival or the Horseshoe Crab Environmental Summit and use the experience as an opportunity to think about the environment, so that we can pass this natural environment on to future generations and make it sustainable.

We hope to continue our environmental conservation activities together with all of you. Thank you for your support.

From the Writer

The Horseshoe Crab Environmental Festival is a place where Kasaoka City will declare its commitment to Nature Positive, while also offering a festival-like event that everyone can enjoy, with LEGO activities, food trucks, and more.

Why not visit HAGIHARA Blue Sea Hall (Kasaoka Civic Hall) and use the horseshoe crab as a starting point to think about the future of the marine environment?

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