One day in October 2011, marine ecologist Masahiro Nakaoka donned his scuba gear, paddled into the waters of Funakoshi Bay in Iwate Prefecture, and braced himself for his first glimpse of its underwater communities since a massive tsunami triggered by the Great East Japan Earthquake swept through seven months earlier, on March 11.

Nakaoka knew the bay well. He works at Hokkaido University’s Akkeshi Marine Station and studies the seagrass meadows that dot the coasts of Iwate, Aomori, and Miyagi prefectures in the Tohoku region of northeastern Honshu. The meadows are not large, he says, but they are extremely valuable.

“They are unique in terms of species diversity and structure. They also attract fish so they are a valuable economic resource for local fishermen,” he told me by phone on a recent morning. The meadows provide abundant hiding places for fish to lay eggs, and in several bays in Iwate Prefecture there are seagrass specimens as high as a two-story building — the tallest in the world.

Nakaoka suspected the tsunami had damaged the seagrass, and as he dove down his hunch was confirmed. Funakoshi Bay’s once-lush meadow was almost entirely gone. But then he noticed shoots sprouting on the seabed. If they grow into mature seagrasses, Nakaoka predicts the beautiful underwater meadow could be back within half a decade.

Recovery, however, is far from certain.

Towns and cities all along that Pacific coast are building massive seawalls and breakwaters aimed at protecting them from future tsunamis. If not carefully planned, these could cut bays off from one another, from the ocean, and from the rivers and underground spring-fed water courses that carry nutrients down to them from the mountains. Nakaoka says seagrasses cannot thrive in such a segmented environment. The same is true for other coastal ecosystems damaged by the tsunami, such as tidal flats, wetlands and marshes.

Humans’ focus on their own recovery and security, in other words, could hinder the wider natural recovery — as many biologists would likely say if they were invited to take part in the recovery planning process now entering its final phase in cities all along the Tohoku coast. But Takao Suzuki — a Tohoku University ecologist who, at age 61, is a leading national expert on the region’s tidal flats — says that he, for one, has not been invited.

One morning late last month, Suzuki drove me out to the Gamo tidal flat, 16 km due east of his campus office in Sendai, Miyagi Prefecture. We passed through the still-desolate coastal portion of the city. Concrete foundations and a few hollowed-out buildings were all the tsunami had left behind. Then, leaving the car in a parking lot by the ocean, we stood looking down on the 13-hectare patch of sand and water at the mouth of the Nanakita River.

If seagrass beds are the coast’s nurseries for fish, intertidal flats are their “international airports for migrating birds” and “water-purification plants,” Suzuki said. These sheltered areas that are alternately exposed at low tide and submerged at high tide are packed with clams, worms, and other bottom-dwelling (or “benthic”) animals.

Even since the tsunami, Suzuki has found more than 120 animal species in the tidal flats around Sendai, with as many as 8,800 individuals per square meter. As the tides wash in and out, these animals feed on plankton and detritus in the water, and later become food for birds, fish and people.

To me, however, the Gamo tidal flat looked as desolate as the demolished neighborhood we had just left behind. A twisted strip of latticed concrete — the remains of a seawall — slumped along the sand next to rocks. In the distance, smoke puffed from the red-and-white towers of the Nippon Petroleum Refining Company.

Suzuki pulled out his binoculars. “See those gulls over there?” he said, gesturing to a flock pecking at the sand a dozen meters away. “They’re here because there’s something for them to eat. Probably ragworms.”

Ragworms are fast-growing and prolific crawlers that burrow in the sand. According to Suzuki, their numbers are now booming because the tsunami wiped out some of their predators.

He climbed down to the sand and turned over a rock. “Crabs! They’re moving a little slow because it’s so cold, but they’re alive alright,” he said, scooping five of the fingernail-sized creatures into his palm.

Earlier, in his cozy book-lined office, Suzuki had told me what happened to Tohoku’s tidal flats during and after the tsunami. Following the disaster he surveyed the damage at 10 locations as part of a Ministry of Environment study (Nakaoka did the same for seagrass meadows). As he’d done similar surveys for the ministry nearly a decade earlier, he could systematically compare before-and-after species abundance and diversity.

He found that damage varied hugely from place to place. At some sites that took the force of the water head-on, nearly all the species from his previous survey had disappeared. In some cases habitat vanished as land was reshaped. Elsewhere the damage was less extreme, and in some areas it was nearly undetectable.

Impacts were probably more moderate further out to sea, said Katsunori Fujikura, a biologist at the Japan Agency for Marine-Earth Science and Technology who has been surveying the tsunami-zone seabed at depths of 200 to 1,000 meters. He added that in some places, tsunami debris is providing new habitat for flatfish, sea anemones and other sea creatures.

At Gamo, the tsunami washed away a sandbar that had sheltered the tidal flat. Three months later the bar had re-formed. One month after that, Suzuki and a group of students unearthed 44 percent of the benthic species he had found there in 2004. A year later, the figure was up to 49 percent.

To get back to 100 percent, Suzuki said, these damaged areas need two things: a healthy tidal flat nearby that can serve as a “seed bank” of species; and an uninterrupted path between it and the damaged areas for those “seeds,” or larvae, to travel. In their larval stages clams and many other benthic creatures drift out to sea for a period and then return to the coast to mature. That is where the problem of seawalls and breakwaters comes in.

Most towns are now building higher, more continuous walls along the shore than existed before the disaster. However, the higher a wall the wider the base must be to support it — and bases can sometimes be so wide as to extend into the intertidal zone.

“If walls are built in the middle of tidal flats, larvae won’t be able to return. We have to preserve routes for them,” Suzuki said. Local governments should also avoid obliterating tidal flats with concrete or blocking the flows of fresh and salt water that bring nutrients, he added. However, he said that planners have not drawn on the detailed ecological knowledge that he and his colleagues can offer, and construction is already underway in many places.

“The overall plans are not going to change. But we may still be able to save some important areas,” he said.

The day after I met Suzuki, I drove up to Kesennuma, a port town at the northern tip of Miyagi Prefecture, to meet one of the few Tohoku residents aggressively challenging seawall construction.

Makoto Hatakeyama is an oyster farmer, environmental educator and activist who lives in the village of Nishimone, beside a miniscule bay at the foot of a mountain. He is the son of Miyagi’s best-known environmental activist, Shigeatsu Hatakeyama, who, in the 1980s, founded Mori wa Umi no Koibito (literally, “The Forest is the Lover of the Sea”), a movement to plant broadleaf trees in watersheds that feed their nutrients into oyster bays.

The tsunami destroyed all 33 houses in Nishimone except for Shigeatsu’s, which is perched on a hill. As evening fell I climbed up to the small adjacent office where Makoto Hatakeyama, 34, now works.

He told me that the summer after the tsunami, he learned of plans to build a 9.9-meter seawall on the inner edge of the little bay. Its base would likely be 20 to 40 meters wide. He shared the news with his neighbors.

“Everyone here thought I was lying,” he said. “Didn’t even the highest walls break in the tsunami? But people were distracted with more urgent things. The bureaucracies moved forward methodically with the plan. There was no discussion over whether to build it or not. We didn’t have a seawall before and we didn’t want one.”

Moreover, he pointed out, “The whole village is relocating to higher land. We decided we didn’t need to waste tax money on something unnecessary. There would be environmental impacts, and the wall would make it harder to use the bay because it would take up most of the flat space.”

Hatakeyama and a group of concerned locals fought and defeated the plan. He says his is the only community so far to have succeeded in doing so. The victory may be an isolated local one, but it shows that the future of Tohoku’s coast is still open to revision.

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