Walking barefoot on the sands of Maunalua Bay at low tide on Tuesday morning, Ellis Chen, 11, harvested limu as part of a service project at Honolulu Waldorf Middle School in Niu Valley.

“This is gorilla ogo, an invasive species they brought over to put in poke,” Chen said.

The fast-growing, matlike brown plant, Chen explained, threatens native species in the ocean and the adjacent Kalauhaehae Fishpond, which the Waldorf students are helping to clean and restore, planting native plants, under the direction of staff at the Maunalua Heritage Fishponds Center.

But that’s not all. The goal of the project is to restore the Niu Valley ecosystem within a one-mile radius of their school. “That’s our classroom,” said Alicia A. Mehle Tsadok, the middle school initiative class teacher who is directing the program.

Their ambitious undertaking has received monetary support and mentoring from nonprofit environmental groups Kupu and Kokua Hawaii Foundation, which co-founded Hawai‘i Youth Sustainability Challenge Projects, now in its second year. In two years, the initiative has resulted in 39 completed projects and the disbursement of more than $30,000 to the public, private and charter schools that applied to participate, according to program coordinator Emily Ishikawa.

In 2018-19, awards went to 29 schools, and students from six of these will give free public presentations on their projects at the Hawai‘i Conservation Conference at the Hawai‘i Convention Center from 3:15 to 4:15 p.m. Wednesday.

The projects are: provision of reef-safe sunscreens to beachgoers in exchange for sunscreens containing toxic oxybenzone by Maui Huliau students; building a rainwater catchment system for the garden at Sunset Beach Elementary; building a device that uses human motion to charge batteries at Hawai‘i Tech Academy; adding plant-based meal options in the cafeteria at ‘Iolani School; creating animated videos about sustainability at Laupahoehoe Community Public Charter School; building an automated, vertical aquaponics system at Hawai‘i Tech Academy; and collecting campus food waste to make compost for the garden at Hawai‘i Baptist Academy.

Hearing Maya Liao, 17, an incoming senior at Hawai‘i Baptist Academy, describe the buckets full of the school’s daily meat and dairy leftovers that go into a “hot” compost pile, one imagines it must be the size of a mountain and pack a sizeable odor, as well.

No worries. “The pile is about 6 feet in circumference and 2.5 feet high. It breaks down quickly,” Liao said. “Typically after we put the food on and cover it with dirt, we can’t smell anything.”

The pile is a passive system: “We don’t actually turn our piles, just rely on heat, bugs and microorganisms to break down the waste,” said Claire Mitchell, who teaches advanced placement environmental science and oversees the project. “We layer the food with mulch, parfait style, and water it, poking holes to aerate it.”

Vegetable scraps go to the worms in their raised, moist, shaded bin. Both the vermicompost and pile compost nourish the tomatoes and basil in the school garden, Mitchell said, but broader benefits include keeping methane, the most powerful greenhouse gas, out of landfills from which it escapes into the atmosphere, and educating students in a hands-on way.

They recycle from 30 to 100 pounds of food waste per week. “Because it’s such a large scale, we really had to learn teamwork, ingenuity, hard work and leadership skills,” Liao said of the 60-member environmental club that conducts the project.

Challenges included educating students that there was chicken stock in the vegetable soup so it couldn’t go in the worm bucket, and students who forgot and threw their food into normal trash cans, “a problem we haven’t totally remedied,” Liao said with a laugh.

While Waldorf Middle School students will not be presenting Wednesday, they are in the process of painting a 31-by-11-foot mural on a wall at the school with the fishpond as its central theme.

“We worked to restore the environment in the mountains and valleys where the water comes from” as part of restoring the fishpond, said Opal Weber, 14.

The students cleared invasive species in the forest— including a Jackson’s chameleon that was taken home as a pet — and collected seeds of native wiliwili and ohia for cultivation on campus before replanting them in the upland. They plan to build a star compass on Kuliouou Ridge with the guidance of Hokule‘a navigator Nainoa Thompson, whose daughter Puana is a Waldorf student.

“The location they chose for the star compass is far forward on the ridge, almost like you’re on a canoe overlooking the entire ocean,” Tsadok said, adding the students can see an area in Maunalua Bay where they are restoring the reef by planting native coral.

“The rocks for the compass will come from Uncle Nainoa’s grandparents’ wall,” added Michael Shin, 12.

In a similar multigenerational repurposing, the mural incorporates three mosaics made by Waldorf high schoolers in the early 2000s.

For a list of all 29 Hawai‘i Youth Sustainability Challenge projects, go to kupuhawaii.org.